Model A & B

Ford Garage

Tremec T170FT RTS Four-Speed OD

3+1 Overdrive Transmission Conversion

Procure this book! Fifty-seven pages of detailed official 1984-87 Ford disassembly and reassembly photos, diagrams, description, and instructions specifically for RTS/TOD and RUG/SROD 3+1 Truck transmissions. The similar 1977 Ford Chassis Service Highlights publication covers the earlier iron case RUG-BP/SMOD 3+1 Car (and follow-on truck/van) transmissions. The 1979 Ford Chassis Service Highlights publication covers the 1979-83 aluminum RUG SROD 3+1 Car (and truck) transmissions.

The 1984-87 Ford RTS top shift overdrive transmission was made for Ford by Tremec, and it is known variously as a T170FT RTS 3+1 TOD. It was produced in three different overdrive ratios for use in Ford full-size light-duty 2WD and 4WD F-150 pickup trucks and Broncos.

With its cover-mounted cane shifter, the T170FT RTS 3+1 TOD transmission has been a popular choice for Model A and early V8 Ford overdrive transmission conversions, and a number of people have made complete kits available to do the transmission swap and conversion.

This Ford Garage page is the single most comprehensive, complete, and correct source of technical information on the RTS transmission and T170 family to be found on the web. If you have additional info, or potential corrections to contribute, please contact me by clicking my name at the bottom to initiate an email. Thank you!

Ford-Tremec T170 3+1 Family Variants

The Ford-Tremec T170 manual transmission family includes three types/variants of four-speed toploaders having the internal 'third' gear position configured as the top/overdrive gear ('fourth' to the driver). They are also known as 3+1 overdrives. The major visual differences are in the style of gear selection, and the case materials used.

In these transmissions, the overdrive (top gear) is actually in the 'third' gear internal position, and power is NOT directly transferred in-line through the input to the output shaft in top gear, unlike a conventional non-overdrive four-speed transmission.

Instead, the power in the T170 in overdrive operation is routed through the input main drive gear, into the cluster gear, back into the overdrive gear teeth on the main/output shaft, and then on to the universal joint. The countershaft and all bearings and the case are always under load and stress during overdrive.

The continuous offset loads on all the bearings, and on the main, cluster, and overdrive gears during overdrive operation is one reason that these 3+1 transmissions originally developed a somewhat poor reputation for robustness when abused, compared to that of the top gear loading in a planetary or conventional non-overdrive transmission.

The durability reputation of the 3+1 was especially aggravated by the many abusive pickup truck and van owners who were routinely towing heavy loads in overdrive, instead of in the direct drive (1:1) gear recommended by Ford.
In spite of this reputation, the aluminum-case T170FT RTS 3+1 transmission is robust enough in overdrive for the task at hand for usage in a Model A or Early V8 Ford.


1984-87 Tremec T170FT RTS (TOD) Description

Ford Parts and Service Division
Ford Service Manual Description:

The top shift overdrive (TOD) is a four-speed manual transmission with fourth gear as an overdrive.

It is fully synchronized. All forward gears are helical-type and are in constant mesh. The forward gear changes are accomplished with synchronizer sleeves.

Reverse is provided through a reverse idler sliding gear which slides on a reverse idler gear. The reverse idler gear is in constant mesh with the countershaft gear. In reverse the spur-type gear on the reverse idler sliding gear meshes with the gear on the 1-2 synchronizer hub.

The top mounted shifter operates shift rails in the transmission cover assembly. The first-second fork and the reverse fork are attached directly to these rails.

The third and overdrive shift fork is attached to a shift rail which is mounted in the transmission case.

Third and overdrive are shifted by means of a shift pawl mounted on a rail in the transmission cover, contacting an overdrive shift control link in the transmission. This shift control link contacts the shift fork in the transmission.

A shift interlock system located in the transmission cover prevents the engagement of more than one gear at a time.

The transmission case, cover, and extension housing are aluminum. The mating surfaces of these components are sealed with Anaerobic Sealer (Gasket Eliminator).
OEM Application: 1984 - 1987 Ford F-150
Ford Type: Four-Speed Manual TOD
Topshift Over Drive
Manufacturer: Tremec
Tremec Type: T170FT RTS
Remote Tower/Top Shift
Case Material: Aluminum alloy
Fully Synchronized: All forward gears
are helical type
in constant mesh
Lubricant: 3.5 US Pints
1.7 Liters
SAE 80W
D8DZ-19C547-A
(ESP-M2C83-C)
Driven 80W-90 GL4
or equivalent
Do not use GL5 !
Notes: Case has no drain plug
No gaskets are used;
Anaerobic sealer only
TOD = Topshift Over Drive
RTS = Remote Top Shift
The information published in the official Ford Parts and Service Division TOD and SROD Service Manual identifies three different gear ratio configurations offered in the Tremec T170FT RTS and the T170FS SROD series truck transmissions, and they are specified as 'B ratio', 'C ratio', and 'D ratio'.

'B' ratio = 27.6% overdrive (5.0L 302 V8, also some 4.9L 300 I6)
'C' ratio = 37.9% overdrive (5.8L 351 V8, also some 4.9L 300 I6)
'D' ratio = 41.1% overdrive (4.9L 300 I6)

These Ford ratio letters are utilized in Column 1 in the Transmission Specifications table below to organize the part gearing information of the three different RTS overdrive configurations.


1984-87 Tremec T170FT RTS 3+1 (TOD) Identification

There is both a Ford part number and a Tremec part number cast into the LH side of the aluminum RTS case. The first (1984) style case is marked RF-E4TR-7006-AA and C-2604877, and the second (1985-87) style case is marked RF-E5TR-7006-AA and C-2605524.

You may also find a similar four-speed 'RTS style' non-Jeep-input, top shift aluminum case transmission, but without Ford casting numbers or logo, and having only a Tremec case number C-2605275.

These 'RTS clones' were made by Tremec, but are not marked 'RTS' on the steel tag. I believe they may have been non-Ford replacement F-150 transmissions supplied by Tremec to aftermarket transmission shops. Anybody know different?

1985 F-150 2WD Regular Cab Pickup
1987 F-150 2WD Regular Cab, Six Cylinder with Tremec T170FT RTS transmission

When still in a vehicle, the Tremec RTS 3+1 (TOD) transmission can also be identified by the Ford transmission Type 'B' (Tremec OD) printed at the bottom center of the VIN/GVWR/Tire Information label (applied inside the drivers door opening) of a Ford F-150 pickup truck, as shown above.



The overdrive ratio of a Tremec RTS transmission can be identified by a steel tag which is riveted to the front RH side of the case. This is useful when evaluating a loose transmission at a junk yard or swap meet.

The first three characters on the Tremec tag will be 'RTS', and are immediately followed by a two-character alpha code as shown in the pic above, and in Column 1 in the table below.
The two-character alpha code identifies the overdrive ratio as originally built by Tremec.

Beyond identifying the OD ratio, the two-character alpha code following the 'RTS' identifies the original transmission assembly as being for a 2WD or 4WD, and identifies which speedometer drive gear it was originally equipped with (function of tire size and rear axle ratio combinations).

Other than identifying the specific transmission OD ratio, the RTS two-character alpha code is unimportant in adapting the T170FT to the Model A or early V8 Ford.

The various other codes stamped on the Tremec tag identify the production date, the Ford service designation number, and the Tremec unit serial number.



1984-87 Tremec T170FT RTS 3+1 (TOD) Specifications

The Transmission Specifications table below shows the Ford and aftermarket part numbers and tooth counts of the various gears in each RTS transmission configuration.

Peach-shaded cells indicate parts which are still generally available new in the aftermarket.
T170FT RTS 3+1 (TOD)
Aluminum Top Shifter
Transmission Codes

Ford, Tremec, and Aftermarket Part Numbers and Tooth Counts
Tremec Codes
T170FT
Steel ID Tag
Alpha Codes
% OD
Gear
Ratios
Countershaft
Cluster Gear
(Input-4-2-1)
(3 distinct)
Input Gear
1-1/16" Dia
10 spline
(2 distinct)
3rd
Gear
Sleeve
4th OD
Gear
(2 distinct)
2nd
Gear
(1 common)
1st
Gear
(1 common)

'D ratio'

RTS-

AB, AC, AG,
BM, BS, BT,
BY

84-87 F-150/Bronco
4.9L 300 I6

good for case,
shifter top,
input gear/shaft,
1 & 2 gears,
reverse gears,
synchro hubs,
output shaft

(can be converted to
RTS 'B ratio' using
27.6% RUG 3+1
cluster and OD gears)
'D' ratio

41.1%

1st=3.2508
2nd=1.9213
3rd=1.0000
4th=0.7087
32-43-23-15

E0TZ-7113-A
2604234
T170-8H

(convert RTS 'D'
to 'B' ratio using
RUG 3+1
T170-8C gear)
21T

E0TZ-7017-B
2604484
T170-16N

8-7/8" long

(interchanges
w/ RUG 3+1)
3rd
Direct
20T

E0TZ-7B340-A
2605212
T170-11H

1G central

2-21/64"
diameter

(convert RTS 'D'
to 'B' ratio using
RUG 3+1
T170-11C gear)
29T

E0TZ-7102-A
(2604232)
2605214
T170-21F

3-53/64"
diameter
32T

D9BZ-7A029-B
2604300
J8132389
T170-12B

4-36/64"
diameter

'B ratio'

RTS-

AD, AE, AJ,
BJ, BP, BU,
BV, BZ, CS

84-87 F-150/Bronco
4.9L 300 I6
5.0L 302 V8
'B' ratio

27.6%

1st=3.2508
2nd=1.9213
3rd=1.0000
4th=0.7837
32-35-23-15

D8UZ-7113-A
2603740
T170-8C

1G central 15?
21T

E0TZ-7017-B
2604484
T170-16N

8-7/8" long

(interchanges
w/ RUG 3+1)
3rd
Direct
18T

E0TZ-7B340-B
2604242
T170-11J

(interchanges
w/ RUG 3+1)
29T

E0TZ-7102-A
(2604232)
2605214
T170-21F

3-53/64"
diameter
32T

D9BZ-7A029-B
2604300
J8132389
T170-12B

4-36/64"
diameter

'C ratio'

RTS-

AA, AF, AH,
AK, BN, BR,
BW

84-87 F-150/Bronco
4.9L 300 I6
5.8L 351 V8
'C' ratio

37.9%

1st=3.0061
2nd=1.7767
3rd=1.0000
4th=0.7247
31-35-23-15

E0TZ-7113-B
2603243
T170-8J
22T

E0TZ-7017-C
2603806
T170-16P

8-7/8" long

2G equal

(interchanges
w/ RUG 3+1)
3rd
Direct
18T

E0TZ-7B340-B
2604242
T170-11J

1G forward

(interchanges
w/ RUG 3+1)
29T

E0TZ-7102-A
(2604232)
2605214
T170-21F

0G

3-53/64"
diameter
32T

D9BZ-7A029-B
2604300
J8132389
T170-12B

2G central

4-36/64"
diameter
IMO, the "Goldilocks" Tremec RTS transmission for a Model A or Model B is the combination of the the 1st and 2nd gear ratios of a Ford RTS 'C ratio' transmission, combined with the 4th gear overdrive ratio of an RTS 'B ratio' transmission. Refer below for the necessary RUG 3+1 parts to swap into an RTS case to accomplish this.

Refer to the Drivability and Suitability ~ Recommended Combinations section further down this page for explanation of why that configuration would theoretically be the "Goldilocks" transmission for an early Ford conversion.


Earlier Tremec T170F RUG 3+1 (SMOD), and T170FS RUG 3+1 (SROD) Specifications

Peach-shaded cells indicate parts which are still generally available new in the aftermarket.
T170F RUG 3+1 (SMOD)
Iron Side Shifter
Transmission Codes
% OD
Gear
Ratios
Countershaft
Cluster Gear
(Input-4-2-1)
Input Gear
1-1/16" Dia
10 spline
3rd
Gear
Sleeve
4th OD
Gear
2nd
Gear
1st
Gear
D7DR-7006-AA
2603606 case*
2602885 retainer,
(T160-6G)
*209/307 bearings

Orion RUG BP
Ford RUG BP


77-78 Granada/Monarch
3.3L 200 I6
23.6%

1st=3.2889
2nd=1.8381
3rd=1.0000
4th=0.8094
37-40-26-15

D7DZ-7113-A
2603885
T170-8B
24T

D7DZ-7017-A
2603596
T170-16E

8-7/8" long
3rd
Direct
21T

D7DZ-7B340-A
2603884
T170-11B

2-32/64"
diameter
31T

D7DZ-7102-A
2603612
T170-21B

3-50/64" ?
diameter
32T

D9BZ-7A029-B
2604300
J8132389
T170-12B

4-36/64"
diameter
D7DR-7006-AA
2603606 case
2603718 retainer
308/308 bearings
with input spacer ring

Orion RUG CB
Ford RUG CB
D8TR-KA


78-79 F-150


Orion RUG CD
D8TR-MA

78-79 F-150
4.9L 300 I6
5.0L 302 V8

Orion RUG CL
Ford RUG CL
D8UR-EA


78-87 Econoline
4.9L 300 I6
27.6%

1st=3.2508
2nd=1.9213
3rd=1.0000
4th=0.7837
32-35-23-15

D8UZ-7113-A
2603740
T170-8C

(to convert
RTS 'D ratio'
into
RTS 'B ratio')
21T

D8UZ-7017-A
2604484
T170-16F

8-7/8" long

2G central

(interchanges
w/ RTS)
3rd
Direct
18T

D8UZ-7B340-A
2603737
T170-11C

2G wide

(to convert
RTS 'D ratio'
into
RTS 'B ratio')

2-29/64"
diameter
29T

D8UZ-7102-A
2603738
T170-21C

2G wide

(iron case,
interchange
w/ RTS?)

3-53/64"
diameter
32T

D9BZ-7A029-B
2604300
J8132389
T170-12B

0G

(interchanges
w/ RTS)

4-36/64"
diameter
D7DR-7006-AA
2603606

Goldilocks Gearing
Taller 1-2 gears
Favorable 2-3 gap
plus 27% OD

(not originally
configured in RTS case)

78-87 Econoline
78-79 F-150
5.8L 351 V8
27.0%

1st=3.0061
2nd=1.7767
3rd=1.0000
4th=0.7874
31-34-23-15

D8UZ-7113-B
2603745
T170-8D

1G central 34?
22T

D8UZ-7017-B
2603806
T170-16G

8-7/8" long

1G central

(interchange
w/ RTS?)
3rd
Direct
19T

D8UZ-7B340-B
2603744
T170-11D

1G central
3G even?

(interchange
w/ RTS?)

2-37/64"
diameter
29T

D8UZ-7102-A
2603738
T170-21C

2G wide

(iron case,
interchange
w/ RTS?)

3-53/64"
diameter
32T

D9BZ-7A029-B
2604300
J8132389
T170-12B

0G

(interchanges
w/ RTS)

4-36/64"
diameter
T170FS RUG 3+1 (SROD)
Aluminum Turret Shifter
Transmission Codes
% OD
Gear
Ratios
Countershaft
Cluster Gear
(Input-4-2-1)
Input Gear
1-1/16" Dia
10 spline
3rd
Gear
Sleeve
4th OD
Gear
2nd
Gear
1st
Gear
D9BR-7006-AB
2604194 case casting

RUG DB, E0TR-BA
RUG DC, E0TR-BA, 351, 21T input?
RUG DE, E0ZR-EA, mustang?
RUG DG, E1TR-AA
RUG DH, E1TR-BA, 351
RUG DL, E1TR-CA
RUG DN, E1TR-DA
RUG DP, E1TR-EA
RUG DR, E1TR-AB
RUG DS, E1TR-BB, 351
RUG DT, E1TR-CB
RUG DU, E1TR-GA
RUG DV, E1TR-HA, 21T input?
RUG DY, E1TR-JA
RUG DZ, E1TR-KA
RUG EF, E1TR-SA 2WD F150
RUG EJ, 21T input?
RUG EM, E2ZR-AA
RUG EW, 21T input?
RUG FD, 80-83 2WD F150
RUG FE, 81-83 4WD F150?
RUG FM, 21T input?
RUG FN, 21T input?
1979-83 Car Aluminum SROD Transmissions ~ Uses 209/307 Bearings


79-83 Fairmont/Zephyr
3.3L 200 I6
23.6%

1st=3.2889
2nd=1.8381
3rd=1.0000
4th=0.8094
37-40-26-15

D9BZ-7113-A
2604182
T170-8F
24T

D9BZ-7017-A
2603827
T170-16H

9-5/8" long
3rd
Direct
21T

D9BZ-7B340-A
2604181
T170-11F

2-33/64"
diameter
31T

D9BZ-7102-A
2603894
T170-21E

3-50/64"
diameter
32T

D9BZ-7A029-B
2604300
J8132389
T170-12B

4-36/64"
diameter


79-83 Fairmont/Zephyr
5.0L 302 V8
35.6%

1st=3.0720
2nd=1.7169
3rd=1.0000
4th=0.7376
36-41-26-15

D9BZ-7113-B
2603927
T170-8G
25T

D9BZ-7017-B
2603926
T170-16J

9-5/8" long
3rd
Direct
20T

D9BZ-7B340-B
2603924
T170-11G

2-26/64"
diameter
31T

D9BZ-7102-A
2603894
T170-21E

3-50/64"
diameter
32T

D9BZ-7A029-B
2604300
J8132389
T170-12B

4-36/64"
diameter


79-83 Granada/Monarch
4.1L 250 I6
23.6%

1st=3.2889
2nd=1.8381
3rd=1.0000
4th=0.8094
37-40-26-15

D9BZ-7113-A
2604182
T170-8F
24T

D9DZ-7017-A
2603899
T170-16K

8-7/8" long
3rd
Direct
21T

D9BZ-7B340-A
2604181
T170-11F

2-33/64"
diameter
31T

D9BZ-7102-A
2603894
T170-21E

3-50/64"
diameter
32T

D9BZ-7A029-B
2604300
J8132389
T170-12B

4-36/64"
diameter


79-83 Granada/Monarch
5.0L 302 V8
35.6%

1st=3.0720
2nd=1.7169
3rd=1.0000
4th=0.7376
36-41-26-15

D9BZ-7113-B
2603927
T170-8G
25T

D9DZ-7017-B
2603925
T170-16L

8-7/8" long
3rd
Direct
20T

D9BZ-7B340-B
2603924
T170-11G

2-26/64"
diameter
31T

D9BZ-7102-A
2603894
T170-21E

3-50/64"
diameter
32T

D9BZ-7A029-B
2604300
J8132389
T170-12B

4-36/64"
diameter

RUG DA

79-83 Mustang/Capri
Hydraulic clutch
4.1L 250 I6
23.6%

1st=3.2889
2nd=1.8381
3rd=1.0000
4th=0.8094
37-40-26-15

D9BZ-7113-A
2604182
T170-8F
24T

D9ZZ-7017-A
2603898
T170-16M

11-1/16" long
3rd
Direct
21T

D9BZ-7B340-A
2604181
T170-11F

2-33/64"
diameter
31T

D9BZ-7102-A
2603894
T170-21E

3-50/64"
diameter
32T

D9BZ-7A029-B
2604300
J8132389
T170-12B

4-36/64"
diameter

RUG CS
RUG EM

79-83 Mustang/Capri
5.0L 302 V8
35.6%

1st=3.0720
2nd=1.7169
3rd=1.0000
4th=0.7376
20T?

209 bearing

?" long
3rd
Direct
1980-83 Truck Aluminum SROD Transmissions ~ Uses 308/308 Bearings, with input main drive gear bearing spacer ring

RUG DB
E0TR-AB, 2WD


80-83 F-150
4.9L 300 I6
'D' ratio

41.1%

1st=3.2508
2nd=1.9213
3rd=1.0000
4th=0.7087
32-43-23-15

E0TZ-7113-A
2604234
T170-8H
21T

E0TZ-7017-B
2604484
T170-16N

8-7/8" long
3rd
Direct
20T

E0TZ-7B340-A
2605212
T170-11H

1G rearward

2-21/64"
29T

E0TZ-7102-A
(2604232)
2605214
T170-21F

3-53/64"
diameter
32T

D9BZ-7A029-B
2604300
J8132389
T170-12B

4-36/64"
diameter

RUG EL
E2TR-FA


80-83 F-150
5.0L 302 V8
4.9L 300 I6
'B' ratio

27.6%

1st=3.2508
2nd=1.9213
3rd=1.0000
4th=0.7837
32-35-23-15

D8UZ-7113-A
2603740
T170-8C
21T

E0TZ-7017-B
2604484
T170-16N

8-7/8" long
3rd
Direct
18T

E0TZ-7B340-B
2604242
T170-11J
29T

E0TZ-7102-A
(2604232)
2605214
T170-21F

3-53/64"
diameter
32T

D9BZ-7A029-B
2604300
J8132389
T170-12B

4-36/64"
diameter



80-83 F-150
5.8L 351 V8
'C' ratio

37.9%

1st=3.0061
2nd=1.7767
3rd=1.0000
4th=0.7247
31-35-23-15

E0TZ-7113-B
2603243
T170-8J
22T

E0TZ-7017-C
2603806
T170-16P

8-7/8" long
3rd
Direct
18T

E0TZ-7B340-B
2604242
T170-11J
29T

E0TZ-7102-A
(2604232)
2605214
T170-21F

3-53/64"
diameter
32T

D9BZ-7A029-B
2604300
J8132389
T170-12B

4-36/64"
diameter
Peach-shaded cells indicate parts which are still generally available new in the aftermarket.
RTS 3+1 Component Parts Part Numbers
RTS Aluminum Main Case

Face-to-Input Nose 6-7/16"
Case-to-Retainer Nose 3-21/32"
T170-1F
E4TZ-7005-B
C-2604877
C-2605524
Front Bearing Retainer
Overall Length 3-13/16”
Outside Diameter 1-7/16"
For 1-1/16" input shaft
Retainer OD 4.850"
T170-6C

2605314 CI RTS
E4TZ-7050-A CI RTS
w/ pry notches

2603718 CI RUG 3+1
D8UZ-7050A CI RUG 3+1
w/o pry notches

E0TZ-7050-A AL SROD
326724A

RF-E0TR-7050-AA AL SROD
C2604224-1B
Main Drive (Input) Gear Ball Bearing
Main (output) Shaft Ball Bearing

2.5mm input spacer ring
308L4
40mm ID x 90mm OD x
23mm Wide, w/ lock ring

Ford D8OZ-7025-A
KOYO 83763-1
KOYO 83763-3
Ford D8UZ-7025-A
Ford E3TZ-7025-D
Ford E5TZ-7025-C
KOYO NU308C3
743202-L4
MRC 308 SZZG double shield
6308 2RSNR double seal
SKF 6308 2RS1NR double seal
Input Shaft Oil Seal CR/SKF 11111
CR/SKF 11123
D8UZ-7A283-B
E3FZ-7A011-A
National 3638
Victor Dana 45820
Input Shaft Cylindrical Roller Bearings
15 required
C417Q
BCA Federal Mogul
Main (output) Shaft
2WD (23-11/32")
32-37-28 Spline
T170-2K
E0TZ-7061-C
2604483
Main (output) Shaft
4WD (19-11/32")
32-37-31 Spline
T170-2M
E1TZ-7061-C
2604466
Counter Shaft
(7/8" diameter, 10-1/8" long)
WT296-3
2602657
Counter Shaft Cylindrical Roller Bearings
42 required
QAR33724
BCA Federal Mogul
C1086Q
Reverse Idler Shaft WT296-35
2602658
Reverse Idler Cylindrical Roller Bearings
44 required
C407Q
BCA Federal Mogul
Reverse Idler Gear
16T
25 Splines
3-17/32" long
T170-10B
2603617
8132399
D7DZ-7141-A
Reverse Idler Sliding Gear
19 Spur Tooth
T170-10C
WT296-10C
2605066
8132402
D9BZ-7D223-A
1-2 Synchro Sleeve
w/ Mainshaft Reverse Gear
22 Spur Tooth
WT296-81
2605139
1-2 Synchro Hub & Sleeve Asm
(long keys)
1AT170-80B
2670167
3-4 Synchro Hub & Slider Asm
(short keys)
1AT170-2.5B
1-2 Fork T170-23E
3-4 Fork T170-23F
Reverse Fork T170-23G
RTS Shift Lever Steel Cap E4TZ-7220-A
Iron RUG 3+1 Cluster Gear
32-35-23-15T

Use w/ T170-11C, 18T Overdrive Gear
from a 1978-87 Iron RUG CB, CD, or CL
to convert an RTS 'D ratio' from 41.1% to 27.6% OD, or for
use as a replacement gear in an existing 27.6% RTS 'B ratio'
T170-8C
D8UZ-7113-A
2603740
Iron RUG 3+1 4th Gear (OD)
18T

Use w/ T170-8C, 32-35-23-15 Cluster Gear
from a 1978-87 Iron RUG CB, CD, or CL
to convert an RTS 'D ratio' from 41.1% to 27.6% OD, or for
use as a replacement gear in an existing 27.6% RTS 'B ratio'
T170-11C
D8UZ-7B340-A
2603737
41.1% RTS 'D ratio'
AB  2WD
AC
AG
BM
BS  2WD
BT  4WD
BY

27.6% RTS 'B ratio'
AD
AE
AJ
BJ
BP
BU  2WD
BV  2WD
BZ  4WD
CS

37.9% RTS 'C ratio'
AF
AA
AH  4WD
AK  2WD
BN
BR
BW

E4TR BA



E6TR JA
E6TR KA





E4TR JA


E6TR LA
E6TR MA
E6TR RA





E4TR HA
E4TR NA




Drivability Considerations ~ Torque and Power

Overdrives are a Physics problem, not just a Mathematics problem!

Increased Torque and HP at the right RPM are required to go faster at lower engine RPM, not just mechanical overdrive gear ratios!

Any Model A or B Ford would benefit from the added engine torque and horsepower of a 5.5 or greater compression ratio cylinder head and a Stipe IB330 camshaft.

Essentially, top vehicle speed will occur when aerodynamic drag equals power output.
Proper gearing keeps the engine RPM in the useful range between "just below max torque" to “around max power” for all road speeds.
Stock Model A Torque and Horsepower Curves
Improper gearing results in lugging the engine at low RPMs and destroying Babbitt engine bearings!

Lugging occurs when the engine is operated under load at below peak torque for any length of time.

Also, don't forget to improve your brakes!


Drivability and Suitability ~ Recommended Combinations

Highlighted below are the relative drivability improvements of various transmission gearings compared to the stock Model A gearing. Assumptions are based on stock tire sizes and engine configuration.

Blue-shaded attributes are equivalent to the stock Model A.
Green-shaded transmissions, ratios, and attributes are preferred for improved drivability compared to stock Model A.
Yellow-shaded attributes are questionable.
Violet/Red-shaded are the least desirable.
Three Speed
Transmission
Rev 1st 2nd 3rd 4th % OD Optimal Drivability and Suitability ~
Recommended Combinations and Usage Notes

Stock Model A
1928-31
3.745:1 3.12:1 1.85:1 1:1 ~ ~
  • 4.11 rear axle in a heavy-medium weight car and/or hill terrain.
  • 3.78 rear axle in a medium-light weight car.
  • 3.54 rear axle in a light weight car and/or flat terrain.

Stock Model B
1932-34
3.383:1 2.820:1 1.604:1 1:1 ~ ~
  • 4.11 rear axle in a heavy-medium weight car and/or hill terrain.
  • 3.78 rear axle in a medium-light weight car.
Synchronized 2nd and 3rd gears.
15% Taller 1st and 2nd gear ratios are similar to Model B.

When coupled with a 28% Mitchell driveshaft overdrive unit (or 33% OD unit with a 4.11:1 axle), this transmission approaches the "Goldilocks" solution for both low speed and high speed drivability, though without a transmission overdrive gear.
CON: Significant added OD mass on torque tube.
CON: Extra OD shift lever on floorboard.

1931 Ruckstell
Dual High
2.50:1 1.00:1 0.80:1 ~ 25%
  • 4.11 rear axle in a heavy-medium weight car and/or hill terrain.
  • 3.78 rear axle in a medium-light weight car.
1st gear ratio is even taller than Model B.
2nd gear ratio is direct, 1:1.
3rd gear ratio is a 25% overdrive, not 1:1.
Increased engine Torque and HP are highly recommended.

Mitchell Synchro
15% 2nd only
Model A
3:12:1 1.61:1 1:1 ~ ~
  • 4.11 rear axle in a heavy-medium weight car and/or hill terrain.
  • 3.78 rear axle in a medium-light weight car.
Synchronized 2nd and 3rd gears.
15% Taller 2nd gear ratio is similar to Model B.
CON: No improvement in 1st gear ratio.

Mitchell Synchro
15% 1st & 2nd
Model A
2.71:1 1.61:1 1:1 ~ ~
  • 4.11 rear axle in a heavy-medium weight car and/or hill terrain.
  • 3.78 rear axle in a medium-light weight car.
Synchronized 2nd and 3rd gears.
15% Taller 1st and 2nd gear ratios are similar to Model B.

When coupled with a 28% Mitchell driveshaft overdrive unit (or 33% OD unit with a 4.11:1 axle), this transmission approaches the "Goldilocks" solution for both low speed and high speed drivability, though without a transmission overdrive gear.
CON: Significant added OD mass on torque tube.
CON: Extra OD shift lever on floorboard.
3+1 Overdrive
Transmission
Rev 1st 2nd 3rd 4th % OD Optimal Drivability and Suitability ~
Recommended Combinations and Usage Notes
Stock Model A
1928-31
3.75:1 3.12:1 1.85:1 1:1 ~ ~ BASELINE REFERENCE - Stock tire sizes and engine configuration
Stock Model B
1932-34
3.38:1 2.820:1 1.604:1 1:1 ~ ~ BASELINE REFERENCE - Stock tire sizes and engine configuration

RTS 'C ratio'

37.9%

Tremec
T170FT RTS
F-150 TOD
3.01:1 3.01:1 1.78:1 1:1 0.72:1 37.9%
  • 4.11 rear axle in a heavy-medium weight car with added power and/or flat terrain.
  • 3.78 rear axle in a medium-light weight car with added power and/or flat terrain.
  • 3.54 rear axle in a light weight car and/or flat terrain.
Fully synchronized.
Taller 1st and 2nd gear ratios are much more favorable compared to stock Model A.
4th gear (overdrive) ratio is less favorable for Model A and early V8 era Fords compared to code 'B ratio' transmissions.
Better suited for city driving and general driveability.
Increased engine Torque and HP are highly recommended for highway driving.

Goldilocks
Gearing


27.0%

T170F RUG 3+1
gears in a
T170FT RTS case
3.01:1 3.01:1 1.78:1 1:1 0.79:1 27.0% For Model A and Early V8 Ford.
(never originally configured in a F-150 T170FT RTS case by Ford/Tremec).
See Specification Table at top of page for exact RUG 3+1 parts required to configure.
  • 4.11 rear axle in a heavy-medium weight car and/or hill terrain.
  • 3.78 rear axle in a medium-light weight car.
  • 3.54 rear axle in a light weight car and/or flat terrain.
Best suited for both city and highway driving, and across a range of weights and terrain.
Increased engine Torque and HP are recommended.

RTS 'B ratio'

27.6%

Tremec
T170FT RTS
F-150 TOD
3.25:1 3.25:1 1.92:1 1:1 0.78:1 27.6%
  • 3.78 rear axle in a medium-light weight car.
  • 3.54 rear axle in a light weight car and/or flat terrain.
  • 3.27 rear axle in a light weight car and/or flat terrain.
Fully synchronized.
1st and 2nd gear ratios are worse than stock Model A.
2nd to 3rd gear gap is worse than stock Model A.
4th gear (overdrive) ratio is more favorable for Model A and early V8 era Fords compared to 'C ratio' and 'D ratio' transmissions.
Better suited for highway driving and/or underpowered engines.
Increased engine Torque and HP are recommended.

RTS 'D ratio'

41.1%

Tremec
T170FT RTS
F-150 TOD
3.25:1 3.25:1 1.92:1 1:1 0.71:1 41.1% Not Recommended - no benefits for most cars!
  • 4.11 rear axle in a medium-light weight car.
    Bad 1-2, 2-3 shifts.
  • 3.78 rear axle in a light weight car and/or flat terrain.
    Poor 1-2, 2-3 shifts. Poor 4th gear ratio.
  • 3.54 rear axle in a light weight car and/or flat terrain.
    Bad 4th gear ratio.
  • 3.27 rear axle in a light weight car and/or flat terrain.
    Bad 4th gear ratio.
Fully synchronized.
1st and 2nd gear ratios are worse than stock Model A.
2nd to 3rd gear gap is worse than stock Model A.
4th gear (overdrive) ratio is very unfavorable for Model A and early V8 era Fords compared to 'B ratio' and 'C ratio' transmissions.
Increased engine Torque and HP are required for highway driving.
Rev 1st 2nd 3rd 4th % OD
Blue-shaded attributes are equivalent to the stock Model A.
Green-shaded transmissions, ratios, and attributes are preferred for improved drivability compared to stock Model A.
Yellow-shaded attributes are questionable.
Violet/Red-shaded are the least desirable.


Conversion and Installation Considerations

It is recommended to use the Model AA truck four-speed transmission clutch (bell) housing rather than the Model A three-speed transmission clutch housing as the basis for the conversion.

The 1929-31 Model AA truck clutch housing is shorter fore-aft than a Model A three-speed housing, and its use requires less (if any) modification to the frame center crossmember for clearance to the transmission and U-Joint covers.

Both the Model AA and BB truck clutch housings have the same critical dimensions.
The inside diameter of the opening for the transmission front drive gear retainer is 4-3/4 inches (4.750").
The fore-aft dimension between the flywheel housing contact surface and the transmission case mounting surface is 5-9/16 inches (5.5625").

The Model BB clutch housing does not have any front radius rod (wishbone) mounting provisions compared to a Model AA housing, but the BB housing is necessary when using a Model B/BB flywheel housing and uncut Model B oil pan. Model AA and BB flywheel and clutch housings are not interchangeable with each other. They must be paired along with the corresponding oil pan.

Use of either the Model AA or BB clutch housing does however require fabrication of brake and clutch pedal mounting provisions. A provision for mounting the emergency brake handle to the transmission must also be fabricated.

The shift lever opening position in the floorboard and mat is slightly affected, moving rearward from the stock Model A position.

The Model AA throwout bearing hub, clutch release shaft, arm, and pressure plate are used.a 1949 Ford clutch disc. A Ford 8N-7550 clutch disc,
A C5NN-7600 pilot bearing and C0NN-7580-A throwout bearing can also be used.

Alternatively, a 9 inch diaphragm pressure plate and matching clutch driven disc for a 1983-88 Ford Thunderbird or 1984-86 Mustang SVO 2.3L turbocharged four cylinder can be mounted to a lightened and faced Model A or B flywheel by drilling and tapping six additional holes. The Thunderbird's 9 inch clutch disc hub has the same 1-1/16 inch x 10 spline as the Tremec RTS input shaft.

The system conversion based on the Model AA clutch housing also requires the shortening of the Model A torque tube, drive shaft, and rear radius rods approximately 1-1/2 inches.

To provide clearance to the crossmember flange at center, cut off the top center bolt hole tabs on the inner and outer Model A universal joint upper clamshells, or alternatively, use the early V8 era four-bolt clamshells. Design the hole pattern in the rear main bearing retainer for the chosen clamshell design.
Modification to the Tremec transmission itself involves:
  1. Drilling and tapping the front of the case for the Model AA clutch housing attaching bolt locations.
     
  2. Reduction of the front main bearing retainer outside diameter size to fit the Model AA clutch housing bore (4.750 inches)
    (for reference, the stock Tremec retainer outside diameter is 4.850 inches, and the throwout diameter is 1.430 inches)
     
  3. Enlargement/sleeving of the front main bearing retainer diameter to match the AA throwout bearing hub.
     
  4. Shortening of the (main drive gear) input shaft pilot nose length by about 5/8 inches, and removal of about 1/4 inch of spline length from the front of the shaft.
     
  5. Replacement of the tail shaft extension with a suitable rear bearing retainer adaptor plate.
    (for reference, the stock Model A rear bearing retainer thickness is 1-5/16 inches (1.3125") between the gasket mounting surfaces.)
     
  6. Shortening, splining, drilling and tapping of the rear of the transmission output (main) shaft for mounting the Model A universal joint.
     
  7. Adaptation of the shift lever to suit the user's needs. A 1980-86 Jeep T176 one-piece cane shift lever can be easily adapted to replace the Ford stub shifter shaft. Search for Crown Automotive 5359835 shift lever.
     
  8. A very nice 1-7/8" diameter black engraved 4 speed shift knob (3/8"-16) is available from core-shifters.com to fit the Jeep lever.


Disassemby and Reassembly Tools

Because of the unique internal design, construction, and gear diameters of the RUG 3+1 and RTS overdrives, neither the input nor output shaft can readily be removed from the case without first pulling the ball bearings from the shafts and case. The opposite sequence is necessary for reassembly. Special Ford service tools were made in order to accomplish this while the trans was on the bench.

Even after removing the bearings there are a number of steps in particular sequence necessary to get the case emptied and the entire transmission apart. It is not as easy or straightforward as working on a conventional four speed performance toploader of the 1960s-70s.

Ford Rotunda/OTC Essential Service Tools for Toploader Transmissions
Number Bold-on-Green shaded tool numbers are useful for RTS   
T57L-500-B Bench Mounted Holding Fixture
T64P-7111-A Dummy Countershaft Tool
T64P-7140-A Dummy Reverse Idler Shaft Tool (4") (RAB, RAN, RUG)
T75L-7025-A Transmission Bearing Service Set
T75L-7025-B Remover/Replacer Tube (Short) (308-024)
(RTS Input Shaft Bearing Remove/Install)
T75L-7025-C Remover/Replacer Tube (Long) (308-025)
(RTS Output Shaft Bearing Remove/Install)
T75L-7025-D Bearing Collet (2), Car-Large
(HEH, RUG, RUG-BP Output, 35/80/21mm 307 size)
T75L-7025-E Bearing Collet (2), Car-Small
(Output, 35/72/17mm 207 size)
T75L-7025-F Bearing Collet (2), Truck
(RUG-Cx 3+1, RTS, SROD, 40/90/23mm 308 size)
T75L-7025-G Bearing Collet Sleeve (Car) (308-029)
(HEH, RUG, RUG-BP Output) (207/307 size)
T75L-7025-H Bearing Collet Sleeve (Truck) (308-030?)
(RUG-Cx 3+1, RTS, SROD) (209, 308 size)
T75L-7025-J Forcing Screw (15/16"-12 x 8-3/8")
(RUG 3+1, RTS Input Shaft Remove; 2WD Output Shaft Remove)
T75L-7025-K Bearing Shaft Collar Installer (308-031)
(RTS Input/Output Shaft Bearing Install)
T75L-7025-L Threaded Shaft Adaptor (308-032)
(Internal/External Threaded) (for RTS w/ Model A U-Joint Splines)
T75L-7025-M Bearing Shaft Collar Installer (308-033)
(0.960" ID Ranger M5OD-R1)
T75L-7025-N Bearing Shaft Collar Installer (308-034)
(0.812" ID Ranger RAD)
T75L-7025-P Bearing Shaft Collar Installer (308-035)
(1.065" ID RTS 2WD Output Shaft Bearing Install; Ranger M5OD)
T75L-7025-Q Replacer Dummy Bearing (308-036)
(Borg Warner T-18, T-19; 35/40mm ID, 72/90mm OD)
T75L-7025-R Bearing Shaft Collar Installer (308-037)
(Borg Warner T-18, T-19)
T75L-7025-S Bearing Shaft Collar Installer (308-038)
(Borg Warner T-18, T-19)
T77F-7050-A Seal Installer (Input Bearing Retainer)
T77F-7050-B Seal Remover (Input Bearing Retainer)
T77L-7025-A Bearing Collet (2), (3.3465 OD) (308-065)
(HEH, RUG, RUG-BP Input, 45/85/19mm 209 size)
T77L-7025-B Dummy Bearing (308-066)
(HEH, RUG, RUG-BP Output 35/80/21mm 307 size)
T77L-7025-C Remover/Replacer Tube (Short) (308-067)
(RUG 3+1, RTS, SROD Input Shaft Bearing Install)
T77L-7025-D Shaft Clamp (308-068)
(RUG 3+1, RTS, SROD Input Shaft Bearing Install)
T77L-7025-F Transmission Bearing Service Set (RUG-BP)
T84T-7025-A Bearing Replacer (308-091)
(RTS 4WD Output Shaft Bearing Install)
T84T-7025-B Forcing Screw (15/16"-12 x 11.5") (308-092)
(RTS 4WD Output Shaft Bearing Remove)
Fabricate Bearing Installer ~ Double-Stud Adaptor
(for modified RTS Output Shaft with Model A U-Joint Splines)
(use with T75L-7025-L and T75L-7025-B )
Fabricate Alternate Bearing Installer ~ Heavy Bushing
(for modified RTS Output Shaft with Model A U-Joint Splines)
(use with T75L-7025-K, T75L-7025-R, T75L-7025-B, and hex bolt )
Fabricate Bearing Remover ~ Button-Head Centering Stud
(for modified RTS Output Shaft with Model A U-Joint Splines)
(use with T75L-7025-F, T75L-7025-B, and T84T-7025-B)
Fabricate Alternate Bearing Remover ~ Hex Bolt Centering Stud
(for modified RTS Output Shaft with Model A U-Joint Splines)
(use with T75L-7025-F, T75L-7025-B, and T84T-7025-B)
Purchase Pry Bar, Pin Punch, Hammer, Snap Ring Pliers, 1/2" & 5/8" Tools,
Chain Wrench for Shift Lever Cap


More related information on Ford Garage:

  1. For more Model A & B related information, use the Site Search box at the top or bottom of this page.
  2. Model A Ruckstell Dual High Transmission
  3. Model A Mitchell Synchronized Transmission
  4. Model A & B Rear Axle Gear Ratios
  5. Model AA Four-Speed Transmission Clutch Housing

December 2017