Transmission Conversion?

[MurphyJ]

I would like to convert my stock 3-speed, column shift transmission on a 1955 F-100 6 cylinder to a modern T 170 RTS 4 speed overdrive top loader transmission. Can anyone direct me to where I might find if such a conversion is possible and where such information can be found. Many thanks for any help or suggestions.

[rotorwrench]

There have been several folks ask this question for early F100 pickups. It is do-able but like any conversion, it will take some ingenuity on your part. The RTS pickup transmission has the butterfly pattern bolt up like most top loaders. Getting one to bolt up to a Y-block bell housing will be the lions share of work. The Tremec RTS also has part of the old Borg Warner narrow pattern but only three of the bolt locations are usable. Some folks weld ears on the bell housing to pick up the bolts and others fabricate a bolt on adapter. Bolt on adapters may also require a spacer on the flywheel so that could be problematic in this application.

I've not tried it so I have little more to add and few have responded to this question with much more information than this. The parts for this transmission are not well supported so what ever you find needs to be in good condition. They are popular in the model A crowd and some have been set up for the later V8 cars & pickups with closed drive. A vehicle with open drive like the F100 would save some of that effort for sure. The Type B transmissions coded as follows; AD, AE, AJ, BJ, BP, BU, BV, BZ, & CS all have the 26.7% overdrive reduction and are the best ones for V8 applications. They were always mounted on the 302 V8 pickups in the years that they were available from 1984 through 1986 plus some early 1987 models.

[MurphyJ]

Thanks Rotorwrench for you prompt response to my question and providing such helpful information. A few years ago I did put a RTS transmission in a Model A and it was a neat and fun conversion. Sure would be fun to have one in my 55 F-100.

[flathead 53]

I was looking to do that conversion on my 53 f-100, there are several issues to address , #1 the clutch linkage ,#2 your bell housing is part of engine mount, also its cast iron,forget about welding ears to it. you might look into cornhuskers ,they have a complete kit to mount CHEVY S-10 ,5 SPEED to your truck,this may be a better way to do it ,I'm on hold with my conversion on the 53 , may go with the 5 speed ,I have my t-170 for sale now , good luck.

[MurphyJ]

Thanks Flathead 53, more helpful information. I came across John Mummert's webpage and he adapts the bell housing to accept the T-5 transmission bolt pattern and I plan to contact him regarding his ability to do the same for the T-170 RTS. He is located in Southern California at phone number 619-596-0312 if you are still interested.

[rotorwrench]

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Cast iron can be welded but it is best done by those who have a lot of experience and the heating equipment to get it done right.

[flathead 53]

Another way that may work, would be to get a bell housing from a 53 to 56 f-250,the bolt pattern may work for your trans. check it out there are a few on ebay now.

[MurphyJ]

Thanks Flathead for the tip as I did not know there was a difference in the bell housings,
F-100 to F-250.

[miker98038]

I’m using one of Mummert’s truck bells in front of a TKO500 in my roadster. I’ve done 3 stoker motors with his parts. He’s good and straight, but can be a bit hard to get hold of.

[flathead 53]

Another issue is you will need to fab a bracket for your clutch linkage , the stock transmission has a mounting point cast into it , the t-170 does not ,you will need to mount a plate on top of new trans and come out to a point where attach the clutch linkage to ,I started to make one out of 1/4 inch plate to mount to top of trans then makes a 90 deg bend ,and has holes to mount clutch bracket. look at stock set up ,you will see what I'm talking about.

[Daves55Sedan]

I've never heard of anyone trying to do it on a 6-cyl. The '55 would have been a 223 Mileage-maker. It would certainly require a custom made starter plate. If I remember correctly, The 223 has two transmission bell-housing bolts at the top and one at each side down at the bottom for a total of four engine-to-bellhousing bolts.
I could see laying a flat piece of 1/16 inch thick steel plate down on the floor, then laying your old starter plate over it to mark all the holes (the crankshaft flange hole, and four engine mounting holes). Then lay your conversion bellhousing over it so you can mark all the holes, including the centerline of the starter. Cutout the outer profile of the plate to match the conversion bellhousing. Cutout the crankshaft hole. Measure the diameter of the hole needed for the starter. Use a compass to mark off the hole for the starter from the centerline you had previously marked. Cutout that hole. Drill or punch-out all the bolt-holes with the proper size tools.
You'd ruin lots of metal-cutting jigsaw blades cutting out the outer profile, the crankshaft hole and the starter hole. Maybe start the cutouts with an abrasive disc in a Dremel rotary tool just enough to get you jigsaw blade to fit into.
This whole thing would be impossible if it turned out that one of the original 223 mounting holes interfered with the location of one of the conversion bellhousing holes.

[Ole Don]

I had a SROD overdrive behind a Y block in a 55 car. The ratios really suck. If you need to spend real money on a gearbox, step up to a T5 five speed. They are so nice, you will find it money well spent.

[rotorwrench]

The SROD and RTS share a lot of parts but have a different shift set up. The shift rail set up feels funky when you shift it. The turret top on the RTS is more positive. The T170 RTS transmissions that were used behind the 302 V8 engines have a 26% ratio overdrive so there isn't as bad a drop when shifting into OD. The only problem is that a lot of them also have the 4WD housing on the back for the transfer case bolt up. Those are good candidates for the closed drive Ford vehicles prior to 1949 since that stuff comes off anyway. The 6-cylinder RTS transmissions have different rear axle ratios so they had two taller overdrive ratios on them. It is quite a drop in rpm when you shift into OD on those.


Three of the inner pattern bolt holes on the RTS case will fit a 4-bolt early Borg Warner pattern. The fourth one, if attempts are made to use it, will affect the top case cover so it's really not usable at all. Most folks that modify a bell just add one chunk to the bell to catch the wider pattern bolt in lieu of the one odd bolt. The bore of the bell that catches the input bearing retainer sleeve may also need to be opened up a bit but I don't know. Some folks have had to put a sleeve on the bearing retainer in order to use a different throw out bearing hub.


A lot of the 6-cylinder 223 bell housings have the narrow Borg Warner pattern. The Y-block V8, I'm not so sure. The 4-speed housings have a pattern for the big T98 transmission. That would likely have to use an adapter plate. The length of the input shaft would govern whether a crankshaft spacer would have to be fabricated for the flywheel. A person has to watch for clutch clearance in the bell if they go that route.

[tailgaterdude]

https://transmissionadapters.com/col...ord-223-to-aod

[MMB]

A better bellhousing starting point as was alluded to earlier with reference to the F250 is the T98 four speed bellhousing which was an option on F100's also.