The Stovebolt Site Forums The Shop Area Driveline Auto trans conversion questions

Plan is to get Langdons adapter and put a THM350 behind my '54 3100's 235. Does anyone know if I'll have to modify the floor other than for a shifter hole? It's got a flat floor. Also, anyone have a pic of their DIY rear transmission cross-member? I need a couple of ideas besides buying one.
Thanks

You may want to look through these Pictures. No floor mod was necessary.

Thanks Dave, also reminded me that I needed rear engine mount mods. Those pads look familiar, '51 front car pads?

The mounts are 1935-51 pass front.

I made one. It's pretty easy.

http://img.photobucket.com/albums/v...ion%20and%20differential/Crossmember.jpg

http://smg.photobucket.com/user/Ave...0differential/Undersidecomplete.jpg.html

This is a '58 with a 4 speed, but the concept is the same.

I didn't make that nasty hole in the floor, the PO did that for me....

Would you need to remove or modify the existing cross member at the engine/transmission intersection?? Someone said it had to be removed, which weakened the frame some....

John

I put a TH200-4R behind a 248 in a GMC. Should be basically the same as what you are doing. I cut a notch out of the rear crossmember and left it in place for strength. Pictures here. I also had to cut the floor.

Isn't the issue with cutting the crossmember out under the bellhousing actually frame flex at the spring mounts? I think a better option would be a modified crossmember for transmission clearance, but leaving the reinforcement in there to stabilize the suspension. Modifying one thing often creates problems with a totally unrelated system. Of course, the support at the rear of the transmission is a necessity.
Jerry

I'll try to notch out the stock member then fab the side & rear mounts if time permits.
Was thinking about how to do all of this in my sleep last night, with your input, it's looking much simpler now.
Thanks guys

Any other DIY rear x-members out there.

In my case, using a 235 mounted in it's stock position, using a TH350, in a 1955 1st Chev PU, there was no way to leave the crossmember.

I would in no way do this conversion on my own truck but with customers I have to do what they want(I warned him first).

The main thing I do not like about cutting out or weakening the crossmember in any way is that the front cab mounts attach on brackets on the outside of the frame in this same area.
If you modify the crossmember the cab mounts will be allowed to continually flex the frame on every bump.
This is already a weak area of these frames. I have needed to weld up cracks in many of these frames in this same area.

I have noticed it sure leaves a long gap w/o any support so I've been looking the net but haven't seen any mods to address removing that cross-member. Having not got to that point yet I thought maybe lower and/or move the member down-forward. What are your thought?

The truck I installed this in was lowered, so I could not drop the crossmember lower.
It would be tough to move it.
Most people just cut it out.

Don't some of those automatics eat up a lot of horsepower. I know that the Powerglide was designed for the 235 but some of these other ones were designed for more powerful engines.

The truck I linked pictures to ran well with a 235 TH350 for several years. I recently swapped out the TH350 for a 200R4 and he loves it.

I recall seeing numbers posted from Car Craft putting them roughly in order from least to most HP loss:
PowerGlide
200-4r
T350
700r4
T400
4L80
but don't quote me on this.
I figure if I want an auto I'm going to have to sacrifice power.

I've been watching the development of the automatic transmission since my father was the first man to repair them in Nashville Tennessee in the very early 1950's. They have become far more efficient and reliable in those 60-something years. I'd much rather have a modern 4L60 or 4L80, or something similar than the Ford C-4's and Turbo 350's I made a living repairing for a lot of years. They consume less power and last longer, plus they have an overdrive top gear that reduces engine RPM for highway cruise. Just don't go too high on the final drive gear. Once the engine drops below its torque curve, gas mileage and performance goes out the window.
Jerry

Another possible stumbling block.

There appears to be two different crankshaft pilot openings, small 1.686 for std. trans engines and large 1.703 for auto engines. Transition was around 1954 when all cranks where made large.

So if I find that my '54 truck engine is the small type what are my options?

Machine torque converter?
Machine crankshaft?
Replace crankshaft with new one, which one?
Thanks

Machine the crank.

It isn't the pilot bushing bore but the larger bore outside of it. I did it to put the 700R4 in this '48 235.

Not too difficult.

That way if you need to change a converter later, no need to machine again.