[avbates]

Hello. I just had my TH400 go out this weekend, and was looking around and managed to find one from a 71 Olds 98. Both have the long tail, and I am
curious about swapping the Olds in to my Deville. I am fairly certain they will work alright length-wise, but have not a clue about bolt pattern. Anyone
have a clue?

 

[avbates]

Found this: Buick / Olsmobile / Pontiac / Cadillac
Buick engines and TH400's are natively compatible when choosing a Buick V8 or V6 version of the transmission. All Buick, Olds, Pontiac and Cadillac TH400's share the same engine pattern, commonly refered to as the "BOPC" pattern. on https://www.novak-adapt.com/knowledge/th400.htm.

Seems like a done deal.

 

[aeronca36606]

Unfortunately your 1967 Deville has the 429ci engine. This has a different bolt pattern then the 71 Olds. The olds does have the BOP bolt pattern. The 429 has a different bolt pattern. In 1968 the 429 was replaced with the 472 which does have the BOP pattern. Your 67 should also have a switch pitch torque converter. This was discontinued in 68. I believe the output shaft is also larger on the 68 and newer but of that i am not sure. Memory is fading in my older years!

What symptoms do you have with your current transmission. The THM400 is one of the strongest transmissions ever made and usually lasts a verry long time. You may have a problem that could be an easy fix.

 

[avbates]

I am fairly confident in my ability to get these together. The problem with my original transmission is a lot of lateral play in the output shaft. I don't really want to get inside
a transmission, but I would be interested in what the cause could be. There was vibration in the car and I evaluated everything I could think of narrowing it down to the
drivetrain. Then with the rear tires jacked up I put the car in gear and there was a lot of movement (other than the good rotational kind) in the drive shaft (propellor shaft according to the manual). I assumed universal joint, but after taking the shaft down, I found the shaft and joints were fine and it was the transmission that was the problem.
I don't mess with transmissions, but I would think that some rear bearing on the output shaft must be shot and allowing the shaft to spin but not keeping it concentric.

I'm open to ideas, and defer to your wisdom.

 

[aeronca36606]

You need to check the front universal joint centering ball. Your front joint should be of the constant velocity type. There is a centering ball in the center between the 2 u joints. If this is worn it will allow the drive shaft to run off center and can cause a lot of vibration. The center ball was originally not replaceable on the 66 but this was changed in 67 or 68. I do not remember which year.

You could also have a bad bushing in the tail shaft. If this is the case you would probably also notice wear on the front slip joint outer bushing area. The tail shaft housing may be able to be replaced on the car. It has been a while since i had a THM400 apart. Your trans may be ok but due diligence is required.

 

[avbates]

I will most definitely take a look at that. I am pretty fearless, but I have never opened a trans. Always swore I wouldn't, but I also said that about differentials and I rebuilt a Dakota so I may be bad about swearing things off.
I am going to buy this trans anyway. It's been rebuilt (guy has receipt) and it's only 450. I am not going to get to this repair for a while, but having things to look at in the
meantime is helpful. If anyone has any other ideas I would love to hear them.

 

[aeronca36606]

If your trans is indeed bad remember the 71 trans will not bolt up to your 67 engine, You will have to disassemble the trans to swap the cases. I am not sure if you will run into any issues with incompatibly with the internals. Since you already have to completely dissemble the trans it might be better to get yourself a Transmission rebuild kit and rebuild your original trans. THM400 are relatively straight forward and much simpler than today's Front Wheel Drive Transmissions. Your costs will be about the same or maby even cheaper (as long as you do the work yourself).