TH400 on a Nailhead

[jshanks]

Can anyone tell me which, if any, Nailhead engines will bolt right up to a Buick Turbo-Hydramatic transmission? I know adapters can be purchased for the older engines (322, 364 etc.), but I'm weighing my options, and a direct bolt-up may be easier . . . Thanks

[Guest]

One of our members in the North Texas Chapter did this with his 1962 LeSabre, which has its original 401 V-8. I don't recall what modifications he had to make, if any, but I can put you in touch with him if you want. He is not a mechanic by any means, so I can assure you that it did not require much in the way of modifications.

Pete Phillips, BCA #7338

Ector, Texas

pphillips@netexas.net

[Guest]

The only TH400 that will bolt directly to a nailhead is the Buick ST400 made from '64 to '66. The only nailhead it will bolt directly to is the 401-425 from '64 to '66. The earlier 401-425's have a larger guide hole in the crank shaft for the dynaflow converter. Avoid the '64 ST400 ... it's a bit different than the '65-'66 400's requiring a different rebuild kit and only has 5 shifter detents (has only low and drive). The '65-'66 400's are actually pretty much the same as all other TH400's made since then except for the round bell housing to match the nailhead engine. Plus the switch pitch converter of course.

[NTX5467]

The conversion on the '62 LeSabre was done by Phoenix Transmission in Weatherford, Texas. Not much modifications as such were needed, but there were some brackets and other linkage items that were procurred from a local salvage yard.

I know that it made a huge difference in the way the car performed. Enough so that he had to hide the keys from his teenage son.

Enjoy!

NTX5467

[Mrbuick714]

I put a "400" on a 63 401 by using a 64 Crankshaft and flex-plate. It worked very well.

[jshanks]

Thanks everyone, I'm going to try to find a reasonably priced 401 and an ST400.

At least I'll be able to keep my '55 "all Buick". By the by . . . I'm also planning to change (not modify) the rear-end. Any suggestions?

Right now my plan is to try to find an open drive shaft(not a torque tube) GM rear-end that is about the same width as the original and weld stock coil mounts, the pan hard mount and a 4-link to it. Does that sound reasonable for a street car?

Thanks Again

[Guest]

I have a '55 special done pretty much the way your thinking of going. I didn't keep it all Buick though. I used a '77 lincoln Versalie rear end (9" ford) with disk brakes. The four bar suspension works quite well. Mine is a triangulated four link instead of parallel so no need for the panard bar. I'm not sure, but I think a '69 to '72 GM A body rear end may be close to the correct width if you want to keep it all Buick.

[Guest Skyking]

NTX, your answer is contrary to what Neverdone said. He claims the 62 can't be done. The reason I ask is I will probably want to make that change in my 62 in the future. Would I have to change the crank??

[NTX5467]

When I approached Greg, who owns and operates Phoenix Transmission, he started talking about what parts would work with what and such and made it sound like it was no big deal. He knew what years of what other full size GM cars that certain things would be needed from to make it work, probably a driveshaft length change too, and that a local salvage yard usually had what was needed. Our chapter member dropped the car off and it was ready about a week later. No engine work or crankshaft change was needed.

I have no intimate knowledge of the various year models of Nailhead V-8s, but in this particular situation, it was just transmission items that were affected on this particular '62 401 LeSabre. No doubt, Greg knew what torque converter would work and made that happen too. Greg is also a Buick buff so obviously he'd "been there" before with some of his street rod customers that used Nailheads in their cars.

So, with all due respect, I do know that such a conversion on a particular '62 LeSabre 401 did happen and happened very successfully several years ago. I don't have a parts list of what was needed or used, but most was available locally in a salvage yard that had many middle '60s GM full size cars in stock at that time.

NTX5467

[Guest Skyking]

Thanks NTX, a few years ago I also heard that the TH400 would fit a 62 with no major changes.........

[Guest]

The original question from jshanks was which nailhead engine will bolt DIRECTLY to a TH400. Answer is '64 to '66 nailheads to '64 to '66 TH400. Prior nailheads will require work. Going into a "55 buick, he may as well just drop the entire "64-"66 setup in.

[NTX5467]

I believe that it's already been mentioned that ONLY a THM400 with a "B-O-P" case/bolt pattern will work as the THM400 for Chevrolet motors matched the Chevrolet blocks' bolt pattern, which was different. There might be some "dual pattern" cases on the THM400s too, as there have been on other GM automatics in prior times, but suspect they will be in the minority if they exist at all.

NTX5467