1939 Buick Special Trasmission Woes

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Let me update you on my transmission woes. I’ve run this car in Great Race for the last 3 years. I don’t think the transmission is up to the constant shifting and loading. After all this is a 4000 pound car and a 60 pound transmission. Good for normal driving, not good at stress.

I now own 3 1939 Special transmissions. #1 parts are in a bucket under my workbench, having failed in a most spectacular fashion during the 2022 Great Race. The rear bearing failed (I suspect because the main shaft internal pilot bearing went bad, allowing too much runout on the shaft), the fluid escaped and everything internal overheated badly. I bought #2 transmission and gave it to a local old time tranny rebuilder who was really dubious about the internal parts from #1. I put the rebuilt #2 in the car and ran the 2023 Great Race without problems. BUT then in a weekend practice rally last October it locked up with 10 miles left in the event. I got it out of lock, finished the rally and towed the car home. When I checked the fluid it was full of metal.

So, I bought transmission #3. Which was supposed to be very low mileage. Not true. I swapped transmissions and found #3 leaked at both ends. I then gave #2 to a recommended tranny shop and pulled #3 to reseal it. My machinist friend Jim and I took #3 apart and found the bearings were worn, we replaced them and everything looked good after re-assembly. Felt good too. There didn’t seem to be any problems. So I put it back in the car, went out for a test drive and found that the darned thing would not stay in second gear.

On a side note, the first transmission guy went out of business right after I picked up the rebuilt #2. I called my 2ndtransmission guy last week and got his answering machine which said he was in the hospital and wouldn’t be back at work until the end of May. It is getting harder and harder to find people to work on these old cars!

Transmission #3 runs great in reverse, first and third. It stays in 2nd on deacceleration, but when accelerating it pops out. It’s hard to even hold it in gear. I dragged out my 39 shop manual and went through the transmission shifter adjustment procedures. Several times! No change. It still won’t stay in second gear.

Now I’m wondering if anyone in the Buick community has an inkling why? I suspect there is something internal that is bad, but when we had it apart, there was no sign of it. My machinist Jim swears the problem must be external. The synchros don’t have teeth and ours looked very good, we re-used many of the spacers and retainer rings that were in it, I bought new detent springs, but they were much larger than the originals and we didn’t use them. As I said, it went back together and shifted easily and precisely on the bench. In the car not running you can feel the detents when you shift it. But under load…



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