Dear Members, I need your help. I am getting ready to pull the Hydramatic trans out of my 61 Bonneville. The unit leaks badly and loses about a pint of fluid about every 100 miles. I want to rebuild it to handle a bit more power as I will be rebuilding the 389 engine to 425A specs. My question is who sells performance components for these transmissions or better yet, who offers a complete performance rebuild service for these units. Best Regards Gerry
slim jim rotohydramatic ? the old timers at the olds dealer were still bitchin about them 20 years ago
Thanks for the input, I thought about switching to a Turbo 400 also, I was told their is a problem because of the starter location on the 389. I am considering swaping out the engine and transmission and holding onto the original drivetrain in the event I sell the car. I know for sure this is not a slim Jim trans because Pontiac held over the 4spd Hydramatic for the Bonnevilles only for model year 61. I was hopeing their was some salvation for this trans. Thanks for your thoughts regards Gerry
Yes I am on the Performance years however, I didn't get receive feedback from the Forum. I will follow up with Cliff Ruggles. Thanks Pitts64. Regards Gerry
The four-speed dual-coupling hydro is more fun to drive than a TH400 and it basically locks up in high gear like your modern OD trans converters do, so you get better fuel economy with one. If all it does is leak, put some gaskets in it and go and just don't beat on the thing. They put them behind 421s too - The D-C Hydro was used on all Pontiacs in '60 and Bonneville only 61-64. Cadillac also used them into '63. As for a swap, you need an adapter that has a starter mount on it to run a later trans with the '63 and back blocks. Originally they mounted to the bellhousing - and even the auto trans uses a short bell to mate up - before the ear was added to mount them on the block.
Thank you for your input. I will have to re-seal the trans, the bulk of the leak is coming from where the cooling lines go into the transmission. I spoke with the transmission shop that used to build my racing transmissions Select Performance in Babylon NY. Ed senior the owner, is a Pontiac lover and familliar with these units. I will have them do the rebuild. Thanks again for your insight. Sincerely Gerry
I have a '63 Bonneville that has the exact same trans and had nearly the same problem that you are describing. The problem turned out to be the torque converter. Well, it really wasn't the torque converter, it was the gigantic o-ring that is between the two halves that form the torque converter. The two halves are bolted together and the o-ring acts as a seal between them. Over time the o-ring became as hard as kellsy's nuts and no longer provided a proper seal. My tranny guy has been in business for a long time and knew exactly what the problem was and where to get the proper parts to fix it. The trans now is leak free and shifts like a dream. They really aren't bad a transmission and if you are looking to get back on the road without a lot of drama involved in switching over to a TH 400 (there are adapters available, but last I looked they were about $750!!!), a rebuild of your present trans can be a good path to follow. In any event, good luck.
Thanks for the information regarding the converter. This explains the huge leak that I have in the front of the trans that leaves the 6"wide oil slick on the garage floor. I'm telling you between this and the leaky rear main seal it's like parking the Exon Valdez in my Garage!! Best Regards. Gerry
The 4 speed hydros are neat. I used to enjoy driving my street 60 Ventura with the old hydro. I found a guy in Leesburg who understood these trannys and he rebuilt it.. You can shim the pressure relief valve with some 5/16 flat washers for a stiffer shift and play with TV rod to alter shift points. Keep them full of fluid and they are damned near bullet proof. The granny gear first gear gets all the mass moving even with a decent road gear. FWIW: I believe GM didn't call them torque converters...they were fluid couplings IIR.
Having owned a 61 Bonneville for 7 years, ('65 / '72)...I'm all in favor of finding a good trans person to rebuild that 4 speed unit. The only problem mine ever had was the governor going bad,...which was a relatively quick fix. Wish i still had that car !!!! 4TTRUK
Gearstar.net can do it. They qouted me $1800.00 and about 2 weeks turnaround time. They have a monthly add in Street Rodder. I got an answer back to my inquiry within 2 days. Bill
B&M used the original design, which was discontinued in early in the '56 model run. The dual range hydros, used from '52-'56, were considered the best cores.
If you join the PY forum, look for member name stevep in the 1961 or older folder - he's a transmission expert and he's in Massachusetts - he can help you out with the rebuild. As far as I know there are no real performance parts for them anymore, but a good stock rebuild will hold up to a 425A engine without problems. I had a '61 Bonneville convert with the four speed automatic for many years, it's a great transmission. The hardtop I have now is a 425A / four speed stick car.
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