ClassicOldsmobile.com - Transmission

TH400 new to me

Tirediron — Thu, 28 May 2026 13:49:38 GMT

I've just finished a 455 motor rebuild and now it's transmission time. The trans came with the motor and I dont know anything about its history. It has no obvious leaks at front or rear seal or pan and that's all I know. And, tho ive rebuilt a few manual trans, I've never been inside an automatic.

Should I just change the oil and bolt it up and hope for the best, or should I do something more?
Like drop the pan and change the filter?
Replace front and rear seals?

Thanks for any advice.

1964 F85 2 speed to 3 speed swap stall converter question

Cmpeirce123 — Sat, 16 May 2026 17:23:18 GMT

Hey,

Been a while I haven't posted since covid for my 425 build in my 1964 F85. I had a th400 built for it a couple years ago and am now making time to swap it in. I need to get a converter for it. I've put all my specs in to chatgtp and it suggests a 3200 stall. What brand works best? My engine is a 65 425 that's

.030 over
Cam is 230/234 @.50 .496/.504 lift from Mark
Edelbrock rpm intake
HEI distributor and MSD ignition
Roller rockers
Long tube headers to 3 inch thrush welded mufflers
Rear tires are 255/60r17 so 29 inches tall

Still have the stock 2 speed and 2.73 gears in the car. So definitely a mismatched driver terrain. Was planning on a ford 9in with 3.50 gears but have had two kids since covid and allocate funds else where lol. A rear end will be next though or possibly just swap gears for the time being. Any input is appreciated!

Most recent video of the car if anyone is interested in seeing it. -

Thanks,

Cameron

Transmission hesitation

Furbody — Fri, 15 May 2026 14:07:36 GMT

My 69 VC, has developed an issue, when under power everything works as it should, but when letting off gas, and the tr@nsmission drops to a lower gear, then giving gas again there�s a noticeable hesitation between the gears, but only when not under power, when under power the transmission shifts as it should. The vacuum line is as old as the car, it�s my first thought on a cause, could that be the problem, or is there something else.

1983 Delta 88 transmission leaking

DeltaDude88 — Fri, 08 May 2026 04:04:02 GMT

Hello everyone. My transmission is leaking and I'm not sure from where. I replaced the pan gasket today but that wasn't the issue. There is a steady stream coming from between the bell housing and the transmission pan. I've attached a photo. Any suggestions would be helpful and appreciated. I plan on dropping the transmission but are there options I can try before doing that?

66 Cutlass Th350 install

DDRock — Tue, 05 May 2026 11:53:15 GMT

So I am going to install. TH350 in my father�s 66 Cutlass that has a 330/ST300 2spd column shift. I understand the install is straight forward and have done trans replacements. The only thing I can not figure out is the kickdown cable. He has a 4barrel Quadrajet on his 330 with all the factory linkage. I don�t see how to hook up the kickdown cable to the throttle arm of the carb. There is no hole for it. See pics below. I know I can buy an aftermarket bracket and cable but not sure how it would attach or if the factory linkage would be in the way. Car is in FL and I am in NJ. He is brining it up for me to do the swap. Is there factory parts I can get from a later model?

Thanks,
Derek

2004R users- TCC lockup?

DocN — Fri, 01 May 2026 17:14:14 GMT

Those of you who have done a swap to a 2004R, what did you use as a TCC controller?

I'm just in the wrapping-up stages of my install, and went for a setup I've been calling the "three switch" kit. I used a kit from Painless that has a pressure switch, a vacuum switch and a brake switch.

I've also seen everything from a manual switch on the shifter, to an aftermarket computer controller. I asked around on some of the other boards I'm on, and couldn't really find any personal experiences with any of the various options. Just curious to know what you used, and how you like it.

Doc.

Vibration after TH400 reinstall � smooth in Neutral, shakes in Drive - 1971 442

keyboard — Tue, 28 Apr 2026 20:43:24 GMT

Hi everyone,

I’m looking for some advice regarding a vibration issue that started after recent work on my 1971 Oldsmobile 442 (TH400 automatic).

Here’s the full context:

A few days ago I brought the car to my mechanic for several jobs:
- Water pump replacement
- Fan clutch replacement
- Radiator replacement
- Thermostat replacement (180�F)
- Coolant outlet neck replacement
- Power steering pump seals replacement
- Engine oil and filter change
- Fixing a leaking exhaust manifold (co-driver side)

Additionally, I wanted to replace the rear main seal. To do that, the transmission, torque converter and driveshaft were removed. However, once everything was apart, we realized that accessing the rear main seal would require removing the crankshaft, so we decided not to proceed and reassembled everything exactly as it was.

Important note:
The torque converter was not drained separately and was reinstalled together with the transmission. The driveshaft was also reinstalled, and according to the mechanic, it was placed back in its original position.

The problem

Since getting the car back, I have noticed the following:
- A noticeable vibration and humming noise starting around 50 mph (~80 km/h)
- The vibration is felt throughout the whole cabin (not just steering wheel)
- It gets more noticeable as speed increases
- The car initially felt sluggish and the transmission was behaving erratically

After checking, I found the transmission fluid level was incorrect (likely due to radiator replacement and cooler lines). I corrected the ATF level properly (hot, engine running), and now:
- The transmission shifts correctly again
- The car no longer feels “lazy”

However:
- The vibration is still present exactly the same as before.

Key observation (very important)

At around 50–60 mph, when the vibration is present:
- If I shift the transmission into Neutral (N) while rolling, the vibration immediately disappears.
- When I go back into Drive, the vibration returns.

What I suspect so far

Given this behavior, I believe the issue is related to something that only happens under load, possibly:
- Torque converter issue or misalignment
- Driveshaft (U-joints or angle issue)
- Transmission output shaft / yoke
- Something related to how the transmission was reinstalled

Before this work, the car had no vibration at all.

Questions for the experts:
- Have you seen similar behavior on a TH400 after removal/reinstallation?
- Could a torque converter that “seems fine” still cause this type of vibration?
- Is it possible for U-joints or driveshaft angle to cause vibration ONLY under load but not in Neutral?
- Any known quirks on these cars regarding transmission alignment or crossmember positioning?
- Could an exhaust component (especially after working on the driver-side manifold) be touching the frame or transmission and cause vibration only under load, disappearing in Neutral?

Any insight or similar experiences would be greatly appreciated. I’d like to narrow this down before taking the car apart again.

Thanks in advance!