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Hagerty
Hagerty Employee

Piston Slap: Giving the Camaro's gearbox the full "Monte"?

I have a 200-4R transmission out of a 1987 Monte Carlo SS installed in my 1969 Camaro (behind a 375-hp small-block Chevy). It runs great and shifts fine, but after I stop for a period of time I get a massive oil leak that appears to be coming from someplace at the top of the transmission.
https://www.hagerty.com/media/maintenance-and-tech/piston-slap-giving-the-camaros-gearbox-the-full-m...
4 REPLIES 4
relton
Advanced Driver

This sounds a lot like a leak in the dipstick tube or seal.

When the engine stops, fluid in the top half of the torque convertor drains back into the transmission case. raising the level significantly. It is not uncommon, in older cars, for a small rust pinhole leak to form in the tube. It's relatively easy to pull out the tube and check, and replace the seal at the bottom.

It's also possible, though less likely, that the seal around the shift selector shaft, is worn and leaking. Same results. It can usually be replaced while the transmission is still in the car.

Hydra-matic transmission don't have an "overflow tube". They have a vent tube to the atmosphere. If the transmission is overfilled, the fluid can foam and com out the vent tube. This condition corrects itself after enough fluid is expelled. Th fluid will be foamy.

Long shot possibilities are the rear seal, and the gasket between the case and the case extension.

If the transmission has to come out, you might consider replacing it with a 700R4 (AKA 4L60). It's a much better transmission in every way, stronger and far more reliable.

My experience with the Ford 4R70W is that external leaks are usually around the shift shaft seal. Ford has a somewhat complicated arrangement here.

Chrysler Torqueflites always leak around the throttle lever linkage. Older ones don't even have a seal here, a certain leak.
Swamibob
Technician

I agree on most of what you say here. I think the more likely problems are the TV cable seal or the tube seal. I've had that myself, on a couple automatics.
I'd have to disagree a bit on the 200 4R vs the 700 R4. I've read a lot on both transmissions and both compare favorably. The great thing with the 200 4R is it fits in place of a short tail TH350 or a powerglide and you can use the same driveshaft. I've done that twice, on early Chevelles.
The 700 R4 is a much larger case and in small cars, like the Camaro, will require surgery of the floor pan to make it fit properly.
If it were my Camaro, I'd take the auto out and install the new Tremec TKX 5-speed, (they have a smaller case than their TKO cousins and will fit in that car without floor surgery also) but I really like to row gears. 🙂


gkala
New Driver

I reached out to Sajeev on this and, by chance, had tried a few of his suggestions in the interim. I bought a scope and discovered the top of the transmission was absolutely dry. I used the scope and checked everything I could but came up clean. The front pump was dry as well.

While under there I noticed that the braided hoses looked a bit damp at the swivel (https://photos.app.goo.gl/vGpw32XUzhiUr2Gy7). I swapped them out for some tried and true rubber to eliminate that as a possibility. I thought it was unlikely as I didn't think they would drip back to the case and on the pan (where the drips were visible). I was right, it made no difference. I should point out that when I say after a period of time, it would sometimes be days before the leak manifested.

As I'm researching I came across adapters for the 1/4 inch fitting to AN6 for the 200-4R on a performance parts site and noticed something shocking. They had o-rings!

When I put this transmission in, oh so many years ago, the internet did not have the wealth of information it has now on all things automotive. I pulled the stock brass fittings, saw that a 1/4 fitting threaded in, and ordered 1/4" NPT to AN6 fittings. 25 years later, I find out that there is such a thing as 1/4" NPSM. (https://photos.app.goo.gl/jTxTURWWvBZrFCVU8)

I replaced the fittings 2 weeks ago and it's been bone dry ever since.
Sajeev
Community Manager

It's amazing the things I have learned because of the Internet...well, it takes a while to sift through the garbage on the Internet, but it's worth it! 

Congrats on finding the fix!