Piston Slap: Giving the Camaro’s gearbox the full “Monte”?

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George writes:

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. It does not leak while running. Maybe it is the overflow tube or maybe the seal at the TV cable?

Is there anything else that could be causing the level to rise after I stop?

Sajeev answers:

You’re on the right track, George. Transmission leaks can happen at a seal, especially as tolerances open up as the gearbox cools down. I reckon you have a bad seal or gasket in one of three places: the front pump, overflow tube (if applicable), or the TV cable. I vaguely remember having this problem years ago, when the front pump on my Ford 4R70W started puking ATF a few minutes after I parked the car.

I quickly learned that accessing the front pump is kinda tough (as it lives inside the case), so try to eliminate it from the list. Check for leaks from the other two places, and this is when a smartphone-based inspection camera makes life unbelievably easier. If the camera’s view is inconclusive because of caked-on dirt, clean those two areas, re-run the Camaro and check again after it cools down. If the base of the TV cable and overflow tube are dry (and therefore leak-free), remove the transmission to inspect/address the front pump. The video below isn’t 100 percent applicable, but it should get the point across.

Considering the labor involved in removal and reinstallation of a gearbox, sometimes it’s beneficial to get the whole thing rebuilt at this point. And if you are unsure of the condition of the donor Monte Carlo transmission upon removal, going “full Monte” on it now is a wise move in the long term, because if the front pump seal is worn, what else is going on in there?

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