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Transmission leak after changing fluid

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May 16, 2017, 7:29 PM

Post #1 of 8 (769 views)
Transmission leak after changing fluid Sign In

Changed the tranny fluid and filter on my 77 Pontiac Trans Am. THM 350 auto trans. No leaks before fluid change. About 60,000 miles on car. It is not leaking from the pan gasket. Or the main seal. Double checked both. The fluid is dripping from the right (passenger) side corner of the pan above the gasket. Again not from the pan gasket. Also it doesn't appear coming from the file tube. Had no drips until the fluid change. Also it doesn't appear to leak when the car is running. Starts about 15 minutes after shut down. Any ideas on where it coming from?

Tom Greenleaf
Ultimate Carjunky / Moderator
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May 16, 2017, 9:59 PM

Post #2 of 8 (748 views)
Re: Transmission leak after changing fluid Sign In

OK - You just did a standard drop pan, replace filter and gasket and refill job - right? Now it has this strange leak?

First - you tell me/us (have a trans specialist should be by) if this pan just drops down or a pest with things in the way? Was that a fight to get out and back in?

Is this an alloy or steel pan? If steel did you check that it's straight with a straight edge? Those (used all over the place many pans + assorted vehicles) will lift in between bolt holes mostly from being overtightened and you straighten that while off car. NEVER OVERTIGHTEN THOSE BOLTS AND EASY WITH ANY GASKET CEMENT IF ANY USED.)

Dipstick tube: You checked. Guessing now you used a long neck funnel hard to keep in place and may have spilled from top of funnel or a problem with end of dipstick tube and funnel? Maybe did that happen?

Would take a while to finish dripping down if so with some caught up who knows where.

I think cooling lines run on that side also on those so were they OK and not disturbed? OE there were clips that hold those tight to each other so they don't rub and quickly wear holes in each other might have waited to leak just a little till this job. If those lines can rattle around do something about it. New clips or split insulation so they can't touch each other to rub or wobble around - had several assorted wear right thru right after having been touched at all.

All questions so would check the work up to drop the pan again and get another gasket checking the pan carefully you say doesn't leak but I'm not convinced yet.

Note: You shouldn't need a sealer cement for gasket but surfaces very clean. Gasket should have enough smaller holes that about 4 or so bolts hold gasket in place for installation but could still fold a corner.

It just happened so again would go right back and just a gasket and if only the ATF in the pan lost so be it go new again it already mixed with the other two thirds,



May 17, 2017, 3:04 AM

Post #3 of 8 (742 views)
Re: Transmission leak after changing fluid Sign In

There should be your kickdown cable/linkage just above the pan, clean it down with some carb cleaner or brake kleen to pinpoint the leak


May 17, 2017, 1:46 PM

Post #4 of 8 (714 views)
Re: Transmission leak after changing fluid Sign In

Did not do the fluid change myself. Is was done by the shop that does all the work on the car. Going back in the shop 3 o'clock on Friday.
Did standard pan drop and replaced filter and fluid. Nothing in the way of the pan to remove or replace.
Steel pan. Not sure if checked by straight edge.
No fluid spilled.
Got under car myself yesterday. Cooling lines look good all dry. Looks to me like its leaking from where the cable goes into the trans right above the pan on the right side of the trans.
Shop owner said he is going to drop the pan again and check it himself.
Talked to a local transmission tech today. He said if its not the pan its either the fill tube or where the speedo cable goes in to the trans.
I think I should have left well enough alone and didn't change the fluid.


May 17, 2017, 1:50 PM

Post #5 of 8 (712 views)
Re: Transmission leak after changing fluid Sign In

Thanks for the reply. Looks like the leak is where you said. Looks like a plastic fitting with a cable going in it. held in with a 10mm hex bolt.


May 17, 2017, 5:25 PM

Post #6 of 8 (701 views)
Re: Transmission leak after changing fluid Sign In

So the kick down cable is leaking, sometimes its a pain to unhook the cable from the top, sometimes its easier to drop the pan and unhook it from the valvebody, depending on the year, it either takes a boot or o-ring. Gary


May 20, 2017, 2:30 PM

Post #7 of 8 (673 views)
Re: Transmission leak after changing fluid Sign In

Tom and Gary thanks for your input. It was the kick down cable leaking. We dropped the pan again and changed O rings on the cable fitting and fill tube. Checked the cooling lines. They were showing signs of rubbing together as Tom mentioned. Fixed that also. Car has been in my garage for over 24 hours. Not a drop on the floor. Thanks again for the replies.


May 20, 2017, 6:31 PM

Post #8 of 8 (664 views)
Re: Transmission leak after changing fluid Sign In

Great, thanks for letting us know

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