ZL1 Rear Diff Cooler Leak

[Tomtom87]

A few weeks back, after taking the car out of storage, I observed a very small transmission fluid leak near the rear differential. I suspected it was a line leading into the differential for the cooler.

I took my car to a shop and they told me that the leak was coming from the differential cover itself and not the line and that they were leery on taking the cover off due to it being aluminum and parts being discontinued.

Since alot of you know these cars inside and out better than I do, does that make sense? If its leaking from the cover wouldnt that mean the trans fluid is contaminating the diff fluid? Any advice would be appreciated. Thanks

[CamaroCracka]

It would take a lot of trans fluid leaking into the diff to make the gear oil redish. Your diff would have to be overfull. Pull the fill plug to see if it's overfull and compare the color of the diff fluid to what you see leaking. IIRC, those cooler fittings have an o-ring that could need replacing.

[bsn]

Your transmission is isolated from your differential by the driveshaft. I would be very surprised it would be the cover it's pretty beefy, I am even more surprised if they thought it was the cover why they would balk at fixing it-looks to be pretty simple to do and flange sealant or a high quality silicone would work. More likely it may be the front pinion seal and oil is migrating down. If it is the pinion seal if you don't have any play in your pinion bearing, automotive oil stop leak may fix it. The pinion seal is hard to find. I would suggest getting a second opinion from someone reputable. Even if the cover has a crack or porosity its an easy fix to tig weld it and machine it. No reason to live with a leak.

[Tomtom87]

Only reason I dont suspect its diff gear oil is because the color of the fluid is red and its definitely trans fluid. If it was near the pinion it would be gear oil ya?

[Tomtom87]

Originally Posted by CamaroCracka

It would take a lot of trans fluid leaking into the diff to make the gear oil redish. Your diff would have to be overfull. Pull the fill plug to see if it's overfull and compare the color of the diff fluid to what you see leaking. IIRC, those cooler fittings have an o-ring that could need replacing.

I may need to take it somewhere else. I do think it could be an o ring on the cooler fitting

[bsn]

The trans cooler lines go forward not rearward has your differential fluid ever been changed with a non factory oil? With a little baby powder and a lift the exact source of the leak should be simple to find.

[Tomtom87]

Originally Posted by bsn

The trans cooler lines go forward not rearward has your differential fluid ever been changed with a non factory oil? With a little baby powder and a lift the exact source of the leak should be simple to find.

The diff was serviced last year by the dealer , with i assume would be factory gear oil.

[NZZL1]

Originally Posted by Tomtom87

I observed a very small transmission fluid leak near the rear differential. I suspected it was a line leading into the differential for the cooler.

If its leaking from the cover wouldnt that mean the trans fluid is contaminating the diff fluid? Any advice would be appreciated. Thanks

Do you mean the area circled in red?

If so, I doubt that it would be the cover, as then there would diff oil and not trans fluid leaking. There are a number of clips and seals used with the diff cooler pipes that might be the cause of the leaking.

https://www.camaro5.com/forums/showthread.php?t=452920

https://www.gmpartsgiant.com/parts-l...ing_lines.html

[Tomtom87]

Originally Posted by NZZL1

Do you mean the area circled in red?

If so, I doubt that it would be the cover, as then there would diff oil and not trans fluid leaking. There are a number of clips and seals used with the diff cooler pipes that might be the cause of the leaking.

https://www.camaro5.com/forums/showthread.php?t=452920

https://www.gmpartsgiant.com/parts-l...ing_lines.html

Yeah im starting to think i may need to take the car to someplace else. This was the dealers diagnosis.

[CamaroCracka]

Originally Posted by bsn

The trans cooler lines go forward not rearward has your differential fluid ever been changed with a non factory oil? With a little baby powder and a lift the exact source of the leak should be simple to find.

ZL1s have a cooler in the diff that is fed trans fluid from the trans. Fluid runs from the radiator to the cooler in the diff and from the diff cooler to the drivers side of the trans. It is used to keep the diff cool with track use. Same story for Z28.

[NZZL1]

Originally Posted by Tomtom87

Yeah im starting to think i may need to take the car to someplace else. This was the dealers diagnosis.

I don't wish to diminish your capabilities or inclination to undertake mechanical maintenance, but as a guess I am thinking it will be the rubber "grommet / seal" behind the square end of the pipe(s) that connects to the diff cooler, and it will be an easy repair.

I have removed my manual transmission a couple of items, and the same square ended pipe is used in the diff cooler return line, and it is surprising loose but this pipe is positioned high on the transmission so does not leak. Most of these diff cooler pipes are "plug-ins" with retaining clips that are easy to connect/disconnect but don't seem to leak, and I guess the square ended portions will be just as easy to work on.

Review the links to determine in advance the parts that you may need. I am guessing for each line (if you do both) you will only need 22786616, and perhaps but probably not 19210848 and 22786620 from the linked following. It may be no parts are required and that 19210848 and 22786620 just need tightening a little.

https://www.gmpartsgiant.com/parts-l...ing_lines.html

Note that the numbering 16, 17, 91, 20, 21 in the part "descriptions" above corresponds with the numbering shown on the following.

https://www.camaro5.com/forums/showthread.php?t=452920

Unfortunately, most of the GM parts websites no longer provide such exploded diagrams or parts details. Give your own repair a go, if you feel brave or so inclined.

[bsn]

Quote:
Originally Posted by bsn View Post
The trans cooler lines go forward not rearward has your differential fluid ever been changed with a non factory oil? With a little baby powder and a lift the exact source of the leak should be simple to find.
"ZL1s have a cooler in the diff that is fed trans fluid from the trans. Fluid runs from the radiator to the cooler in the diff and from the diff cooler to the drivers side of the trans. It is used to keep the diff cool with track use. Same story for Z28."

My ZL1 only has 11K so I have never changed the diff fluid-I know the diff calls for 75W-90 and the trans is ATF so are the coolers connected somehow where trans fluid can get in the diff?

[CamaroCracka]

Originally Posted by bsn

Quote:
Originally Posted by bsn View Post
The trans cooler lines go forward not rearward has your differential fluid ever been changed with a non factory oil? With a little baby powder and a lift the exact source of the leak should be simple to find.
"ZL1s have a cooler in the diff that is fed trans fluid from the trans. Fluid runs from the radiator to the cooler in the diff and from the diff cooler to the drivers side of the trans. It is used to keep the diff cool with track use. Same story for Z28."

My ZL1 only has 11K so I have never changed the diff fluid-I know the diff calls for 75W-90 and the trans is ATF so are the coolers connected somehow where trans fluid can get in the diff?

The cooler is inside the diff and sealed off from the diff fluid. It takes "overcooled" (GMs words not mine) fluid from the radiator trans cooler and runs it through the diff cooler to drop the 300+ degree temps the diffs seen on the track. Then the fluid returns to the trans on the driver side.

Pretty sure you're correct on the diff fluid but I use 75w145 because I run it pretty hard. Plus, I occasionally think I hear a tiny whine on acceleration, but it might just be the tinnitus. I've already put away a master rebuild kit just in case.

[Shodown]

It's probably one of these 2 lines from the cooler. The ZL1 as previously stated uses ATF from the trans to cool the diff. I bet of the o-rings went bad. Very easy and cheap fix. I've never heard of a ZL1 diff seal leaking.