90 Suburban transmission leak?


19k40rocky
08-19-2012, 09:00 PM
I was pulling a motorcycle trailer down the interstate about 75 mph for about 4 hours. When we got home I noticed it looked like there had been an oil leak. I looked underneath and it appears like tranny fluid spewed out of the top vent tube on the tranny. I have a 4x4 with a Automatic overdrive. It was tranny fluid and it does not appear that it was low on the stick when I checked it. We were pulling some hills and it would downshift but it seemed to be working fine. Seems to still work ok. We had the tranny rebuilt about 50,000 miles ago. Does anyone know what this means? is there anything I should be doing about it?

j cAT
08-20-2012, 07:43 AM
I was pulling a motorcycle trailer down the interstate about 75 mph for about 4 hours. When we got home I noticed it looked like there had been an oil leak. I looked underneath and it appears like tranny fluid spewed out of the top vent tube on the tranny. I have a 4x4 with a Automatic overdrive. It was tranny fluid and it does not appear that it was low on the stick when I checked it. We were pulling some hills and it would downshift but it seemed to be working fine. Seems to still work ok. We had the tranny rebuilt about 50,000 miles ago. Does anyone know what this means? is there anything I should be doing about it?

when you tow you do so in 3rd gear not overdrive.

what occured was you overheated the tranny fluid. I would replace the fluid now. only use dexronVI. DO NOT USE DEXRON III.

HOPEFULLY YOU HAVE DEXRON VI IN THE TRANNY NOW. this GM approved fluid [2006] which replaced dexron III can take more heat.

19k40rocky
08-20-2012, 09:01 PM
Thanks for the info. I had dextron/mercon V in it. I had heard it was ok to tow in OD if it was not doing alot of downshifting. It did some in the hills but didn't seem to do alot. Apparently that was incorrect. If I had not noticed the oil splatter on the back of the bumper when disconnecting the trailer I would not have known anything about it as it had shifted and pulled just fine. I will go ahead and change the tranny fluid again. I last changed it about 10,000 miles ago/2 years ago. We only use it mostly to take the boat to the lake or tow one of the kids cars etc back and forth if they break down. Will Dextron VI mix ok with Dex/Merc V? or should I just put Dex/Merc V back in it? I really appreciate your help on this. Thanks a bunch! I will look forward to your reply

j cAT
08-21-2012, 08:19 AM
Thanks for the info. I had dextron/mercon V in it. I had heard it was ok to tow in OD if it was not doing alot of downshifting. It did some in the hills but didn't seem to do alot. Apparently that was incorrect. If I had not noticed the oil splatter on the back of the bumper when disconnecting the trailer I would not have known anything about it as it had shifted and pulled just fine. I will go ahead and change the tranny fluid again. I last changed it about 10,000 miles ago/2 years ago. We only use it mostly to take the boat to the lake or tow one of the kids cars etc back and forth if they break down. Will Dextron VI mix ok with Dex/Merc V? or should I just put Dex/Merc V back in it? I really appreciate your help on this. Thanks a bunch! I will look forward to your reply

dexron VI is fully commpatible with dexron III. If GM did not make it compatible that would be quite a BIG problem.

since you did this towing in OD the fluid did indeed overheat to the point where it come out the overflow tube. this will require fluid replacing now. not after the damaged fluid eats at the internal parts. DEXRON III turns into an acid when overheated.

when towing/hauling loads the transmission always slips slightly. when in OD the design is to reduce slippage by lockup of the torque converter. with towing this then causes the fluid to get hot . in 3rd gear the flow is not creating this heating effect on the fluid.

with the newer models like I have [2000] you tow in 3rd gear with the tow/haul mode switch in. now you have the transmission downshifting sooner when you load up the engine going up a grade or accelerating.this helps reduce heat build up.

with the fluid replacement you will notice after a few hundred miles quicker upshifts. the reverse engagement will be quicker.

I also found in cold weather below 20 deg f no shift issues, shifted like normal / no delay.

19k40rocky
08-21-2012, 10:30 PM
Thanks again for your help. I dropped the pan and drained the fluid this evening.

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