Q: Slow transmission fluid leak which the mechanic I went to says was caused by a faulty seal even though it was replaced last week.

asked by on July 17, 2017

Last week I had a major transmission leak. Found out the bracket holding the dipstick tube in place broke and the seal which held it in was not functional. I replaced it. I found out 4 days later that another tube from the transmission pan was bent and I brought it to the shop and had it replaced by a mechanic. After sitting in my garage for 6 hours, I noticed transmission fluid on the floor under my vehicle. It started fine and showed enough fluid when I checked. The fluid was very small but prevalent. I took it back to the same mechanic who told me it the seal was bad and that was where the leak was from. My question is - why did it take 5 days for this particular leak to emerge? Does it really take 5 days of driving to build up that much pressure for a leak to emerge?

My car has 120000 miles.
My car has an automatic transmission.

Hi there. The problem with trying to diagnose this transmission fluid leak issue you have with the Hummer is that it’s quite possible that the leak could be caused by multiple issues. Certainly a loose transmission fluid tube or damaged o-ring can cause a significant leak. However, an external or internal seal leak can take time to build up pressure to leak as well. It’s also possible that the leak of fluid from the tube reduced the pressure inside the case. When that leak was fixed, it most likely increased the pressure inside the hydraulic lines which exposed existing issues with the seals. These are all SPECULATIONS - and POSSIBLE reasons, but it would require a detailed inspection to determine exactly why this has occurred.

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