2015 LML Transmission Leak

[t2timmy]

Hello all,
So ive got a small trans fluid leak under my truck only when I start it in the am to warm up. The truck and trans is bone stock. The drip is the size of a quarter or so. I drive it once a week on the weekend for dump/beer runs. It only has 55K miles on it. Ive only seen the leak twice in the last month. Its winter here so its cold out. But the truck is garaged all the time. Checked the trans fluid and its at a good level. Also crawled underneath it both times and I cannot find fluid anywhere. Not one drop. I just got home and had her running in the garage and shifted it through the gears and no leaks!!

Soooo where is it coming from? Why so seldom? Why only when running? Im confused.


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[Chevy1925]

well... if its red fluid under the trans area, its coming from the trans for sure. from there, its a total guess to us since we cant see the truck.

my best suggestion, pull the bellhousing inspection cover thats on the bottom of the bell housing and see if there is any fluid in there. might be an input shaft seal leaking.

 

[t2timmy]

Thanks for the reply! I may have to pull the inspection cover like you suggest.

Its def red trans fluid. I changed the fluid when i first got the truck back in 2020 when it only had 45K miles.

But there is no visible fluid anywhere around the trans and I just ran it for 10 minutes with not a drop. Is it possible from sitting all week and then starting for first time that pressure in the trans pushes some fluid out of the air vent?


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[Chevy1925]

Thanks for the reply! I may have to pull the inspection cover like you suggest.

Its def red trans fluid. I changed the fluid when i first got the truck back in 2020 when it only had 45K miles.

But there is no visible fluid anywhere around the trans and I just ran it for 10 minutes with not a drop. Is it possible from sitting all week and then starting for first time that pressure in the trans pushes some fluid out of the air vent?


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na and you certainly would see a trail down the trans case to where the pan bolts to the case.

iirc there was an old TSB out there for LBZ and maybe LMM about a trans leak during first start up when cold and going into high idle. i dont remember what the fix was though. i know that info is on this site though

 

[2004LB7]

When the engine and transmission are cold the pressures can be higher then when warm when the fluid is thinner. It's possible it seeping out only when cold. I think there where several people that had the bell housing bolts behind the converter leak. Was able to see a drip or two on the bolts when they looked through that inspection port. The crush washer on the bolts that was supposed to seal it up was not doing a good job or the casting had some porosity in it that allowed the fluid to seep through at that spot

 

[t2timmy]

Thanks for the reply. Im gonn let her sit overnight. Check trans fluid in am. Then start it up in the garage, check for leaks and if i find one, il NOT move the truck and see if i can get an idea where its originating from.

Every time ive found the little puddle drops its been after ive left the house and came back.


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[Trimox]

Transmission fluid level needs to be checked with engine at operating temp and running (if you move it it through all the gears before checking even better).

 

[t2timmy]

Yes i did check it while warm and running.
When you check it cold should it also be started and running? Or is that check done not running?


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[2004LB7]

When you check the level cold, you are basically just making sure you have some fluid in there. Then you know it's safe to start it and check again. But it doesn't give you an accurate reading until up to temperature

 

[t2timmy]

Update: Still trying to get her to leak again.. obviously I dont know where the leak is coming from cause I cant identify where/when the drip occurs. Ive got tar paper under it now to help ID its origin the next time it may of may not leak.
Next time it leaks il post.


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