Keep breaking oil pans

[Dpayne]

Hello all. New guy with a question. I got a 2005 tahoe z-71. Recently my 3-4 clutch pack went out. Removed the tranny to have it rebuilt. Had the castec heads that started loosing coolant. So i pulled the motor, new heads. Front and rear main seals etc etc. Put on the pan. Re installed the motor , trans. Started noticing a small oil leak agian. Thinking it was the new main seal i started looking around. Found a crack on the passanger side. Researched it, found out that i probably did not align it correctly. Got a new pan. Followed the instructions. About a week goes by and all is good. Started seeing oil agian. Oil pan cracked at the rear most two bolts along the rail. Damn. Ok so oil pan # 3. Got it put ontoday. All was good. Was idling and i litterly heard a tink. Rail on the drivers side broke. What the heck am i doing wrong here ??? Thanks for any input. Just for reference the motor has 280k and never had any oil pan isssue.

 

[iamdub]

It's gotta be an alignment issue. IIRC, the rear of the pan has to be flush with the rear of the block. I believe most just realign it with the bellhousing when removing just the pan. If you had the pan and the trans off at the same time, then one or the other is not sitting where it should and putting stress on that same point when you use the bolts to snug it into place.

 

[Erickk120]

Whats been the mile interval before you notice them crack? and yes its an alignment problem.

 

[Dpayne]

The original pan was about 50 miles. The second pan was probably the same. Third pan was maybe 30 minutes. On the second and third pans. I snugged up all the bolts to the pan. Left them just loose enough so i could shift it. Put the bell housing bolts in and snugged them up first to alighn the pan flush to the bell housing..the worked my around the pan in several sequences to get my my final torque.

 

[swathdiver]

The original pan was about 50 miles. The second pan was probably the same. Third pan was maybe 30 minutes. On the second and third pans. I snugged up all the bolts to the pan. Left them just loose enough so i could shift it. Put the bell housing bolts in and snugged them up first to alighn the pan flush to the bell housing..the worked my around the pan in several sequences to get my my final torque.

Well Darren, put some lipstick around the edges of #4 anywhere you think it will touch something, snug up the bolts, remove them and have a look. Then gently remove just enough material (from the pan or whatever it's hitting) to solve the problem.

 

[Lancem]

My guess is the trans isn't tight to the block, remove the pan, tighten the trans bolts, then install the pan. If the pan was too far to the rear on the first install then the trans could be cocked slightly and hung on the alignment pins, so instead of just being touching the bellhousing is pushing on the pan.

 

[asand]

rear main seal plate not sitting flush with the pan rails?