Just for background, I have a 6.0 in a 67 Buick. It was stock with a carb conversion. I was running an rpm intake with a 770 holley and the msd box. Trans is a T400 with a shift kit and B&M converter. I drove this combo for a summer with no issues that I was aware of. Probably 1000 miles. I added a cam, springs, and trunnion upgrade. While tuning it, the awful screech of the thrust bearing started. Probably an hour of run time at the most. I had good oil pressure and no other warning.

What is the most likely culprit? I have heard of trans pressures and all, but this trans was not fresh, I have used it with other engines without any issues.

Where should I look first before I put this back together and trash it again?

 

Dealt with this issue and after knocking out a couple of thrusts, the tranny builder put the tranny on his dyno with an off-the-shelf converter and it had about 85psi @ 3500, a tad high but workable. Did it again but this time with my PTC converter and the pressure shot up to 130+ @ 3000!! Since it was the tranny shop, it was an easy fix trying different pressure port sizes on the input shaft.

Not everyone has access to a tranny shop with a dyno, so put a pressure gauge inline on the tranny-to-cooler line and check the pressure @ idle then start increasing the RPMs. You don't want to see more than about 75psi. If it is high, probably easier for a tranny shop to fix it or look up "Hutch" in the tranny section on YB and see about buying a kit he sells to address this.

Also check the converter spacing and make sure it is not jamming in the back of the crank. Was told by PTC not to be concerned about the spacing between the converter and the flexplate, but instead, get the converter about 3/16 off the pump and use spacers for whatever space there is between the flexplate.

Frustrating issue and you don't want it happening more than once. Good luck.

 

I lost a thrust too. Frustrating problem because finding the definitive cause can prove extremely difficult.

 

LeMans, if you're using an early version of lq4 (99-00) be aware of the extra length on the crank flange, we have run into issues with converter free play or lack of it using early truck cranks. No room for expansion is
certain death for thrust bearing.

 

It was an 04 with the 4l80e behind it so it had the spacer and flat flex plate. Everything bolted together easily. I guess I will buy and install a gauge and check the pressure when I reinstall the engine. I will double check the converter depth as well.