Thanks for the advice. The 3-4 steels were ok. One or two looked burned, but no scoring or warping. With new frictions, there was perfect end-play. But, why were they smoked? Couldn't have happened when driving 2 miles to the shop in 1st gear. The low forward frictions were still in great shape. Here's what I think happened. Tell me what you think.

A little history. When I tore it down the first time to rebuild, it seemed obvious someone just recently rebuilt it - like less than 1k miles earlier. I say that because the 3-4 piston hadn't been replaced and leaked badly, and the 3-4 frictions were still almost at new thickness. All they did was replace frictions and "some" seals. It failed because the forward planetary gear bushing failed, overheated, then the forward planetary output gear snapped off. The earlier rebuild did not install load release springs.

When I was rebuilding it the first time, I read arguments for and against installing load release springs. Both sides of the argument made sense. I went ahead and bought a set and installed them. In only about 500 miles, the 3-4s were smoked. I think the load release springs were keeping the 3-4s from fully disengaging, so I didn't reinstall them this time.

What do you think?

 

Sorry. Forward planetary bearing, not bushing

 

I suspect you were driving with low line pressure for much more than 2 miles.

The use or lack of load release springs has a minuscule effect and I don't think it is relevant here. For a stock rebuild the ATSG manual recommends not using the load release springs. For a performance build with a shift kit and tight 3/4 clutch clearance, I recommend the load release springs, but 49% or even 51% of pro builders would disagree even then.

 

The load release spring didn't burn the clutch pack down, Not getting into the Pro's & Con's.....But hundreds of thousands of these units are out there that run over 200,000 miles with the springs.....

 

I run load release springs in probably 95% of my builds. I leave them out of some, too. It just depends upon the application. That's not your problem, as clinebarger said. You have a line pressure problem...

How was the 3-4 clutch stacked up? How many discs, disc sizes, clutch clearance, etc? There are many, many ways to assemble this clutch, but only a few that actually work in the long run.

EDIT: Didn't see your post where you said the boost valve was coming out. That will definitely cause a lack of line pressure!