Fresh TH400 lost all forward gears but good reverse?

[6.2puller]

OK I have a TH400 in my V3500. I rebuilt it about two months ago. IT has under 1000 miles on it. The other day I added a tranny cooler and fixed a coolant leak. Got in and no more forward gears. It isn't even trying to engage. Reverse works great. Thuds right in and off we go backwards

So I am hoping this is something stupid and easy that can be resolved without removing it from the truck again. Any ideas?

 

[Jason4x4]

If you added a trany cooler, did you refill the trans?

 

[6.2puller]

Yes sorta. I was trying to give it a test run to warm the fluid for a final check. Their is enough fluid to hit the dipstick add mark when cold.

 

[southernspeed]

Ouch, my 350 did that when it broke the lip on the forward clutch that holds the big circlip. That was another rebuild! I had 400 miles on that. I think it was the shift kit giving tired old parts a hard time!
I hope yours is better news!

 

[6.2puller]

Anybody else got a guess? Maybe even something I can try without removing the tranny again.

 

[southernspeed]

Drop the pan. If it is the forward clutch there'll be shrapnel!
If you have pressure gauges you could check line pressure through the gears.

 

[dyeager535]

You can try manually running through all forward gears while giving it some gas. Not sure exactly what this "unsticks", but I had a TH400 that after rebuild wouldn't go into 3rd gear a couple of times. Asked a transmission builder friend about it, he suggested when it's doing that, go through all forward gears MANY times, and eventually it did work, and the problem never returned.

Seems a bit odd with no forward gears, if you check out an ATSG service manual, it may even list your specific problem and cause. Don't have mine handy or I'd look.