I know this is a camaro and firebird forum but....I Recently rebuilt and did an LS Swap in my 1971 C10 and installed a refurbished 4L60E from a reputable transmission shop while doing so. After 2000 miles on the motor and transmission while cruising on the highway at 70 MPH the transmission pump failed (verified when taken apart). Previous to this there were no signs that the transmission was failing...no abnormal noises, no shifting issues, no fluid lose, no high temperatures...nothing. I didnt really put any major load on the transmission from the time I installed it to the time it failed as well. I rebuilt the transmission myself after the pump failed (first time doing so but made sure I followed every step and ensured everything was right as I went and ensured all the tolerances were correct) installing all new parts and recommended upgrades, replaced all the usual items in addition to a new pump...gaskets, o rings, seals, raceway bearings, friction plates (3-4 plates were all a little burnt), steels, accumulator pistons, sun gear, rear planetary gear that was starting to have some play, etc. As I was dissecting it to find out why the pump failed I did not really find anything that would of caused the pump to fail in the transmission. I chalked it up to maybe it was just a bad pump. So after 100 miles after rebuilding the transmission and reinstalling it...same thing happned...while cruising on the highway at about 70 MPH the pump failed again.
The tolerance between the flex plate and the torque convertor was spot on so I dont think it was causing any mechanical pressure on the pump, the flex plate appears to be true and not cracked or damaged, the torque convertor isnt making any noise and doesnt show any abnormal wear issues and the line pressure is regulated by the engine management system I installed (Terminator X Max) and i didnt set up with any crazy pressures...I am at a loss here as to what else could have made this thing go bad twice now! i dont want to just throw another pump in without checking out everything else it could be. If anyone has any ideas I am all ears!

 

Let's start with what failed in the pump. Did the rotor brake?

 

Did the rotor break? The slide? Give us some details here...I'm assuming rotor
What do you consider "spot on"
What do you consider "not crazy pressures"

Check converter runout on the snout.
What rotor are you using? 10 or 13v?
Any modifications to the slide or slide spring
Did the converter have proper pilot engagement?


I'm usually one to throw the "BS" flag when someone says they were *just cruising along when it broke*
But in this instance it has happened to me personally twice. So I don't doubt for a second you probably were just cruising along no big deal...then all of a sudden it's neutral soup.

Get us some more info and we can get you some good help.

 

That's quite a bit for 2000 miles from a "reputable" builder

Anyway, my assumption is the converter isn't spaced correctly and its coming uncoupled from the pump rotor then trying to rengage breaking the rotor. Pictures of the inside of the rotor showing how much engagement will help. Also manually seeing actual pump pressure would also help

 

Yes the rotor broke.

 

The spacing between the flex plate and Torque Convertor was a little more than 1/8". The pressures were set up stock but I bumped them up a little. Not sure the exact pressure but the shifts are not super neck breaking shifts. The rotor is a 10 vane rotor and no modificatiosn to the slide or spring. The convertor looked to have the proper pilot engagement as well.

Being 100% Honest here...not sure what you mean by convertor run out on the snout? Can you explain how to check that?

And yes i can agree that usually its BS when someone says they were jsut cruising along but in this case I was and your analogy of neutral soup is spot on! LOL

 

Interesting......

 

He is asking if the converter hub has been checked for straightness. Is the hub bent or welded on strait? This is checked with a dial indicator.

The Flex Plate to Torque Convertor should be 1/16 (0.63) to 1/8 (0.125). You are on the high side of this if not over. On assembly try installing some shims or 3/8 flat washers. I just measured a washer that I have, and it was .072. If you hit it with a flat file and knocked the sharp edges off it, it will be a little thinner.

 

bbond...his spec of slightly over 1/8" is correct

1/16 is much too tight

If converter pullout is between .125 and .175 it should be mint

 

I was at a trans seminar back in the late 90s and the presenter told of 4L60s sucking in a big gulp of air and breaking the pump rings and suggested installing hardened rings in every rebuild. Has anyone inspected the filter and filter seal at the pump? This is the only other thing I can come up with if converter hub run out is okay.

 

That was true back in the day of 200-4R's and 700R4's when they had the orange filter seal. After so many pump failures GM started using the hardened pump rings we see today in the 4L60E. It seems as though GM has always been behind the aftermarket transmission industry for items like that. The PR valve buzz was another one. We were grinding flats on the valve long before GM adopted that into the manufacture of the PR valve itself. I think they started that with the 4L60E to cover their butt..

 

The pump slide can also "slap" from one position to another and cause issues.
This is why I like to limit its travel and use a stiffer spring rate to control the rate of travel better.