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4L60E Slips in Reverse only when HOT!

aflesch

By aflesch
in Ask A GM Technician

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aflesch Enthusiast

aflesch

Posted
Posted

I just finished rebuilding the 4L60E in my neighbor's `03 Avalanche Z71. The problem I am having is that it slips in reverse but only when it is hot. It shifts through all forward gears with no problems and even when it's hot I still have engine braking in manual 1st. This lets me eliminate the Low/Reverse clutch circuit as a possible cause.

 

Line Pressure Test Results:

 

Cold: Idle 1500rpm

Drive: 60psi 210psi

Reverse: 68psi 270psi

 

Hot: Idle 1500rpm

Drive: 60psi 210psi

Reverse: 62psi 120psi

 

 

This tells me that I can also eliminate the Pressure Control Solenoid as a possible cause since it functions properly in Drive. I am left with a problem in the Reverse Input Clutch circuit.

 

If the problem was the Teflon Sealing rings on the nose of the pump wouldn't my problem only occur when it was cold since the rings expand when they get hot? Same with the piston lip seals?

 

 

Have you ever seen this problem? Or do you have any thoughts?

 

 

 

Thanks,

 

-aflesch

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted

Pressure in reverse should not be losing 150psi when hot. You have a bad seal or seal surface. How was the surface that the teflon seals ran on? I have zero experience with these trans, but loads of experience with the old torqueflytes. They had issues of the teflon seals on the front pump support shaft wearing grooves into the housing. From your pressure readings you have a serious leak somewhere in the system that gets worse with heat. I think you may be pulling the trans again to find/fix it. I don't know how this trans gets reverse, but, a torqueflyte applied the rear band, plus a clutch pack. I can only tell you how I would troubleshoot that system, maybe it will give you a hint on this trans. I would look at the band and servo, making sure all servo rings are good. Make sure servo housing is not cracked, and servo its self is ok. Then pull trans and check front clutch pack, seals and sealing surfaces. O rings on shafts as well. Hope it helps.

aflesch Enthusiast

aflesch

Posted
  • Author
Posted

The surface that the teflon seals ride on was fine. No scoring or grooving. This trans gets reverse by applying the Low/Reverse Clutch and the Reverse Input Clutch. I have narrowed the problem to the Reverse Input clutch circuit. My real question is what would only leak when it's hot? If it was leaking cold I would say it was a seal, but only leaking hot is what has me second guessing that. Seals expand when they gets hot so they should seal better than when they are cold. That's the part that has me scratching my head.

paoutlaw Enthusiast

paoutlaw

Posted
Posted

sounds like a crack to me heat = expanded crack. in my opinion

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted

The surface that the teflon seals ride on was fine. No scoring or grooving. This trans gets reverse by applying the Low/Reverse Clutch and the Reverse Input Clutch. I have narrowed the problem to the Reverse Input clutch circuit. My real question is what would only leak when it's hot? If it was leaking cold I would say it was a seal, but only leaking hot is what has me second guessing that. Seals expand when they gets hot so they should seal better than when they are cold. That's the part that has me scratching my head.

 

 

On torqueflytes, it was the opposite, slip when cold, good when hot. Like no high gear or reverse until trans warmed up. But, it can work either way. You have a crack (like paoutlaw suggests), or bad seal/sealing surface. Is there an overrunning clutch/sprag in these trans?

aflesch Enthusiast

aflesch

Posted
  • Author
Posted

I hadn't thought about a crack...I bet the Reverse Input Clutch Apply Piston is cracked. That would account for all of these symptoms. $H!t. Well, I'll pull the tranny this weekend and find out.

 

Thank you guys for your help.

aflesch Enthusiast

aflesch

Posted
  • Author
Posted

ok...pulled the tranny today and tore it apart. No seals are bad. Nothing is cracked. A mechanic friend of mine suggested maybe the teflon sealing rings are compressed too far and that when the hub expands it is pulling away from them. Wouldn't the rings expand also and continue sealing? I am open to any thoughts related to SPECIFIC 4L60E components to check. (please no general blanket statements) I have checked all of the obvious so aparently it is something obscure. Thanks in advance for any help.

 

-Adam

aflesch Enthusiast

aflesch

Posted
  • Author
Posted

UPDATE: Had a tranny shop install a new set of Teflon Sealing Rings on the pump stator shaft using their special $180 tool and everything works perfectly. Got it all back together today and no more slipping in reverse. Note to anyone attempting a 4L60E rebuild: pay a tranny shop $10 to install the Teflon rings! It will save you tons of time in the long run. Thanks for everyone's help.

 

-Adam

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted

The teflon rings on the torqueflytes were a mitrecut ring. Thats the best way to describe it. They were sliced in a way that pressure actually made them expand. They would expand with so much force that they would wear grooves in the steel hub. These seals were nothing more than strips of teflon. Looked like plastic though.

What do the teflon seals look like in the 4L60E? Happy to hear the fix was so basic. Its nice when the fix simple.

aflesch Enthusiast

aflesch

Posted
  • Author
Posted

They are a single piece continuous ring. They have to be stretched over the pump stator shaft and then there is a special resizer tool to compress them back down to the proper diameter.

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