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goodwrench9124
goodwrench9124, ASE Certified Technician
Category: GM
Satisfied Customers: 3420
Experience:  37 years of dealership exp. Ase Master Certified, GM Master Certified Tech. Awarded GM Top performer
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4l80e trans no reverse

Customer Question

4l80e trans no reverse
Submitted: 4 years ago.
Category: GM
Expert:  goodwrench9124 replied 4 years ago.
Hello, and welcome. I take it all the forward gears worked ok?
Customer: replied 4 years ago.
yes all forward gears are ok
Expert:  goodwrench9124 replied 4 years ago.
Ok, did the transmission make any noises when it would pull in reverse? and did this happen all of a sudden?
Customer: replied 4 years ago.
started to back up no noise and quit all forward gear ok
Expert:  goodwrench9124 replied 4 years ago.
Ok, there can be alot of causes for this, so lets take a look at one part at a time. how does the rear band look? any signs of being hot or burnt?
Customer: replied 4 years ago.
not burnt
Expert:  goodwrench9124 replied 4 years ago.
Ok, how about the band servo?
Expert:  goodwrench9124 replied 4 years ago.
Just a thought, do you know if manual 1 st gear worked ok?
Customer: replied 4 years ago.
band servo ok all interal trans parts ok oil ok will not evan try to reverse wheels roll forward inreverse truck on jack stands
Expert:  goodwrench9124 replied 4 years ago.
Ok, take a real close look at the sungear and reaction carrier. the reaction carrier is like a one way clutch, it should turn free one way and lock the other direction
Customer: replied 4 years ago.
manual 1st gear working ok
Expert:  goodwrench9124 replied 4 years ago.
Ok, good, look at the sun gear and reaction carrier. make sure the gear is not stripped and the reaction carrier is not turning both direction on the inside
Customer: replied 4 years ago.
one way clutches working good all internal parts good seems to go into nuteral in revers
Expert:  goodwrench9124 replied 4 years ago.
really, most of the ones I have seen have either the sun gear stripped or the clutch is bad in the reaction carrier. little strange, if maual low works, this pretty much says the low and reverse band servo is good. how about the Intermediate Clutch Sprag Assembly?
Customer: replied 4 years ago.
i have completly striped trany could not find a real problem only thing found was rear output shaft seal replaced it also elertric presure valve noticed holes in vale body plate warn teardrop shape reinstalled trany in truck same problem no revers /????
Expert:  goodwrench9124 replied 4 years ago.
ouch, sounds like you have been pulling your hair out on this one. is this something you need a answer on tonight? I have a couple 4l80e cheat books at the shop. can you wait until tomorrow? while I do some research?
Customer: replied 4 years ago.
SURE 9124 APRECIATE THE HELP
Expert:  goodwrench9124 replied 4 years ago.

Ok, I will let you know tomorrow!!!!

 

Have a great evening

Expert:  goodwrench9124 replied 4 years ago.
Hello, do you recall if the trans has any engine braking on decell?
Customer: replied 4 years ago.
No it does not have a decell brake.
Customer: replied 4 years ago.

There is was a malfunction in the ABS braking system and it had been disconnected three weeks before the failure occured. John

Expert:  goodwrench9124 replied 4 years ago.
really, if there is no engine braking on decell,that would tend to lead that the low and reverse band is not appling.I would recheck the low and reverse servo and pin for proper operation. also make sure you have 11 check balls, pay real close attention to check ball 7 and 11. another thing, have you check the reverse boost valve in the front pump?
Customer: replied 4 years ago.

Sorry for the delay as I was very busy lately and of course very computer illeterate.

 

there is only 7 check balls in this valve body. No balls situated in location 7 and 11.

 

transmission has worked for 150,000 km with no problems and then without warning quits reversing.

If I disconect all the electrics to the transmission, can the transmission work strickly on hydraulic pressure? Truck still on four jack stands.

Expert:  goodwrench9124 replied 4 years ago.

ok, there are 8 check balls in the valve body and 2 in the case, the ones in the case are for reverse

 

 

 

 

 

 

 

graphic

(1)Overrun Clutch
(3)Front Band Apply
(4)2nd Clutch
(5)3rd Accumulator
(6)4th Accumulator
(8)3rd Clutch
(9)Reverse
(10)4th Clutch

 

 

graphic

 

(7)Lo/Reverse
(11)3rd Clutch/Reverse

 

Expert:  goodwrench9124 replied 4 years ago.
Hello, just wandering if you come up with anything yet?
Customer: replied 4 years ago.

Transmisssion has to come back out. Definetly has to be an internal problem that was missed on initial inspection. Ordering new transmisson will take this old transmission apart and try to fix it. I would like to contact you in the near future and let you know exactly what I find. Thank you very much 9124 have a good holiday season.

Appreciate your help but the problem still exist.

Expert:  goodwrench9124 replied 4 years ago.
good, just let me know how things come out?

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