4L60E No reverse - Wear gloves to handle this post

[davidavidd]

Hi TYF members and friends! I appreciate all your opinions and replies to find the origin of this situation

To make a long story short:

My transmission was working fine until this week. I rebuilt it with your help two years and 65.000 miles ago when the pump went bad.

I drove the Tahoe on a small family trip (perfect road in Colombia, nice wheather, 120 miles, 5 people). Already in place when trying to park I discovered that the reverse gear did not have enough force to move the truck, it moves but very little, five seconds later it started to sound like metal parts rubbing against each other (I thought it was the diff dying), turned off the engine and when I put it back in reverse it simply didn't move anymore (reverse = neutral).

The only strange thing I noticed this day (one hour before failing) was a lack of acceleration and force in first gear (like limp mode until finally reach the 2nd gear).

Since I couldn't spend the night at the site I decided to take the risk and drive back home. No reverse but the truck worked fine in forward gears.
This weekend I was expecting to find a carnage with my sun gear on pieces or the sun shield without teeths but that was not the case. Other than some endplay between parts and contaminated oil (with clutch and steels particles), the only visible damage was the low/reverse frictions and steels (pistons ok, check balls ok, valve body gasket ok, sprags ok). Please see the photos, the low/reverse clutch pack and steels looks like charcoal.

Technical summary
2007 Tahoe, stock Engine 5.3, RWD, 275/55/R20
Street use only/not towing.

Oil was at normal level at time of failure (I checked before leaving in the morning).
The transmission filter and the neodymium magnet in the pan were full of particles and debris from clutch discs and steels.
Pressure measured in transmission before disassembly: 85PSI at idle and 120 in R.
After opening the torque converter I only found normal dirt for this type of damage. Bearings and inner clutch in OK condition.

In the first repair of this transmission I changed: sunshell (but not sun gear) frictions, internal parts of the pump, pistons, corvette servo, checkballs and everything included in a rebuild kit: seals, gaskets, bushings, bearings, sprags, etc. plus a transgo shift kit (the basic one). The hard parts/case/converter was reused.


Codes found w/ my scanner:
P0741: Torque Converter Clutch Circuit Performance or Stuck Off
P0745: Pressure Control Solenoid Malfunction

PD: I thought a lot about the engineer's mom who decided to put the Torx-50 sh** in the transmission bell (it took me 4 hours, sweat, pain and all kind of tools to remove a bolt with stripped head). These bolts won't come back, I'm going to replace them with low-profile bolts.

 

[OR VietVet]

Wow. I am not an internal transmission guy and cannot offer any usable info but hopefully @rockola1971 will chime in with his expertise.

 

[Just Fishing]

Yup, something failed and caused the clutches to slip!

I would start with an air test of everything to find some sort of a leak.

I had a pump rotor fail one-time, off brand junk, plus I had the pressures cranked (700R4).
With the way it shifts, I'm still surprised I haven't broken that early 84 case yet.


if air checks all pass, then it's probably a solenoid or something in the valve body.

Also spend time looking through the documentation on the sonnax website, there might be a "known cause/cure" for it.

 

[davidavidd]

Yup, something failed and caused the clutches to slip!

I would start with an air test of everything to find some sort of a leak.

I had a pump rotor fail one-time, off brand junk, plus I had the pressures cranked (700R4).
With the way it shifts, I'm still surprised I haven't broken that early 84 case yet.


if air checks all pass, then it's probably a solenoid or something in the valve body.

Also spend time looking through the documentation on the sonnax website, there might be a "known cause/cure" for it.

Hey @Just Fishing, thanks for answering!

It's been a few days now and I've been a bit busy to finish my journey with this transmission but I have been able to reach several conclusions:

The manual valve was causing a leak in the P/R circuit
EPC solenoid failed causing low pressure
The low/reverse discs and steels began to wear against each other and released particles that ended up clogging the main filter, the pump filter and the valve body filters (exacerbating the low pressure problem).

As you can see it was a combination of several factors that led to the death of my transmission, 3-4 discs were fried too. It only remains to start over without reusing any parts and with a remanufactured valve body. Cross your fingers for me

 

[NickTransmissions]

Hey @Just Fishing, thanks for answering!

It's been a few days now and I've been a bit busy to finish my journey with this transmission but I have been able to reach several conclusions:

The manual valve was causing a leak in the P/R circuit
EPC solenoid failed causing low pressure
The low/reverse discs and steels began to wear against each other and released particles that ended up clogging the main filter, the pump filter and the valve body filters (exacerbating the low pressure problem).

As you can see it was a combination of several factors that led to the death of my transmission, 3-4 discs were fried too. It only remains to start over without reusing any parts and with a remanufactured valve body. Cross your fingers for me

Were your forward and reverse input clutches also fried? Did you get any dtc codes when trans was operating, vehicle still on the road?

Have you flushed your lines and cooler(s)?

 

[davidavidd]

Were your forward and reverse input clutches also fried? Did you get any dtc codes when trans was operating, vehicle still on the road?

Have you flushed your lines and cooler(s)?

Hey @NickTransmissions, let me give you a short summary of what I found:

- Pump: 4/5 (some contamination but nothing major)
- All pistons: OK
- Forward Clutches: OK
- Reverse Input Drum: OK
- 3-4 Clutches: Fried
- Teflon seals: OK
- Bushings: OK
- Sprags: OK
- Band: OK
- Servo: OK
- Sun gear, sun shell, planetaries: 4/5 (some end play but nothing major)
- Valve Body: full of metal/clutch particles, I also suspect that it has several leaks in the valves due to use. It was never replaced.
- Manual Valve: faulty with bore damage (sorry I don't know the right word), but just by using a flashlight and looking at the L/R circuit diagram one can conclude that there was a serious cross-leak there.
- Low/Reverse Clutches: Non-existent, I only found the steels and the metal cores of each clutch

Codes found w/ my scanner:
P0741: Torque Converter Clutch Circuit Performance or Stuck Off
P0745 P0748: Pressure Control Solenoid Malfunction.

I'm almost done putting all the pieces together, tomorrow I'm going to flush the lines, I hope to finish before traveling to the US again.

 

[NickTransmissions]

Hey @NickTransmissions, let me give you a short summary of what I found:

- Pump: 4/5 (some contamination but nothing major)
- All pistons: OK
- Forward Clutches: OK
- Reverse Input Drum: OK
- 3-4 Clutches: Fried
- Teflon seals: OK
- Bushings: OK
- Sprags: OK
- Band: OK
- Servo: OK
- Sun gear, sun shell, planetaries: 4/5 (some end play but nothing major)
- Valve Body: full of metal/clutch particles, I also suspect that it has several leaks in the valves due to use. It was never replaced.
- Manual Valve: faulty with bore damage (sorry I don't know the right word), but just by using a flashlight and looking at the L/R circuit diagram one can conclude that there was a serious cross-leak there.
- Low/Reverse Clutches: Non-existent, I only found the steels and the metal cores of each clutch

Codes found w/ my scanner:
P0741: Torque Converter Clutch Circuit Performance or Stuck Off
P0745 P0748: Pressure Control Solenoid Malfunction.

I'm almost done putting all the pieces together, tomorrow I'm going to flush the lines, I hope to finish before traveling to the US again.

View attachment 395056

The torque converter failed in that unit (the code is almost always associated w/converter failure), the metal shavings were likely a combination of both TC stator damage, bushing disintegration as well as l/r clutch burn up. I have torn down hundreds of 4L60Es and have never seen damage in the manual valve area though i've seen plenty with actuator feed limit (AFL) bore wear (excessive wear to the AFL valve reduces AFL oil to the EPC and ultimately leads to applied element (clutch/band) failure. Were the sealing rings on the low reverse piston still supple or were they hard...The sealing ring in the middle of the piston is what typically fails though I've torn down units that had sealing rings that were as hard as plastic and literally shattered upon removal.

That said, replacing the valve body was a wise move as all those little metal shavings can aggressively wear the bores in a very short period of time...Anytime a converter failure comes in, I test the pressure regulator (PR) valve location and visually inspect the pump cover for damage. I also replace the VB with a reman one since the VB is typically scored up (that's probably what you saw when inspecting the manual valve but it by itself was not likely the source of the L/R clutch pack burn-up). Low overrun and reverse abuse valve wear can cause low reverse burn up but leave the rest of the clutch packs unmarred. The EPC seemed like it was on its way out but when we see an EPC failure, all the clutches and band are heavily stressed or burnt. The 3/4 clutch pack failure was likely caused by both EPC weakness as well as GM's inherent design flaws in that clutch pack. The EPC failure may or may not have been caused by an excessively worn AFL valve and/or bore.

Did you replace the sun shell w/ a hardened and heat treated one?

If not, i'd go back in and replace it as the factory shell will fail. The splines will strip or the splined "neck" will separate from the rest of the body, resulting in loss of reverse, second and forth gears. The forward sprag should also be replaced as they are typically on the verge of failure after 150k miles or so...If it rolls over and fails, you'll lose all movement in 'Overdrive' though you will be able to move the vehicle in manual 1, 2 and Drive 3 but only the coast clutches will be on and moving the vehicle in Drive 3 (the two little clutches towards the front of the forward drum). I always install a new forward sprag on all rebuilds. On the other hand, the low roller clutch is almost never bad, those are pretty robust and it's only holding on take off (first gear in all ranges).

Did you remove the load release springs in the 3-4 clutch pack?

Never re-use them as they aren't necessary and create more problems then they were trying to solve (centrifugal clutch apply at high RPMs in 1st and 2nd gear). I run the 3/4 pack clearance down to between .035-.050 on all stock builds...High performance gets .025-.035 clearance and I do reinstall those load release springs (as well as make other mods) if the trans will regularly see 5000+ RPMs.

I'd also replace all your solenoids, pressure switch manifold and wiring harness as they may or may not be contaminated with shavings/debris and solenoids are cheap. I am assuming you've replaced all your frictions, bushings (especially the rear stator bushing in the pump as that will trigger all sorts of issues as it wears and begin's to let significant fluid blow by) as well as 3/4 and L/R steels...

 

[Geotrash]

The torque converter failed in that unit (the code is almost always associated w/converter failure), the metal shavings were likely a combination of both TC stator damage, bushing disintegration as well as l/r clutch burn up. I have torn down hundreds of 4L60Es and have never seen damage in the manual valve area though i've seen plenty with actuator feed limit (AFL) bore wear (excessive wear to the AFL valve reduces AFL oil to the EPC and ultimately leads to applied element (clutch/band) failure. Were the sealing rings on the low reverse piston still supple or were they hard...The sealing ring in the middle of the piston is what typically fails though I've torn down units that had sealing rings that were as hard as plastic and literally shattered upon removal.

That said, replacing the valve body was a wise move as all those little metal shavings can aggressively wear the bores in a very short period of time...Anytime a converter failure comes in, I test the pressure regulator (PR) valve location and visually inspect the pump cover for damage. I also replace the VB with a reman one since the VB is typically scored up (that's probably what you saw when inspecting the manual valve but it by itself was not likely the source of the L/R clutch pack burn-up). Low overrun and reverse abuse valve wear can cause low reverse burn up but leave the rest of the clutch packs unmarred. The EPC seemed like it was on its way out but when we see an EPC failure, all the clutches and band are heavily stressed or burnt. The 3/4 clutch pack failure was likely caused by both EPC weakness as well as GM's inherent design flaws in that clutch pack. The EPC failure may or may not have been caused by an excessively worn AFL valve and/or bore.

Did you replace the sun shell w/ a hardened and heat treated one?

If not, i'd go back in and replace it as the factory shell will fail. The splines will strip or the splined "neck" will separate from the rest of the body, resulting in loss of reverse, second and forth gears. The forward sprag should also be replaced as they are typically on the verge of failure after 150k miles or so...If it rolls over and fails, you'll lose all movement in 'Overdrive' though you will be able to move the vehicle in manual 1, 2 and Drive 3 but only the coast clutches will be on and moving the vehicle in Drive 3 (the two little clutches towards the front of the forward drum). I always install a new forward sprag on all rebuilds. On the other hand, the low roller clutch is almost never bad, those are pretty robust and it's only holding on take off (first gear in all ranges).

Did you remove the load release springs in the 3-4 clutch pack?

Never re-use them as they aren't necessary and create more problems then they were trying to solve (centrifugal clutch apply at high RPMs in 1st and 2nd gear). I run the 3/4 pack clearance down to between .035-.050 on all stock builds...High performance gets .025-.035 clearance and I do reinstall those load release springs (as well as make other mods) if the trans will regularly see 5000+ RPMs.

I'd also replace all your solenoids, pressure switch manifold and wiring harness as they may or may not be contaminated with shavings/debris and solenoids are cheap. I am assuming you've replaced all your frictions, bushings (especially the rear stator bushing in the pump as that will trigger all sorts of issues as it wears and begin's to let significant fluid blow by) as well as 3/4 and L/R steels...

What a fantastic post! Grateful to have your expertise here.

 

[NickTransmissions]

What a fantastic post! Grateful to have your expertise here.

Thanks, Dave! Happy to help out where/when I can.

 

[davidavidd]

Hi @NickTransmissions, what an amazing answer, thank you very much for your time.

I also thought the same about the converter but I saw it open and it was fine, anyway I'm installing a reman. converter. All my suspicions are on the valve body and the EPC. In the new valve body I included all the Sonnax products I could find, especially the abuse valves famous for constant cross leaks.

The seals in the L/R piston were fine when removed, anyway I replaced this piston (fearing a metal crack that I couldn't see with the naked eye) and added new seals and springs.

So to recap I'm adding:

- Reman T. converter
- Full set of hard parts (without end play)
- Sonnax Smart Shell
- New steels and frictions + plates (stock)
- Reman VB
- New solenoids
- Tested pump with new valves from Sonnax
- New sprags
- New bushings (inc. sun gear wide bushing)
- Pressure switch manifold
- Release springs
- Pistons
- Case saver (1 million times easier to install than the famous anti-clunk spring)
- Seals and bearings
- Band

The only thing I didn't change is the input drum, but I cleaned it well and air tested the one I have. 3-4 clearance was set to 0.030 +/-.

I'm on my way to flush the lines and put the transmission back in the Tahoe.

Greetings from Colombia and Thanks for your help!