4L85E Front Seal Leak

L31MaxExpress said:

Figured out what has knocked out two front seals in 25K miles in my 4L85E. The torque converter support bushing in the pump is smoked. Unit was operating flawlessly to that point. Very clean inside the pan as well. Pump is apart, going to drill the seal drain back to 0.250", install a new bushing, reseal the pump, toss it back in and let it eat. I have a feeling the bushing smoked itself when the seal popped out years ago. 4L80E derivatives are definitely a beast to remove yourself.

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L31MaxExpress said:

4L80E derivatives are definitely a beast to remove yourself.

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NickTransmissions said:

Id drill .055 line to lube (pump cover) and .125 for od roller clutch lube (stator) as well, while it's apart.

Put a Sonnax boost valve kit, preexisting one may be worn (you can confirm/deny before spending $$ if you have a Sonnax vac tester).

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L31MaxExpress said:

I did all 3, except I was reading a PDF for the fluid mods and they specified a 0.067" line to lube. It is cleaned and back together though. Will be stabbing it back in its home in the AM.

My local Transtar was out of the Sonnax boost valve kit and I do not own the vacuum checker. First 4L80E I have been into. This unit has always knocked your head off when it shifts as it is even at stock line pressure settings at heavy throttle even with the looser converter in it. I plan to replace this transmission with a 6L90E at some point in the future anyway. Just needed to get it back on the road for now. It shifted perfectly, just started dribbling fluid out.

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NickTransmissions said:

97+ units aren't known for super harsh shifts like the first gen (91-96) 4L80Es but harsh shifts can be an indicator of high line pressure...High line pressure is often caused by a worn boost valve and sleeve where the valve gets partially hung up, resulting in line pressures being higher in proportion to throttle angle (i.e driver input on the gas pedal)...If left untreated, hard parts can start to break. You can replace the boost valve with the trans in the vehicle, as you probably know so it can be addressed at any time. The Sonnax valve is available on Amazon, eBay, Transparts Warehouse, Transtar, etc...

.067 line to lube should be fine, I typically do .055-.062 but don't see a problem with .067.

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L31MaxExpress said:

I will get one into it at some point. I feel like the firmer shifting is also due to the line pressure mapping in the 0411 or P59. It increases with engine torque delivery and there is plenty of that. The torque model is resonably accurate to what the engine is making. A bit over 500 ft/lbs. It only shifts extremely firm at higher throttle, light part throttle and mid throttle shifts feel like any other 4L80E I have been around.

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L31MaxExpress said:

@NickTransmissions

Off the top of your head, any ideas what would make a 4L80E have a good 1-2 shift then not even try to shift to 3rd or 4th? It does not neutral when it commands 3rd or 4th, just hangs in 2nd, let off the throttle and coasts, pull it down to 3rd and it will engine brake so I am fairly certain nothing is slipping clutch wise. No codes either after multiple short drives. Hard to drive it much because even at 40-45 mph it is screaming in 2nd with a 4.10 gear. I can see the PCM call for 3rd and nothing happens, just stays in 2nd. It has both an accurate VSS and ISS signal. The unit in question only has the internal manifold pressure switch and the PCM is seeing the shifter positions accurately. If the shifter is moved from Drive or 3rd to 2nd you can feel a slight bump and it engine brakes in 1st as well. Has me at a bit of a loss. 2-3 shift solenoid or valve issue? I would think it would set an invalid ratio code fairly quickly or a stuck solenoid code but it does not. I checked and the unit has a 4L80E operating system in the PCM via reading the Memcal in it and the harness pinout seems correct as well. FWIW this is a 1994 TBI truck. FWIW I also back probed the connector with the truck on stands, accelerated it to 50 mph showing on the speedo and the 2-3 shift solenoid wire from the PCM pulls low so fairly certain it is not a wiring issue in the unit or to the PCM. The shift solenoid Yel/Blk wire has 12V on it before the PCM pulls it to ground.

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NickTransmissions said:

Did this just start happening?

Off the top of my head: Sol B (2-3 shift sol) mechanical failure , possible bad ground/short somewhere or 2-3 shift valve/spring. Shorts/ground issues as a cause are less likely since it appears to have passed your voltage test on jack stands, speed sensors are functioning and no codes are present.

Recheck wires, grounds etc just be sure then drop the pan, replace the solenoid. While the solenoid is out, push on the 2-3 shift valve with a pic or very thin flat screwdriver to see if it moves and returns back to its position against the roll pin. Maybe it's stuck/sticking or the inboard spring broke.

It may not be a bad idea to drop the vb so you can install Sonnax 1-2 and 2-3 shift valve springs and Sonnax tcc regulator valve. If you have a Sonnax vac tester, you can test the entire valve body for circuit sealing issues...

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