TCC issues on 4L60

[gmbellew]

1990 V1500 Suburban. I've owned it for 5 years and changed trans fluid and filter every 30kmiles. 200k miles on the truck, of which I have put on about 75k. unknown maintenance history before I got it, but I keep up on things and it wasn't hacked to pieces when I got it.

after some highway driving yesterday, the idle was really rough and almost acted like it would stall, but didn't. I've been working on tuning some idle issues with a tuner, mostly related to O2 feedback and worn valve guides. but idle was way worse than it had been all of a sudden after highway driving. I couldn't find any obvious ignition issues and the data stream from OBD1 showed no issues to explain the sudden decrease in idle quality. I wasn't even thinking about the Torque Converter Clutch, yet...

Then, at the tail end of a 4hr highway trip home, I noticed the RPMs weren't dropping all the way out when the Torque Converter locks. it was like it was cutting the RPM about half what it normally does when it locks. the electronic part seemed good, as I can see the Torque Converter Clutch lock command and there is a small RPM drop. RPMs in lockup were running about 200rpm higher than normal when locked at same speed (normally would be 2050rpm at 75mph and was 2250rpm) occassionally the RPM would drop like normal, but then come back up. No shuddering and the gears seem to shift fine.

Looking for a shop to diagnose and repair, but I wanted to get any thoughts to be informed when I go. It seems like it could be the Torque Converter slipping itself or, hopefully, the solenoid acting goofy and sometimes only partially opening or closing or both?

let me know your thoughts!

 

[CalSgt]

Perhaps a transmission shop would give some free advice but if you’re planning on paying a shop to diagnose, you could swap in a new TC for about the same price.

get a TC with woven fiber friction material instead of paper.

 

[gmbellew]

i am not following. doesn't Torque Converter replacement require pulling the trans (and transfer case that is in tge way)? the solenoid is accessible from pulling the pan?

 

[Matt69olds]

Pin F or the ALDL is converter clutch. If I remember correctly, if you put a test light on pin F the light should be on until the PCM provides the ground, then the light should go off.

The ECM looks at lots of engine/drivetrain data to determine when the converter should lock. Things like engine speed/temp, vehicle speed, engine load, etc, might be nice to know IF the ecm is actually commanding the converter clutch on. Then you will have a better idea of which way to go with diagnostics.

 

[gmbellew]

Pin F or the ALDL is converter clutch. If I remember correctly, if you put a test light on pin F the light should be on until the PCM provides the ground, then the light should go off.

The ECM looks at lots of engine/drivetrain data to determine when the converter should lock. Things like engine speed/temp, vehicle speed, engine load, etc, might be nice to know IF the ecm is actually commanding the converter clutch on. Then you will have a better idea of which way to go with diagnostics.

ECM is commanding it to lock like it should. I am using a cable with ALDDroid and can see the data. issue is it isn't locking all the way or something, because RPMs aren't dropping as much as they used to.

also, the after highway driving when the TCC has been locking, the idle quality is horrible. idle is good around town where the TCC never locks at all.

I haven't been on the highway again yet to test that theory.

 

[Matt69olds]

It’s easy enough to test the TCC solenoid once it’s out of the trans. Pull the solenoid, use a rubber tipped blowgun to apply air to the tip of the solenoid, air should exhaust thru the solenoid. Apply power (make sure you observe the polarity, some solenoids use a diode) the exhaust should close.

If the converter has been slipping, the fluid will let you know. You could also pull the inspection cover and take a look. Most converter rebuilders paint the converter, if you see scorched paint on the flywheel side of the converter the clutch has been slipping.

 

[gmbellew]

It’s easy enough to test the TCC solenoid once it’s out of the trans. Pull the solenoid, use a rubber tipped blowgun to apply air to the tip of the solenoid, air should exhaust thru the solenoid. Apply power (make sure you observe the polarity, some solenoids use a diode) the exhaust should close.

If the converter has been slipping, the fluid will let you know. You could also pull the inspection cover and take a look. Most converter rebuilders paint the converter, if you see scorched paint on the flywheel side of the converter the clutch has been slipping.

I haven't noticed any slipping or shuddering. gears shift fine. I just had the fluid/filter changed about 1k miles ago because it had been almost 30k since the last time. I was having the rear end rebuilt and the transfer case resealed, so I had a professional do it so he could give me an assessment based on the pan contents and fluid.

I noticed the RPM drop wasn't what it usually is on the last 20min of highway driving of a 4hr trip. I hope that wasn't enough time to fry things inside the transmission. drove it around town today, no issues. but I never got into a TCC lock up situation.

I don't mess with transmissions too much besides fluid/filter changes. so I'll likely be taking it to a shop for this. fingers crossed it is just the solenoid and things are still good elsewhere.

 

[gmbellew]

I'm gonna roll the dice and replace the TCC solenoid. seems easy enough and will cost less than just a diagnostic fee at a transmission shop. also, based on the symptoms the solenoid seems like a very likely culprit.

 

[gmbellew]

pulled the old solenoid. it was cracked and I could move air both ways just by blowing and and sucking on it indicating the crack was affecting the seal and check valve functionality. the new part only let air move one way. so i am pretty sure that was my issue. I installed a replacement, but haven't gotten a chance to get it on the highway to confirm that was the culprit. I noticed my water pump is leaking out the weep hole, so I need to get that fixed before I get too far from home and have the water pump leave me stranded. I'll update this post if the TCC issue isn't resolved with the new solenoid.