4l60 unlocks on longer drives (1 Viewer)

[workingdog]

This is a 4L60 behind a 5.3l vortec with a magnason supercharger in an 84 FJ60. I've blown the 4L60 twice in this truck in less than 10,000 and I'm not sure why - and that's without putting my foot in it very hard (i'm scared to death of the truck now). So this time, after spending thousands on my 3rd heavily built tranny, I'm trying to figure out what's going on. It's fine around town, but it always acts up on longer drives. So I took it to the Sierras over the weekend to see what happened and it did something it's done in the past which I think is related.

3/4's of the way to Donner Summit from Auburn (where the climb starts) or about 45 minutes in the hill (and 2 1/2 hours into the drive - it seems to take some time for this to happen), I'm on one of the longer sustained climbs, the OBDii gauge says I'm putting out about 110 to 120 hp and about 300 foot pounds of torque (just about 0 on the boost gauge), near the top (and Cisco Grove) the transmissions seems to unlock. I used to think this was a downshift, but this time I'm pretty sure it was the torque converter unlocking (based on the rpm change and rpm behavior on and off the gas). And just like last time, it didn't lock back up at the top of the hill, in fact, uphill, downhill, it didn't matter, it stayed in that mode. About 10 minutes later, as I'm pulling the final bit before the summit, I experience a 'clunk' and it locks back up and it's fine from then on.

Does anyone understand this behavior? I can't find anything that might explain it online.

I can't use my OBDii to read tranny temp, so the temp stored in the PCM/TCM is useless to me, so I'm putting a mechanical temp gauge this week and I'm going to have them install an additional tranny cooler as well.

 

[lazy]

I'm no pro, but curious....so I'm probably little help. But, I'd like to learn if you don't mind.

What was the problem with the past transmissions? Did you "burn them up?" Have you replaced the TC w/ the trannies? The 16 cylinder, 2000 HP cummins diesels w/ allison transmissions that I run at work, we monitor the trans temp very closely and without "lockup" we'll burn those up pretty quickly.

I don't know if this is something related to the computer, other sensors telling the computer to unlock your TC etc. Here is a thread where a guy had to change "misfire tables." Apparently the computer can read a misfire, but not report it? And cause the tranny to fall out of lockup?

 

[workingdog]

They broke bands. Yes, TC was replaced each time (as the crap loose had broken them too).

 

[workingdog]

Wow - that's a fascinating thread. That could definitely be my problem because it only happens under load. Now I have to figure out misfire tables even do and why I might be misfiring - bad tune?

 

[lazy]

Supercharger and not normal compression and not properly tuned. Something worth investigating....

 

[workingdog]

Yes, that's my thinking too. It's running the Magnuson tune, but clearly it needs more work. I have to find someone local that can help me.

Peter

 

[workingdog]

I wanted to say thanks again for the misfire table idea. That really opened up a lot of options. I'm taking it down to a local shop with a Dyno that program the PCM and we are going to look at the misfire problem and the tune in general under load. Never been able to get past 120 hp and 300 ft lbs and I'm wondering if that's a tune issue too.

 

[lazy]

hopefully it fixes your issue. please report back your findings.

 

[lazy]

how did the tune go?

 

[workingdog]

May 2nd

 

[SNLC]

Just an FYI, I had a lot of probs with the TCC and a 4L60e. Couldn't figure it out for like 4 months. Finally figured out the brake switch was messed up and confusing the TCC. It caused the trans to lock and unlock often, just driving around normal on the HWY or whenever. Otherwise no issues I could see. Fix the switch and problem gone for good. I beat the crap out of my 4L60e and it never gave me any issues, even super hard work in the dunes for hours on end in 95* heat. Towed 5,000lbs with it over the Rockies and it just never gave me any issues besides the brake switch drama.

Can you get no support from the vendor that supplied your last 4L60e? Thousands on a HD 4L60e is a lot, heck Monster Trans best 4L60e is like $4 or $4.5k and is good to over 500hp. I would think the vendor should/would help and stand behind their product.

Cheers

 

[lazy]

Did the tune happen yesterday?

 

[workingdog]

No, the brand new transmission went out over the weekend - total loss of drive. So it's at the tranny shop and the tune is moved to the 16th. The gods are very much against this truck every running reliably. I think I need to sprinkle some Budweiser and chewing tobacco on her to rid her of her evil spirits.

 

[workingdog]

Here's the update.

RMP says there are no misfires at all. The engine is running fine. TC is behaving fine. There is some concern about fuel pressure at the fuel rail, but on the Dyno and on the road they aren't seeing any problems at all. I described the 'unlock' on Donner pass to him, he had no explanation for me at all as to what was happening. So at this point, I am looking at options for datalogging trans data - which at this point looks pretty complicate.

He's going to being a wire up from the harness that I can run through a led to show TC status, I'm also hoping I can get some kind of indication of gear (since it's not entirely clear if just the TC unlocked or it unlocked and downshifted).

Any informed suggestions would be appreciated.

 

[workingdog]

I took the rig on a 3 hour drive from Santa Rosa to Auburn and flat towed my FJ40 back. Driving there, everything is prefect, running in 4th at 2000 rpm at 70mpg. On the way home, with the FJ40 behind us, 3 times, on flat ground, for no apparent reason, it dropped into 3rd gear. The guys at RPM said that based on the change in rpm I was seeing, it was not the TC unlocking, but a down shift. It stays in 3rd around 2,600 to 2,800 rpm. Twice, we hit a bump and it dropped back into 4th and it was fine for a time. The third time, we ended up slowing down. From a stop, it seemed like the ship points for 1->2 and 2->3 had moved up several hundred RPM. It definitely wasn't shifting at the normal points, and it wouldn't go into 4th. 20 minutes later, it pops into 4th and it's fine the rest of the way home, shift points back to normal.

Can anyone shed any light on what's going on? It's like the transmission decided I was towing 10,000 pounds. The FJ60 had no problem towing the FJ40, we are were cruising at 65 at 180 ft lbs and 75ish horse power.

 

[boots4]

If shift points are changing what about a TPS (throttle position sensor) problem? Or other input sensor problems?

 

[workingdog]

Yes, TPS is a consideration.
Transmission guy is convinced it's just overheating.
And given this only happened when we put my FJ40 on the back or on long climbs it makes sense. My trans temp gauge and sensor finally arrived. I'm putting it on next week.
The challenge is that there is no where in the engine bay to fit the cooler. I'm going to have to get creative.

 

[NCFJ]

You can put a trans cooler in behind the grill

 

[lazy]

Curious, what in an overheated transmission causes erratic shifting?

 

[workingdog]

Tranny guy said, it will refuse to go into overdrive and shift points from 1->2 and 2->3 will go up. Like it's trying to keep RPMs up to move fluid.