GM's 8L90

[440Magnum]

Originally Posted By: supton

I guess I'll have to think about that some more. I've been forcing a downshift whenever I notice the convertor unlock, so as to force it to lock up. And run cooler.


I definitely would re-think it... You sense the convertor unlock... so you force a downshift and make it lock again (incurring wear), rather than just let it run unlocked and incur NO wear? Heat? Cars and trucks and Greyhound busses had torque convertors that *never* locked under any circumstances up until the late 1970s. The heat generated is less than you think, and the transmission can dissipate it easily.

"Hunting" is a different thing altogether, whether it be hunting between gears or hunting between lock and unlock. That's a case where intervening and just holding a lower gear is definitely a good thing.

 

[IndyIan]

So is a "partial lock" just slipping a wet clutch on the torque converter? Seems like not a great idea but I suppose with a multiplate clutch, there lots of wear material to be had.
My parents 06 CRV does it and I find it annoying, I wish I could just tell it to use 4th locked until I judge its ready for 5th locked, but Honda doesn't allow that.

 

[Hokiefyd]

Originally Posted By: IndyIan
So is a "partial lock" just slipping a wet clutch on the torque converter?


I think so, yes. I think there are different designs for these lock up mechanisms, but I'm sure that there has to be some type of a clutch there somewhere. There is probably a lot of wear material, and the fluid presumably keeps things relatively cool...cooler than a dry clutch slipping anyway. And since it only does it under low-load conditions, I reckon that true wear is very minimal.

 

[supton]

Originally Posted By: 440Magnum
Originally Posted By: supton

I guess I'll have to think about that some more. I've been forcing a downshift whenever I notice the convertor unlock, so as to force it to lock up. And run cooler.


I definitely would re-think it... You sense the convertor unlock... so you force a downshift and make it lock again (incurring wear), rather than just let it run unlocked and incur NO wear? Heat? Cars and trucks and Greyhound busses had torque convertors that *never* locked under any circumstances up until the late 1970s. The heat generated is less than you think, and the transmission can dissipate it easily.

"Hunting" is a different thing altogether, whether it be hunting between gears or hunting between lock and unlock. That's a case where intervening and just holding a lower gear is definitely a good thing.


Then why is it the kiss of death while towing?

On mine it revs up to about 2k unlocked, which is around stall speed. It does make a good deal of heat there.

 

[CBR.worm]

On the tundra, the transmission knows if you are going up/downhill and will pick a gear accordingly. If you are going down a long hill and touch the brake, it should downshift a gear or two. If you are in rolling hills, it may lock out the top gear or two. Behavior changes with CC set also.

 

[supton]

Cruise control is broken on this truck. It will often do a double downshift, overshoot on speed, then hunt between gears. Maybe it tries too hard to hold out, using the tallest gear possible. All I know is, my right foot keeps it from shifting if I don't use cruise. Or once in a while it just unlocks.

 

[SteveSRT8]

Originally Posted By: CBR.worm
On the tundra, the transmission knows if you are going up/downhill and will pick a gear accordingly. If you are going down a long hill and touch the brake, it should downshift a gear or two. If you are in rolling hills, it may lock out the top gear or two. Behavior changes with CC set also.


No offense here, but GM trucks have done this since around 02-04 models. It's nothing new or unusual. Our newer vans have 'grade braking' as an option in the vehicle setup...

 

[CBR.worm]

Yep, my first '00 Tundra did this - that is where I am getting my info from.

 

[440Magnum]

Originally Posted By: SteveSRT8
Originally Posted By: CBR.worm
On the tundra, the transmission knows if you are going up/downhill and will pick a gear accordingly. If you are going down a long hill and touch the brake, it should downshift a gear or two. If you are in rolling hills, it may lock out the top gear or two. Behavior changes with CC set also.


No offense here, but GM trucks have done this since around 02-04 models. It's nothing new or unusual. Our newer vans have 'grade braking' as an option in the vehicle setup...


My 545RFE only does that in Tow/Haul. It'll downshift on long downgrades regular mode if cruise control is on and the speed gets over the setpoint.

 

[javacontour]

Is it that the lock up never wears out, or that you just can't tell when it's gone? Is it possible that unlike a dry clutch, if the lock up fails, the vehicle still functions, albeit as one that only has a conventional torque converter?

If the average motorist wouldn't know when the engine goes for 8 to 4 cylinders; would that same motorist recognize when the torque converter no longer locks up?

 

[SteveSRT8]

Originally Posted By: javacontour
Is it that the lock up never wears out, or that you just can't tell when it's gone? Is it possible that unlike a dry clutch, if the lock up fails, the vehicle still functions, albeit as one that only has a conventional torque converter?

If the average motorist wouldn't know when the engine goes for 8 to 4 cylinders; would that same motorist recognize when the torque converter no longer locks up?


Relative to GM trucks, they will throw a code if the converter slips beyond a pre set value. Our older ones were still driveable like that but would lock out overdrive gear.

Drove many cars for decades, one of them had a 4500 rpm stall converter, no lock up in that beasty!

 

[supton]

Originally Posted By: javacontour
Is it that the lock up never wears out, or that you just can't tell when it's gone? Is it possible that unlike a dry clutch, if the lock up fails, the vehicle still functions, albeit as one that only has a conventional torque converter?

If the average motorist wouldn't know when the engine goes for 8 to 4 cylinders; would that same motorist recognize when the torque converter no longer locks up?


Probably not. Notice that is. Not unless if it locks out overdrive or similar.

W/o lockup though it likely will run hot, which might lead to shorter life. Hmm, wonder if some trans die for that reason--lockup convertor goes first, then eventually something else dies, possibly from never having the fluid changed, and it is not only loaded with material but isn't as good as it was. Cascade of failures, that is.

Anyhow, once it throws a code, it wouldn't pass inspection up here. So it wouldn't go for long before needing repair. I'd think though that if the convertor wore out, then the rest of the trans wouldn't be far behind.