700R4 Torque Convertor Troubles

[arveetek]

The lock-up TC on my '81 is starting to fail. I noticed the trouble on our recent camping trip. I have it wired up so that I can manually lock it up in 2nd, 3rd, and 4th gears. I can also switch it to where it automatically locks in 4th gear only.

I usually just use the manual feature when towing. Often I'll leave the tranny in 3rd gear when pulling our 5th wheel, and have the TC locked. Well, I noticed after pulling away from a stoplight and attempting to lock the TC up that nothing seemed to happen. Usually the RPMs drop quite a bit and you can feel the engine pull harder. After arriving at our desitnation and allowing the truck to cool overnight, the next day I could tell the TC was locking up, but not holding.

So, the TC does lock up, it will hold on deceleration, but not acceleration. It will hold at mild throttle input, but give it too much throttle, and the engine overcomes the lock-up feature and the RPMs rise.

I've put over 120K miles on the tranny, and I bought it used, so it has served me well. I'm sure increasing the power output of the 6.2L hasn't helped either. The TC that's in there now is a 3-bolt gasser unit.

Can I simply install a new TC? The tranny itself still shifts well and firm. There's no sign that the rest of the tranny needs service, just the lock-up TC.

Any advice would be greatly appreciated, as well as where to purchase a good quality TC to go behind the diesel.

Casey

[BobND]

I would start by fropping the tranny's oil pan, to see what's in there, and change the filter, while you're at it.

I could be a worn-out convertor clutch, or a bad seal ring, or debris in the TCC lockup valve, or the electric solenoid valve.

[mhagie]

Casey,I can't think of a reason why you would need to replace anything other than the torque converter.
I would however stop trying to lock it up as there could be particles from the clutch that could possible harm the tranny.
For what its worth I have a 700R4 from a 91 gasser that has been rebuilt and has a new diesel lock up converter that is unused.
The tranny has about a thousand miles on it,it has a B&M shift kit and a corvette servo, and the little gooodie that stops it from downshifting, plus a B&M converter lock up module that lockes converter at the speed you choose.
Probably more than you want but I do have it and its available reasonable.
Merle

[CleviteKid]

Casey,

Your trouble is very likely NOT in the torque converter, but in the tranny. The pressure to apply the lockup is bled off through the clearance between the main bushings between the input shaft and the main vane pump in the transmmission. If the bushings wear, the pressure is decreased, and the ability to hold falls off, just like you described.

I had the same thing happen on my Fourth Gear Inc. tranny, and Don found that the coating on the Torque-Drive shaft and drum chewed up the bushings. Don built up a new tranny for me, and he polished off the coating on the new Torque-Drive unit so it would be kinder and gentler to the bushings, and it has been working like a charm ever since.

So don't pitch out the TC just to have the same problem with you new one - have a knowledgeable tranny guy check out your bushings.

Dr. Lee :cool:

[arveetek]

Thanks guys!

Dr. Lee,

That's good info to have.

I have a spare 6 bolt TC out of an '82 or '83 700R4 (I forgot I had that tranny behind the shop). Is it compatible with the '90 tranny, and is it worth the effort to swap in to try it out, or should I just drop the tranny and have it rebuilt? I know the rear output bushing is worn as well, it's sloppy and causing a driveline vibration. *sigh* Really, it looks like it's time for a tranny rebuild.....

Like I said, this tranny probably has close to 200K miles on it, at least 150K....the time was coming for some service....

Casey

[CleviteKid]

I think the spline count increased about 1985, so the old TC and the new tranny would probably not even slide together.

Dr. Lee :(

[G. Gearloose]

I think you did extraordinarily well getting that milage out of it..

[Subzilla]

Casey,
Not that I'm disagreeing with Dr. Lee, but I had the exact same symptoms about a year ago (See 8-18-2004, "700R4 troubles again?", 6.2 forum). I had several transmission shops tell there is no way it could slip as described and basically told me to "go away and come back when I have a problem!" I contacted my trans buddy and fellow DPer, John, in California and he said the TC is your problem. I replaced only the TC and it has been fine since (approx. 15,000 miles). Transmission still shifts normal and TC locks up when it's suppose to, with no slipping. Good luck and have lots of patience.

[arveetek]

Since I ought to replace the TC in a good rebuild anyway, perhaps I'll start with buying just a new TC first. If that doesn't fix it, then a full rebuild is probably due.

Next question: any recommendations on where to purhcase a good quality TC?

Casey

[CleviteKid]

http://www.protorque.com/index2.htm

followed by

http://www.protorque.com/shopping/shopdisplayproducts.asp?id=6&cat=700R4%2F4L60E

You will want the PTC B29XLS. If your tranny does not accept the newer 30 spline input shaft, get another one.


Dr. Lee :cool:

[arveetek]

Funny you should post that Doc! I was just looking at that page! I was reading over your article to see where you got your TC, and determined that the PTC B29XLS was probably the one I needed.

I've been looking at other sites, but so far none of the others list that low of a stall speed. Bowtie Overdrives lists a 1600 RPM stall heavy duty model for $195, while the Pro Torque model is a 1200 to 1500 RPM stall for $295.

I wonder what the stall speed of my current model is? It's a gasser TC, but I've always liked the way it pulled. I'm afraid of installing a lower stall convertor and it lugging the engine more than I'd like. I've always wondered if the higher stall gasser model has helped my truck become the hot rod I think it is.

Is there any way of telling what stall speed my current TC is? I don't have a tach in my truck. I should have checked that out when I had Merle's timing meter.

I wonder if I might like a lower stall speed for towing, though.

As you can probably tell, I've been through the GM diesel engines about as much as any shade-tree mechanic can, but I have little experience working with the transmissions. Never really had to, honestly. All of 'em I have owned have always worked well for me. I've usually sold or modified a vehicle before the tranny gave out. This used 700 of mine has worked wonderfully since I purchased it in 1996.

Casey