Screwed the Pooch!

This weekend I decided to be really nice to the Wagon and give it some attention to the rear diff and transmission(1991 4L60). I changed the diff dope and all went well there.

I changed the trans filter as well, and added Dex VI to it since GM said it was OK to use. It was about 4 quarts.

On the first test drive, the torque converter wouldn't lock up. It goes through the gears ok, but that's about it. It would previously spin at about 1800rpm at 70mph, and now, depending on the steepness of the road, it can be well over 2500.

I sincerely doubted an electrical issue, since it was right as rain before the change. But, just in case, I had the pan off again tonight, checked to make sure that I hadn't buggered up the few wires inside, and put it back together, topping it back up with another 4 qts of Dex VI, the last I had left. Luckily, it was plenty.

There was no change. I took it back on the highway and drove it at a consistent speed for about 12 miles, occasionally tapping the brake with my left foot to get the solenoid to reset, trying to get it to do SOMETHING but to no avail.

I worked at a garage for 6 years doing fluid changes, must have done hundreds of trans services, from cars of all ages, and not one customer ever came back with an issue. I've changes trans filters on half the cars I've owned, mostly high mileage beaters, without incident. I've done total fluid swaps to some of them too. Never a hint of a problem. Heck, my 94 T-bird had a problematic shift accumulator, which fixed itself after a fluid swap, albeit after an hour of driving. It works fine to this day, eight years later.

I know I messed it up, but what on earth do I do now? Would it be worth my time to find some good old Dex III to stick in there? I hear the Dex VI is thinner stuff and maybe the olde 4L60 doesn't like it.

Or might it improve by driving around? My commute into work is 12 miles one way with no hills to speak of. Plenty of opportunity there to get its act together.

It's unlikely the fluid itself caused the problem.

http://www.impalassforum.com/vBulletin/5-drivetrain/252894-should-you-flush-your-trans-fluid-if-hasnt-been-maintained.html

That thread is all over the place. Now I really don't know. I guess "keep flushing" is the theme of it?

Don't believe the hype about Dex3 being bad.  It's not bad, it's just that Dex6 is way way better.  But back then Dex6 was a lot more pricey than Dex3 and the transmission expert said he'd much rather see me swapping my trans fluid every other oil change with Dex3 than to put in Dex6 and leave it.  Comparative pricing may have changed in your area so see what it costs and you decide for yourself.

How dirty and oxidized was the fluid you took out?

quick summary:
Yes, keep flushing until it stays clean.  When you pull the dipstick out, there should be no grit or black dust on the rag.  Just red fluid.  If the trans was really dirty it doesn't take long for the new fluid to get filthy.  I saw new fluid turn to mud in 60 miles.  

Use the cooler line method to pump out and swap fluid.  I can do it quicker than an oil change and with these cars and milk jugs you can do it by yourself.
/quick summary

Honestly though going from 1800-2500rpm at 70mph sounds like it's only in 3rd gear.  Torque converter lockup should only drop it 200-300rpm.  The 1991 4L60 is mechanically controlled except for the TCC if I recall correctly.  Are you SURE the shift linkage is working properly? Or you may have a shift valve that got hung up with grit circulating around with new fluid (just a possibility).

I hope that your problem is only the Torque converter. The lock up should result in drop of about 200RPM. You are stating a much larger number.

I have never had a 4L60 but I did own a TH200-4R which I believe uses the exact same system to control the converter lock-up, that is: 12 volts applied directly to the Torque Converter Control Valve. The 12 volts was supplied by the “computer” through the switch mounted on the brake pedal (opens the converter clutch when the brake is applied).
I installed a toggle switch wired in series with the brake pedal switch, on the shift lever, allowing me to unlock the converter “at will”.

With this information, you should be able to find the circuit to the lock-up (at the brake pedal) and determine if the 12 volt “lock-up” signal is being applied to the transmission. The car will have to be driven to the lock-up speed (40-60 mph) while a test light is connected to the circuit.

On the older OBD 1 data connector, if you connect port "A" and "F" (top right and top left) you will command torque convertor lockup. Crossing out these ports when in 3rd or 4th you should see 200 - 300 RPM drop (more when in 4th). If you don't, then check the wiring into the tranny. If that checks out, the TCC solenoid is probably suspect.

If you do get lockup, check the TPS connection and other electrical connections in the circuit. If everything checks out then you will have to dig deeper but this should be your first checks.

Bill

Thanks Bill, thats info I can use on the go. I will try to command it separately.
To the others, yes, it is shifting to 4th, as when I put it in third it will drop a gear.
The revs only go high in fourth if i am going up a hill.

One thing it is doing since yesterday, I am getting ONE lockup opportunity after it starts cold. I just drove home and the trans behaved normally the whole time, but I was careful not to downshift on the way home. Revs stayed solid 1800 rpm at 72mph.

When I got off the highway, it went back to not locking up.

And yes, the fluid was dark the first flush. I am going to get a 12v fluid pump to simplify all of this. Northern tool has a decent cheapy, that way I don't have to take it apart all the time. I'm a maintenance man by trade, and I work the night shift, and have to care for my young children in the mornings while my wife works, so the easier I can do this, the better.

Probably not what you want to hear but the same symptoms occurred with my 91 before it got a diesel stuffed into it. Turned out, the throttle body was plugged up and wasn't running right. This created a situation that too much throttle was needed to do the job, placing the TPS out of range to lockup the tranny. Cleaned up the throttle body, did a good tuneup and all was well again.

After the conversion, just hooked up a simple switch attached to the before mentioned terminals and took over the job of locking up the tranny manually.

Bill

The drive today was a little more promising. The trans worked as it should for much longer. In fourth, I was able to disable the lockup several times in a row by tapping the brake as I pushed the gas. It locked back up after I released the brake. After 10 minutes, it stopped working, but this is the longest period of time it has worked.

I rigged up the switch for the lockup, and it works. Still losing it after I get off the highway, but while I'm on it, the converter locks up as it should. It seems to work for longer, albiet slightly longer with each drive.

After much searching, I found a guy thatll rebuild it. Not a lot of good choices where I live for trans work, so he's a little further out, but hes a big 4L60 fan. He suggested a vette TC with 200rpm higher stall and I suggested an upgrades 3-4 clutchpack which he agreed with. Talked my ear off about all kinds of cars, engines, etc, so he definitely has passion for it. Lets hope it goes well.

OurCircuitMessSlobmodel wrote:

After much searching, I found a guy thatll rebuild it. Not a lot of good choices where I live for trans work, so he's a little further out, but hes a big 4L60 fan. He suggested a vette TC with 200rpm higher stall and I suggested an upgrades 3-4 clutchpack which he agreed with. Talked my ear off about all kinds of cars, engines, etc, so he definitely has passion for it. Lets hope it goes well.

Really stinks that this happened, but glad it sounds like you found a good source to fix it right.

I got the wagon back today. The dude is a total class act. I told him I wouldn't be able to get the car since my wife was at work, so he got a buddy of his, plus his wife to deliver it right to my house. He even saw that my rear trans mount was dilapidated, and gave me a good one out of his stockpile. It made it silent at highway speeds, whereas before I was thinking maybe one of my u-joints was getting a little sloppy.

Anyway, I will tell you this, the wagon now acts like its from two separate planets. The higher stall TQ which he says wouldn't be noticeable is actually quite noticeable. I guess I'm just sensitive. It works predictably, feeling more sluggy off the line in normal driving. It wakes up when I give it the beans for sure. I don't know if I like it yet, but at least it is behaving as it should with the new TQ.

It revs to 4750 whereas it used to shift at WOT at 4500 on the dot. Probably the TV cable is in a little different spot than it used to be.

Now, in lockup it is another story. It BITES down and will buck like a manual. It never would lock up in 3rd, but it does now, which means I can actually use the geriatric trick of putting it in 3rd on the pokey 35mph roads. Once I install my trans cooler, I won't do that anymore.

In 4th I am getting a few more mph compared to what it was even when it was working correctly. I drove home at 70 tonight, under 1800 rpm. He put a set of single sided steels in it. I hear they are a good thing.

As it does its thing, the TQ switches on and off like a led lamp as I modulate the pedal. It used to take its sweet time to finally decide I was going a steady enough speed to lock. I'm not used to this sort of immediacy in the top gears.

How it used to be, it felt tight in the 1-2 shift and soggy in 3-4. Now its soggy in 1-2(the shift is very quick tho) and tight in 3-4.

I live in rural Georgia, so stoplights aren't all that common, so while the results aren't what I expected, I think it is a good thing.

I will wait a week to give him a glowing review(thats fair, right?), but the price was very good I'll say. For not much more than Jasper would sell me one, he did the whole thing, perhaps better than they would.