Making metal -- automotive trannie qx

I'm no expert on your tranny, but have you done the basic root cause analysis yet? Clearly, whatever was changed by rebuilding the transmission didn't fix your problem. Hence, I'd ask myself what _didn't_ change, and go looking for faults there.

- Converter?

- Solenoids & other actuators?

- Sensors?

- Computer? Is it grounded correctly? I have a mechanic friend who knows squat about electronics, yet regularly fixes computer problems just by making sure that they have all their grounds done up cleanly and correctly (check the engine to frame ground while you're at it).

- Vacuum leak? Plugged line to sensor? Line to sensor fallen off? Do they even use vacuum for this?

- All wires unbroken, insulation intact, connections right and tight?

As I said, this is all general diagnostic stuff, yet it almost has to be where your problem is.

Tim Wescott fired this volley in news:FcCdnT6DY-OqnZjanZ2dnUVZ snipped-for-privacy@web-ster.com:

Yep...done all of that, and more, and I've pretty much exhausted my expertice in all those areas. I'm a _good_, logical trouble-shooter, but with little knowlege of the transmission, I'm sort of working blind.

Your list of possible things replaced -- all were. I've fixed a couple of minor vacuum leaks - no change. Yes, even with a computer, that trannie also has a vacuum modulator.

The only way I can tell if the computer is doing this is to install an indicator light on each of the TCC lock and TCC-PWM solenoids (and of course, might as well do shift-A,B,&C at the same time), then watch them during driving. It's a fairly ugly task; getting cables through the firewall on that car is a neat trick. It did it with ONE conductor for the tach pretty easy with the "sewing needle" trick through a grommet wall, but a five-conductor cable will be harder.

LLoyd

Lloyd, put the indicator lights in a minibox and temporarily mount the box outside the windshield with the wires coming out the hood gap, that is unless you plan to leave them on permanently. that way you save yourself the hassle of trying to go through the firewall and there will be no hole remaining when you remove them. The box could be clamped to the lip of the hood edge with one of those "gutter mount" antenna mounts. Did you ever find anyone to take care of the items you needed built?

Jim Chandler

Jim Chandler fired this volley in news:1b8Ni.3649$6Y5.325@trnddc07:

Yep, that's the option. The tach will probably stay -- great trouble- shooting aid, and first-alert of new problems. That's the only reason I'm leaning toward making the shift lights part of the setup.

Did, indeed, Jim. One of our regulars here.

LLoyd

There usually is a pressure test port on the transmission, where you can rig a pressure gauge. Either use an electric pressure sender or make DARN sure the lines are very secure and can handle several hundred PSI of hot oil. You sure don't want something letting go and spraying you with oil at 100+ C while you're trying to stay on the road at 55 MPH. Some transmissions, at least in the old hydro-mechanical days, changed the pressure relief valve setting for different modes. I'm not sure they do that anymore, except maybe for reverse.

I haven't had a car that did the converter lock-up in anything but highest gear, but they are all different. And, usually the lock-up is at about 45 MPH, after you've held steady throttle for a few seconds.

It is also possible that this is a computer or engine sensor problem. (Oh, yeah, the standard "Car Talk" show question "Oh, by the way, is the Check Engine light on?")

Finally, some (maybe all) transmissions are designed with extremely marginal grip on the clutches, to get that smooth slide into gear. If the wrong transmission fluid is used, they may never lock up properly when they are supposed to. I think my wife may have killed her tranny a few years ago, when somebody told her to add transmission fluid at a gas station. It took a $1300 rebuild the next week. Of course, they may have been right, the tranny was already sick, and the fluid really had nothing to do with it. I'd guess a rebuilder would know to put the right stuff in there.

I do agree with you that if this slipping in and out of converter lock-up is not being commanded by the computer, then you have a real problem. It is not as bad as another clutch slipping, since the converter still carries some of the torque (unless this one drains the converter on lock-up, some do) but it is a sign something major is wrong. If it is being commanded by the computer, it may be a quirk of the drive-train management software, and may be fully intentional to keep the engine out of a specific RPM range or some other oddity they wanted to do.

Jon

Jon Elson fired this volley in news:t92dnZvqP6Cuu5janZ2dnUVZ snipped-for-privacy@giganews.com: If it is being commanded

I hadn't even considered that, but it's a good likelihood. The lights will tell the trick.

LLoyd

Just a wild guess. I would suspect a worn converter lockup valve bore. Repair kits are available; reamer, sleeve and valve.

I believe a GM rebuild routinely includes this.

--Andy Asberry--

------Texas-----

See if you can borrow a "Professional Grade" OBD-II scanner that can watch the real-time ECU transmission control parameters on the fly - it may even have a transducer and readout to watch the transmission line pressures and other stuff that can lead you to a faster resolution. It will put up on-screen flags when the computer locks or unlocks solenoids, so you don't have to do any hardware hacks on the car.

And with luck being the way it is, the extra load from the tell-tale lamps you tapped off the wiring screws up something, or blows a chip in the ECU...

I want a Laptop based OBD-II interface if I can find one that is done right - and that includes not charging a King's Ransom for the inevitable periodic updates. Much less expensive than inventing and building a display and interface system from scratch, they can invest their energy in the software.

And I can just plug it in if there's a hiccup to ID and banish.

-->--

JR North fired this volley in news:MsudnbTqeuQWBJjanZ2dnUVZ snipped-for-privacy@seanet.com:

It's not throwing any codes, so the PCM thinks things are normal. LLoyd

Bruce L. Bergman fired this volley in news: snipped-for-privacy@4ax.com:

Yeah... Mine will snapshot the ECU, but not read in real-time.

Nah... that's not likely to happen. I have a couple of decades of designing digital interfaces, and am pretty comfortable with fan-in/fan- out characteristics. 'Sides... the PCM presents a simple open-ended mosfet to ground that will sink about two amps for each solenoid control output... pretty bullet-proof when all you're doing is monitoring its level with a cmos gate input through a series 100kohms.

ID is often easier than banish.

LLoyd

I exchanged emails with "Sinister Performance", a group of very helpful, very tech-oriented guys.

They're not sure there is something wrong, but they're going to ask their expert tranny hop-up guy to comment.

I talked with the rep at the chain who did my rebuild, and he says the PWM doesn't engage with 100% duty cycle until after 65mph.

That sort of jibes with GM's literature that says they were attempting to mask the lockup-feel on "luxury" sedans. On some 98 models, they never completely lock up, slipping at 20-30 rpm relative to the input shaft at all times _when_in_lock_.

Hmmmm.... mebby I'm chasing a ghost.

LLoyd

Bruce L. Bergman wrote:

Probably old and useless info but...

My old 700R4 tranny (1982) has at least three requirements to lock the converter. You have to be in at least 2nd gear and a certain speed. There is an interlock switch on the brake pedal. If the brake lights come on (shared switch) it disengages. There is another switch on the throttle linkage. If you don't give it enough gas or let off the throttle it disengages.

Old stuff, but that it how mine was done. Oh one other thing, there is a special four wheel drive switch too. If it is in 4x4 it will only lock the torque when it is in overdrive (4th gear) and all the other conditions are met.