4l60e in 96 Yukon jumping around gears intermittently

[jmshawii]

1996 GMC Yukon 4-door, 4x4, 5.7, AT, 252K At least 1 and possibly 2 transmission replacements WAY BACK-I think there were a LOT of problems with these back in the day, no?

Speedometer not working correctly for years now-goes from 0-100 MPH very quickly upon starting to move and stays way high. I've read this is a small gear issue in the cluster itself. Regardless, has been this way for several years with no transmission issues.

Brake light switch stable and seems to be functional.

Cruise control worked at least sometimes up until fairly recently (6 months or so-4000 miles or so), but would occasionally spontaneously cut off. Now it seems not to work at all, though noticed this was not working completely separately from the transmission issues..

Shifts all feel normal for the most part. No hard shifting nor any really SLOW shifting in getting up to speeds. Starts off from stand still as well as it has for the last several years. Has been in the family since new and well cared for and well maintained all its life.

MAIN SYMPTOM is that it frequently will start "jumping" out of and back into OD when at 50-60 or so miles per hour. If I step on it and have it under "more load" the problem seems to go away or at least be less frequent. And I can sometimes get "underneath" it as well, by letting off of the accelerator and slowing a bit and it will seem to hold in what I guess is 3rd.

SOMETIMES it drives fine for fairly long periods/distances, but rarely. SOMETIMES it seems to jump between 2nd and 3rd a little bit as well when at lower speeds. SOMETIMES, even if I am manually in 3 and not in OD it still seems to want to jump around a bit.

I did late last summer/fall notice that I had some fluid cross-contamination with the radiator, which I think I caught very quickly and remedied. At that point I had not noticed any funny symptoms in the operation of the transmission. I had to use Bars Leaks kind of stuff in desperation at the time to close the leaks, and changed out the tranny fluid and filter and everything seemed fine for at least a couple thousand miles.

I first noticed the OD jump happening about 6 months ago (a month or two after fluid change and after driving those couple thousand miles) and it was MUCH less frequent/quite rare. But I definitely noticed it and began paying attention. Because of the reputation of these transmissions and the miles on it (I have receipt from the most recent transmission change and I'm pretty sure it had two, but haven't checked the mileage-I'm thinking this trans should have about 150k on it) and the former problems we had with the trans even when newer, I became worried I was going to need a new tranny. I did another fluid change/flush (through the lines-not removing the pan or filter this time) shortly after noticing this jumping around activity for the first time. I also tried to add a little bit of Lucas Trans-Fix, but it was SO thick I could hardly get any to drain out of the bottle and into the trans fluid tube!

It acted pretty good for some time, but occasionally would do this. I had to drive from GA to the UP of MI and it made it most of the way pretty well, but started acting up eventually and was doing this a lot more. I was pretty loaded down so started running just in 3rd and it did okay and got me there. Still didn't jump around TOO much after that, but would now and then. Then I had to drive to Toledo (450 miles), and, again, it actually did quite well and only jumped from OD-3rd a couple times the whole trip. A week later made the return trip with maybe a LITTLE more jumping, but still not bad. But after that, about 2 weeks ago, it has been MUCH more frequently jumping back and forth and occasionally jumping the lower gears, too, as I mentioned earlier.

So, because the shifts generally feel to me pretty normal-even when jumping back and forth they are very clear shifts-not "slippery" nor HARD shifts-and because it is not just 1+4 or 2+3, and because the fluid doesn't look or smell bad, level is good etc, and though at one point RIGHT after the big drive up from GA to MI it seemed that the trans was making QUITE a "whirring" sound ALL THE TIME-even when sitting still (I read somewhere on line about someone having blocked lines and wondered if the pump wasn't running a little dry due to some kind of blockage [back to that even thicker goo than normal LUCAS???] that finally freed itself or something) it really feels and acts normal in almost every way except for jumping back and forth between gears sometimes, so because all of that, it "feels" to me much more like an electrical kind of thing than a physical/mechanical thing. Yet it sounds like if it were selenoids, they affect the different gear pairs, and this seems to jump across all of those combinations. And if it were some other problems it seems there would be hard shifts or SOFT shifts or non-shifts! None of those seem to be a problem.

Thus, I have been looking at those possible causes, but none of the descriptions I've read on other threads really completely match mine (I've probably been through about 30 between this site and some others), so was looking for input here.

My main ideas right now are TPS and VSS and just wondering who has what input and why? And if there is a way to more conclusively test these to figure out if they might be bad. And if you think I'm totally off base, please let me know as well.

So, sorry for the long post, but TRYING to include as much detail as possible, because I know it gets sloppy when you have to keep answering all kinds of individual questions and your info ends up spread out over 7 pages of posts and no one can possibly get all the info.

Thanks for any help and advice! And thanks for being here.

 

[Schurkey]

Is this REALLY a problem with OD, or is it the torque converter clutch disengaging under load?

Connect a scan tool and find out what the trans is trying to tell you.

 

[jmshawii]

Is this REALLY a problem with OD, or is it the torque converter clutch disengaging under load?

Connect a scan tool and find out what the trans is trying to tell you.

Thanks, Schurkey, for the input. I was curious about this. Does the regular, OBD2 scan tool give this type of info or is there a specific transmission scan tool of some sort? I know I've heard mention of the pressure tester to mount on the trans, but don't know if there is something more involved than an OBD2 reading for the trans. Does it give the info with just the key turned on or does it have to be while the vehicle is running/driving AND while the problem is occurring?

And I do NOT believe at this time it is an OD problem at all, which is why I am asking about the sensors. I think I said in the list of symptoms above that it SOMETIMES (though more rarely) seems to do the same thing between 2nd/3rd as well as 3rd/OD(?). I suppose this COULD be the TCC or something, but would that make for a solid shifting feel or for a "sloppy/slippery" shift feeling? Also, I'm not sure about "under load." I know that simply driving it IS putting it "under load," but putting more ooomph into the accelerator usually CURES the problem, which is putting the transmission under HIGHER load, is it not? Although I understand that these are "different loads," so it could still be something about the particular level of load.

On another note, it was acting VERY good last night and I was not noticing ANY of the jumping around. SO this AM, after taking my dogs to the dog park which is located at our local airport (Delta County Airport, Escanaba, MI), I went down to the end of the airport where there is about a 3/4 mile long "dead end-ish" straightaway road and put her through the gears a few times. NO slippage/jumping anywhere. Good, smooth shifts, etc. Could NOT get it to act up. SO got on the highway and went about 10 miles down the road at varying highway speeds, then turned around and came back. NOTHING. Ran a couple of errands around town, went out another direction about 5 miles at highway speeds, etc, and the worst thing that I ever noticed was MAYBE one SLIGHT blip in tranny performance, but one of those that was so small I wasn't sure I hadn't simply twitched my foot a hair and caused it myself. So, in terms of how intermittent it is, this is another indicator. And to me this still seems like something NOT mechanical/physical because of this. If something were worn and causing it, I feel like it would be there all the time. IN a case like this, it still feels to me like a sensor that occasionally acts up (now more often than when it operates normally) or as some have said in my research, like the wires in the pigtail to the VSS could be damaged and occasionally find the right position where they are all functioning properly until the get jerked out of position again.

Lastly, went to AutoZone this AM during errands for a scan. They have their super basic FIXFINDER tool, which I understand to be a VERY, VERY basic version of a scanner. I don't think it shows as much detail as a more professional version, and they even admit that. It showed Catalyst system below optimal on both banks and O2 heater circuits on Bank 2, sensors 1 + 2. I'm thinking that in about any 25 year old rig the catalyst system is probably below optimal, as well as often the O2 sensors, but is there any input on if these could somehow be contributing to the shifting issues?

So, more description of symptoms, but big question for you here, Schurkey, is are you referring to an OBD scan or something else? And the questions about if it will give the code even after the Yukon has gone back to behaving normally?

Thanks for your time!

 

[Schurkey]

A REAL scan tool will communicate with every "computer" on the vehicle.
Engine
Transmission
Air Bags
Instrument cluster
ABS
OEM security system
and whatever else the doofus engineers have dreamed up.

So, yes, you need a GOOD scan tool (NOT a "code reader", not a bottom-feeder consumer-grade unit) to communicate with the trans. And, of course, that tool needs to have software suitable for the vehicle you're working on. "Generic" software is far more limited than vehicle-specific software.

"Codes" can be very helpful. The live data is probably more important--input speed, output speed, whether the TCC is commanded "on" or not...etc. You'll likely get useful info with the key on, engine off, AND driving down the road.

There may come a time when you want to connect a pressure gauge to one or more test ports on the transmission. Should be available as a "loaner tool" from various auto parts stores. But I'd scan it first, before I bothered to connect a gauge.

In the same way that many "carburetor" problems were fixed with repairs to the distributor, many trans problems can be fixed with repairs to the engine (and the other way around.) If you know you have engine issues, yeah, you might as well take care of them and see what happens.

 

[JWOK]

Follow Schurkey's advice, you sound to have multiple issues going on. Determine whether your trans TCC is cycling in that 50-60mph range rather than shifting gears and read up on the TCC regulator/isolator valve problems common to 4l60E if it is TCC cycling.

 

[jmshawii]

Follow Schurkey's advice, you sound to have multiple issues going on. Determine whether your trans TCC is cycling in that 50-60mph range rather than shifting gears and read up on the TCC regulator/isolator valve problems common to 4l60E if it is TCC cycling.

JWOK, thanks for the advice. I have done EXTENSIVE reading on the TCC valve issue and in every description that I have read there is SOMETHING different in the behaviors than mine, which is why I am even posting my issue. As I said, I have done a LOT of research over the last week or so and every problem I read about has some symptom that always seems associated with THAT particular problem that mine does not have, or I have something going on with mine that definitely does NOT go with the other description. Because I have read so much and so many different threads and watched so many youtube videos, etc, I don't recall exactly WHAT it was that lead me away from that being the problem, but I assure you, I have probably read at least 10 COMPLETE threads, meaning EVERY comment by both the poster and the repliers/commentors, and watched at least 3 or 4 videos that dealt with the valve wear and reaming, spring replacement, etc. There was SOMETHING that made me think that was likely NOT what was going on with my transmission.

On another note, I do have several "real" mechanic friends of different levels, one of whom owns his own high end performance Mustang business, and checked in with him on getting an OBD scan with a "REAL" scanner. He very kindly obliged and I just went to get it scanned. It came back with the same results as the Auto Zone "FIX FINDER" scan and nothing else-O2 sensors. Nothing trans related. No TPS. No VSS (not sure scanners show that). He has what I think is considered a "REAL" scan tool-an almost new Autell Maxi-Pro like this one: https://www.amazon.com/Autel-MP808K-Diagnostic-Diagnosis-Bi-Directional/dp/B07R2N9K31

He was surprised that it didn't give any trans info after discussing the symptoms, but I reminded him that '96 was VERY early in the OBDII process and that maybe that early era of the system was not quite up to sending as much information as later years. We decided either that, or that it was one of those problems that has to be occurring for it to read, though he still didn't think that was the case either. He felt that if it had been acting up the computer should have remembered it and the scanner should show it.

And, to repeat what I had said earlier, the trans is behaving flawlessly now. It hasn't jumped around the gears in at least a day and a half now that I am on the case! I'm hoping if it starts to act up again he will let me take the scanner out and attach it while driving to see if it finds a problem.

In the meantime, I am going to get those O2 sensors fixed just to be safe.

Thanks for the input.

Other input still gratefully accepted.

 

[Steve A]

The early 1996 GM trucks/SUVs had transmission problems because of the PCM (or VCM depending on whose vernacular you use). As I understand it, the original "black box" PCM has 2 boards inside it and the problem was a poor ground between the two boards. GM issued a TSB and repair kit to remedy this and later PCMs had internal changes that corrected this situation. FWIW, early 1996 models that had the transmission rebuilt would NOT be warranted by most shops unless this TSB had been accomplished, if a GM authorized repair facility performed the repair this TSB was included.

 

[gearheadE30]

Watch the VSS on a scanner and make sure the PCM is actually seeing the right vehicle speed. If it's bouncing around or intermittent, that would definitely cause the problems you are seeing. You may not be able to see it drop out depending on the refresh rate of the scanner so it's not totally definitive. I'd suggest fixing the speedo issue though as it might fix the rest.

the TCC unlock can be caused by misfires, for example if something like the cap and rotor are getting worn. You can have enough misfires to make the torque converter unlock, but not enough to trigger a fault code.

That TSB is an interesting one; seems like it could also be the culprit.

 

[jmshawii]

Weird question... In this set up (96 4x4 Yukon 1500, 5.7, 4l60e) how can one see/access/tighten torque converter bolts? Can't find a direct proper video on YouTube. Have a funny take affiliated with all of this, and it is very similar to the nose when I had torque converter bolts work there way out in an old IH 345 with Chrysler 727 transmission. Want to check that rattle asap to make sure I don't lose tq bolts...

Also, I guess while I'm asking... Could that be causing just enough "unexpected movement" or "unusual movement" in the tq to cause computer/electronic "confusion" and maybe be part of the jumping gears situation?