What's wrong with my transmission?

[jeremyj]

This is officially an everyday thing, now. I did notice something odd today, though. On the freeway, going 60+, the lockup failed as usual. Then I hit some stop and go traffic for a couple of miles, until I got off the freeway. After a few blocks of city driving, I turned onto a smaller highway where I was going about 45. The lockup worked fine on the highway. I tested it by keeping my right foot on the gas while tapping the brakes with my left foot. It would unlock with each tap, and then lock back up like it should.

I don't know if this will provide any additional insight to the issue, but it's good to know. I cleaned the TCM grounds on the block last night, which obviously didn't help anything. I guess I'm going to remove and clean the VSS and NSS next.

 

[jeremyj]

Just yesterday, it was about 95 degrees and I was cruising on the freeway with the AC on. The tranny dropped into neutral and wouldn't let me accelerate anymore. I pulled over and ran through the gears. 1-2, N, and R all worked normal, but it refused to go into three or four. When in drive, it would go from first to second and then it would dump into neutral, which limited me to about 25-30 MPH.

So this gem happened again this morning. It was in the low fifties and rainy, so definitely not heat related. This time, I had the presence of mind to drop it into neutral while still rolling, shut it off and immediately restart it, then put it back into "D". That fixed it. Back to regular shifting. This has to be an electrical issue, right? I would think a mechanical issue wouldn't care about a super brief on/off/on cycle, while still in motion. I am beyond frustrated with this thing and I'm seriously considering a manual swap.

 

[Ecomike]

Not sure why you did the driving in neutral restart? What exactly was wrong?

I would strongly suggest a hot wire/toggle switch by pass to manually turn on the power the TC clutch to see if the problem is wiring or the solenoid itself the next time the TC clutch lockup dies. If it turns out to be an intermittent solenoid (trash coming and going in the hydraulic side of the solenoid?), then hot wired power to the valve will not lock it up. If the toggle switch does lock it back up when it cuts out for no good reason, you know to look elsewhere.

Speaking of elsewhere, the VSS does sound like a very good idea!!!! But would it not also show up on the dash as a wandering speedometer reading?

 

[jeremyj]

The trans shifts down into first gear and then dumps into neutral until I slow down enough to catch first gear again. I'm limited to maybe thirty mph when this happens. This is only the second time it's done this, but the solenoids are new since the last time it happened, so I'm pretty sure it has nothing to do with them. Shutting it off and restarting immediately resolves it, not unlike the couple of times it has gone into limp mode and stuck in third gear.

I haven't noticed the speedo acting up at all.

 

[Ecomike]

The shifting into neutral is puzzling, unless the transmission itself is slipping at that point. Over my pay grade, but I wonder if there is a hydraulic safety that dumps it into neutral overriding the solenoids when it tries to go into first at too high of a vehicle speed. It could still be wiring from the TCU to the AW4 solenoids, or the NSS, or even a ground issue.

 

[jeremyj]

At some point this week, I'm going to try to remove the NSS and VSS to clean them out and reinstall. I need to pick up some dielectric grease for the NSS and wait for a dry day before I dig into it.

 

[Ecomike]

That reminds me, our 89 Cherokee refused to start 3 months ago after going through rain/water and I jump started it, bypassing the NSS at the starter/ignition solenoid near the battery. 10 hours later it was fine and never gave us any more trouble, yet. But it has spent most of that time in the driveway getting an entirely new front end.

May be time to install that new NSS on her, before she goes back to DD service.

 

[jeremyj]

New stuff. Sometimes the converter will unlock and then just refuse to lock back up until the next time I drive it. It has also downshifted kind of hard on a couple of random occasions. All new things. Whatever my issue is, it's getting worse and affecting more aspects of the transmission's operation.

Any time it gets stuck in a lower gear (which has only happened a couple of times), all I have to do is restart it and the problem immediately solves itself, which sounds electrical. The fluctuating lockup does not go away with a restart, though. That's my main concern.

 

[jeremyj]

I just ordered a new NSS, brake switch, and a Mopar TPS. I'll update this again when they're installed.

 

[68datsun510]

Following, my 98 is behaving almost identically

 

[jeremyj]

I installed a new Mopar TPS this weekend and so far, it's alright. I'm not saying it's fixed, because I haven't really driven much yet. It was fine on the way to work this morning, which is a promising sign, but I'm not getting excited until I drive a bit more.

Here's the Mopar TPS on the right, compared to a generic one that I got a few years ago at either Autozone or O'Reilly's.



I also have a new NSS and brake switch that I'm going to install soon.

 

[jeremyj]

Well, so far the lockup issue hasn't shown up, but instead, the tranny stuck in second or third gear one time. It also jumped from first to second too quickly another time.

I've been spending some time researching a manual swap.

 

[Ecomike]

Have you cleaned and inspected the main bulk connector from the TCU to the Transmission? It may also be the lines to the NSS? The Transmission ground wire?

What about the Transmission or transfer case VSS, vehicle speed sensor that the TCU uses for selecting shift points in combination with the TPS sensor input?

 

[jeremyj]

All the connectors and ground wires have been cleaned and reconnected. I have a new NSS that will be installed shortly. The VSS in the TC is pretty much only for speedometer readings, but I have been looking into the transmission VSS. It's on my list of parts to buy that probably won't fix it.

 

[Ecomike]

Too my knowledge there is no VSS in the transmission of 4WD jeeps? In 2WD it is in the transmission and in 4WD in the Transfer case, I think.

 

[jeremyj]

There is indeed. It's at the tail of the transmission, same side as the speed sensor on the transfer case. It's called something like "vehicle speed output sensor" or something like that.

 

[Caner.]

maybe you've considered it, but after all that diagnostic and money spent, can't you just try to get a new tranny from the junkyard? at this point you've replaced everything else, so if the JY one needs new solenoids or something like that, at least you already have the parts.

 

[jeremyj]

Two reasons:

1. I've already done it. This is the second transmission in the Jeep and I really don't want to do it again, unless I'm swapping to a manual.

2. I've read about other people swapping the transmission and converter, only to still have the same issues persist. This just makes me think it's something on the Jeep itself, instead of the actual transmission.

Another thing I haven't put a lot of thought into until these past couple of days, is the fact that all of these issues were gone for about nine months after I changed out the solenoids and fluid. So maybe flushing the fluid and trying some of that Trans-X stuff could push out something that's clogging up the hydraulics inside the tranny. I know that it's just a little bit above the full line, and maybe that's causing the fluid to get whipped up by the mechanics, heating up, and varnishing up some of the passages or solenoids. It may be a little far-fetched, but it certainly won't hurt anything to change the fluid again. Maybe leave the fluid just a little bit lower than the "full" line on the stick.

 

[Ecomike]

I never ever fill transmissions to the full line even when hot, maybe just the cold line full mark (if there is one) or just into the hatch mark between the add and the full marks for hot. Transmissions are very touchy about the fluid level and do not read properly unless parked on level ground and sometimes the drain back on the tube gives false readings if you rush it. Too much or too little fluid can make it foam and make the pump and Tconverter cavitate and damage parts and burn the fluid into a varnish that makes valve body parts stick. Under the best conditions the DEX-III is only good for 25,000 miles. And there is no way to drain 100% of it out, it holds about 10-12 quarts as I recall and unless you use the transmission pump to pump it nearly dry using the lines that go to the radiator it must be partially drained and transfused about 3 quarts at a time. Using the pump and tube will get at least 1 gallon to 1.5 gallons. Walmart has dirt cheap DEX III, $12.xx / gal

Trans-X has fixed so many dead transmissions for me it is scary!!!! And I am a chemical engineer in the paint-solvent-varnish field among others....so I am very familiar with this. The trick is to be gentle and add a 1/2 pint to a pint, run it in idle for 30 minutes parked. Drive it some and run it through all the gears. Drain it hot if you can, refill it with Trans-x (.5 to 1 pint) and bring up to just over the low mark on the dip stick. It has taken 2,3,4 and 5 of these flushes to restore a transmission depending on how bad the fluid was abused. This process dissolves the varnish slowly so it does not come loose all at once and jam up the valve body valves

You are using Dex-III right??? (I forget the entire story here)

 

[Ecomike]

There is indeed. It's at the tail of the transmission, same side as the speed sensor on the transfer case. It's called something like "vehicle speed output sensor" or something like that.

Is it actually attached to something or is it an artifact of a 2WD transmission now used for 4WD or was the jeep upgraded once???? Not sure why they would use one on both on 4wd, but I may have forgotten some of what I thought I new about the 2wd and 4wd variations.

Also I think the VSS part changed between 1996 and 2001, so maybe there is a part mismatch now? Just tossing out rare ideas....so we don't overlook anything