What's wrong with my transmission?

[jeremyj]

Yes. Proper Dex-III every time.

 

[Ecomike]

Yes. Proper Dex-III every time.

atriot:

 

[jeremyj]

So I rechecked the quarts I have left in the garage and this is what I actually put in it last time. It was was I was told to use. To be honest, I'm not sure what the difference is between Dex/Merc and Dex III.

I replaced the NSS this weekend, because the reverse lights weren't coming on consistently, and it seems to have cured that particular issue. I haven't driven enough for the shifting issues to act up, but I also picked up a quart of Trans-X. I'm going to drain some fluid and top it off with that this week, drive for a day or two, repeat until the quart is all in the tranny, then drain and refill with fresh trans fluid again.

I would really like to switch to some sort of synthetic fluid so I wouldn't have to worry as much about varnishing. I use Modil 1 full synthetic in the engine and both diffs and it's been great.

 

[kastein]

All ATF is full synthetic as far as I know.

As for speed sensors, here's the answer once and for all.

The VSS on 91-01 XJs is ONLY FOR THE ECU AND SPEEDO. The TCU doesn't see it. It's in the trans tailhousing next to the OSS on 2wd XJs, it's in the tcase tailhousing on 4wd XJs.
The one you refer to is the OSS, output speed sensor. It reads the trans output shaft speed. The ECU never sees this one, but the TCU does and uses it to determine what gear it should be in.
The other one no one mentioned is the ISS, input speed sensor. It reads the trans input shaft speed *after* the torque converter, and is only present on 98-01 4.0L XJs. The TCU gets this info, again, and the ECU does not.

e: counts per turn and per mile:
ISS: 16 pulses per trans input shaft revolution.
OSS: 98-01 4 pulses per trans output shaft revolution. 87-97 1 pulse per trans output shaft revolution.
VSS: 8000 pulses per mile, 8 pulses per VSS input gear rotation. The speedo gear is selected so that the 13-tooth worm gear on the output shaft of the transfer case will turn it 1000 times per mile, then each of those 1000 rotations is converted to 8 pulses by the VSS.

The reason to have a VSS and an OSS is because the TCU and ECU don't know if the transfer case is in low range or not, or what its ratio is. So trans output speed and driveshaft speed aren't necessarily the same. Both are stuck in the back of a 2wd XJ's transmission simply because it's easier to keep the electronics unaware of all of this and feed them the same signals on 2wd vs 4wd than it is to account for it in hardware/software and significantly complicate things.

 

[Ecomike]

I am pretty sure the Dex III, I pay $12.xx/gallon for at Walmart is not synthetic. It is way too cheap to be synthetic. I think I heard once that Dex III was based on peanut oil. I found references to the additives being based on peanut oil in the bobstheoilguy web site.

I read many posts here about ten years ago where people tried the synthetics on the older AW4s like Renix era aw4s, and pre OBD-II and they had very bad results. Some later year AW4s loved synthetic in their AW4s. I stayed with the old cheap Dex III and 25,000 mile transfusions.

 

[Ecomike]

Kastein, Awesome input on the speed sensors and computers. I saved it to my notes Far more complex in the later years than I thought.

Are you sure the PCM and TCU do not swap data or output calculation results that give the PCM some control of the PCM and thus the AW4 (and visa versa)? I ask this because the TCU and the ECU get TPS data directly on the Renix rigs, but the TCU gets TPS data of some kind only from the PCM/ECUs.

 

[jeremyj]

Standard Dex III fluid is not synthetic. At best, it's a blend. Given how much luck I've had with Mobil 1 synthetic fluids, maybe I'll give this a shot after I drain the Valvoline/Trans-X out of it.

http://shop.advanceautoparts.com/p/...ned=1&prefStoredSet=1&prefZC=98002#fragment-1

 

[Ecomike]

Be warned that if there is still varnish and junk stuck to it, pure synthetic will free it up fast and may finish off the valve body (shove a bunch of junk in the valves all at once, like pure Trans-X would do). Also if the seals are old and worn the synthetic will go past the seals (it cleans them too much) and may cause low pressure keeping the valves from operating.

Drastic changes in fluid properties for old transmissions is never a good idea.

 

[jeremyj]

I'm attempting your recommended, gradual Trans-X procedure before I do any fluid changing. I'm hoping to knock all that shit loose before trying the synthetic fluid. Also, it's still Dex/Merc, just higher quality. Given how much fluid the whole system holds, including my aftermarket cooler, it will be a bit of a mix until I've drained and refilled a few times.

I've put full synthetic in every vehicle I've ever owned, some of which were high-mileage vehicles with a life of cheap oil before my ownership. Never once has the synthetic switch caused any sort of issue for me. Granted, we're talking engines, not transmissions. Besides...with all the crap this tranny has put me through, I think I'll be okay if it finally dies on me.

 

[Ecomike]

I tried synthetic once on my 87 Wagoneer, at 225,000 miles (new to me) and it started leaking and drinking 1 quart every 200 miles and leaked like a sieve ever since until I replaced every single gasket and seal on it, and it still ate a quart in 200 miles and I went back to dyno oil, 20W50. I use about 1 quart in 1000 miles now and that is with two bad valve guides leaking and burning oil and me cleaning the 2 spark plugs every 600-800 miles.

Synthetic? Never again, unless I buy a new vehicle. Glad to hear it works for some of you. It is a superior product if the vehicle is built for it and was run with it.

 

[jeremyj]

I've been slowly draining fluid and replacing it with Trans-X. I've got almost the full quart of it in there now and the rest of it will be in there some point this week. I took the Jeep on the freeway over the weekend and it immediately dumped out of lockup again, so it isn't working yet.

 

[Ecomike]

I've been slowly draining fluid and replacing it with Trans-X. I've got almost the full quart of it in there now and the rest of it will be in there some point this week. I took the Jeep on the freeway over the weekend and it immediately dumped out of lockup again, so it isn't working yet.

I thought it was not even going into gear lately? Is this just a TC lock up issue now? That sounds like a great improvement?

 

[Ecomike]

BTW, synthetic means made from pure natural gas in a series of hydrogenation reactions in chemical plants. The old stuff, dyno oil, is made from cracking, destructive distilation of crude oil, and non syn ATF was made from peanut oil, at least in part once IIRC, otherwise I guess also made from crude oil. Both are man made ( Syhthetic in a way ) from fossil fuels LOL, but the label symthetic refers to assembling the oil molecules from pure hydrogen and carbon made from pure Nat Gas, Methane CH4 molecules.

All ATF is full synthetic as far as I know.

As for speed sensors, here's the answer once and for all.

The VSS on 91-01 XJs is ONLY FOR THE ECU AND SPEEDO. The TCU doesn't see it. It's in the trans tailhousing next to the OSS on 2wd XJs, it's in the tcase tailhousing on 4wd XJs.
The one you refer to is the OSS, output speed sensor. It reads the trans output shaft speed. The ECU never sees this one, but the TCU does and uses it to determine what gear it should be in.
The other one no one mentioned is the ISS, input speed sensor. It reads the trans input shaft speed *after* the torque converter, and is only present on 98-01 4.0L XJs. The TCU gets this info, again, and the ECU does not.

e: counts per turn and per mile:
ISS: 16 pulses per trans input shaft revolution.
OSS: 98-01 4 pulses per trans output shaft revolution. 87-97 1 pulse per trans output shaft revolution.
VSS: 8000 pulses per mile, 8 pulses per VSS input gear rotation. The speedo gear is selected so that the 13-tooth worm gear on the output shaft of the transfer case will turn it 1000 times per mile, then each of those 1000 rotations is converted to 8 pulses by the VSS.

The reason to have a VSS and an OSS is because the TCU and ECU don't know if the transfer case is in low range or not, or what its ratio is. So trans output speed and driveshaft speed aren't necessarily the same. Both are stuck in the back of a 2wd XJ's transmission simply because it's easier to keep the electronics unaware of all of this and feed them the same signals on 2wd vs 4wd than it is to account for it in hardware/software and significantly complicate things.

 

[jeremyj]

The lower gear issues have been there all along, but incredibly sporadic. The TC lockup has been there since the beginning, before the lift and tires, before anything else. It also seems worse now than it ever was in the past. Since it basically quit happening for nine to eleven months after I changed out my solenoids and fluid, I haven't given up on the fluid being the culprit.

Even though it looks clean on the dipstick and doesn't have a ton of miles on it, the fluid looks pretty dark when I've drained it. I don't know if that's because I've never flushed the system completely, or because it's just getting too hot and burning. It doesn't smell odd and I do have a decent aftermarket cooler inline with the factory tank in the radiator. I'm contemplating a flush and some different fluid.