slipping transmission

S

scott00tj

NAXJA Forum User
Location
Medina, OH
I've heard the term of a transmission slipping, but I don't know if I understand the issue. What are symptoms of this so I know if my aging XJ ('99 XJ, 4.0L, AW4) starts or is starting to have this problem.
 
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engine RPMs go up but you're not moving (or not accelerating as quickly as you expect based on engine RPMs.) Low fluid can cause this as can mechanical problems.

You will probably know if you feel it slipping.
 
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There are a series of clutches and brakes inside an automatic transmission. Hydraulic pressure is used to apply the clutches and brakes based on the gear selection/engine load/TCU. Old transmission fluid is the biggest cause of slippage, slippage causes heat, heat further damages the fluid and eventually the transmission itself.
 
If you are feeling different characteristics of shifting, be sure that the fluid is fresh (red, not brown) that the fluid does not smell "burnt", and that the fluid is at the correct level on the dipstick with the engine and transmission fully warmed up, level ground.
 
What I've been noticing with my '99XJ is that right about 40-50 mph the Jeep feels like it cant make up its mind as to what gear its wants to be in. It's switching back and forth between 4th and 3rd. This happens about 20 min into my drive to work (when I start getting to roads with that speed). I don't know if the cold could have anything to do with it or if its something major? The AW4 has 100K on it and will be getting a filter and fluid change in the next week or so.
 
Overfull can cause the same problem. When the fluid level is too high it foams, causing low hydraulic pressure. That is why you need to check the fluid when it is hot. My '98 XJ hunts for what gear it wants to be in when it is cold, at about that speed. Once it warms up it stops doing it. It only does it when it is below 20° outside. I read in JP Magazine that Lucas "Stop Slip" works as a temporary fix for the AW-4. Never tried it myself.
 
The AW4 being electronically controlled MUST have good data for the TCU to decide the correct actions.

Things that can screw with the TCU's input data/AW4 operation: trans shifter cable is out of adjustment; the NSS is dirty/out of adjustment; the TPS is bad or has bad "spots" in its range of movement; the throttle pressure cable is out of adjustment; the fluid is old/contaminated/burnt (Dex III MAX life is 30k miles, cut that by one half for every 20 degrees of overheat); the brake switch is out of adjustment (tc lockup releases when the brake pedal is depressed); a little low in the fluid level is better than overfull. That leaves the solenoids and the harness, or just plain old mechanical/hydraulic problems.
 
by one half for every 20 degrees of overheat
---------------------------------------------------------------------
A badly overlooked fact. That often leads to early tranny pooping out.
B, If your engine overheats bad/often change the trany fluid too more often.
 
You might want to try and adjust the Throttle Cable. Takes 5 seconds and it often cures
a transmission that can't seem to make up it's mind when shifting gears on it's own.

There are 3 cables going to the Throttle Body. The one you want to adjust is the one
that is most toward the front of the car.

I looked up the procedure on adjusting the cable in the factory manual and it seemed
overly complicated.

Simply:

With engine OFF:

1) Press the Release Button (grey, half-moon shaped plastic button) and hold
it down.

2) Push the exposed Conduit (exposed cable sheath) all the way up into the cable
bracket, and then let go of the Release Button.

3) Manually open the Throttle all the way (Wide Open Throttle).

The Cable Sheath should ratchet itself out of the cable at the correct position
and you'll be good to go.


Addendum: When I did Step 3, it seemed to take a scary amount of force to open the throttle to get the Conduit to ratchet out a few clicks.

Instead, what I did for Step 3 is ... continue to hold down the Release Button while grasping the cable on the right side (starboard) of the cable bracket to maintain
cable tension. Turn and hold the throttle at wide open. Then let go of the Release Button.
 
metaldemon7 said:
Overfull can cause the same problem. When the fluid level is too high it foams, causing low hydraulic pressure. That is why you need to check the fluid when it is hot. My '98 XJ hunts for what gear it wants to be in when it is cold, at about that speed. Once it warms up it stops doing it. It only does it when it is below 20° outside. I read in JP Magazine that Lucas "Stop Slip" works as a temporary fix for the AW-4. Never tried it myself.
Click to expand...

Yeah they said it was filled with unicorn boogers. ;)
 
I keep checking the fluid level after my drive home from work (20-25 min) and its right in the middle of the fluid level gauge on the dip stick. Could it be something else and if so what and how can I start to trouble shoot?

I did recently do a fluid and filter change on the AW4, but I know that's not a "full flush". I added half a bottle of the lucas stop slip at that time in addition to new fresh dex III. The issue described was happening before the change. I plan to drain the sytem again this weekend and put in more fresh fluid to slowly cycle the old out.
 
Did you ever run the full gauntlet of adjustments and tests that were recommended previously?
 
scott00tj said:
What I've been noticing with my '99XJ is that right about 40-50 mph the Jeep feels like it cant make up its mind as to what gear its wants to be in. It's switching back and forth between 4th and 3rd. This happens about 20 min into my drive to work (when I start getting to roads with that speed). I don't know if the cold could have anything to do with it or if its something major? The AW4 has 100K on it and will be getting a filter and fluid change in the next week or so.
Click to expand...
My '89 is twice as old and with twice the miles as yours, although the trans may have been rebuilt. I just never put it in (D) unless I'm on the freeway and going over 55. Really no problem driving that way and it doesn't keep searching for the most "economical" gear.

Did you change the fluid yet? It seemed to help mine drive smoother.

Mike
 
Funny but no one asked what tire size, gear ratio, road conditions and load you are carring in the XJ,...or did I miss that? :dunno: :eyes:
When I changed the tires on my XJ from 225 - 70 -15 to 30X9.5 - 15 I had those very same symtoms when going up an incline that it would have gone up prior to the tire change without even noticing it. My solution was to manually shift to 3 until the hill was crested.
 
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