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AW4 Slipping at High Speed and High Temp

Old 02-22-2019, 12:10 PM
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Default AW4 Slipping at High Speed and High Temp

Hey all,
I already consulted with Cruiser54 on this but I wanted to see if anyone on here had experience with a similar issue to this.

This only happens when driving the Jeep on the highway (average speed 65 MPH), but at some point after driving consistently at speed for a bit, my AW4 (1988, 230k Miles) transmission will slip out of gear like it's in neutral. I'll get it off the highway with a prayer, and park it. After it cools down and sits for a few hours, the transmission is working fine again. I even took it on a 50 mile round trip to the junkyard the other day, avoiding highways and using back roads. The back roads in So. Cal are generally very winding and go up a lot of steep grades through hills and mountains. Absolutely no problem, got there and back without an issue. Drove it again last night over the mountains and into Beverly Hills, made it there and back, no problems. Just happens when driving on the highway for a while consistently and at speed

So far I serviced the NSS and replaced all three solenoids (which I might add are shifting at lower RPM than I would like them to making me think it's again something electrical or sensor related). This only seems to happen when at high speed and temperature which makes me think it's something electrical. Has anyone had a similar issue? Is there an external ground for the solenoids? Any insight would be greatly appreciated.
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Old 02-22-2019, 12:41 PM
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Check the fluid level. When cold, a transmission can read a little above the full mark. It will drop once the engine starts, and then come back up as it reaches operating temp. Check the fluid condition. Does it smell burnt or have chunks in it? If its burnt, a drain and fill should take care of it. If its got chunks in it you can feel, thats usually bad.

Last edited by fb97xj1; 02-22-2019 at 01:01 PM.
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Old 02-22-2019, 03:07 PM
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Fluid level should be good, just replaced it after I did the solenoids, but I will quadruple check. Fluid that came out didn't have any telltale smells or funky chunks.
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Old 02-22-2019, 03:26 PM
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My first guess is that your torque convertor is not locking up as it should in over drive. So at highway speeds and extended periods of time it is probably allowing the fluid to get extremely hot. Eventually this will start to cause other problems in the transmission (some might be temporary until it cools, others might be doing longer-term damage).

1. Achieve cruising speed of 55-60mph (enough to be cruising in over drive)
2. Maintain constant speed and note engine RPM
3. With left foot lightly tap brake pedal
4. Engine RPM should quickly increase by around 300 RPM
5. After a few seconds - the engine RPM should return to the value noted in step #2

If #4 and #5 do not happen - the torque converter is not locking up as it should. This allows the torque converter (and trans fluid) to get extremely hot. If your transmission lines run into your radiator (like stock) you will also notice engine coolant temperature getting higher than it should be.
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Old 02-22-2019, 04:24 PM
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does the vehicle have an air cooled trans cooler in front of the radiator ?

its possible to fit a temp gauge by removing the torx screw in the AW4 case, shows you how in the technical writeups on this forum (i think)

you could also fit an external temp probe to the trans pan
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Old 02-22-2019, 05:14 PM
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I'm thinking this is a torque converter lockup issue as well. You can "shoot" the transmission pan with an IR heat gun and see what kind of temps you are seeing. The test procedure posted by Jordan96XJ should tell you if you're getting lockup as well.
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Old 02-28-2019, 06:34 PM
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Originally Posted by jordan96xj View Post
My first guess is that your torque convertor is not locking up as it should in over drive. So at highway speeds and extended periods of time it is probably allowing the fluid to get extremely hot. Eventually this will start to cause other problems in the transmission (some might be temporary until it cools, others might be doing longer-term damage).

1. Achieve cruising speed of 55-60mph (enough to be cruising in over drive)
2. Maintain constant speed and note engine RPM
3. With left foot lightly tap brake pedal
4. Engine RPM should quickly increase by around 300 RPM
5. After a few seconds - the engine RPM should return to the value noted in step #2

If #4 and #5 do not happen - the torque converter is not locking up as it should. This allows the torque converter (and trans fluid) to get extremely hot. If your transmission lines run into your radiator (like stock) you will also notice engine coolant temperature getting higher than it should be.
So I did the test on the way to the junkyard to look at the absolute ****tiest XJ I have ever seen in my life (Looked like it was pulled out of the ocean, the seat brackets were so rusty they were turning to dust), and on the way I did this suggested test. Performed exactly as you said it should, it started at about 1500 RPM, jumped to about 1750-1800, then came back down again after a few seconds.

What next? This is again making me think it still might be electrical.
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Old 02-28-2019, 08:48 PM
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Sometimes worn transmissions just need extra fluid. Have you tried adding an extra 1/2-1 quart?

Was the fluid regularly changed? How many filter changes has the transmission had?
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Old 02-28-2019, 09:54 PM
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have you disconnected the TCM plug, and operated the trans manually ? this will go a fair way to determine if it is inside the trans or electrical

my "new" XJ does not pass the highway speed torque convertor test..the TC solenoid measures ~13 Ohms, I will have to look into whether the brake signal is not getting thru next .
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Old 02-28-2019, 09:56 PM
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Have put about a total of 40k miles on it in during my ownership. Trans fluid and filter was changed around 20k miles ago, and also approximately a couple hundred miles ago when I did the solenoids.
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Old 03-01-2019, 06:57 AM
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Does it recover if you wiggle the shifter back and forth?
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