AW4 Transmission Slip at Startup

I've been noticing my transmission slip after start up and I wasn't able to find anything searching this forum or others related to my unique situation. Just wanted to see if any transmission experts have any ideas what to try?

Specs: 99 XJ 4.0 4x4 AW4 currently with 203,000 miles

Symptoms: At startup I put the Jeep in drive and when I pull away the engine revs up just fine, but you can feel partial power passing through the transmission to the ground. Once it catches then you feel all power transfer to the ground and it shifts to 2nd like normal. When it catches there is no clunk, its a soft transition like you feel when it shifts into different gears. Once it gets past this delay or slip it drives normal. So the transmission fluid is still cold at this point. No other shifting issues after this point. If I turn the engine off and restart within under a 4hr period it doesn't do this. I just does it when it sits for 4hrs or more.

Done Already: I have changed the fluid several times over the last 1.5years using the dilution method by draining whats in the pan and refilling it. Using Valvoline Maxlife Dex/Merc ATF.

Fluid level is always perfect when I check it.

Ive adjusted the throttle kickdown cable.


I'm wondering if the oil pump in the transmission is starting to get weak or possible bad solenoid.

Any ideas what else I can check or what is likely the culprit? I'm capable of changing the solenoids and doing other minor transmission work. If a full transmission rebuild is needed... Ill find a good shop for that!

Thanks!

Testing the solenoids is a good idea, as is testing the Throttle Position Sensor. Google for the AW-4 Service Manual, it has complete troubleshooting and testing information.

Good point on following the manual... lol! Is the AW4 service manual the same as the service manual for the whole vehicle? If so, I have that. It does have a decently detailed section on the AW4.

Anybody else has ideas too, feel free throw out ideas. Thanks

Father in law has a similar problem with his 3rd gen CTD Dodge: unless he lets the motor idle for a couple of minutes to warm up, the converter slips from a stop, eventually "catches" then drives normally for all takeoffs/shifts, etc after that. Transmission shop diagnosed it as a leaking seal in the torque converter (leaks back into the trans, thankfully) that allows all of the fluid to drain and run the converter dry. Shop said wasn't necessary to fix if he could live letting it warm up every time. It's been a couple of years and multiple trips towing 15,000-ish lbs of fifth wheel without issues.

The one thing they did say was to let it warm up a bit so the converter isn't run while dry.

Rockwood, Thanks! Ill give that a try and see it that helps too.

trans plugs

Over near the transmission dipstick tube are 2 rather large connectors. One is black and goes to the NSS and the gray connector goes to the transmission itselfTCU fuse TCU location

. These 2 connectors carry all the info between TPS, TCU, NSS, speed sensor, and transmission solenoids.

Unplug each one, visually inspect for corrosion or bent pins, spray them out with electrical contact cleaner and plug them back in.

Additionally, if your Jeep is an ’87 to ’90 Renix, it’s always a good idea to reach up under the glovebox area and unplug the connector to the TCU and spray it out along with the receptacle of the TCU. While you’re there, find the fuse right in that area for the TCU. Remove it and spray out it’s receptacle and clean any corrosion from the fuse.

Revised 1-31-2016

Mine 95 has been doing the same thing for a few years. Acts just like my A518 on my first gen ram. If it sits for more than a couple days I start it shift to neutral and bring to 1500rpm for a few seconds. Then Into drive and all is normal. I plow with this XJ as well.

Cummins90 said:

Mine 95 has been doing the same thing for a few years. Acts just like my A518 on my first gen ram. If it sits for more than a couple days I start it shift to neutral and bring to 1500rpm for a few seconds. Then Into drive and all is normal. I plow with this XJ as well.

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Have you ever adjusted your tV cable per the link above?

I hope that some simple adjustment on the transmission can solve your problem. When I rebuilt my AW4 transmission on my 88XJ, I remember some similar looking washers/bushings had different thickness. I also recall questioning whether I had placed the correct washers/bushings in the proper places. To check, I disassembled the trans, while on the trans holding fixture, numerous times to make sure. What I ended doing was miking each washer/bushing and placing them into marked plastic ziplocks. See the trans rebuild manual for washer/bushing thickness. Likewise, to check for "nicked" o-rings, I applied air to check action of the clutches as recommended in the rebuild manual. It was a PITA at that time, but my 88XJ has been running well and I've put on about 150,000+ miles since then. I hope a simple adjustment solves your slipping problem.

Best regards,

CJR

cruiser54 said:

Have you ever adjusted your tV cable per the link above?

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Yes TV cable is adjusted but with just the slightest amount of preload on the cable. I like to feel like I'm driving a redneck vette. I am aware of the clutch packs possibly decreasing in lifespan. This is a $400 Jeep that I bought for one winter 5 years ago. Haven't been able to kill it yet. Put a turbocharger on it. Took it off. Plow with it. DD it 60 miles per day.