AW4, no forward when cold until it warms up

87 Renix, Wagoneer, 4x4, AW4....4.0 L.

This is not a new issue, somewhat of a rehash, but now that I have my TCU and TPS working perfectly, great ECU and TCU and TPS grounds, perfect smooth idle, great power, great shifting, and so on and the AW4 fluid level is at the exact correct level, nice pretty pink new color and smell, but I still have one nagging problem that worries me some.

On cold mornings when the drive train is cold, below about 45 F, I have to let the engine run for 5 to 10 minutes depending on how cold it is before it will shift into forward. Reverse always works perfectly right away, not affected by temperature, so it is not the torque converter! If I put the tranny in reverse or neutral the warm up time is shortened to about 3 to 6 minutes. Once it has warmed up the forward drive works perfectly, flawlessly. All the gears work and the torque converter lock up works. If the drive train is already warm, or if the overnight temperature stays above about 50 F, there is no problem what so ever and the first gear, forward gears works right away. It has been like this for 3 winters now and about 20,000 miles.

I am starting to think about dropping the pan and doing a first gear band adjustment.

The tranny fluid in the AW4 was installed before I bought this beast used, but I do not recall this problem the first winter I had it. The fluid was new when I bought the jeep.

Any thoughts from you all?

Have you checked the Fluid level **at idle in neutral**, Sounds like it is low on fluid to me. The fluid will expand when it warms up and allow the trans to build enough pressure and move the vehicle. If it is low top it off with Dexron III.
Im sure you are probably checking the fluid correctly because you said it was full......Just a thought.

JEFF said:

Have you checked the Fluid level **at idle in neutral**, Sounds like it is low on fluid to me. The fluid will expand when it warms up and allow the trans to build enough pressure and move the vehicle. If it is low top it off with Dexron III.
Im sure you are probably checking the fluid correctly because you said it was full......Just a thought.

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Actually when I was debugging the early upshift problem that was killing the power (also had no downshift at all even at WOT, and terrible gas mileage), which turned out to be a span problem on the TCU side of the TPS, I had it filled to the dip stick full mark (per the dip stick instructions) when hot, after a nice long highway drive.

Then when I took it for a good drive after replacing the TPS, the AW4 started leaking fluid, so I rechecked the hot fluid level and it was too full, too high on the dip stick. I had to suck 1 pint of tranny fluid out of it to get it back to the full mark on the dip stick when it was hot, at normal operating temperature. So, the cold tranny problem existed even before I drained the excess pint of T fluid out of it. Therefore, the problem exists even with an overfill of 1 pint! I forget what the dip stick says, park or idle, IIRC it is idle, but it is exactly at the full when hot mark on the dip stick with no leaks now.

My only other thought was a sticking solenoid (first gear) when cold. Kinda like me, needs to warm up a bit to get moving first in the morning, LOL. But the fluid looks like the day it was installed, no burned color, no burned smell, and if it was varnish making it stick, I am not sure the temperature warm up to 50 F letting it work would be so thermally predictable.

It does have 251,000 miles on the odo, but it had several prior owners, and so I do not know the real age or entire history of the AW4.

I have read in the AW4 FSM that there is a band adjustment on the first gear band right above the fluid pan.

Has anyone here ever adjusted their band(s)??????????? or ever had this exact problem and solved it?

There is no first gear band on these transmissions. For first gear you need the forward clutch to apply along with a couple other one way clutches to hold, but those are not going to work sometimes and not others. It's not a solenoid either according to a shift chart. I suspect a leaking forward clutch piston seal or similar, you'll have to put a line pressure gauge on it to verify.

JJacobs said:

you'll have to put a line pressure gauge on it to verify.

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X2 on checking pressure. If you don't have capability to do this yourself, find a reputable shop and have them check it when it is cold and most symptomatic.

birchlakeXJ said:

X2 on checking pressure. If you don't have capability to do this yourself, find a reputable shop and have them check it when it is cold and most symptomatic.

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"Reputable Shop", now that is a real oxymoron, :clap:, Good One!

At least down here they don't exist. In fact no reputable shop down here will even work on a 20 year old jeep, or 20 year old anything, and their rates are out of site!

So back to the discussion, I will reread my AW4 FSM, but I could swear it listed a first gear clutch ( I called it a band, because I was thinking of a round style band clutch that is adjustable in diameter, thus band adjustment, and I thought the FSM called it a band adjustment for a band style clutch). Hmm. If your right, I might be able to solve it with some snake oil tranny additive to swell the seal a little.

What chart are you looking at? The AW4 is electronically shifted using electric solenoids, thus first gear is engaged by an electric solenoid.

birchlakeXJ said:

X2 on checking pressure. If you don't have capability to do this yourself, find a reputable shop and have them check it when it is cold and most symptomatic.

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That might not happen for another 6 to 7 months. It already hit something like 85 F here this week.:sunshine:

JJacobs,

I re-read the manual and it looks like your right on the band - clutch subject, there is no band adjustment (I must be thinking of another vehicle / tranny, that I was working on recently) but I am pretty sure the first of 3 electric solenoids is either on or off (reverse of neutral what ever that is) to get first gear, versus neutral.

In first gear a solenoid is indeed on, but that solenoid is not required on to engage first gear. Now when it shuts off the trans will cause a shift. This is why the test for the computer gets the results it does. With no power to the solenoids at all you will have first, 3rd, and 4th all from the manual valve. Look at your diagrams again.

don't be afraid to try a little Trans-X detergent in it as well. I have solved more than one "slow to go until warm" transmission with a good cleaning to remove varnish and foreign junk from the valve body.

JJacobs said:

In first gear a solenoid is indeed on, but that solenoid is not required on to engage first gear. Now when it shuts off the trans will cause a shift. This is why the test for the computer gets the results it does. With no power to the solenoids at all you will have first, 3rd, and 4th all from the manual valve. Look at your diagrams again.

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JJacob,

Thanks for the help, OK, I see that, with all solenoids off, in drive, it does select a gear, but it selects OD according my copy. So if solenoid #1 is not on yet (lets assume it is stuck with varnish), and I have it in drive, what would overdrive from a dead stop feel like during take off? My guess, is that with a hydraulic torque converter (unlocked) it would feel like the torque converter or clutches are slipping until solenoid number 1 finally kicks in. Is this right or wrong, and why?

Ok, I see notes on the manual valve, pg 6, but my cold, no forward problem, is the same in 1-2, 3, or D. So once again I am thinking the first solenoid may be sticking when it is cold, leaving it in OD, 4th gear for take off.

The other options per the manual are a slipping overdrive clutch, slipping forward clutch, or low line pressure, or a mal adjusted shift linkage (Mine is adjusted per the FSM).

It was about 70 F this morning and it went into first gear in less that 2 seconds from a cold start.

:speepin: