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AW4 Transmission Has No Reverse


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#1 tom58c

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Posted 21 March 2014 - 09:12 PM

Hello. The last couple weeks I've been trying to figure out a problem I have with my aw4 in my 93 xj. Just rebuild the engine and everything is fine there. Its been over the course of 5 years. The transmission worked perfect when pulled and was sealed and wrapped up out of the elements the whole time. It was taken out because of the engine failing. In getting everything ready to go after breaking in the engine I go to reverse with no results. Just the engine idle picking up slightly .Go to drive and the transmission engages as it should. After checking voltages for the solenoids and what order they should be in, checking the shift cable adjustment, neutral safty switch and so on. Everything is in good working order. The next test was disconnecting the TCU. Once I did reverse doesn't work unless you go to drive first. Then rock it to reverse and it works. Only so long as you are moving while reverse engaged. Otherwise if you stop moving it looses reverse and the motor free revs like in neutral.

 

I took the jeep on the road even with these problems to see what all the forward gears would do and how it would shift. Well, it shifted through all the gears and cruised at 65 with out issue. The shifts did feel pretty lazy though. After this, getting back from a actual drive I looked at the fluid level and condition. The level was right at full and no foaming.

 

I have chased wires, ran voltage tests, tested without the TCU to test all the gears manually. The things that make reverse happen are solenoid 1 on, overdrive clutch, direct clutch, first reverse brake, and overdrive one-way clutch. I did all the gears in manual and also put the transmission in 1-2 and start moving in 1st gear, then let off the gas to see if it brakes instead of coasts. It brakes. Shifting through all the forward gear automaticaly and doing all the manual tests tells me the transmission should be in working order.

 

So what am I missing? Could it be a terminal problem like O ring seals drying and craking from sitting for the 5 years. Or is it just something simple I'm over looking?

 

Thanks for reading :)



#2 Moses Ludel

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Posted 21 March 2014 - 11:54 PM

tom58c...Thanks for posting your issue with a thorough accounting of what you have done to date and the tests you have run.

 

I would pressure check the AW4's hydraulic system, following the factory guidelines.  Given that the clutch and brake apply pressures seem to be inconsistent, you need to check the fluid pressures in the individual circuits.  These conclusive tests are not difficult to perform, and it sounds like you're adept at getting to the bottom of a problem.  From the description of your current tests, it sounds like the transmission would "fail" a simple stall test in reverse, maybe in the forward gears, too.  Given the free-wheeling symptoms, I would not run a stall test, as damage to the transmission's clutch and brake units could result.

 

A bigger concern is that testing and driving the vehicle with these symptoms can actually cause direct clutch and brake damage.  Friction discs are fragile and only work well with normal line pressures.  The apply pressure for clutch and braking units must be high enough to facilitate quick, minimal-slip shifts.  The AW4 has a history of providing a very long service life, and this is due to significant line pressure and proper shifting patterns over the long haul.

 

If you need more details on running a hydraulic test, I would be happy to provide them.  If you need simple stall speed test procedures, I can furnish the steps.  However, I again emphasize that such a stall test with the current symptoms could cause severe damage.

 

As a footnote, have you changed the transmission filter?  Could the transmission be starving for fluid?  Is the filter not sealing at the valve body?  A clogged or loose filter can cause a large pressure drop or allow debris to infiltrate the valves and precision fit parts in the valve body.

 

Moses



#3 tom58c

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Posted 22 March 2014 - 10:29 AM

I changed the filter before installing the transmission with the motor. I don't know if its sealing properly. It appeared to be when I bolted it down to the valve body.

 

What I was told by a friend today to check the fluid level in neutral instead of park. He had a similar problem and there was a 2 quart difference in fluid level between park and neutral. Did some reading and across many forums and it was being said there is no difference between P and N. Did this little test just to see ( my luck works weird that way ;) ). As the forums said, there was no difference. The only thing that could change the fluid level would be the larger transmission cooler I installed to get rid of the overly small factory cooler. Knowing I wasn't going to drive the jeep I just added fluid anyway just too see if it would react different. I can drain the fluid back out easy enough. Didn't change anything other then with the TCU unplugged it would go into reverse without going to drive first. Once plugged back in same story. No reverse. Just like neutral.

 

As for the fluid pressure test I am going to have to hold off until I can get a gauge. It is sounding like if the pressures are low it still requires removing the transmission to fix the issue. Or just rebuilding the unit completely. Thats how my luck has been with past transmissions I have had to rebuild.

 

Thanks for the reply Moses.



#4 tom58c

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Posted 22 March 2014 - 10:37 AM

I have been going by this.

 

http://www.scribd.co...ic-Transmission

 

Just so people know.



#5 Moses Ludel

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Posted 22 March 2014 - 04:40 PM

You raise a concern, tom58c...When you installed the replacement cooler, did you eliminate any factory anti-drain back provisions in the lines or cooler?  If you did, there may an issue of fluid draining back from the converter when parked.  This condition usually occurs when you first start the engine and find that the converter takes time to charge before the vehicle will move. 

 

If your transmission's condition persists after initial startup, I would still evaluate whether the aftermarket cooler installation removed a factory means for keeping the torque converter charged with fluid.  On the Chrysler (non-Aisin AW) RE/RH RWD transmissions, the anti-drain back valve is notorious for sticking either closed or open.  Open, it allows fluid to drain back from the converter, which can starve the converter and even burn up the front pump bushing.  See my comments in this article at the magazine:   http://www.4wdmechan...nsmissions.html.  This reference is strictly to foster some ideas around the cooler installation, the AW4 does not typically have the same issues as the Chrysler units. 

 

Glad to pursue this discussion further before you consider a complete rebuild.  Let's look at in-chassis fixes first...

 

Moses



#6 tom58c

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Posted 22 March 2014 - 06:14 PM

With this jeep before, it was not using the factory cooler in the radiator. Just straight lines running to the factory cooler and it worked fine the few years the engine was running for me. I installed the new cooler the same way.



#7 Moses Ludel

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Posted 22 March 2014 - 07:50 PM

You replaced the factory "heavy duty auxiliary cooler" with a bigger cooler.  There is the additional internal radiator transmission cooler, like on the magazine's 1999 Jeep XJ Cherokee 4.0L, that fits within the driver's side end tank of the radiator. 

 

This internal radiator cooler has been blocked off and by-passed on your '93 XJ Cherokee?  This would not make a world of difference with the larger surface-to-air oil cooler you installed—unless your transmission or engine is having overheat problems.

 

Moses



#8 Msy93xj

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Posted 30 July 2014 - 08:13 AM

Tom58c... Did you find a solution to your problem?!?!
I am experiencing the exact same symptoms as you describe except mine is after a (AW4) tranny rebuild, also I installed an aux cooler plus an external filter.

#9 Moses Ludel

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Posted 30 July 2014 - 09:16 AM

Where do you each stand here?...I'll watch for Tom58c's response...Glad to pursue this further if there has been no fix for either AW4 transmission...

 

Moses




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