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AW4 Transmission Pump Failure - common? fixable?


NAXJA Forum User
Atascadero, CA
So after a day on the trails I lost all gears while traveling home down the highway doing 65. No issues on the trail, but I may have noticed a slight lack of power at times or a little sluggish feel in the past week when warm.

Mechanic says I've got no pressure, likely pump failure.

Is this common and if so, what are the common causes?
Can I replace the pump?
Should I replace/rebuild the entire transmission?

lifted w/ 35's and 4.88s
Get a new mechanic, what your describing is un-heard of.
Get a new mechanic, what your describing is un-heard of.

LOL! I was in a rush when I posted...should have included back story.

A few weeks ago we found that the previous owner (i've had it 6 months) had swapped the engine and didn't torque the bolts on the bell housing. I had 3 that were broken, 1 was barely holding after a day in big-bear. Had horrible noise from the flex-plate/torque converter as it was moving around way too much and the flex-plate bolts were also loose.

We fixed that issue (removed trans, drilled out broken bolts, tap, new bolts, replace trans) and it ran fine for 3 weeks, now this.

I'm wondering if the torque converter being off-center (it was making some awful noise when loose) could cause stress on the pump and break something?

We've got noise again and no gears. Flex plate and bell housing are still solid.
That changes everything. A couple possible problems that your not going to be able to diagnose without at least pulling the motor to start. It's very likely you did damage within the trans.
Before I did anything I would put a dial indicator on the flex plate. It may help to steer in the right direction.
OK, I've seen one pump failure on the AW4. Here how I would handle this. Pull the dipstick and see where the fluid line is at. It should be up on the 'Z' bend. Then start the motor. It should go down between the fill lines. If it doesn't, then your pump is bad. Also, look at both sides of the dipstick. The line will show high on the one side. If pump is good and fluid is at the correct level, then I'd pull the fuse for the trans or the plug to the TCM (trans computer). It is on the trans tunnel up by the radio. Then see if it shifts manually. Need to know you will not have trans braking. So, need to slow down with brakes before down shifting. Also, does reverse work? I believe reverse dose not use the solenoids.
So, if you determined that the pump is good, then its an electrical problem. You will need to check the Ohms resistance of the solenoids. Also, could be some other electronic sensors. Get to this point first.
With a basic Internet search, you can find the AW-4 Service and Diagnostic Manual. ( Don't click on any .ru Russian websites. )

Complete trouble shooting and test procedures are provided in great detail.

As suggested, unplug the TCU and see if you can shift the trans 1/2, 3, Reverse with the shift lever.
Check throttle body to trans cable. If that's broke or not connected, you might not get any shifting.

All of the damaged pumps I have encountered were from failing to ensure the t/c was fully seated before bolting the bellhousing up. If it's not rotated and fully engaged on both sets of splines you will damage the pump. The proper way is to install the t/c into the trans first, rotate until it drops all the way in. Do not leave the t/c bolted to the flexplate and try to stab it into the trans. You should have a little bit of forward-back play in the t/c when you go to bolt it up to the flexplate again.