HELP!! Sliding on MU automatic 4x4 transmission

[astro49]

My 4x4 MU automatic trans/transfer case now has a severe problem of sliding clutch condition. From stand start it already slides so i have to take off slowly till the clutch bites and then I gain a slow acceleration. Slides badly more so on inclines. With this problem I've burned 2 ATF oil changes within 2 months.

Just yesterday we pulled down its tranny. Its 1st and 2nd gear linings were almost black indicatiing its burnt condition. We now replaced all its clutch linings, front oil bump, torque converter and filled it with fresh ATF (Castrol dextron 3).

UNFORTUNATELY, the sliding condition still remains. Could this be a valve body problem? We dont have experience dismantling valve bodies so left this as is.

Any suggestions?

Btw the replacement parts and linings we installed were pulled out from a known good condition Toyota Crown V6 tranny that had identical components with the MU. the only difference we saw was the valve body of the MU had 3 oil tubes as compared to the Crown which only had 2 tubes.

We plan to install the Crown valve body tommorow for a short road test just to isolate the problem of slippage, even though it only has 2 tubes. We suspect the 3rd tube goes to the transfer case (ofcourse we wont activate the front drive on this test), which also needs oil supply for its small valve body.

Any suggestions or diagnosis would be highly appreciated

[astro49]

Btw, we also replaced the solenoids at the same time we changed the clutch linings.

Now we tried the valve body of the Toyota Crown which has only 2 oil tubes but all external looks seemsto be identical. The result is the following:
1. Sliding clutch persists
2. On normal speed, it doesnt now go into 4th gear. 4th gear seems to have disappeared. And from stand still, it now starts on 2nd gear.
* Automatic transmissions normally start on 3rd gear from stand still on a flat road right?
3. The 3rd oil tube on the MU valve body is possibly for the transfer case valve body. Now using the Toyota valve body (2 oil tubes), the front drive doesnt work anymore. Either on 4L or 4H
4. Sliding clutch still exists grrrrrrrrrrr!!
5. Tried disabling the tranny computer box but tranny still slips
6. Also tried disabling the kick down cable, still slips

What could be causing the clutch to slip? We've replaced most of the major components of the transmission! Except for the transfer case, that I think is all what we havent touched or opened up since we think its not related or causing the slip problem.

Help please!

[jack4x4]

The tranny from the Toyota Crown while similar to the MU tranny is probably an A340E which is only a 2 wheel drive version.

Toyota used also used the A340H which is exactly the same as the MU 30-80LE unit. The A340H and the 30-80LE both have a hydraulically actuated tranfer case and yes perhaps that is what the 3rd tube is for.

What about the torque converter....did you do a stall test?
Seems as if your losing line pressure somewhere.
Line pressure rise is controlled by the throttle cable.

I think you should use the original valve body or you won't have 4x4.
Do you have the tranny repair manual.

I guess you'll be opening the tranfer section soon. The transfer section is like a separate tranny and has its own pump and clutch packs.

[astro49]

jack4x4

Thanks a lot for your inputs.

Yes we did a stall test but even on a small incline (going up our 15 degree garage ramp), it already slides and couldnt move forward even with about 4k RPM. What i do is release the gas pedal then rev it up again then after a few tries it'll go up.

On the valve body switch, we just tried out the A340 valve body just to isolate the problem of slipping (knowing the 3rd oil tube was for the transfer case). Knowing that this A340 valve body works but the slippage still persists, what else could be causing the slipping problem?

We havent checked line pressure yet since we dont have a pressure gauge on hand and dont know excatly where to make a tap.

[jack4x4]

I have a Jackaroo with manual transmission and 4JB1T engine so I don't know a whole lot about autos.

My son has an MU auto that had some annoying problems with the overdrive dissappearing intermittently, so we have been investigating the auto tranny.

I'm thinking that because several of your clutch packs have failed, then this would suggest that the oil pressure is not high enough to hold the discs from slipping.

You did say that you changed the pump so that's probably OK.

Reduced line pressure can be caused by.....

Throttle cable out of adjustment
Throttle valve defective.
Regulator valve defective.
Oil pump defective.
O/D direct clutch defective.
Transfer direct clutch defective.
Transfer front drive clutch defective.
Transfer low speed brake defective.

I hope that someone more knowlegeable about autos can help you out.

[astro49]

Thanks again for giving more insights on the probable causes of the slippage. What we did now is tear down the original 30-80 valve body and we saw a few valves and needles that were frozen in place and some debris in it. We're hoping this are the culprits. I'll update as soon we re-install the valve body and tranny tomorrow.

Btw, I have a downloaded copy of the manual for the 30-80LE trans I got from the Geeves mail server. Thanks Geeves!

[geeves]

I wouldnt of tryed second hand clutches. Even if they are expensive they are just too hard to get at to do the job twice. If it still doesnt work correctly is there an auto trany expert you can take it to?

[astro49]

Unfortunately the tranny still slides after cleaning the valve body. We then were able to talk to some local A/T tranny experts and they too had a few sad experiences with this sliding problem persisting after almost a total overhaul complete with new O-rings, clutches, front pump and torque converter. They found it was the tranny housing which caused the low oil pressure. The case probably had cracks on its oil gallery or valve body. I was already impatient and stressed so opted to buy a Japan surplus tranny we personally pulled out from a 4JB1-T. It cost me converted to AU$530.00. Luckily that tranny worked perfectly and shifted smoothly. I'm so happy my MU is alive and kicking again ready to be my working companion again