[flipjarg]

Hoping someone can give me some insight on this. I don't have a lot of money and cannot afford to keep paying mechanic to keep trying things until this is fixed. My 96 OBW that has trouble in low gears. When I first start the car and start driving, the following doesn't happen. It is only once I stop at a stop sign and take off again.

When I lightly press the gas or even coast slowly it sounds like someone left tool in the transmission! It feels normal then every half second it thuds enough to shake the whole car. People outside of the vehicle can hear it very clearly. It does this over and over and would probably endlessly do this unless I speed up and get into second gear. It is worse when I turn and always happens when I am turning but also happens when I am driving straight at times.

When the car shifts into second gear it will sometimes shift super hard. It feels like it is mainly coming from the rear wheels. Although it is happening at times when the rear wheels should not be engaging (like on dry tar).

One other thing I have noticed is that when it is above 20°F outside, it is much worse.

 

[rasterman]

Verify that all 4 tires are the same brand, model, size, age & inflation.

Mismatched tires on a Subaru AWD system can cause problems like what you describe, and too many mechanics overlook it. The ideal test is to put a measuring tape around each tire. There should be less than 1/4" difference in measurement from biggest to smallest.

If left that way for too long you'll permanently wear out parts of the AWD system, which is largely built into the transmission.

If this is the 4EAT Trans, you can temporarily put it in FWD mode for diagnostic purposes.

 

[flipjarg]

When I bought this car, the previous owner had put brand new tires on it. I took your advice and checked that they were all the same brand and size. They were.

One suspicion I had was that the car was towed improperly (like they tow front wheel drive cars). Could that be a possibility? If so, what would have been damaged in the transmission (I will probably be able to look that up)? The reason I think it may have been towed is because the crank shaft pulley key busted and the owner just parked it the car thinking worse damage was done.

A friend of mine said something about dropping the rear part of the transmission down (sorry I don't know anything about trans.) and shimming the gears. Any comments on that?

 

[rasterman]

Towing one of these with one axle on the ground is a pretty sure way to wreck the trans. Flatbeds or dollies only.

 

[rasterman]

I'd try FWD diagnostic mode and see how it handles. Look for a fuse holder under the hood, should not have a fuse in it. Put one in, you should get an FWD dash light, and the trans will electrically uncouple the rear wheels. Temporary use only, though.

 

[flipjarg]

Okay, I finally got a chance to try the FWD test. I got a fuse put it in, the FWD light came on and I tried and tried to make it thud/jam.... I could not (it actually felt like it ran more smoothly too). I took the fuse out to back to normal driving and tried again. Immediately when I started turning it thudded in normal mode.

Now, my next question is, what does this mean? (I will begin searching!)

 

[rasterman]

It means something is wrong with your AWD system.

A few possibilities in no particular order:

ATF: low quantity, incorrect type, beyond wear limit

MPT clutch pack burnt out (this is what actually transfers power to the rear propshaft)

Duty C solenoid (regulates MPT clutch, was locked out with the FWD fuse)

Propeller shaft U-joints

Rear differential

Rear axle shafts

I guess I'd start by evaluating the ATF.

 

[HiPowerShooter]

Okay, I finally got a chance to try the FWD test. I got a fuse put it in, the FWD light came on and I tried and tried to make it thud/jam.... I could not (it actually felt like it ran more smoothly too). I took the fuse out to back to normal driving and tried again. Immediately when I started turning it thudded in normal mode.

Now, my next question is, what does this mean? (I will begin searching!)

It means your MPT clutch pack is "all blowed up". No more troubleshooting required...

 

[flipjarg]

It means your MPT clutch pack is "all blowed up". No more troubleshooting required...

That's awesome that I don't have to trouble shoot anymore... Not awesome that it's my transmission. I had to look up what a MPT (Multi-Plate Transfer) Clutch is. I've never worked on a transmission. I'm going to have to bring it to a mechanic.

Thanks for the help, to everyone who replied.

If anyone has suggestions on where to purchase a new MPT Clutch Packet (or everything I need to fix this problem), please let me know. Thanks!

 

[plain OM]

Not awesome that it's my transmission.

The fact that the fuse was effective in disengaging the transfer clutch might be more significant that is being appreciated.

It means that the clutch plates are not mechanically locked together, and it means that the AWD solenoid control valve and the related transfer valve are working, to a degree. However, it appears that the valves aren't modulating the pressure on the clutch -- it's either off (fuse in), or on (fuse out), whereas, when going slow, as in turns, the clutch should be only partially engaged, allowing for the different turning radii of the wheels.

There could be a sticking problem in the control valves, such that once they are opened even a bit, they stick open, and/or don't let the hydraulic pressure bleed off when it should.

This is why it might be worth doing a few drain-and-fills of the ATF. If the problem is blockages or sticking of the valves, fresh fluid might be enough to clear it. It's a small investment (the car uses Dexron III type ATF which is readily available), and relatively easy to do (the tranny has a drain plug at the bottom and is refilled through the dipstick tube. Three drain-and-fill cycles, with some driving in between to mix the ATF and allow the new fluid to dissolve deposits and suspend contaminants so that it can be drained off, should provide results if this is the problem. For more info on the procedure see this thread: http://www.subaruoutback.org/forums...ansmission-fluid-easy.html?highlight=changing

And as for as the mechanics inside, perhaps start by looking at this thread: http://www.subaruoutback.org/forums...on-rebuild-without-removing-transmission.html. Different problem, but you'll get the idea.

Has the ATF in the transmission ever been changed, and if so, when?

How many miles on the car/transmission?

It's still possible that there's a mechanical problem, such as severe grooving of the clutch hubs (as seen in the second linked thread), which can cause the clutch plates to bind once a bit of pressure is applied. This can only be fixed effectively by replacement.

 

[HiPowerShooter]

IMHO the fact is that there is internal mechanical damage to the pack itself regardless of what caused it. I would be replacing it...

Even IF changing the fluid a few times works(which I highly doubt with that much noise) there are issues which need to be addressed with the clutches themselves.

I will say that the ATF fluid change is easy, and if it does anything to help confirm the diagnosis it certainally can't hurt. You may also add an aftermarket friction modifier which also may help "clean things up" in there during the first flush. If you have some cheesecloth or a fine strainer, I might also look for any signs of debris when flushing also.

 

[flipjarg]

Plain OM and HiPowerShooter,

Thank you for the extra info. I spoke with a mechanic today who works on foreign cars. He suggested draining the fluid as well. The car has 183,000 miles on it and probably never had the transmission replaced/modified. The previous owner parked it because the key on the crank shaft pulley was broken and he didn't know what to do with it. I will definitely check with the cheese cloth method when I drain the fluid and throw in some friction modifier (assuming that is additive of some sort) and see if that is an easy fix. I didn't pay a ton for the vehicle so if I have to put money into it, I won't feel so bad. I'll just have to save up.

I'll let you know if that helped when I get to it. Thanks for the links, I was going to do some searching on that today :29:

 

[rasterman]

I agree with the advice I'm seeing in this thread- the MPT might be toast, but it might just be clogged valves operating it wrong. Well worth the cost of a few gallons of Dexron and an afternoon to find out.

 

[tdelker]

Does this version have the ATF cooler? If so, try a full flush by breaking the line running back to the transmission and turning the car on to pump out the old fluid. This will give a much more complete change. See http://legacygt.com/forums/showthread.php/diy-5eat-atf-flush-197248.html

 

[plain OM]

IMHO the fact is that there is internal mechanical damage to the pack itself regardless of what caused it. I would be replacing it....

Very possible. But what makes this interesting is that with the fuse installed . . .

the FWD light came on and I tried and tried to make it thud/jam.... I could not (it actually felt like it ran more smoothly too). I took the fuse out to back to normal driving and tried again. Immediately when I started turning it thudded in normal mode.

With the fuse installed, the only thing that changes is the transfer clutch isn't being engaged. The AWD solenoid and transfer valve mechanisms are fixed in position that drains the hydraulic fluid from behind the clutch piston, allowing the clutch plates to move away from each other. Otherwise, everything that was turning with the fuse out -- wheels, axles, drive shafts, reduction gears, even the clutch hubs and plates -- are still turning as the car rolls along. If something is indeed broken, one would tend to expect some sign of the problem even with the fuse installed.

That said, the one thing that is different with the fuse installed is the absence of "torque" on the rear drive train.

With the transfer clutch engaged (fuse out), the front and rear drives are not free to turn at different speeds and anything that might lead to this, such as turning, causes a build-up of torque in the drive train which can lead to noises and wheel hopping (classic "torque bind", and 4WD, symptoms). On a car with lots of mileage, worn drive shaft U-joints, axle shafts, transmission mount etc could all lead to the noise as the drive train tenses up and releases this stress.

With the fuse installed, the rear drive train is still moving as before, but there's no build-up of torque stress due to turns etc. As the symptom disappears with the fuse in, the cause of the noise could be due to torque build-up in the drive train.

In regard to the clutch pack, towing with the front wheels up is more likely to cause the plate friction surfaces to wear due to lack of lubrication and cooling from the ATF that is normally pumped throughout the transmission when the engine is running. This would subsequently mean the clutch would not work (plates would slip). It could also damage the bearings on the rear output shaft.

However, if I understand the situation correctly, there is only a suspicion that the car was towed, and then a further suspicion that it was towed incorrectly. Without knowing for sure, this could be an unintentional "red herring". The fact that the transfer clutch is remaining engaged when turning slowly (with fuse out) is apparent, and that is something that has to be addressed at one point or another.

Incidentally, this thread, that I linked to earlier, shows a rather significant break in the transmission AWD clutch assembly (clutch hub broken away from the reduction gear). Interestingly, even this did not cause unusual/noisy operation other than the apparent loss of drive to the rear wheels, as described in the author's original thread, http://www.subaruoutback.org/forums...7832-my-awd-just-quit-i-think.html#post269426.

 

[CNY_Dave]

It could be the solenoid valve (just because it goes full-shut and full-open doesn't mean it's not bad) or the spool valve it operates, tolerances are tight enough a tiny speck of anything could cause a problem.

The plates could be 'physically' fine, but have been overheated and are now 'grabby', happens to motorcycles. The metal plates could have been overheated and are now warped. The symptom can also be caused by grooves in the outer or inner clutch basket.

Diagnosing beyond 'gotta pull the tailshaft off' is tough, if it is the plates just being grabby the fluid change may help, I have heard of folks adding limited-slip diff additive as well (no ide what out there is compatible...)

 

[flipjarg]

Well, I just ordered a filter kit for the car and all of the oil. After looking over my Chilton manual and watching a few YouTube videos, I am feeling pretty comfortable with this. I'm going to try running some Seafoam (rated for transmissions) in it and then drain it. Then put some new fluid in with a little Seafoam. We'll see how it goes. I will post the results when I'm done. I'll probably do this all on Friday.

 

[tdelker]

Just to be sure, all the tires are the same size and wear?

 

[whiteOutback]

Just purchase a 2003 OB wagon with 155K miles. 4EAT Car started to make clicking noises when making right turns as you get out of the turn. Since I just got the Trans Dipstick unstuck, I found the AT fluid is overfilled above the HOT-FULL even when it is cold before driving out in the morning. I just installed the AWD fuse today, it seems the car drives better and made a few right turns, no clicking noises.

I will try to do AT fluid drain and fill, how long can I leave the fuse in there ? I need to drive about 6 miles tomorrow.

 

[rasterman]

6 miles at moderate speeds ought to be fine, just don't make a habit of it