Can shuddering be normal in a 4EAT?

[whitemr2]

I just got my '91 Legacy wagon (auto, AWD) back from the shop where it got its tranny rebuilt (plus a transgo shift kit and external tranny oil cooler added!). I noticed a problem though. If I came to a complete stop, turned the wheel, and accelerated, I had a bad shudder in the car. I took it back to the mechanic, and his thought was that it was the center diff/transfer case, but he was puzzled why that'd be a problem as he replaced all the clutches in that during the rebuild. He recommended I drive it a little more and see if it changed, before opening everything back up again.

So, I did some checking online, found comments about tire pressures causing this. Sure enough, my tires were very low - 26-27 psi all around. I bumped them up to 32 and took it for a test drive.

The shudder is MUCH less pronounced now, this definitely seemed to have helped. I could be mistaken, but it almost feels different than before - not as mechanical. However, it STILL shudders. It's almost absent in 1st gear (manual mode), but noticeable in 2nd. There is no noticeable shudder once you get going (5-10mph?), it's just when you first start out.

The tires are almost brand new Yokohama Avid H4, stock size (185/70R14).

So, this all got me thinking. Could this be perfectly normal behavoir for a 4EAT? I'm hoping some of you guys can help shed some light on this. My theory is that the shudder I'm feeling is actually the tires slipping then regaining traction as the car shifts torque front to back...so, front tires slip, torque to rear is increased...so front tires grab, torque is shifted back forward, where the front tires slip again, starting the cylce all over again? My car is a stock non-turbo, so I'm guessing you turbo guys have more experience with torque and may have experienced this if my theory is true.

[Legacy777]

I think it's probably a cause due to brand new componants. Give it some time to break in and such.

Also....could be CV joints.....have you looked at them recently?

[eastbaysubaru]

Yeah, I've got the same symptoms. I'm 90% sure it's due to failing front driveaxles. One of the CV boots is ripped and the other one had it's CV boot replaced ~1 year ago. I think some crap got in there during the period where it was open so I'm going to be replacing both axles this weekend. I'll let you know how it went and if that solved my problem.

-Brian

Oh, and it only shudders during slow hard turns, mostly in parking garages.

[whitemr2]

Both front axles were replaced with aftermarket ones (one new, one rebuilt) a few months ago. I havn't checked the rears, I'll do that later today.

I plan on taking it to an empty parking lot at lunch today and doing some more tests, including sticking a fuse in the FWD connector to see if that makes a difference.

[Legacy777]

Yeah....that's a damn good idea.....Do the fuse thing. That'll tell you right away whether it is AWD components.

Are all your tires the same brand & have reasonably the same wear patterns.

[whitemr2]

Are all your tires the same brand & have reasonably the same wear patterns.

Yeah...they're all identical and only a couple months old.

[DLC]

Sounds like torque bind to me. I had those symptoms, and less than a year later, the AWD didn't work at all.

I swapped in a 5MT, been unbelievably happy ever since.

This problem is related to worn and bad compenents in the rear section of the transmission, where the power transfer happens. Apparently there's a solenoid there that malfunctions over time. In the later models, from about 95-97.5, the case itself would actually wear. It's a known problem, believe it or not, and i got this info from a tech at the local Subaru dealer.

Dave

[eastbaysubaru]

Which symptoms Dave? I'm just having a problem at low speeds and full or almost full lock on the steering wheel, at which point it goes "clunk clunk clunk".

-Brian

[whitemr2]

I did some testing in a rain-soaked parking lot at lunch, here's what I found:

- With the FWD fuse installed, there is no chattering, just a fair amount of wheelspin.

- In manual mode, the chattering seemed much less, usually absent in fact.

- This car corners like it's on rails! I was amazed by the grip and acceleration in corners (this is the first time I've really pushed it in adverse road conditions).

The fact that manual mode was smoother than auto was strange. This would lead me to believe that the transfer case is NOT the culprit, would you all agree? I'm wondering if it could be bad motor mounts (since the engine load will be different in manual mode vs. auto, as the shift points are being controlled differently).

[Legacy777]

All the manual button does is keep the tranny from going into first gear.

To test the torque bind......leave shifter in D, turn the wheel full lock one way and slowly keep turning in a circle.

Then do the same thing with the FWD fuse holder in.

Compare the differences. You can move the gear selector into the 1 position to keep it in 1st. Again, compare results.

Move the gear selector in the 2 position, push manual button, tranny will stay in 2nd gear.....again, compare results.

[whitemr2]

Will torque bind manifest itself at a steady speed, under acceleration, or both? My problem only appears under initial acceleration, 0-10mph or so.

[DLC]

That's a perfect description of torque bind, the low-speed, turning and acceleration. It won't happen much over 10mph or when going in a straight line.

Dave