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Shuddering Forester?

Well, my mechanic is confused, so maybe one of you guys offer something to help him (and by extension, me) out?

I’ve got a 2000 Subaru Forester that’s had a hard life. I bought it used from someone who didn’t know much (ANYTHING) about foreign cars and whose mechanic knew less. Good thing it was cheap. The problem it’s having now is that whenever I go around a curve in the road, the car shudders - almost as if the wheel wasn’t on tight enough - through the curve. After I’ve straightened out, the shuddering eases off till it’s gone completely. It does this whichever way I turn but seems more noticable when I turn right.

My mechanic thought it had something to do with the all-wheel drive. It does feel sort of like what you’d experience in 4WD on a dry road, but continues for a while after you’ve straightened out, which is not like a 4WD. He changed the fluids in the rear differential (or whatever you call that part at the back of the drive shaft that makes this thing an AWD) when it was in recently for it’s inspection. The fluid change had no effect, except for maybe reducing the fuel economy of the car (from 25 - 20 mpg).

He’s ready to try again, when I’ve gotten a few bucks saved, but I wanted to see if there was anyone here who might have dealt with something like this and could give us some advice?

Sounds like it could be torque bind.

Brilliant. This is exactly what it sounds like. I’m printing this off for him now. Thanks for the prompt reply!

I just noticed yours is a 2000, so the fix they discuss in that link might not be relevant. Still sounds like torque bind, but I would search the boards at and where they’ve discussed this pretty extensively. Also, changing the fluid in the rear differential shouldn’t have any effect on gas mileage, so I’m not sure what’s going on there.

Oh, OK. Yes, I see from that link it was talking about older Legacys. I will try that. Just a thought - Do you think putting in the FWD fuse keep this from happening? If it is happening in that rear diff.? I’ll go search those sites and see what else I find. Thanks.

A halfshaft with an odd wear pattern can also cause this. Since it’s more noticeable while turning right the left halfshaft might be the one to check.

Sometimes if no noticeable slop can be felt in the halfshaft it may require removal and a physical inspection (a careful inspection I might add) while out of the car and on the bench. Of course, if you’re that far along you’re better off replacing it if it has high mileage on it.

I agree that it is probably torque bind.

Most likely, the clueless previous owner ran the car with mis-matched tires, thereby causing damage to the viscous coupling/center differential.

Actually, is it possible that you are running the car with mis-matched tires currently?
Your tires need to be identical in size and circumference. If there is noticeably more tread on some tires than on others, you are doing damage every time that you drive the car.

No, my tires are not mis-matched - all four are under a year old and the exact same size, type and brand. Though I have no idea what the clueless owner did. The car’s got 115K on it now - 78K when I bought it 2 years ago. I wouldn’t have considered that particularly ‘high’ mileage for a Subaru though - but with the way this guy took care of it, I suppose I have to expect things to wear prematurely. sigh

When your mechanic changed the rear differential fluid, did he also change the front differential and transmission fluids? Not that those necessarily have anything to do with torque bind, but it sounds like this car was subjected to some neglect by the prior owner and those are some simple things you’ll want to make sure are taken care of. You’re also due for a new timing belt if you’re at 115K, which I would get done ASAP if you haven’t already.

Subarus do not take kindly to neglect.

Since you mention the FWD fuse your car must have an automatic transmission. The AWD systems are slightly different between the automatics and the manuals.

The manuals use a viscous coupling to connect the front and rear axles, the automatics have a transfer valve and clutch pack.

The transfer valve and clutch pack, which hydraulically controls the rear drive, is located in the rear of the automatic transmission. If you insert the FWD fuse you should be able to disengage the rear drive completely and the binding may stop, although if the valve is worn badly enough it may not work.

If the transfer valve and clutch pack are worn you will experience binding as you describe when going around corners. This is usually noticed only on tight turns, like turning into a driveway or parking space. The fact that you notice it all the time does not bode well. If the car has been driven this way for a length of time the transmission may be damaged internally.

The fix is to replace the valve and clutch pack. This cost around $750 when I had it done to my Legacy a few years ago. If the transmission case has been damaged the cost will be significantly higher.

I suggest you take the vehicle to someone who is familiar with Subarus, preferably an independent, because a dealer will REALLY empty your wallet. This is not a job for someone unfamiliar with the Subaru AWD system.

Before you panic, have the transmission fluid and the fluid in both differentials replaced (with the CORRECT fluids) and see if it helps. The symptoms you describe sound severe, but try the fluid change before you spend any real money.

At 115K you need a new timing belt, water pump, etc, too. I hope you didn’t pay much for this neglected Subaru, because it’s about to cost you some money.

You put into words what I wasn’t able to. For the OP, mcparadise has given you a great rundown on how you’ll want to proceed with this.


Thanks for the info - I doubt the timing belt’s been changed so I’ll ask about that next time.

He didn’t mention changing the front differential fluid, but I’ll ask him. The transmission on this car is one system that I think fared poorly under it’s former owner. It was overflowing with fluid when I first went to look at it and my mechanic didn’t like that. He didn’t tell me why that was a problem, but I suspected it was overfilled to hide a leak in the rear seal that we found (and later fixed). Would an overfull transmission (or possibly one that had been run while low on fluid) have caused a problem with the differentials?

Likewise, if this is torque bind, would putting the FWD fuse in mediate the problem? At least until I can fix it properly?

First off, this shuddering doesn’t happen all the time - just while going around corners - and usually only while going around them at a little faster speed than I probably should. I do have a good independent mechanic (my dad was one, so I know not to go to dealerships) and he’s already replaced the rear differential fluid. I’ll ask him to check the front and change its fluid too. I assume he used correct fluids - he’s a Subaru specialist and I’ve had him for all three of my last cars (a Brat, a Legacy and this Forester) and he’s not steered me wrong yet.

“I hope you didn’t pay much for this neglected Subaru, because it’s about to cost you some money.”

LOL!! It has already cost me money. And no, I didn’t pay much for it. Mechanic looked at it before I signed the check and we agreed I would be able to pay for the repairs it needed (a cat. converter/wheel bearing) and still be ahead of the game. Though maybe he was looking at making his next boat payment with my repairs, I don?t know.

Blushing Edit: It was rude of me not to add this - THANK YOU for this very detailed info. It is exactly what I needed.

Center differential, confirm by removing the extension housing on the rear of the transmission. If there is a lot of broken pieces in there and bearing damage, it’s cheaper to replace the transmission w/ a good used one.

Ouch! Though thank you for the advice. A used transmission is not hard to come by, but expensive to put into the car (1000+, if memory serves). Considering the abuse this car has suffered through, if it’s that, I may just find a newer car. At this point, I’m still ahead of the game - the low cost of this car made it worth it to invest in the repairs it needed, but a transmission would put me over that threashold.

I’ll mention what you suggest to my mechanic (when I can afford to see him again - LOL!). Thanks for the advice.

Before assuming the worst case scenario, you should not omit the comparatively simple things.
The halfshaft problem I mentioned or even front end alignment can cause this.

Oh, of course. I will definitely look to simple stuff first. In fact, I’ve printed off this entire thread for my mechanic.

My alignment is OK - just got new tires and alignment at the end of last year and my tread ware doesn’t show any issues. Also, wouldn’t an alignment problem show up even while driving straight?

I’ve not had a chance to get back to my mechanic yet, but I did put in the fuse to change the car from AWD to FWD. The vibration is not gone completely on curves but it’s about 75% less. Would this still suggest the halfshaft problem?