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Hey guys, been lurking for a while and usually get my answers from searching through the threads, but I'm pretty stumped right now so here goes my story... 

 

1990 AWD Legacy, automatic

New tires, alignment, struts.

No MIL and it does function.

No binding while cornering.

Is my niece's car, she drives like a grandma in the mountains of the front range. Mostly pavement though some dirt roads.

 

I went out of town and she said her car wouldn't accelerate over 40mph. I get back and the rear diff is PUKING 80-90. So I replace it with a good, used unit. I also replaced both rear axles because one was binding, and one looked horrible.

 

She drives for a few days and then states car won't go over 20mph. I drive it and it's fine. Next day I drive it again and the car is bucking and vibrating like the torque converter is locking and unlocking randomly. Weird. So I toss in a tranny, still does it. Next day, nothing. Day after that, as soon as the car accelerates to 20mph horrible vibrations. Take my foot off the gas and it instantly stops. The car will happily roll to 50mph as long as I'm not accelerating. Decelerating is fine. Next day, drives like nothing is amiss for 20 miles. (what the...???)

 

I put a fuse in the FWD holder (yeah, I should have tried that first!) and the vibration almost disappears. Pulled out the prop shaft (even though I eyeballed it during the tranny and diff replacement) and I can faintly hear needles moving in the carrier when I spin it. But there's no play and u-joints are good... so after throwing some time consuming darts I don't want to just throw a prop shaft at it. I also noticed the rear diff has a lot of movement  when I was getting it on the stands, but I don't think it's excessive.

 

So with the car in the air I have my son accelerate and decelerate while scouring the drive train for movement but don't see anything alarming. I'm guessing there isn't enough load with the wheels in the air. 

 

Ideas? Thoughts? I'm kind of at a loss and am pretty darn frustrated right now. Any input would probably help out at this point.

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A few months old. We also put in a new ball joint on the driver's side and brakes with rotors before the alignment about a month ago.

 

Whoever did the alignment said there was a rear bearing going bad but I'll be damned if I can find which one. Of course, the pvc tree was cracked and leaking and the same guy said the oil was coming from a blown head gasket that he offered to fix for $2200. So he may have felt the beginning of the mystery vibration and assumed it was a bearing during his test drive?

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A mechanical problem typically wil not be intermittent (there one day, gone the next). A stuck brake caliper can cause bad vibration but will need to be driven some to heat up the rotor first. Axle/bearing/u-joint problems just don't come and go, when they wear out they will cause a constant and repeatable problem.

 

An engine running issue can be very intermittent, and with OBD1, the damn thing could be on fire and it wouldn't trip a CEL.

You could have the beginning of an ignition coil failure. This can come and go at random, and will usually be most evident when under load.

 

Wheel bearings on these are very difficult to diagnose. They can make noise for a LONG time before ever having any noticable play.

 

Not real sure why the rear diff was leaking gear oil other than maybe a seal was damaged by a previous axle replacement. The rear diffs almost never have problems.

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"An engine running issue can be very intermittent, and with OBD1, the damn thing could be on fire and it wouldn't trip a CEL."

 

 

Now that's FUNNY!

 

Unfortunately I have to agree with Fairtax on this one. lol  

 

My grandfather's '87 Ford ranger won't trip a damn CEL, but it had 2 codes in the system when I checked it.  Both are causing it to miss at an idle and get horrid fuel mileage (for a v6).  

 

The '90 subaru I had would trip the light for a second, then it would go away but store the code.  If I hadn't noticed the light coming on once I never would have checked the codes on it.

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I can understand that an ignition problem could cause issues like this, except when the car is in FWD, it runs and drives fine. Has been for days. But as soon as you pull out the FWD fuse, the vibration starts.

 

I'm really bothered by the amount of play in the rear diff so I think I'll try some new bushings on the mount and see how it goes.

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Oh, I missed that before.

 

Only other thing I can think of would be the ratio of the rear diff you put in doesn't match the front diff in the trans.

 

Did the trans and diff come from the same car?

 

Was the vibration issue present before replacing the rear diff?

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^^^ triple check final drive of trans and rear diff.

 

older  4eat clutchplates have a drive drum that gets 'grooves' i think, can cause clutch plates to hang-up. maybe just got unlucky with the trans swap?

 

might just try another trans or, swap just the tailshaft part - if someone can confirm it will fit, try to get a 98 tailshaft or newer - coupla improvements after 97 1/2 from what i read.

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  • 1 month later...

Hi, i have an idea....may be a little out of normal.....you said that have replaced the rear diferential....and when taking off the fuse the problem goes away......i don´t know much about diferentials of auto and manual versions....but if the ratio is different, mi think the vibretion comes from the third diferential in the gearbox trying to normalize the situation....and without the fuse this could not happen....is an idea...

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