Front diferential and or axle/tire problems

[r6speed]

Just bought a cheap subaru, needing some help with it.
93 2.2 NT A/T AWD wagon, paid $800 has 166K (was "supposedly" rebuilt motor and tranny 20K ago)

When I bought it the guy said it needed tires badly and drove very messed up due to this. I arrived and all tires had good tread, one (rear) had a plug. Car drove like crap as expected, ran great, but jerked, wobble, and bounced.

Took car in and had both front tires balanced, made a huge difference, car no longer jerked from side to side and vibration/wobble/bouncing was much much better, problem still not cured though. So I took it to a mechanic, told him I thought it was the driver cv axle, gave him the part, and had it fixed. The CV axle didn't changed anything, the mechanic said it was indeed bad with a lot of play, and the passenger one seems good, well now the problem seems to be coming more from the passenger side or middle. The mechanic also noticed there was ATF in the front diff not gear lube, so I had that changed out for 90W right away of course.
I'm guessing something is messed up in the front diff, but I'm not positive, and if it is, I'm unsure of what it could be internally.
When driving the car it has a slight "bounce" type "vibration" that is consistent with the wheel spin, like at the same velocity of the tire, like something rubs or something happens once per rotation of the tire. If feels like a separated tire on the front passenger, but the tire shop didn't notice while balancing so I figure that can't be it.
The feeling is at its worse at about 20-25mph, gets smoother around 35+, won't drive it over 45.

any help is greatly appriciated
(ideas: hub? pass cv axle even though mechanic said it was good? differential?)

also, all tires are good tread, but one has a plug (rear) and they are all different tread pattern...I know this is not good on awd, but I don't want to dump any money into this until this problem is fixed or figured out.
I checked AND had the mechanic check wheel bearings and ball joints all which seems good. I can grab the passenger cv axle and it has just a little play when tugging on it.

[TBFK]

How big of a difference is their in the tires your using? I know your car isn't a full size Ford, but my truck did the same thing when in four wheel low.

[TurnNburn]

Is it happening at all speeds during all driving conditions? When i picked up my car they also had different tread patterns and varying levels of wear. I didnt realize how big of a difference it was until i noticed my ABS was engaging randomly. I instantly suspected the tires and had them changed to a new set. Fixed my problem. Maybe your problem?

Does your green power light blink 16 times when you start the car?

Are you absolutely sure the mechanic pulled the right dipstick when doing the inspection? Because there are 2 back there. One to the diff and one to the tranny. Just a thought.

[Legacy777]

All tires should be within 1/4" diameter of each other. If they're not, that may be part of the problem. I'd suggest inserting a fuse in the FWD fuse holder on the back of the passenger strut tower. This will disable the AWD, and should give you an indication whether tires may be the cause and/or something may be up with the AWD system.

My suggestion would be to take a string, drive over it on each tire, measure the diameter with the car's weight on the tire and compare all four tires' diameter.


Regarding the differential having ATF in it. The front diff dipstick is on the passenger side of the car, and the ATF dipstick is on the driver's side. If the differential truly was running ATF in it, chances are the ring & pinion gears received some premature wear/damage and metal/metal contact since the diff gear oil has extreme pressure additives for hypoid gears, and ATF fluid does not.

[r6speed]

Yes it was the one on the passenger side that had the atf as well as the driver side. The lube plays said it looked "ok" but was definitely tranny fluid not gear lube like it was suppose to be. They said it looked like it had a recent "bad lube job".
I think by looking at the tires they are all very close in tread and have good tread. I'm suspecting more and more the passenger cv axle, but I'm definitely going to put a fuse in the FWD spot, what size fuse? Does this make it RWD or FWD? I will do the string trick as well just to be sure about the tires.
The Power light does not flash when starting, it comes on, but goes off after started. The transmission seems to shift smooth and work properly, it doesn't seem to have the vibrating wobble until around 15-20mph then at its worse around 25-30 and levels out but still thumping around 35/40/45mph

[Legacy777]

You can stick any size fuse in the FWD fuse holder, 15 amp is fine. It will make the car FWD only.

It probably wouldn't be a bad idea replacing the passenger side cv axle if you rule everything else out. I've had some weird vibration occur due to bad cv axles.

[r6speed]

ok I'm going to put a fuse in the holder even though I'm sure its coming from the front so my guess is it will do the same exact thing, but we'll see.
The thing that makes me think its not the cv is the feeling it gives, like I said above, it has this weird thump/vibration only once per rotation of the tire, which makes me think its something more like hub/rotor/brakes (already excluded wheel/tire)
If I put the FWD fuse in, would it be alright to jack up both sides of the front and drive the car sitting still so I could try and see the cv axle at 20mph? Would that mess anything up? I'm also thinking if it doesn't look like the cv and I want to look at the brakes I could pull the wheels/tires off and drive it that way as well being jacked up (on stands) right?
Thanks again for the help guys!

[Legacy777]

I wouldn't recommend driving the car on jack stands. You can do it, but the big issue is the suspension is fully extended and the CV axles are at a much steeper angle. I did this and ended up throwing grease all over the place....it wasn't pretty, nor fun to clean up.

As for pulling the wheels/tires off and running on jack stands, same comment applies regarding the cv axle angle. Additionally, since the wheels hold the brake rotors in place, you would need to put at least two lug nuts on and screw them down all the way so the brake rotor doesn't move around. If the rotors are old, they're more than likely rusted to the hub, so they won't move, but if they're not rusted, they will be able to move around a little.

[r6speed]

ok so jacking it up and running it off ground OR having a shop lift it and run it for that matter is not a good idea, makes sense now.
So what would you suggest then, start replacing more parts and hope its the culprit every time? That route sucks too haha I'm in a pickle!
Well I guess I will start off with checking out the brakes and rotors more, then if I see no problems I will have the pass cv axle replaced and hope for the best...any better ideas?

[Legacy777]

You can run it on jack stands, and if you do it, I'd suggest going pretty slow and keeping an eye out on the axles. If it is an issue with the axle, it may not show up because the axle articulation is not in the same spot that it normally is during driving.

[r6speed]

right I understand that, so lifting it and driving it won't tell me anything about the cv axle, that and the added danger and grease everywhere, I think I may be better off trying to diagnose a different way...maybe not though, I may have to do it

[r6speed]

Took the car back to mechanic, told him I wanted him to diagnose it. He called me two hours later to explain he had looked over everything and the only thing it could be is that pass cv axle, so he changed it, and once again no difference, still does it.
Next I plan on putting it on stands and running it, then if no luck I will take it to yet another shop. But here is my question, its starting to sound more and more like the differential, what could go wrong inside the diff to cause this? Thanks again for all the help, its greatly appreciated

EDIT:
today I put the FWD fuse in, drove it, had same feeling so I put it on stands and ran it. The driver side tire had all power and would start spinning as soon as you let your foot of the brake, the passenger side however had pretty much no power, I could stop it with my hand. I know open diff only puts traction to one tire when no traction is present, but I thought by giving the pass tire traction (my hand stopping it) it would throw it some power, no? I'm lost on what to do next because when it was on stands I felt no thumping vibration (probably because the pass tire was not going fast enough).
I want to suspect the aftermarket autozone axles the mechanic put it, but I would think even if the old ones were aftermarket crap ones too, by changing them it would have made at least SOME KIND of difference? And it didn't, felt the same before replacing cv's as after...
anyone got any ideas here?? please...

[n2x4]

Chance one of the brake calipers is sticking significantly? This happened to me before and the car shook terribly.

[Legacy777]

If you stop/hold the driver's side tire does the passenger side tire start spinning?

[r6speed]

Yes, if I stop the drivers tire it gives power to the passenger side, at which point you can faintly feel the "thump" in the pass side