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Possible broken rear pinion or ring?


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My son was driving his 1995 Legacy Outback, 5MT, back to college after Thanksgiving and he was hearing a squealing/screeching noise about 70 miles into his trip. He had a flat earlier that day, and the only tire and wheel he had was a slightly larger tire than the other 3. I figured the clutches in the axles would slip a bit but he could make the 120 mile trip OK. When I showed up to help him he tried moving the car and it took a little more effort than normal.

When he pulled over there was smoke coming from the left rear wheel, but I found a frozen brake caliper when I pulled that wheel off. My first guess was a wheel bearing based on the heated up/smoking wheel, but I put it in the air and pulled the wheel, replaced the caliper with a reman, and drove it about 50-60 feet. I can hear what sounds like a grinding, almost crunching/clunking sound coming from the rear half of the vehicle. We couldn't pinpoint it to the wheel bearing. While it has been up in the air, I got the exhaust off it and the center driveshaft skidplate cover. A ton of mud fell out of it and I could see where mud was rubbing on the driveshaft. The last thing I did was spin each of the rear wheels to see if I could pinpoint the noise, now there is no noise, the wheel feels OK up and down, and side to side without much movement so I am guessing that wheel bearing is OK. The thing I noticed, and the reason I am posting my question here is because when I was spinning each rear wheel, the opposite wheel would spin the opposite direction, which is normal, but the driveshaft is not spinning. Do you think the rear axle pinion may have self destructed? I can't think of any reason why you could spin the rear wheels and the driveshaft won't spin as well. Any thoughts or opinions are greatly appreciated. Thank you.

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I'd see if you can find someone to let you borrow and/or help you put the car on a 2-post lift. And then run the car through the gears while it's off the ground. It'll save you a lot of time diagnosing the issue but I couldn't even begin to make a guess as to what it could be. I also don't know if I need to say this but this is pretty sketchy and should be done with a lot of extra precautions in place.
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Mismatched tires is *very* bad on an all wheel drive vehicle. It's pretty much like hitting the gas hard enough to go down the highway in an auto trans car, but holding the brakes so it doens't move. All that energy into the torque converter burns it up. In this case all that energy into the center viscous coupler burns it up. If I had to do that I wouldn't do that, I'd get flat hauled. If I had no other option I would keep it to between 5 and 10 mph just long enough to get where I could get flat hauled.

 

Would I be right in guessing that he was going 60 to 75 mph for a considerable distance?

 

I'd say do as Brighton says and use a mechanic stethescope to listen for bad spots at the wheels, diff and trans. If you don't hear any bad spots I'd say the center viscous coupler is burned up from the mismatched wheel. If you hear noises in the tail end of the trans, same thing. If you're lucky you'll find a bad bearing or brake.

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Mismatched tires is *very* bad on an all wheel drive vehicle. It's pretty much like hitting the gas hard enough to go down the highway in an auto trans car, but holding the brakes so it doens't move. All that energy into the torque converter burns it up. In this case all that energy into the center viscous coupler burns it up. If I had to do that I wouldn't do that, I'd get flat hauled. If I had no other option I would keep it to between 5 and 10 mph just long enough to get where I could get flat hauled.

 

Would I be right in guessing that he was going 60 to 75 mph for a considerable distance?

 

I'd say do as Brighton says and use a mechanic stethescope to listen for bad spots at the wheels, diff and trans. If you don't hear any bad spots I'd say the center viscous coupler is burned up from the mismatched wheel. If you hear noises in the tail end of the trans, same thing. If you're lucky you'll find a bad bearing or brake.

 

Montana. 80mph. I rented a car hauler and hauled it home. It's up on 4 jack stands now. I'll take a look at that center coupler. I forgot about those. What would cause the driveshaft to not spin when I am spinning the back wheels?

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Maybe a failed center viscous creates enough resistence that the diff would rather spin the other wheel.

 

If you are absolutely totally sure the thing is secure on stands, I'd get under there and turn the driveshaft by hand in neutral and see what the wheels do.

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Maybe a failed center viscous creates enough resistence that the diff would rather spin the other wheel.

 

If you are absolutely totally sure the thing is secure on stands, I'd get under there and turn the driveshaft by hand in neutral and see what the wheels do.

 

All the wheels spin when I get underneath it while spinning the driveshaft. I can't not hear any noise now. Would the weight of the car on the drivetrain cause the damaged area to be noisy? Are wheel bearings noisy when the wheels are in the air? I may throw the exhaust back on it and drive it a little.

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That sounds like a good result. I think if the viscous was cooked you would get less or no turning of the front wheels when turning the driveshaft.

 

With a stethescope you should be able to hear bad bearings in the air. I'm not sure if you could hear them without.

 

Test drive sounds good. If you can drive it on pavement so it's quiet and have an assistant listen to each side of the car as you go by at various slow speeds, that would be best. Second best is driving next to a wall on either side of the vehicle so the sound reflects back to you.

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  • 2 weeks later...
That sounds like a good result. I think if the viscous was cooked you would get less or no turning of the front wheels when turning the driveshaft.

 

With a stethescope you should be able to hear bad bearings in the air. I'm not sure if you could hear them without.

 

Test drive sounds good. If you can drive it on pavement so it's quiet and have an assistant listen to each side of the car as you go by at various slow speeds, that would be best. Second best is driving next to a wall on either side of the vehicle so the sound reflects back to you.

 

I pulled the viscous coupler and it looks good. I would think the gears would be chewed up or there would be metal chunks or flakes in the transmission oil, but there isn't.

 

When I started looking for this issue, I pulled the rear driver's side wheel because my son thought he saw it smoking from that wheel when he stopped. I found a seized brake caliper, and replaced it. Now I am wondering if that was the issue all along? I'll get it back together tomorrow and see what I can find. A seized brake caliper doesn't make the terrible sound I was hearing before though.

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Did you replace the rotor or pads?

 

 

If you feel brave enough I would put the car on jack stands and run it in first gear.

 

 

Your rear differential would take all the beating from the mismatched wheel and frozen caliper.

I got it in the air and the noise is coming from the rear differential. The front of the differential mostly, probably that bearing. I found a good rear diff with clean fluid (140k miles) at the local salvage yard for $110. I also heard a noisy left rear wheel bearing that I'll replace as well, and that stuck caliper was replaced.

 

Sent from my XT1650 using Tapatalk

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