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Rear Wheel binding/hopping during tight turns?


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8 replies to this topic

#1 zuzu27

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Posted 16 May 2011 - 11:05 AM

Hi Guys,

I've got a 2000 Subaru Legacy GT Wagon, 5 spd MT, with 120,000 miles on it.

When the car is fully warmed up...usually after 20 minutes or more of driving...during tight turns...the right rear wheel will hop and bind as I'm turning.

I believe it's only the right rear wheel but I could be wrong.

I've checked the rear wheel bearings and they seem to be tight.
I've checked the CV joints and they seem fine as well.
I checked and changed the oil in the rear diff 1.5 years ago and I changed it again 2 weeks ago.
I checked the rear brake rotors and calipers and everything looks fine there.

Since this GT Wagon came with a rear viscous limited slip differential (LSD) I've been thinking that the LSD unit must be failing. Especially since the symptom only appears once the car is fully warmed up.

Has anyone ever hear of these Viscous LSDs going bad?
I thought if the VLSD went bad then it would essentially behave like an open differential?

Also, could this symptom be the result of the center differential failing?
(I've heard of torque bind being caused by a failing center diff).

So is it possible to just change the VLSD unit inside of the rear differential or would I have to replace the whole rear diff unit?
Is it best to buy these brand new or find one in a junk yard?

I plan on keeping the car at least until it hits 200,000 miles.

Any thoughts would be greatly appreciated.

Hi-Fives,

Joey

#2 Fairtax4me

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Posted 16 May 2011 - 11:59 AM

Sounds like Torque Bind. This is a symptom of a bad center differential in the transmission.
The cause is generally mismatched tires. Two worn tires in the back, two new tires in the front. 3 worn tires and one brand new one because of a blowout. That sort of thing.

The difference in tire circumference causes the front and rear differentials to spin at different speeds, and the center differential takes the beating because it is what delivers the power to the driveshafts.
It causes wear on the plates inside the center differential, which is a viscous type. When it gets hot the plates stick together and cause the front and rear driveshafts to lock together similar to a permanent 4wd system.


If the rear differential is a viscous LSD type, it can suffer the same problem.
So here's how to test it. Warm up the car so it starts to bind. Chock the front wheels, jack up the back so both rear wheels are off the ground. Transmission in neutral, spin one wheel and watch the other one to see which direction it turns. If it turns the opposite direction, the diff is open, or is working properly.
If it spins the same direction, at the same speed, block it with a chock or wood block something to keep it from spinning, and try to turn the other wheel again. It should spin, with a bit of resistance, but still spin nonetheless. If it is very difficult or impossible to spin, the rear diff is locked.

#3 zuzu27

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Posted 08 July 2011 - 05:29 PM

FairTax,

Thanks for the help...
I've been driving this thing and basically living with the problem as money and my career haven't allowed me to dig into the problem.
Finally I have time this weekend and I'm going to perform the test you suggested.
I'll share the results someone time tomorrow.

Is there any way to verify if the center differential is working properly?

I'd like to perform that test tomorrow as well.

I really want to make sure I have the problem diagnosed properly since it looks like I'll begin the process of junkyard hunting and/or buying a used part.

Thanks again for the great help,

Joey

#4 nipper

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Posted 08 July 2011 - 08:49 PM

You have already verified that it is not working properly by your description. The rear LSD's rarely go bad on these cars, but can if the tires are badly mismatched.

Before things heat up, go to a parking lot, flat. Make a tight U turn. The car should be able to do it at full steering lock and no throttle or minmial throttle. Let me know if the car fights you.

Do your tires match?
Are they equally worn?

Mismatched rear tires make a slight RPM difference between wheels, the LSD can handle that. That speed difference gets multiplied as it goes through the diff into the center diff. The front diff always moves at a differnt speed unless in a straight line (a square state). The difference in RPM gets dramatic over time/distance (oh like 20 min is the norm) anhd causes what you see or worse. Eventually the car may be undrivabla, and it sounds like you may be there. It can make for bery scary handling on a wet road.

#5 Fairtax4me

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Posted 08 July 2011 - 08:53 PM

Really it can probably go indefinitely with the torque bind. It's not something that will eventually break and leave you stranded, but it can become an issue in snowy/icy conditions. It will tend to make the car drive just like a 4wd truck, which if you've driven one in the snow you know they can be tricky, especially around curves and corners.

#6 nipper

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Posted 08 July 2011 - 09:13 PM

Really it can probably go indefinitely with the torque bind. It's not something that will eventually break and leave you stranded, but it can become an issue in snowy/icy conditions. It will tend to make the car drive just like a 4wd truck, which if you've driven one in the snow you know they can be tricky, especially around curves and corners.



Actually snow isnt that bad with a locked drivetrian, but rain is dangerous.

It really is a saftey issue and only gets worse with time on a manual. Automatics are a b it more forgiving and i havent heard of any terrifying incidenst with an exit ramp wet road and telephone pole in 4eats, just really hard to turn.

http://www.autozine....ction_4wd_2.htm

#7 zuzu27

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Posted 10 July 2011 - 04:55 PM

Okay, I finally got around to testing my rear LSD...here's the results:

The rear wheel will spin (with the other firmly planted on the ground), but it would turn a little and then kind of pop/jerk, turn a little more, and then pop/jerk a little more...

So, I'm guessing this means my rear LSD is totally shot.

Any recommendations on finding a used one.
I'm starting to scour the Internet now.

Thanks,

Joey

#8 johnceggleston

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Posted 10 July 2011 - 05:38 PM

So, I'm guessing this means my rear LSD is totally shot.

Any recommendations on finding a used one.


put in your zip code and sort your search by distance. shipping is expensive.

www.car-part.com

i think you have a 4.11 rear diff final drive ratio. you can use the VLSD from any matching ratio. outback 5 speed or i think, but i'm not 100% sure, legacy auto trans car.

Edited by johnceggleston, 10 July 2011 - 05:43 PM.


#9 Fairtax4me

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Posted 10 July 2011 - 11:43 PM

Okay, I finally got around to testing my rear LSD...here's the results:

The rear wheel will spin (with the other firmly planted on the ground), but it would turn a little and then kind of pop/jerk, turn a little more, and then pop/jerk a little more...

So, I'm guessing this means my rear LSD is totally shot.

Any recommendations on finding a used one.
I'm starting to scour the Internet now.

Thanks,

Joey


Well that could be either the rear or center diff. See if it acts the same with both wheels off the ground. Get a friend to help, turn both rear wheels the same direction at the same time to rule out the center diff. If the pop jerk clunk is not present when turning both rear wheels, the rear diff is at fault. If it's still there, it's the center diff.

The center diffs don't typically fail from what I've read, so a junkyard part has a high chance of being good. They also cost about $465 new from a dealer.
Rear diffs are the same (rarely fail) and cost about $600 for the LSD assembly from a dealer. But then you have to set the backlash, pinion depth, and pre-load, or the ring and pinion gears will be toasted in no time.




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