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Whats wrong - steering twitches


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91 Legacy, 240,000 on steering rack, 180,000 on power steering pump. Driving down the road, in town, 35-40 mph and it pulls/twitches one direction or the other for 1/2 second then is okay. On one stretch of road, I took my hands off the wheel for 5 seconds and just watched it twitch back and forth. Doesn't do it all the time. First started 2 weeks ago when I put the snow tires on. I thought I failed to tighten the lug nuts. Hasn't acted up for the last several days until today. Fluid level in PS is okay. Seems like a surge in hydraulic fluid? Anyone else experience this? I've got to take the car on a 100 mile trip tonight :mad:

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Definitely not wheels or tires. I have two other snow tires, exact same size and tread depth. Swapped them and it still does it. Driving down the 4 lane 55 mph and it almost wants to yank the wheel out if your hand. Comes and goes, will happen 3 or 4 times in a mile. Also happens at 15 mph on a side street.

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First started 2 weeks ago when I put the snow tires on.

I know you say in a subsequent post that it is NOT tires as you have another pair and it does the same thing.

 

Still... You might want to switch back to summer tires and see what happens. It might be endemic to your winter tires. Or have you had these tires on before without problem? How old are they?

 

You also commented that the twitching "comes and goes". This sounds like a beat frequency occurring between the 2 tires. However, I'm a little stumped that you would notice it at such low speeds.

 

Commuter

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Not tie rods. Nothing loose in front end. Car just went thru PA state inspection 2 weeks ago. Tires are 3 or 4 years old but still in good condition. Stored properly when off the car.

How about dirty power steering fluid? Anyone ever change theirs?

 

Or better yet, bad/binding outer CV joint (yes all the boots are intact)? At low speed it seems to occur with the frequency of the tire rotation. And it always twitches to the right. I think tonight I'll swap out the right side half shaft before I even start on the steering system.

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On my old FWD car I had a outer CV going (really contaminated with crud) and I had some pretty violent pulls to the side that was going bad. Probably a good place to look. I would think that a twitch might indicate the beginning of a failure, but with good boots, sounds weird..

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This is one for the books. If there's a new problem that no one has ever had before, let it up to me to have it. This morning I got about 1.5 miles from home and the pull was so bad and consistent for 10 seconds I was about ready to turn around and go home. Then I went around a curve and it went away and stayed away for the remaining 10 miles to work. Came back periodicallly as before on the way home. The pull was to the right. Everyone said it's probably the right side. Last night I swapped out the right side half shaft. So what's left? The left side half shaft. So I put the shaft that was on the right on the left and BINGO. The problems has gone away (so far, I put about 5 miles on the car afterwards).

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Originally posted by Legacy777

So you're saying it's the axle that's the problem?

 

Axles can do this from time to time, but usually this is preceded by the standard CV clacking sound.

 

Some FWD cars are really bad for this, especially the ones with axle extensions from offset mounted differentials, or those with unequal length halfshafts.

 

Sometimes the control valve in the steering rack will cause this too, but this is usually a consistant problem not related to a particular section of road.

 

In your case the section of road likely set up a harmonic vibration in the CV joint causing it to have a great deal more friction than normal. With AWD this friction is distributed through the drivetrain and weird things happen like torque steer.

 

I have only seen this on one Legacy, but one front outer CV joint had a broken ball cage and the balls were loose. It essentially became a three wheel drive car with substantial torque steer in one direction when accelerating and the other direction when braking. It was easy to diagnose since the axle shaft moved a 1/2 inch in any direction within the CV joint and the grinding noise was horrific. When we pulled the axle off the CV joint housing came off and fell on my foot, and the loose CV balls rolled across the floor. We actually got the standard core return amount for the mangled axle shaft!

 

This particular car was a 5MT, I imagine the problem would be a lot worse in the 4EAT since it spends most of its time sending 90% of the torque to the front wheels.

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Originally posted by alias20035

Axles can do this from time to time, but usually this is preceded by the standard CV clacking sound.

 

Some FWD cars are really bad for this, especially the ones with axle extensions from offset mounted differentials, or those with unequal length halfshafts.

 

Sometimes the control valve in the steering rack will cause this too, but this is usually a consistant problem not related to a particular section of road.

 

In your case the section of road likely set up a harmonic vibration in the CV joint causing it to have a great deal more friction than normal. With AWD this friction is distributed through the drivetrain and weird things happen like torque steer.

 

I have only seen this on one Legacy, but one front outer CV joint had a broken ball cage and the balls were loose. It essentially became a three wheel drive car with substantial torque steer in one direction when accelerating and the other direction when braking. It was easy to diagnose since the axle shaft moved a 1/2 inch in any direction within the CV joint and the grinding noise was horrific. When we pulled the axle off the CV joint housing came off and fell on my foot, and the loose CV balls rolled across the floor. We actually got the standard core return amount for the mangled axle shaft!

 

This particular car was a 5MT, I imagine the problem would be a lot worse in the 4EAT since it spends most of its time sending 90% of the torque to the front wheels.

 

No clacking preceeding it. Obviously no offset diff. I don't think road surface had anything to do with it as it would happen in a perfectly smooth parking lot at <15 mph. No torque steer. It was not a constant pull, the wheel twitched back and forth. No obvious play in the joint when I pulled the shaft (have not taken it apart yet, got a WRX trans in the rally car ro pull out that's more important). I say I'm going to find one ball that's badly mishappened and when it rotated the wrong way it would momentairly seize BTW, 5MT not 4EAT.

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I've had this very problem although on an early wagon the moly grease in the inner doj gives up the ghost and the balls start to grab instead of sliding which is where the steering jiggle comes from, the local cv shop/factory here developed a new grease with castrol specifically for subaru inner cvs i've no trouble since using this grease, the shaft is probably ok if you regrease it. It can start with no warning noises btw.

 

regards camo

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