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Shimmy when accelerating


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19 replies to this topic

#1 jmmctighe

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Posted 23 September 2005 - 07:16 PM

Hey all,I posted this on alt.autos.subaru and got some good replies, hoping one of you guys can help me on this.
95 LS wagon 2.2L auto w/ 167K shakes at about 35mph and then between 60 and 75mph. Rides smooth at all other speeds. I had the tires rotated and balanced with no help. Wound up buying a new set of tires (needed them anyway) but the problem is still there. Alignment came with the new set of tires, still have the problem
The shaking seems to occur on acceleration or when there is a load on the drivetrain. I've put in the fuse for FWD to see if this alieviates the problem but it didn't. The gear or RPM does not seem to affect this, strictly certain speeds. Front rotors do not appear to be warped as there isn't any pulsating on the brake pedal or steering wheel.
I'm thinking wheels, anyone else?
--
John

#2 nipper

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Posted 23 September 2005 - 07:55 PM

Is this an AWD ? since it comes when things double i would rule out anything in the engine, otherwise it would happen in the same spot at the same rpm.
Where does the vibration feel like it is coming from. If it is AWD it sounds like its the universal for the rear drivehsaft. This is easy to remove, but can be scary to buy. Go to a drive shaft rebuilder and they will repair it for 1/3 the cost of the new part from Subaru. They fit a ford Uni-joint to it, as the Subaru part is unservicable.

Joe

#3 jmmctighe

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Posted 23 September 2005 - 08:29 PM

Is this an AWD ? since it comes when things double i would rule out anything in the engine, otherwise it would happen in the same spot at the same rpm.
Where does the vibration feel like it is coming from. If it is AWD it sounds like its the universal for the rear drivehsaft. This is easy to remove, but can be scary to buy. Go to a drive shaft rebuilder and they will repair it for 1/3 the cost of the new part from Subaru. They fit a ford Uni-joint to it, as the Subaru part is unservicable.

Joe


Yes AWD. I agree about the engine, seems to only be a part that is "moving" at the speeds above.
I thought that by putting it in FWD with the fuse would eliminate the driveshaft from turning. Is this not

#4 nipper

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Posted 23 September 2005 - 08:42 PM

Ok easy test then. Get the car up on ramps (or a lift if so blessed) and grab the driveshat and shake it. There should be no play. If there is play, it comes out easily and take it to your nearby freindly drive shaft rebuilder. The shaft from subaru is 350.00, the modification from a rebuilder should run around 100-150. This will get worse with time. The reason it does it only at two speeds is that your hitting the critical frequency of the U Joint. Eventually it will get unbareable and the car will be undriveable. This is the only thing i can think of. I do beleive that you can drive the car with the shaft out untill its fixed. I know with my 5sp i could. The way the Subaru tranny is you should be able to too.
the reason it still does it with the FWD fuse in it is because the rear wheels are driving the shaft.

Joe

#5 jmmctighe

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Posted 24 September 2005 - 02:07 PM

Ok easy test then. Get the car up on ramps (or a lift if so blessed) and grab the driveshat and shake it. There should be no play. If there is play, it comes out easily and take it to your nearby freindly drive shaft rebuilder. The shaft from subaru is 350.00, the modification from a rebuilder should run around 100-150. This will get worse with time. The reason it does it only at two speeds is that your hitting the critical frequency of the U Joint. Eventually it will get unbareable and the car will be undriveable. This is the only thing i can think of. I do beleive that you can drive the car with the shaft out untill its fixed. I know with my 5sp i could. The way the Subaru tranny is you should be able to too.
the reason it still does it with the FWD fuse in it is because the rear wheels are driving the shaft.

Joe


Well.....I guess it's not that. I had the car up on ramps and was yanking the drive shaft like crazy and there wasn't any slop movement at all. Too bad 'cuz I was all set to pull it off and go out for a spin to see if the shimmy was gone. I also checked all the inner CVs on all the halfshafts and they seemed to be OK. Only one had a little more play than the others and that was the right front, although the left was only a tad tighter to me.

#6 All_talk

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Posted 24 September 2005 - 05:13 PM

Sounds like a front outer CV is on the way out, try some lock to lock figure eights and circles in a parking lot, listen for clicks and feel for binding.

Just a thought
Gary

#7 nipper

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Posted 24 September 2005 - 06:11 PM

Damn that was my best guess too. Actually I think you just answered your own question.


nipper

#8 blitz

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Posted 24 September 2005 - 06:13 PM

I do beleive that you can drive the car with the shaft out untill its fixed. I know with my 5sp i could

Ooh... I think that puts all the driving torque through the viscous clutch fluid :eek:

...not unlike if the rears were permanently on ice with the fronts on pavement.

#9 nipper

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Posted 24 September 2005 - 06:16 PM

Yes and no. Since the shaft is removed, ther is no resistance, and it will just freely spin with no load. Same for a puter controlled tranny.


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#10 blitz

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Posted 24 September 2005 - 07:51 PM

Well, I can't comment about the suitability of the auto trans to this proceedure, but driving with the driveshaft removed on a manual tranny Sube runs the risk of overloading/overheating the center viscous clutch. This is because of taking output from only half the differential, while letting the other half freewheel into open air (no load).

This scenario forces the clutch it to slip, heat, & grip. If it weren't for the viscous clutch tied accross the center diff, the vehicle wouldn't move (the rear tailshaft would just spin backwards).

It would be wise to drive very gently if doing this.

#11 nipper

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Posted 24 September 2005 - 08:10 PM

Then how can it overheat? The way the viscous coupling works is the fluid thickins when it gets hot. The source of the friction are a set of plates, each have calibrated holes ( or fingers) in them. The differnce in rotational mass causes a diffenrce in rotational speed in the discs. Normally when the roatational speed from the engine is greater then the resistive force of the rear wheels, this causes the fluid to sheer and get hot from friction. With the load removed (no driveshaft) there is no resistance to having the output shaft rotate, so it just free wheels. Overheating of the viscus coupling happens when one set of wheels is spinning and the other set of wheels are not, presneting a load on the fluid. . In essence the rear wheels do not exist so there is no resisitive force, and it will not over heat.

http://auto.howstuff...fferential9.htm

nipper

#12 All_talk

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Posted 24 September 2005 - 08:39 PM

The Subaru 5MT center diff is not a viscous coupling, its a true VLSD diff. As blitz said, if you remove the rear shaft the viscous clutch between the two sides of the diff will have to carry the entire torque load all the time... not good! A VLSD will only hold so much torque, once heated and fully engaged it can still be overloaded and slip. In normal use (with the rear drive shaft in), this would only happen momentarily if ever, with the rear shaft out you could be overloading the viscous clutch all the time and they can be damaged like this.

Gary

#13 Setright

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Posted 25 September 2005 - 03:25 AM

The shimmy could stem from the "half-shafts" between gearbox and front wheels. Remove, balance, enjoy :-)

#14 jmmctighe

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Posted 25 September 2005 - 03:10 PM

Damn that was my best guess too. Actually I think you just answered your own question.


nipper


Yeah, if that is what it is I'm disappointed as both shafts have been replaced over the past three years. They "look" fine, boots are all in excellent condition. Now I'm wondering if I didn't do damage to the transaxle over the past winter with pot holes as the shaft movement appears to come from where the inner shaft mounts to the transaxle with the spring pin. I would stronly suspect that there shouldn't be any movement whatsoever on the transaxle side. Can anyone verify for me? I might get funny looks checking other Legacies in the parking lot at work.

John

#15 nipper

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Posted 25 September 2005 - 04:00 PM

I just read my hayes manual, and it sounds like there should be zero play in the cv joint. ALso if one has play and one doesnt, sounds like you have a cv joint starting to go.

Here is what to do for a really hard to find vibration in the front end, but it sounds like it may be the cv joiint

OK here are some things to try, but it requires finding a really good front end shop. Some shops have a wheel spinner. With all 4 wheels up off the ground, the AWD should not be an issue. For really tough vibration problems, they take a big electric motor and spin the front wheel as a unit. This checks the balance of the entire "system" (tire, wheel, hub, bearing, drivshaft). WHat it may be is whats called tolerance stacking. Any indivdual peice may be within spec, but can be on the high side of the spec. Every spec has a +/- tolerance. Get enough things on the + side, you will get a vibration. This is done with the engine off and the car in neutral to rule out any engine/transmission source.
Also review what should be checked:
Tires for flat spots and broken belts (remove tires for this and look on the inside).
Weigh both tires and see if they are the same weight on a good scale.
Check the wheel itself for runout on both sides and any flat spots.
Check rotors for flat spts, hard spots and to make sure they are perfectly round.
Check the preload on the bearings
Check all ball joints, bearing and busings in the front end.
Inspect motomounts.
Check the hub if possible for runout.
When you remove the tires, mark them in refernce to the lug nuts, then install the tire 2 lug nuts from the original position (one at a time) and see if that changes the vibration. No matter how many times you have had the front wheels off, you cannot guarentee that they did not go back on the same way they came off (murphys law).

#16 1 Lucky Texan

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Posted 25 September 2005 - 05:17 PM

I just read my hayes manual, and it sounds like there should be zero play in the cv joint. ALso if one has play and one doesnt, sounds like you have a cv joint starting to go.

Here is what to do for a really hard to find vibration in the front end, but it sounds like it may be the cv joiint

OK here are some things to try, but it requires finding a really good front end shop. Some shops have a wheel spinner. With all 4 wheels up off the ground, the AWD should not be an issue. For really tough vibration problems, they take a big electric motor and spin the front wheel as a unit. This checks the balance of the entire "system" (tire, wheel, hub, bearing, drivshaft). WHat it may be is whats called tolerance stacking. Any indivdual peice may be within spec, but can be on the high side of the spec. Every spec has a +/- tolerance. Get enough things on the + side, you will get a vibration. This is done with the engine off and the car in neutral to rule out any engine/transmission source.
Also review what should be checked:
Tires for flat spots and broken belts (remove tires for this and look on the inside).
Weigh both tires and see if they are the same weight on a good scale.
Check the wheel itself for runout on both sides and any flat spots.
Check rotors for flat spts, hard spots and to make sure they are perfectly round.
Check the preload on the bearings
Check all ball joints, bearing and busings in the front end.
Inspect motomounts.
Check the hub if possible for runout.
When you remove the tires, mark them in refernce to the lug nuts, then install the tire 2 lug nuts from the original position (one at a time) and see if that changes the vibration. No matter how many times you have had the front wheels off, you cannot guarentee that they did not go back on the same way they came off (murphys law).


Along the same idea - maybe the shafts could be swapped side to side as well?

#17 nipper

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Posted 25 September 2005 - 06:48 PM

Yes they can be, but that is a lot of work. Shafts can also be weighed. The can also be marked and rotated like the wheels.

nipper

#18 jmmctighe

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Posted 26 September 2005 - 06:10 PM

I just read my hayes manual, and it sounds like there should be zero play in the cv joint. ALso if one has play and one doesnt, sounds like you have a cv joint starting to go.

Here is what to do for a really hard to find vibration in the front end, but it sounds like it may be the cv joiint

OK here are some things to try, but it requires finding a really good front end shop. Some shops have a wheel spinner. With all 4 wheels up off the ground, the AWD should not be an issue. For really tough vibration problems, they take a big electric motor and spin the front wheel as a unit. This checks the balance of the entire "system" (tire, wheel, hub, bearing, drivshaft). WHat it may be is whats called tolerance stacking. Any indivdual peice may be within spec, but can be on the high side of the spec. Every spec has a +/- tolerance. Get enough things on the + side, you will get a vibration. This is done with the engine off and the car in neutral to rule out any engine/transmission source.
Also review what should be checked:
Tires for flat spots and broken belts (remove tires for this and look on the inside).
Weigh both tires and see if they are the same weight on a good scale.
Check the wheel itself for runout on both sides and any flat spots.
Check rotors for flat spts, hard spots and to make sure they are perfectly round.
Check the preload on the bearings
Check all ball joints, bearing and busings in the front end.
Inspect motomounts.
Check the hub if possible for runout.
When you remove the tires, mark them in refernce to the lug nuts, then install the tire 2 lug nuts from the original position (one at a time) and see if that changes the vibration. No matter how many times you have had the front wheels off, you cannot guarentee that they did not go back on the same way they came off (murphys law).


OK, couple more clues:
I feel this shimmy more on the gas pedal and in the seat, not the steering wheel
I only feel it when there is a load on the drivetrain, accelerating I've already discussed butalso decelerating downhill. There are a couple steep hills around here and when I have my foot off the gas at the speeds mentioned, I feel it. I think this would rule out any suspension componenets.
I think I'll revisit the driveshaft and see if it threw a weight or something. I didn't check that when I was looking last time. Otherwise I'm just gonna have to live with it until maintenance calls for a replacement of something.

John

#19 redsnake

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Posted 11 October 2005 - 08:42 PM

Yeah, if that is what it is I'm disappointed as both shafts have been replaced over the past three years. They "look" fine, boots are all in excellent condition. Now I'm wondering if I didn't do damage to the transaxle over the past winter with pot holes as the shaft movement appears to come from where the inner shaft mounts to the transaxle with the spring pin. I would stronly suspect that there shouldn't be any movement whatsoever on the transaxle side. Can anyone verify for me? I might get funny looks checking other Legacies in the parking lot at work.

John



I Have the same problem. I replaced both front axels 500 miles ago and now I have slop at the stub shafts coming out of the transaxle. It looks like there is a adjustment ring on the trans axel. Can I use that to take the slop out? Anyone?

#20 AEROCOOK

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Posted 22 November 2005 - 01:02 PM

I think the ring you are talking about is the race for the diff bearing, moving it could affect the preload on the bearing. I took mine off to replace a leaking axle seal and got lucky, put it back on and no noise so far... that was about a year and a half ago. I didnt know what it was till I got it off.
As for the vibration issue, you mention that you just replaced the shafts (rebuilt ones I presume?) I also replaced both shafts on my 1995 2wd Legacy and had bad vibration under accelleration. I replaced them about 2 days apart and after replacing the first one didnt notice a vibration (but I wasnt looking for one) replaced the second one and it was very noticable. I assumed that the second one I put in was bad, so I took it back and exchanged it for a more reputable brand and there was a remarkable improvement, but the vibration was not gone entirely. I will be returning the first one I installed and replacing it with the better brand as well.




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