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Discussion Starter #1
Hi guys,

Long time lurker, first time poster here. I am sorry if this has been covered many times, I have read and tried everything I could to solve my problem to no avail.

I have a 2006 OBXT and have been fighting with a vibration under throttle for about a year now. It only happens at and above 120km/hr, and ONLY on a right hand turn, be it very slight or sharp. Car drives very smooth and normal in all other cases, but when turning right, and applying any throttle (absolutely no issue when off the throttle) the whole front end starts shuddering violently, to the point where all I can do is let off the throttle completely, and it returns to normal.

I have replaced the following in the last year:

-Front wheel hub assemblies (wheel bearings)
-All tie rods
-Both front lower control arms
-Front Axles (Subaru) (2 times now because I was convinced they were the culprits, and the boots failed really quickly on the first set)
-Entire driveshaft assembly (Subaru)
-Tires & Alignment
-Front struts & Mounts
-Complete brake job including all rotors and pads
-Also had to replace the abs speed sensors since I broke them during the first axle change (Also now cruise control will run for about 1 minute, feels like its applying the throttle and backing off really fast, then shuts down and flashes, but this is a less important issue)

At this point I know I should have taken it in to the dealer and had them just fix it, but I am a huge DIY'er and have seen some really shoddy work performed at my local dealer, and I oroginally thought "It's a vibration. How hard/What could it possibly be..."

Sorry for the long post, but I am completely broken down by this car now. I have a road trip coming up this weekend, and absolutely cannot drive it in this condition. I am at a complete loss here, and don't know what else to do but hunt for insight. Any and all suggestions would be very very much appreciated.

Thank you,

Keenan
 

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You might check the motor mounts and possibly look into the front differential having issues. Maybe even try removing (or adding..can't remember) the fuse temporarily to make it FWD to see if the problem changes (if it's an automatic).
 

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Discussion Starter #4
You might check the motor mounts and possibly look into the front differential having issues. Maybe even try removing (or adding..can't remember) the fuse temporarily to make it FWD to see if the problem changes (if it's an automatic).

I'll check the motor mounts today, and at this point I'm really leaning towards a problem with the front diff. I will go try the awd disable right now.
 

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Discussion Starter #5
Have you inspected the following? ball-joints, bushing, steering rack...What condition are these items in?
I had all these items inspected after I replaced the tie rods and had the alignment done, and the reason I replaced the LCA's was because the large rubber bushings in each were cracked. Boots on the ball joints look fine, but I'm not sure how to check for excessive play.
 

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wow, I'd guess you could inspect the magnets for the front and rear diffs for excess metal.

does your 06 have axle stubs? maybe one is not popped into place well.

try measuring the temps at the hubs with an infrared therm after a highway run. compare sides and if one side is 10-20 degs hotter, could be a bad bearing. (unlikely since off-throttle is OK)
 

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. . . the whole front end starts shuddering violently, to the point where all I can do is let off the throttle completely, and it returns to normal.
Do you have to let off the throttle completely, or just back it off a bit to slow the car to below 120 kph (75 mph)?

(Also now cruise control will run for about 1 minute, feels like its applying the throttle and backing off really fast, then shuts down and flashes, but this is a less important issue)
Not a rare problem after a wheel hub has been changed. There's a magnetic strip on the back of the hub that works with the ABS wheel sensor. There's been cases here where aftermarket hubs didn't seem to work well with these same Cruise Control symptoms. It's also possible that the strip was compromised by magnetic tools during installation.

I'm really leaning towards a problem with the front diff.
Hard to think of something in the differential that would impact only when the left axle is turning slightly faster than the right (as in a long slow right turn on a high speed highway) and not show up when doing the same (or a sharper turn) toward the left, or at speeds below 120 kph (75 mph).

I will go try the awd disable right now.
06 turbo has the 5-speed AT; the AWD disabling fuse might not work with this transmission. See if the "AWD" light comes on in the instrument panel.

Is the shuddering a violent shaking of the steering wheel, which would tend to localize the cause to the front, or is it felt in the car body itself?
 

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have you tried moving the tires front to back?

after a warm-up run on the highway, would the car idle through some tight donuts on a flat dry, paved parking lot without jerking or requiring pressing the gas pedal?
 

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Discussion Starter #11
Do you have to let off the throttle completely, or just back it off a bit to slow the car to below 120 kph (75 mph)?



Not a rare problem after a wheel hub has been changed. There's a magnetic strip on the back of the hub that works with the ABS wheel sensor. There's been cases here where aftermarket hubs didn't seem to work well with these same Cruise Control symptoms. It's also possible that the strip was compromised by magnetic tools during installation.



Hard to think of something in the differential that would impact only when the left axle is turning slightly faster than the right (as in a long slow right turn on a high speed highway) and not show up when doing the same (or a sharper turn) toward the left, or at speeds below 120 kph (75 mph).



06 turbo has the 5-speed AT; the AWD disabling fuse might not work with this transmission. See if the "AWD" light comes on in the instrument panel.

Is the shuddering a violent shaking of the steering wheel, which would tend to localize the cause to the front, or is it felt in the car body itself?
I have to back off the throttle completely. One time on a long curve it still wouldn't stop so I had to touch the brakes. It stopped instantly. I caved this morning after I posted and dropped the car off at the dealership. I'll let everyone know what exactly the problem was, if they figure it out. Since I can not afford to keep troubleshooting myself with new parts.
 

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The AWD fuse is not functional in the 5eat. There is a center diff and transfer clutch instead of just a transfer clutch, so no way to disable it.

I'd lean towards torque converter if it didn't happen only while turning. Any chance it's actually the ABS activating on one wheel while turning? That would explain a lot and would point to a wheel speed sensor needing to get replaced.
 

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I'd lean towards torque converter if it didn't happen only while turning. Any chance it's actually the ABS activating on one wheel while turning? That would explain a lot and would point to a wheel speed sensor needing to get replaced.
That is an intriguing thought. The steering wheel vibration over 120 kph could be wheel balance but why only in right swings?

The body shuddering might well be the ABS at one wheel, even a rear. I could imagine an ABS wheel speed signal failing at high speed, leaving the ABS control module to "think" that wheel has stopped turning, i.e. is skidding. Taking this a bit further, I'm not sure, but I don't think the 06 XT had VDC. With VDC out of the picture, ABS pumping the brakes does not activate unless the brake pedal is pressed. So if ABS is activating, it's something really unusual. But again, why only in right turns, and at high speed?

What are we missing? Guess we'll know when the report comes in, but no harm in discussing it in the meantime.
 

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VDC or no, I still think this is something to do with the vehicle speed sensors. If it isn't tripping up the brakes it could still be distributing torque willy-nilly via the transfer clutch.

Only other thing I could think of is a bad engine mount allowing the engine to shift during turns, and tugging on a wire or ground...

I'll be interested to hear, however it goes.
 

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Engine mount is a possibility, but then why only on high speed right swings. As far as the engine is concerned, the forces on the mounts are the same -- the engine is always turning in the same direction -- so if the engine lifts in some way, it should do it in all swings, and for that matter, when accelerating going straight.

The AWD transfer system in the 5-speed is a planetary differential augmented by a multi-plate clutch which tightens up when either the front, or rear, drive turns faster than the other (suggesting a wheel is spinning). As far as I know, in the absence of VDC which does make use of the ABS wheel sensor signals, the AWD clutch control uses only the two vehicle speed sensors (essentially the rotation of the front and rear drive shafts to the front and rear differentials) to assess wheel speed, and does not involve individual ABS wheel sensors. Also, the AWD only affects power transfer toward the front and toward the rear, but not to individual wheels (side-to-side). But again, it's an interesting possibility if something isn't functioning as it should.
 

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Discussion Starter #16
Just wanted to update you guys and let you know that after inspecting, then road testing the vehicle they were able to feel the shudder, but still have no idea what is causing it. The only thing the tech I talked to could tell me was that its "really weird" and they'll need my car all day again tomorrow.

*sigh*
 

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Plain OM: I realize the AWD is only going to regulate torque between front and rear with no authority over left & right. I think you worked out where I was going with it: the cause may be a left-right thing, but the result may not be.

If the AWD is getting bad data and lashing the clutch between limits, I can easily see that resulting as a vibration and it would make for weird handling effects.
 

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Plain OM: . . . If the AWD is getting bad data and lashing the clutch between limits, I can easily see that resulting as a vibration and it would make for weird handling effects.
I'm trying to figure out how much effect the clutch would have in this case, given that the front and rear drives are already mechanically connected full time through the planetary differential. On long, slow, swings to the right, or left, as is common on interstates, is there enough difference in wheel speeds to set up such a serious torque bind-caused shuddering? (Keeping in mind that unlike the 4EAT, where switching the AWD clutch between limits will switch power transfer to the rear on-and-off, in the 5EAT power is always going forward and back through the planetary differential, so there isn't the same on-off effect.) But it's an interesting possibility to pursue.

I wonder if the dealer techs will hook up the SSMIII and monitor transmission and engine parameters to see if something unusual shows up when the shuddering is present.
 

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It could possibly cause it if it was pulsating. But I can't think of a situation that would cause that to happen. Again, the wheel speed sensor could be the culprit, as it is used to decrease transfer clutch pressure during a turn, but it should throw an abs code and cel if it's giving erratic readings.
 

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Discussion Starter #20
Hi everyone,

Just as a followup they are telling me that it was a combination of uneven tire wear, front alignment way out of spec, and that a bolt in the driver's side LCA was very loose. They told me they didn't have time to road test it, so I'll be following up tonight after work when I get my car back. I am hoping they solved it, but everything they are talking about has been changed since the problem started, so I have a hard time believing that it really is fixed.

I'll let you all know!

Keenan
 
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