06 OBXT Shudder

[keenan.corbett]

Originally Posted by plain OM

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.

[Seabass]

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.

[plain OM]

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.

[rasterman]

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.

[plain OM]

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.

[keenan.corbett]

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*

[rasterman]

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.

[plain OM]

Originally Posted by rasterman

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.

[Seabass]

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.

[keenan.corbett]

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