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opel assimilated
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I had the same thing happen when I replaced my rubber donut. As soon as we got it all back together, it vibrated really bad, even worse when someone was in the passenger seat. After many painful hours of pulling my hair out, we noticed the torque tube was pushed a little over to one side more than the other. we traced the problem to mostly the bushings in the trailing arms and the panhard rod, and a little of the problem was at some point in its life, one of the trailing arms were bent. It seems that with the old worn out donut, it let the shaft stay over to one side, then with the new donut, it put a lot of pressure on the other side making me feel the vibration. I fixed mine by changing to new bushings(trailing arm and panhard) and scooting the donut carrier assembly over the to make the shaft more centered. Look at where the drive shaft goes into the torque tube and see if it is closer to one side than the other. Sorry so long and I hope this helps
 

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One question: I found there is no gasket between where the Torque Tube bolts to the differential housing ... should there be one? Instead, I found RTV glue marking the circumference of Tube. Seems to me, if you want a good seal, there should be a gasket in this area but, there is none shown in the 5 Opel GT books I own.

There isn't a gasket between the torque tube and the differential. The differential has a lip seal at the front, where the drive pinion extension shaft (the thin drive shaft inside the torque tube) connects to the drive pinion. The torque tube actually has a small drip hole at the bottom, so that if the front seal leaks, it doesn't fill up the tube with hypoid oil.

HTH
 

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Discussion Starter · #23 ·
Unidentified OpelGT Vibration

Thanks Flipper, Houserc and KWilford ...

I feel completely comfortable saying the vibration is not anywhere forward of the drive shaft. I currently have the drive shaft and Torque Tube out of the car and there is no vibration whatsoever! Flipper's comment is very compelling. I will take note when my new parts arrive (waiting on new urethane "donut" and bearing). To Keith: thank you sir ... I don't notice a leak in the pinion seal and, in the words of another wise man, "If it ain't broke, don't fix it". I'll leave the seal untouched for another time but, don't know why the former owner would've RTV'd it to death!

Thanks again,
- Mark
 

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I would say without question you have a blown/cracked clutch disc hub. Spring retainers crack, springs break and/or depart, and now disc can 'float' relative to the hub. When you were at high speed/high rpm and stepped on the clutch and back off - and the vibe went away is an indication your disc was recaptured in a centered state and no more vibration, at least until the next clutch cycle.

BTDT in my Impala SS with a vibration that drove me nuts as far as locating. It was the last thing I suspected but that one time I cycled the pressure plate and the vibe was gone answered the question of the source. Of course, the pilot bearing fragged; and when the second sprung hub disc went in and failed it ate up a pilot bushing.

This may be a little late, but I sure would like to know the condition of your disc hub assembly.
 

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The phasing of a drive shaft is only important when dealing with a two piece design. (two halves connected by a spline. ) In that type of design, rotating them 90 degrees will produce huge levels of vibration. As far as I know, Opels have always used a one piece design. I guess that the balance of the shaft could change if the yoke was rotated 180 degrees while changing ujoints, but I've never seen this produce significant levels of vibration. When I teach vibration analysis to engineers & vibration technicians I talk about the two things that must be present for vibration to exist.
1. There must be a source ( balance, alignment, bent shaft, bearing damage, gear damage, etc)
2. There must be adequate transmissibility. Things that affect transmissibility are, flexibility, mass, & dampening ( examples would be broken welds, torn or damanged rubber mounts, loose bolts, loose fits, etc.)
Since you have determined that the vibration is related to RPM (3000 in this case) and not speed, the "source" must be between the engine and the input shaft to the transmission. The problem may have occurred however, because of changes you made behind the transmission. "transmissibility" You may have changed the system dynamics through changes you introduced in the drive train. ( replacing the bearing, rubber mounts, etc. ) Those changes may be amplifiying the vibration level caused by a condition that before went unnoticed. ( bad pilot bearing, unbalanced flywheel, etc. ) Since the problem did'nt exist before the recent changes, I would start by confiming that everything is assembled correctly and that all fasteners are tight. Make sure that the driveshaft is free to move on it's spline within the transmission. I don't know what type of bearing is used in the center support so I can't be sure that installing it backwords will change the dynamics of the system, however I would guess that it is a deep groove ball bearing in which case it wouldn't matter. The fact that you haven't been able to duplicate the problem on jack stands, reinforces the theory that this is a "transmissibility" issue. It's a good bet that system dynamics are far different on jack stands than with the car supported by the tires. If this was my car I would take the vibration spectrum analyzer home and go for a ride. Unfortunately most Opel owners don't have one of those in their tool box.
Good luck and keep us posted.
 

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My turn!

I'm bringing this thread back from the dead as I have the same exact problem. I just replaced the center torque tube donut and bushings and now have a drive line vibration above 40 mph... seems worse when accelerating.

Earlier it was mentioned to check that the torque tube is centered. It is.

Three concerns I have:

1. I did not replace the center bearing as I was afraid to screw it up and it seemed to be turning freely with no grit. Somewhere it was mentioned to re-install the bearing with the flange to the front, but I looked at the bearing and it's housing closely before I installed it in the new rubber donut and it looked completely symmetrical. I could see no difference between front and back. Still, I wonder if I missed something?

2. There is a spacer-- a thick washer, if you will-- that rides on the prop shaft. This is not the washer that is under the yoke nut, but another, thicker (plated or hardened) spacer. I do not see it in any of the documentation. It fell out on the floor when I removed the prop shaft from the torque tube and I couldn't tell exactly where it came from, but I'm sure it either goes directly in front of the center bearing or behind it. I tried behind at first and the prop shaft wouldn't turn freely when I tightened the yoke down. So I moved it the in front of the center bearing and the shaft turned freely even when torqued down to factory specs. I wonder if it's in the right location? UPDATE: Found an Opel Manta Haynes manual on-line which shows this spacer as being in front of the center bearing, which is where I have it.

3. I marked the U-Joints and they went back on the same way as it came off, but I did not mark the orientation of the yoke to the prop shaft. U-joints are seated in the yoke properly. Could I have caused the prop shaft be out of balance?

That said, everything went back together easily with no forcing, and I waited until dead-last to reattach the panhard rod, which went on easily. Everything was torqued to spec except the U-joints, which require a box/open end wrench, so I had to guess at them.

The rubber donut looks in the proper position and I can't see anything wrong just by looking at it.

Everything was fine before I replaced the center donut. The old donut was cracked and out of position, but no noise or vibration previously.

I guess I'll be tearing back into it next week, so if anyone has any ideas in the meantime, I'd love to hear them.

Thanks!
 

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I'm bringing this thread back from the dead as I have the same exact problem. I just replaced the center torque tube donut and bushings and now have a drive line vibration above 40 mph... seems worse when accelerating.

Thanks!
By drive line, you mean the vibration is mainly in the body with little or none in the steering?

Harold
 

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By drive line, you mean the vibration is mainly in the body with little or none in the steering?

Harold
Correct. Somewhere between the transmission and the rear wheels, and not evident until about 40 mph. Took a five-mile test drive after replacing the center donut. Wasn't bad at first, but got worse as I drove. At low speeds though everything seems normal.

UPDATE: Swapped U-joints 180 degrees and it's much better, so obviously the pinion shaft balance is critical. Are there indexing marks anywhere so I can match up the splines to the rear diff the way it was before I screwed it up? I still notice it accelerating hard in 2nd gear, especially when turning. I'm going to try loosening up the donut carrier from the chassis to see if something is binding.

I think the OGTS heavy duty donut is a bit more harsh too, so that may be part of it. Between the poly rear suspension and the heavier donut, too much road noise gets transmitted. I'm going to change the rear suspension bushings back to rubber as soon as I can.
 

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Got my problem 90% resolved, so thought I'd pass my experience along in case it helps anyone else down the road. Mostly I tried different ideas posted by others previously. Rotating the drive shaft 180 degrees made the biggest difference. Even though I had marked the relationship of the U-joint to the yoke, the yoke to rear pinion shaft should have been marked as well. I doubt mine is completely in balance now, but it's much better than it was just by swapping the u-joint 180.

Also, my center donut carrier was close enough to the body on the right side, that I think the torque of acceleration in 1st and 2nd gears was causing it to bump against the body a little bit, making it sound worse than it was. I loosened the torque tube front mount where it attaches to the body and pried the torque tube a little to the left before tightening it back down. This also seemed to improve the balance a bit (I jacked back of the car up on stands and ran it up to 60 mph after each adjustment) so the torque tube must not have been centered perfectly. It seems a few 32nds of an inch side-to-side can make a big difference.

What's left I can probably live with, and it's just as likely that it's just extra harshness introduced by the heavier OGTS donut. That's the trade-off for additional stiffness and less movement I guess. New u-joints might help. My theory is that the stiffer donut could be making any vibration in the old u-joints more noticeable.
 

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I had wondered if you just didn't quite get the u-joints seated correctly. I know on some types of driveshafts the really need to go back exactly like they came out.

I believe, as you, that the poly donut is part of the culprit. Are your spacer washers for the torque tube crossmember installed between the body and the crossmember?

Harold
 

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I had wondered if you just didn't quite get the u-joints seated correctly. I know on some types of driveshafts the really need to go back exactly like they came out.

I believe, as you, that the poly donut is part of the culprit. Are your spacer washers for the torque tube crossmember installed between the body and the crossmember?

Harold
I changed it back temporarily just to be sure, and vibration is definitely worse with u-joints in the original position. I was super careful to make sure the u-joints were seated properly as I also wondered if that could be my problem. I think I screwed up when I didn't mark the splines on both the yoke and the pinion shaft. They must be balanced as a unit. Anyway, I mostly only notice it now when accelerating in second gear, and it's more of a "rumble". Could be just an artifact of the heavier donut at this point,

Yes, the spacers are properly installed between the crossmember and the body.
 

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One cool tool that deals with vibs.
First second third harmonics ...say what?

BOSCH AA - Diagnostics OES - MTS 4100 NVH-Analyzer

Anyone know of the worm clamp trick?
I actually tried the worm clamp trick, although I had to do it on the front shaft only as obviously the rear one is inaccessible inside the torque tube. I tried it at 8 different positions (45 degree increments) and it was consistently worse no matter where the clamp compared to with the clamp removed.

I jacked the rear tires up and revved it up to an indicated 60 mph on the speedo, then I'd move the clamp and do it again. The butt-o-meter was the only measurement device I had, but I wouldn't mind one of those Bosch units if you're making your Christmas list up early this year. :yup:
 

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I jacked the rear tires up and revved it up to an indicated 60 mph on the speedo, then I'd move the clamp and do it again. The butt-o-meter was the only measurement device I had, but I wouldn't mind one of those Bosch units if you're making your Christmas list up early this year. :yup:
ROTF
What kind of misdirection is this?
The Butt-meter can be miscalibrated.
When this happens...backfires are very possible resulting in uneven power cycles.
Hope that this helps in some goofy way.
 

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Just wondering if you have a compression spring in the end of your driveshaft? hadn't seen it mentioned, keeps the torque tube assembly tight to the rear axle.
 

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Just wondering if you have a compression spring in the end of your driveshaft? hadn't seen it mentioned, keeps the torque tube assembly tight to the rear axle.
Yep, thanks Brad... it's there.
 

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rear vibration

Does anyone know what the correct torque is for the U bolts, I think they might be too tight. I have a slight vibration at high speed. ( more than the stock 4 speed) I just installed the getrag w/ a new driveshaft, & I was going to rotate the drive shaft 180* also to see if that helps. Thanks
 

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Does anyone know what the correct torque is for the U bolts, I think they might be too tight. I have a slight vibration at high speed. ( more than the stock 4 speed) I just installed the getrag w/ a new driveshaft, & I was going to rotate the drive shaft 180* also to see if that helps. Thanks
The drive shaft U bolts are weird in that you will stretch them before reaching torque.
It would be far more important to make sure they were tightened evenly than torqued to a certain number.

Over torquing them would just bind the bearing cap, at best. Leaving one end of the bolt longer than the other would cause an imbalance.

Rotating the driveline should be the first thing you think about.
 

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Ok, So when I rotate the drive shaft, just tighten the bolts evenly & snug w/ locking tabs, too keep from stressing the caps, or un-even pull on the caps. Thanks FO1981
 
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