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Opeler
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Discussion Starter · #1 ·
I have recently changed my Center Support Bearing, and all accompanying bushings at the head of my GT's Propeller Shaft. Taking it on the road after this was completed, I started experiencing a heavy vibration emanating from the drive train. I am very familiar with the "55 MPH Shimmy", which all Opels are notorious for. Thinking my drive shaft's U-joint may be the cause, I had it replaced, along with balancing the shaft itself - same problem. I put the car on jack stands, and simulated the RPM's necessary to induce the same condition (approximately 3000), while listening to the rear end via a stethoscope - no problem there. In fact, by viewing from below under these conditions, the drive train looks straight as an arrow! The funny thing is, when I get past 4000 RPMs, the vibration starts to dissipate but, returns when I take the lead out of my right foot.

By putting the car on rear-only jack stands, I believe I effectively proved this has nothing to do with the aforementioned shimmy. Similarly, I believe the wheel balancing can be eliminated.

I have consulted Roger Wilson, and he believes there are potentially 4 causes:
1) By replacing the bearing, I could have revealed a bent propeller shaft which could be much more pronounced, now that the new Center Support bearing is in place.
2) I could have inserted the bearing bass-ackwards from it's intended position.
3) The Pinion bearing could be gone.
4) or, since the Center Support Bearing was supposed to be a "Good-used" item, it could be the bearing itself!!!

This last item ("Good-Used") would be an issue that never would have occurred to me. Especially, given the fact that this vendor is well respected within the Opel Community. In my conversation with Mr. Wilson (aka. OMC Pres), he told me I should've waited, or paid 3 times as much to get a new bearing from somewhere else. The funny thing is, if the Pinion bearing is suspect, I do not hear any problem from that area. Car mechanics not being my specialty in life, I wouldn't necessarily know but, I have had others indicate noise (howl or screech) would be indicative. These same folks (respected car mechanics in my area) are just as perplexed. Rather than throw more money at potentially resolving this issue, I figured I should take it to the folks that know best. Can anyone lend me a hand on this issue? It is now prime Opel driving season here in Northern California, and I have reached my wits-end on solving this problem!

Thank you,
Mark
[email protected]
 

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Have you checked for play in anything? Grab the drive shaft and shake it. does it move? Lift the rear off the ground, take the tire and see if it will rock in any direction. Or move in and out at all. have you been ale to determine if the vibration is coming from "for sure" behind the transmission? Is the vibration occurring because of speed, or from engine RPMs? In other words does it start at 50MPH or a variation of speeds at the same RPM. Or does the vibration always occur when you are accelerating?
 

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Mark, my personal experience is that when you have a axle input bearing going bad, you'll know. It is 95% constant hum-buzz that you'll hear behind you when it's halfway gone. It will change pitch or growl with applied torque. I'd be more curious about the replacement part. I think you would need a dyno to load the bearing and watch for tube assy. jump. The more exper-ienced Oplers will have plenty of insight for ya.
 

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Opeler
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Discussion Starter · #4 ·
Unidentified OpelGT Vibration

I appreciate the suspicions guys ...

Although I have not personally checked any of the Wheel Bearings, my professional mechanic friend initially suspected as much. So ... I ordered wheel bearings for all 4. He went so far as to take me on a ride, and "loaded" the rear-end by swerving violently from left to right and back. There indeed seemed to be a rumble from one of the rear areas. When I recieved them, he changed his mind so ... I've got them for the next issue to arrise ... :mad:

I have checked the drive shaft play. I removed it and had it's U-Joints replaced and balanced. Upon re-installation, I can definitely say everything felt solid. I would think you all would be convinced by the fact that I observed the whole drive train while it was running (in gear) on jack stands. There was not so much as a "hairs" worth of wobble to the spin on the shaft.

As far as the "RPM vs. MPH" question is concerned: I can tell you this was on my mind when trying to analyze this problem. I can definitely tell you that it is RPM related. Although initially it seemed to start at 70 MPH (not coincidentally ~3000 RPM with a Getrag and a stock, late GT model Rear-end), I put the car through the gears at about the same RPM - got the vibration through each iteration of gears. Furthermore, on the freeway, I got it up to "Vibration Speed" and hit the clutch - vibration went away immediately. I don't know if it's due to suddenly being below 3k RPM or, what. I definitely don't know what to make of this finding. I would've simply drove it to LA and had Mr. Wilson take care of it for me but, alas - he couldn't be certain. In addition, I didn't know if I would make it without becoming a "MilkShake" on the way down. The vibration is that noticeable. In addition, I didn't know if I'd make the problem worse (by screwing something else up) if I did try to drive the 400 + miles to get to Artesia! Nor did I know for sure whether I would make it without being towed the rest of the way.

Thanks for your contributions ...
 

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Über Genius
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9,391 Posts
Definately sounds like the pilot bearing or the shaft bearing in you r tranny. I once forgot to put the pilot bearing in my GT and had a similr problem. Course i didn't know it at the time. Found out when my clutch plate broke.
 

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OPEL-LESS!!!
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not only will not having a pilot bearing bust the pressure plate, but it can also allow the input shaft to wobble, taking out the input shaft bearing, which takes out the front seal, that creates a leak, and sometimes its not known and trans begins to howel and it eats your synchros from being dry, which is only fixed with a new trans. replaced a trans in my friends blazer not too long ago, and he didnt have a pilot bearing, and i'm assuming thats what took everything out, is my reasoning for everything logical?
 

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Opeler
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Discussion Starter · #7 ·
Unidentified OpelGT Vibration

GreenSmurf, First Opel,

Thanks for your input but, let me just say I didn't have any problem with that area BEFORE I changed the Center Support Bearing. Please understand, I had absolutely no problems with the car prior to this last maintenance. It was solely located in the Propeller-Shaft region of the drive train. I'm really looking for some input (from someone) on the Center Support bearing, Pinion bearing area (located on the rear half of the drive train).

Specifically, if someone can tell me how one can tell whether the Center Support bearing is installed reverse to it's intended direction. By looking at it, I can't tell one side from the other. Niether can my consultant (Pro Mechanic). By my eyes, it looks exactly the same on either lip of the bearing housing. My friend looked at my old one (replaced), and indicated it was not bad. I changed it because the bushings were worn. Since I was already in there, I decided to replace the bearing itself - albeit, the only one I could find (as described in the first post) was a "Good/Used" one.

Keep 'em coming folks ... Thanks,
Mark
 

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Senior Contributor
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msgilch, sounds like you did everything. Have you tried taking the old center to a axle shop and finding out if they could rebuild it? As, like you say, it started there.
 

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This may sound dumb, but if all you did was replace the bearing with a new/used one and you old one isn't bad, swap out the bearings again to see if the vibes go away.

Ron
 

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Über Genius
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But you said it was RPM dependent, not speedometer dependent. The RPM factor is what leads me to believe it is the pilot bearing. If it was speed related, then the reversed bearing theory begins to hold water. Best bet is to check your thoery first as it seems to be the easiest to check. If it doesn't pan out, check your pilot.

It could be a coincidence that the pilot is acting up just as you fixed the other problem.
 

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Old Opeler
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5,564 Posts
Focus!

All you changed was the centre bearing and enclosing rubber doughnut - right?

So we need to concentrate on bits affected by those parts and that proceedure - right?

Start with things you can do and get at without any disassembly.

1) are the "U" bolts that hold the driveshaft on tight and have the U-joint trunions seated properly in the yoke on the end of the diff shaft?

2) is the drive shaft back in the same position or has it been rotated 180 degrees so that the U-joint is in a different position?

3) are the U-joints nice and firm - but not tight?

4) is the spring back in front of the driveshaft yoke - the one that goes between the yoke and the g/box tailshaft?

5) is the plain bearing at the rear of the g/box, that the yoke rides in OK?

6) is the yoke that holds the centre bearing on to the diff extension reseated correctly and the retaining nut torqued up correctly?

7) if you had the diff extension off - is the extension shaft straight and back in correctly? is the outer tube seated correctly and the four attaching bolts tight?

8) ......
 

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Opeler
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Discussion Starter · #12 ·
Unidentified OpelGT Vibration

Guys,

One question that still hasn't been answered: How can you tell if the Center Support bearing is installed backwards??? Let me be clear in my assessment: Since there was only a 2 day turnaround for insertion of the new Center Support bearings/bushings, I would not conclude the pilot would go south. Although I appreciate your input, I can not stop to consider another area of the drive train. Basically, the whole car was restored from scrap. I put at least $5K into all the basic fundamentals, and added some hi-performance to get this car on the road. All aforementioned parts were purchased from a vendor I'm positive 90% of you have used at one time or another. I only have about 30K miles on the car!

Namba: your suggestion is well taken. I am going to put the old bearing back in, to see if I've been bamboozled again by the same vendor. Although rare with the amount of parts I've purchased over the years, I have been burned one other time from the same vendor. Again, not having sustained experience (although I've owned one GT or another for 24 years) in mechanics, I can easily be qualified for most work. However, where it concerns the area in question (Center Support to Properller Shaft), I did not trust myself to get the job done correctly. My friend, who is a 15 year, certified Honda mechanic, did the job for me. Obviously, being into Hondas, he does not know the "tricks of the trade" where it concerns our GTs.

GTJim: I'd like to answer all your pointed questions but, I can't - too dumb I guess. Obviously, you are a master with regard to our cars. I can attest to your first 4 questions with an AFFIRMATIVE. Actually, #2 is something I never considered as a potential hazard. In my 24 years, I have had a drive shaft off many times, and have never even thought of marking which side of the driveshaft originally fit with what side of the receptacle. If this is pertinent, I have failed this test! With respect to #5: I do not know what "plain bearing at the rear of the g/box" refers to. Similarly, I don't know if the nut was torqued correctly. I did supply my partner with 3 GT-specific books, and I assume that he used all the information contained within, to apply the proper seating pressure to the fastener. As far as point #7, all are tight and straight respectively. Obviously, I can't see the condition of the shaft itself which, is still a potential area for doubt.

Thanks again guys ... I really appreciate your input. With my attached response, please consider and keep your comments coming. In the meantime, I'll put the old back in and see what happens.

Mark
 

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Old Opeler
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Which Side Out!

Mark,

Not a Master with regard to our cars; just made LOTS of mistakes but usually each one only twice - the first and last time!

You got me thinking with how can you tell if the centre suport bearing is in backwards - so I consulted all my manuals and came up with this:

"... noting the following points: Install the ball bearing with the flange facing towards the front and pack the area around the bearing with water resistant grease ..." (water pump grease - I guess)

So it looks like there is a right and wrong way to fit the bearing. The pressed sheet metal extension on one side goes forward.

As far as fitting the driveshaft back the same way - just trying to get every thing back in the original, balanced, position. Eliminate every change!

#5 The plain bearing inside the tail shaft is a bush that the shiny bit on the yoke that slides into the g/box rides in and it should have very little up and down movement or the driveshaft will "float" about.
 

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Opeler
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Discussion Starter · #14 ·
Unidentified OpelGT Vibration - Which side out?

GTJim,

Thank you sir, for answering the question that's haunted me. It still may not solve the problem (making sure the bearing is in correctly) but, I will make damn sure this time.

You point about the drive shaft position is well taken. However, wouldn't your point be moot, in the case of rebuilding the same component? You may recall in my earlier post that initially suspecting the drive shaft, or more pointedly the U-Joints, I had the former replaced and the entire shaft re-balanced. This would lead me to the assumption that position wouldn't matter when re-installion was performed. In any case, unfortunately it is much too late - shouldn't consulted you folks before I embarked on this nightmare!

As far as your other comments, thank you for clarifying the "GT/Box" item. If I understand the part you are referencing, it would be in the tail shaft of the Getrag 5-Speed. I admit, I have replaced the outermost bushing the shaft yoke slides into but, did not check the condition of the bearing (didn't know there was such an animal). I can attest to the "play" in this area, and it is very tight - no movement to speak of. Actually, when the drive shaft is in place, there is very little movement on either end of the Drive Shaft! Having said that, it is another good recommendation. Perhaps this area will only show signs of wobble, when under higher RPM/Speeds. If my theory on the problem fails the test (reinsert old center support bearing), your suggestion will be my next area of focus, along with the condition of the propeller shaft itself.

Thanks again,
Mark
 

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On the first bracket racing car I ever built, I managed to reverse the yoke position on the driveshaft when putting it back together, and experienced something very similar to what you're describing. I know you said you took the driveshaft to have it balanced, BUT, the driveshaft shop, following standard automotive practice, would normally have marked the yoke, and put it back together the exact same way you gave it to them, not knowing that the U-joint might have been reversed. If reinstalling the old bearing doesn't work, I'd try reversing that yoke you changed the U-joint out on.
My $.02...
 

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Old Opeler
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5,564 Posts
Bushing

The outer most bushing that you replaced IS the "bearing" that I am refering to. Just semantics. That "bushing" is a "plain Bearing" in my terminology.
Just shows how careful we must be with cross cultural use of English!
 

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Opeler
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Discussion Starter · #17 ·
Unidentified OpelGT Vibration - Update

I have now removed the entire Torque Tube, and found the rubber bushing which envelopes the Center Support bearing, to be partially dislodged in the rear. I could not see this previously, due to the hard rubber bushings obscuring view of this portion of the Center Support area. My question now becomes: Is this the cause of the vibration, or is it more likely the result of the heavy vibration which caused the lip of the bushing to become dislodged? I guess what I'm really asking (perhaps to myself), is whether it was ever installed correctly in the beginning.

I have since talked to the mechanic who performed the original replacement; and he is insistent on the latter (of course) - that this is a result of the vibration. I have also talked to another vendor (different from the first). They have insisted upon installation of a new, heavy-duty poly-urethane version of this component. It is claimed it will never deteriorate. Although I wouldn't know under these circumstances, I went ahead and ordered this bushing, along with a brand new bearing.

Dosaiian, and to those who tried to convince me of the error of my ways with regard to drive shaft positioning (GTJim): Your input did not fall on deaf ears. Upon receipt of these new components and subsequent install, I will heed your information. As Dosaiian implies, it wouldn't be that big-O-deal to rotate the drive shaft 180 degrees, upon finding (God forbid!) I still had the same vibration.

Can anyone tell me if there's any merit, now that the Torque Tube is removed, to replace the Pinion bearing/seal, or any other component likely to go next? I have neglected this area, mostly because I know so little about it. However, since I'm already there I'd like to take care of any more "surprises" before re-installation. I'm definitely not looking for more work but, would rather scuffle through it now, than potentially going through the same grind again.

Thanks to all ... I appreciate it tremendously,
-Mark
 

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If the pinion bearing seal is not leaking, and you're not getting any noise out of the rearend, I wouldn't mess with it (bearing preload issues, etc.) unless you have some reason to believe it may fail (like the car sitting in a foot of water at some point, lol). As Grandpappy used to say, "Why fix it, if it ain't broke, Hoss Fly?" At least you're being smart enough to find the problem instead of just driving it till it breaks, like some people I know... Don't worry, I'm pretty sure you're on the right track now, and the urethane replacement is a good idea. I plan on going thru my own suspension in the near future and replacing all the rubber components, including those on trans and engine mounts, with urethane.
 

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Opeler
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Discussion Starter · #19 ·
Unidentified OpelGT Vibration

Dorsaiian,

I have none of the other symptoms you described, concerning the area in question. Had there been any, it might have been easier to diagnose the vibration problem. This, of course, is not my opinion but, that of a certified mechanic. On 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. Obviously, I could make my own - definitely don't want to wait for another shipment. If deemed necessary (by you all), I will start to work on making one prior to my aforementioned parts arriving by mail.

Thanks,
- Mark
 

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70's Opeler, back 4 more!
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This seems like a pretty well looked over thread and I know there are several members here with more knowledge than me, but let me ask this.

Can your run your engine up to the RPM you notice the vibration at, with the clutch pressed in and notice the vibration? That would tell me the problem is either in the flywheel area, or the engine.

If nothing there, can you remove the drive shaft from the transmission and then run it up to RPM to see if the vibration is in the pressure plate, pinion bearing, or transmission area? (there might be oil slung out of the rear drive area on this.)

These two items would tell me if the problem is before the torque donut area or not.

Any other suggestions out there?
 
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