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Opeler
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Discussion Starter · #1 · (Edited)
Many GT Opelers have experienced high frequency vibration caused by the resonance of the propeller shaft at higher speeds. To quote RB’s statement, it can take out the center shaft, the outer tube, the t/t mounts, the front of the differential, even the floor pan of the car! The cure is to reinforce the driveshaft as documented by RB in one of his posts.
https://www.opelgt.com/forums/clutc...reinforcing-propeller-shaft-2.html#post597842

Couple years ago I have also upgraded my propeller shaft the same way at one of the local shops. High frequency vibration has disappeared but some light vibration was still there. I sent the propeller shaft for balancing but it was destroyed by some idiot who “balanced” it by adding blob of weld. This caused the shaft to warp. Got my money back for “balancing” but the drive shaft was junk.

I bought new reinforced propeller shaft in Germany, since. It is really well done and I can only recommend this shop. The owner, Daniel speaks good English and it was easy to communicate. https://www.ebay.de/itm/OPEL-CIH-ve...h=item41f90c0c9b:g:SjIAAOSwPkBaYxn6:rk:1:pf:0

Being curious, I cut my old propeller shaft and the quick look reviled that the reinforcing pipe was positioned slightly off center. No wonder it caused vibration. I used pieces of botched propeller shaft to make tool for holding differential pinion.
 

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Your Noble Friend ;-)
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I bought one years ago for my Kadett B (which is still not back on the street) from Krause Rennsporttechnik. I'm not making any statements about the one or other being better, just showing options.

Be aware that both prices (from PJ's link and Krause) are prices for the modification. You have to send them your existing shafts or pay up a core fee.

https://www.krause-rennsporttechnik...source=2&refertype=1&referid=107&languageid=2

Also, for a 1.9 or 2.0 engine you don't need them reinforced in the first place. If you have vibration, get them balanced (NOT with weld!!!). These reinforced shafts are helpful when your engine has more than ~160 HP.

Dieter
 

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Opeler
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Discussion Starter · #3 ·
Reinforced of the propeller shaft is certainly useful for high power engines but the main purpose of reinforcement is to increase its rigidity. The shaft is firmly supported at the differential end but the other end it is supported only by the rubber donut. That is effectively a pendulum which at certain speed can create resonance as the shaft starts to “whip”. It feels more like high frequency buzzing rather than the vibration but it could possibly cause catastrophical breakdown even to Opel with standard engine. This has nothing to do with the shaft balance. Actually, standard propshaft has so small rotating mass that balancing is not necessary.
 

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Opeler
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I found one on German eBay for sale, not exchange. I think it originally came from the same vendor as the one provided by PJ. Very nice work and seems to be well balanced.

PJ: didn't you make one yourself along with your machine shop buddy a year or two ago?
 

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Providing the doughnut and U joints are good. Before you do anything with your propeller shaft make sure your driveshaft angles are spot on. The angles weren't that good when the cars were new and with saggy or lowered suspension and/or soft and compressed engine and transmission mounts. More then likely the driveshaft is the cause of the vibration. Improper driveshaft angles can easily transfer harmonics to the propeller shaft. Ideally the angles should be checked with a half a tank of gas and the average passenger weight in the seats. And be sure your U bolts aren't over tightened, that can also cause vibration.
 

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Member
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Providing the doughnut and U joints are good. Before you do anything with your propeller shaft make sure your driveshaft angles are spot on. The angles weren't that good when the cars were new and with saggy or lowered suspension and/or soft and compressed engine and transmission mounts. More then likely the driveshaft is the cause of the vibration. Improper driveshaft angles can easily transfer harmonics to the propeller shaft. Ideally the angles should be checked with a half a tank of gas and the average passenger weight in the seats. And be sure your U bolts aren't over tightened, that can also cause vibration.
I totally agree. The shaft is such a small diameter that it would have to be bent to be out of balance far enough to cause significant vibration.
 

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Opeler
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Discussion Starter · #9 ·
Providing the doughnut and U joints are good. Before you do anything with your propeller shaft make sure your driveshaft angles are spot on. The angles weren't that good when the cars were new and with saggy or lowered suspension and/or soft and compressed engine and transmission mounts. More then likely the driveshaft is the cause of the vibration. Improper driveshaft angles can easily transfer harmonics to the propeller shaft. Ideally the angles should be checked with a half a tank of gas and the average passenger weight in the seats. And be sure your U bolts aren't over tightened, that can also cause vibration.
This is all true but propshaft resonance is different issue. There were several discussions on this subject. Here is one posted some time ago:
https://www.opelgt.com/forums/4b-pr...pel-torque-tubes-arent-strong.html#post170333

Cannot make the link to work, so here is transcript, posted by Don McLean:

6500 RPM for that skinny little driveshaft is a LOT! The failure has to do with the driveshaft reaching critical speed and nothing to do with the torque tube itself. Critical speed is the RPM at which the shaft will reach its first bending mode and begin to go into resonance, where ultimate failure results. The torque tube actually prevented catastrophic damage to the floorpan.

It's the reason long wheelbase vehicles like pickup trucks have 2-piece driveshafts and/or large diameter driveshafts. Believe me, I had some first hand experience with this in my past automotive career

Here's an excerpt from the GKN website and a link to the site:

"Every driveshaft has a critical speed. Critical speed is the point at which a rotating driveshaft begins to bow off its
normal rotating centerline.
Driveshafts begin to vibrate as they approach critical speed. If they are operated at near critical speed for an
extended period, they often fail. This can damage the vehicle and possibly injure persons nearby".
 

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Can Opeler
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Interesting stuff. I have a sudden resonance at 90mph in 4th gear. It doesn’t rattle the car apart or anything, but it’s a huge droning noise that makes some vibrations you can feel. Once I speed up or slow down about 2mph it’s gone. Perfectly smooth from 95mph to 116mph. If I’m below 90mph it’s perfectly smooth too.
I wonder if this is a prop shaft problem.
 

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Opeler
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Interesting stuff. I have a sudden resonance at 90mph in 4th gear. It doesn’t rattle the car apart or anything, but it’s a huge droning noise that makes some vibrations you can feel. Once I speed up or slow down about 2mph it’s gone. Perfectly smooth from 95mph to 116mph. If I’m below 90mph it’s perfectly smooth too.
I wonder if this is a prop shaft problem.
Maybe all that you can do easily to solve a case of vibration at a certain speed is just to get through that speed range asap and not dwell there.

The resonant (or natural or critical) frequency of rotating shafts are mainly dependent on the rigidity of the shaft and of the shaft supports. The Opel torque tube is fairly limber due to the small diameter of the tube and it is semi-firmly supported at the rear end, loosely supported in the front and not supported at all in the center. This configuration almost guarantees that at some point it will encounter a problem vibration point if the operating speed is increased enough.

In the literature, critical frequency of a rotating shaft is sometimes defined as the point at which the deflection of that shaft in the Y axis direction becomes infinite. At the critical rotational speed it will behave destructively, acting more like a jump rope than a rigid shaft and this is when it takes out the torque tube. I don't know what rpm on a GT corresponds to the critical frequency, but apparently some members have discovered it experimentally.

Many engineers like to design rotating shafts to operate at no more than 75% of the calculated critical frequency but this isn’t always possible. Some systems need to operate at speeds above their critical speeds and this is perfectly acceptable as long as the operator quickly passes through the that point on the way up to its rated operating speed. Some shafts such as the very long shafts in power plant steam turbines, may have multiple critical frequencies and in bringing them up to speed they have to tap dance around each one, getting through them as quickly as possible.

I once had to sue a natural gas compressor mfgr. because they flubbed the design and vibration tests of our new compressors. Turns out that all four compressors were in resonance at 900 rpm and that also was the operating speed of the engines, so they started self-destructing from initial start-up. They vibrated so badly that it would hurt your teeth to even stand near them when they were running. The piping welds were crystalizing and cracking from vibration within an hour of initial startup.

Don't know if any of my ramblings are of any use to you, but that is my recollection of resonance in machinery
 

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Just Some Dude in Jersey
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I once had to sue a natural gas compressor mfgr. because they flubbed the design and vibration tests of our new compressors. Turns out that all four compressors were in resonance at 900 rpm and that also was the operating speed of the engines, so they started self-destructing from initial start-up. They vibrated so badly that it would hurt your teeth to even stand near them when they were running. The piping welds were crystalizing and cracking from vibration within an hour of initial startup.
Wow. That company really screwed up. To have not noticed that the self-destruct frequency was the same as the normal operating speed is unfathomable.

On an unrelated point, here at the Post Office plant we had a problem with these spring loaded pivoting levers with pulleys that maintained belt tension. They only have to pivot less than 90*. They had bronze bushings inside for the pivot shaft to rotate within. After 10 years, mine were all showing signs of wear and play, so I ordered new ones and swapped them all out at once. They wouldn't last a week before they would seize up so tight that the pivot shafts would snap off. We would take them apart to find out the cause and all sorts of green corrosion dust would pour out. We would take a part new ones to make sure there was no corrosion and install them and in one week again they would seize up due to the green dust binding everything up. We had to take rat tail files to the bushings to hog them out so that the dust wouldn't bind them. But I noticed that the new pivot assemblies had bushings that looked awfully bright and shiny like gold. Hmmmm......bronze bushings usually have a dark coppery look. I did some research and discovered that the parts supplier had substituted BRASS bushings. Brass bushings can't handle sustained load focused in one area. These pivot assemblies had all the load applied to just one side of the bushings, so they wore out just that one area of their bushings, creating brass dust, which I guess corroded to green. I got some BRONZE bushings from a local supplier and the problem disappeared.
 

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Oh mannnnnn, now I have to buy one of those chubby driveshafts.

:veryhappy
Gordo, think of it as an opportunity, not a requirement! A few well placed LED's along one side of the shaft (light weight, don't worry about the balance) and it will look like a "flashing" light under your car as you drive. If you lift one side (or remove one rear wheel) at the (outdoor) car shows, let the engine idle (in gear and without a limited slip differential) and you can have more under car lighting effects. Set up some throttle actuation (maybe voice driven, or music) and the frequency changes! Lots of new options! ... :lmao:

Doug
 

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Just Some Dude in Jersey
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Brilliant! I'm working on it right now!

I'll spiral wrap the drive shaft in red, white, and blue LED's, like a barber pole, and replace the torque tube with a see through Pyrex or plastic tube!

Wheeeeeee!

:lmao:
 

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This is an old thread now, but is right on topic for my current issue.

I've spent a lot of time dealing with pinion angles and exhaust resonance etc. I have made big improvements and the car is much quieter now. I added a sprint manifold and got rid of the headers, installed new rubber bushings in the rear suspension and added sound deadening. It feels much like a new car, maybe even better in some ways, but one thing still eating at me is the propeller shaft vibrations mentioned in this thread. Pinion angles are good, and my car is great up about 80 mph, then I start to hear a bit of a whirring noise, but no vibration. Starting about 85 mph vibration begins.

With my 5 speed and .72 overdrive ratio I calculated driveshaft speed to be about 4,800-5000 rpm when this happens. I've taken it as high as 91 mph but don't want to push beyond that after seeing the pictures of the what can happen when a prop shaft lets go. Chances of me driving over 90 mph are pretty slim these days, so part of me says to just live with it, but that's not my nature, haha,

This seems to be fairly common from what I've read here. Have these reinforced prop shafts from Germany proven useful at fixing it?

Has balancing the prop shaft helped anyone here who has tried it? I read PJ's earlier post about how NOT to balance it.

Thanks in advance.
 
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