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  #11  
Old 04-23-2022, 05:42 AM
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Ok. So I’ve just put a new guibo on the main driveshaft. The old one looks original as it has BMW on it and SGK which would have been the manufacturer back then. It was all dried up and cracked all around.
There is no record of it having been replaced before and I have all the history on the car.
I’ve been for a drive and it’s definitely lessened the drone / vibration at 1700rpm - not gone yet, so I think im heading in the right direction for that.
Next will be the front shaft guibo to what happens.
I also got to inspect the centre support bearing. It spins smoothly and the rubber is sound so that’s ok.
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  #12  
Old 04-26-2022, 11:15 AM
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Here are two vibration analysis graphs. Can anyone explain..
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  #13  
Old 04-26-2022, 11:17 AM
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Those are two vibration analysis graphs I did today. Can anyone make any sense of it? They were done with the car in P.
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Old 04-26-2022, 12:08 PM
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They are just showing the resonant frequency of where you had the phone. (wherever the phone was touching).

You need to do multiple tests on different things to see the relative number (height).

Eg on the engine directly. Left and right sides, then on the fender inside engine. When car is cold you can do the exhaust, actually use a block of wood you can do carefully when hot.

The goal is to find two different scans near each other that are similar height (strength) and frequency. You are looking for a "sound short".

Example; a dropped tool could wedge between exhaust header and fender; you will get similar readings at both exhaust side of engine and the fender.

The frequency (48) mathed out to be directly related to the power strokes at idle. The 64 is not a harmonic of 48 so likely just some piece of the car that has that resonance frequency.

The other way to track such is with an FFT sound program it will track sounds through the air so can be much faster. Especially if you use the earbud corded mic.
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  #15  
Old 04-27-2022, 02:12 PM
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Quote:
Originally Posted by andrewwynn View Post
Get an app similar to or exactly this one:

https://apps.apple.com/us/app/vibrat...o/id1089589547 measure the exact frequency of the vibration.

Often a little math will help you find the source.

(Eg: when the frequency is 3x the wheel rotation or 4.1x, it's likely a CV axle or CSB). (or GIUBO).
I can confirm that. I took Andrew's advice and got this and it helped me track down a weird vibration. Was able to narrow it to a CV.
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  #16  
Old 04-27-2022, 02:15 PM
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Originally Posted by Themoog View Post
Ok. So I’ve just put a new guibo on the main driveshaft. The old one looks original as it has BMW on it and SGK which would have been the manufacturer back then. It was all dried up and cracked all around.
There is no record of it having been replaced before and I have all the history on the car.
I’ve been for a drive and it’s definitely lessened the drone / vibration at 1700rpm - not gone yet, so I think im heading in the right direction for that.
Next will be the front shaft guibo to what happens.
I also got to inspect the centre support bearing. It spins smoothly and the rubber is sound so that’s ok.
Check the guibo on the front drive shaft as well.
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  #17  
Old 04-27-2022, 02:21 PM
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It was a perfect example.

This case is not an obvious drive train issue since the vibration is at idle.

That said about 1/3 to 1/2 of those cases end up being the CV.

The theory; when the CV wears toy get some back lash: think of the CV as a gear set with a 1:1 ratio.

At the power stroke the drive train binds up and the CV axle acts like a torsional spring and gets wound up.

After the power stroke the stored spring energy throws the drivetrain backwards and the "gear teeth" float until the next power stroke. The "teeth" hammer back together and generate the shock that we feel as vibration
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Old 04-27-2022, 02:22 PM
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Quote:
Originally Posted by Fifty150hs View Post
Check the guibo on the front drive shaft as well.

+1. Giubo. (JOO-boh).


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