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Discussion Starter #23
Alfa Corsa I believe you are thinking of the early mechanical clutch style center bearing, the hydraulic clutch cars like mine have a different setup.

John - are you referring to this firm? http://www.gmtracing.com/contact-us/
 

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Discussion Starter #24
Have you considered that you may have a driveshaft alignment problem? If it is out in either the horizontal or vertical plane it can cause vibrations. I quickly found a post about vertical plane alignment - https://www.alfabb.com/threads/prop-shaft-alignment.664854/#post-8285122
To check the horizontal plane alignment you hang three loops of thread each with a nut in the loop. One around the engine pulley, another around the gearbox output shaft and a third around the differential input shaft. You the sight down them to verify that they are in a straight line. Correction is made by slotting the holes in the tranny mount so that it can be moved from side to side.
Thanks Ed, I have not checked this and there is every chance the alignment is not perfect as all rubber mounts in every position have been replaced by a mechanic of unknown skill level (author).

Will work on this using techniques mentioned, may bring a laser into play for assistance.
 

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Discussion Starter #25
Howd you hang a plumb bob from the trans shaft with the trans mount in place?

IMG_3148.jpg
IMG_3149.jpg
 

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I’m kinda with Alfa_corsa....your photo shows you have the welded-in hoop in the transmission tunnel for ‘early’ cars, with the full rubber centre bearing mount, but without anything to secure the mount to the chassis....ie the u-bolt alfa_corsa refers to. There should be a piece of threaded rod extending downwards from each side of the hollow hoop in your pictures, to which a flat steel section bolts to support your all-rubber bearing support. What is holding your bearing support in place? If there isn’t a solid attachment point, holding the bearing support to the car, I’m not surprised there’s a location and vibration problem. Later cars mount was different, but they didn’t have that inverted tube/hoop. Show us what you’ve got...so to speak.
 

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There should be a piece of threaded rod extending downwards from each side of the hollow hoop in your pictures, to which a flat steel section bolts to support your all-rubber bearing support.
Hi Ranz, the threaded rods are located further to the back. First the hoop, then the bolted bracket and then the rods that hold the bearing support. The rods are just visible in the 2nd pic.
1605672


1605673
 

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Discussion Starter #28
I’m kinda with Alfa_corsa....your photo shows you have the welded-in hoop in the transmission tunnel for ‘early’ cars, with the full rubber centre bearing mount, but without anything to secure the mount to the chassis....ie the u-bolt alfa_corsa refers to. There should be a piece of threaded rod extending downwards from each side of the hollow hoop in your pictures, to which a flat steel section bolts to support your all-rubber bearing support. What is holding your bearing support in place? If there isn’t a solid attachment point, holding the bearing support to the car, I’m not surprised there’s a location and vibration problem. Later cars mount was different, but they didn’t have that inverted tube/hoop. Show us what you’ve got...so to speak.
Heres what I got. I have the driveshaft out of the car and only dry fit the front portion of it here to show the support it is obviously not fully connected and bolted correctly.


IMG_3175.jpg
IMG_3176.jpg
 

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Is it just me, or does it appear the trans mount is sitting high in the crossmember?
Could there be some contact between an upper part of the trans with the body?
 

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The driveshaft alignment will be out if the center bearing is not where it should be. Lowering the center support is one of the ways of correcting misalignment in the vertical plane.

Have you changed the rear ride height?
When that is done the slope of the rear driveshaft tube is changed which changes the angle that the rear U-joint moves through. The two U-joints should move through the same angle when the car is normally loaded or there will be a vibration. This is normally corrected by adjusting the slope of the front tube to match the input shaft of the differential. This is accomplished by either lowering the center support or the transmission mount. It is a bit tricky to measure the slope with the suspension loaded and one Alfa mechanic I knew used to simply lower one of them at a time and see if it improved things.
 

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Interesting. You’re right, my car is a mechanical clutch model, but I was not aware that Alfa changed the location and design of the center support.

-tj in the Cruz Mtns


Heres what I got. I have the driveshaft out of the car and only dry fit the front portion of it here to show the support it is obviously not fully connected and bolted correctly.


View attachment 1605700 View attachment 1605702
 

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The driveshaft alignment will be out if the center bearing is not where it should be. Lowering the center support is one of the ways of correcting misalignment in the vertical plane.

Have you changed the rear ride height?
Changing the rideheight doesn't change the angle of the driveshaft...
 

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Discussion Starter #33
Ive replaced all rubber parts incl suspension trans motor diff mounts with stock items but many of them were purchased from IAP some time back before I was wise to the difference in brand quality and I cant be sure i installed them correctly because I dont have a stock car to compare them too. I know i made efforts to clock the trans mount to match what I removed from the car and can pull it this wknd to verify.
 

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It does from the reasr u-joint back....it has to. That's the reason for the splines. When the car compresses there needs to be a way to compensate for the driveshaft reducing (or extending) it's angle.

-tj in the Cruz Mtns
 

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Changing the rideheight doesn't change the angle of the driveshaft..
Put your car on a lift with the suspension at full droop then jack up the axle and watch the angle of the differential input shaft change.
 

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In addition to the alignment to the centerline (front pulley, output flange diff) that Alfaparticle posted, I remember RJ mentioning that the front shaft has to be parallel with the gearbox (looking at it from the side of the car). If you are interested I do have a (new/refurbished?) 9mm rear driveshaft from alfa-service.com for sale $200+ shipping.
 
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