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Discussion Starter #1 (Edited)
Hello all- This is my first post since taking delivery of my 1973 2000 GTV. It is in good condition but I am sorting thru a few issues one of which has me stumped.

Once road speed gets above about 35kmh a rumble combined with a vibration comes from the rear of the car. You can feel the vibration thru the seat base and it seems worse in the left passenger seat than the right hand drivers seat. At 100kmh it is very noticeable. I have swapped the tyres over with the spare to see if a tyre was faulty. It is not affected by the gear you are in ie it is speed related.

The mechanic who inspected the car for me when I bought it thought it was a rear wheel bearing but there is no noise or play in the bearings when I jack the wheels of the ground.

I would appreciate any suggestions about where to look.

Thanks

Paul
 

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My bet would be the rear prop shaft, including its universal joints. If there's too much friction on the joints, the prop shaft may get out of balance i.e. turning excentrically, as the joints cannot adapt their position quickly enough at higher rotation speeds. Had this problem on my 66 GTV, although not so much the vibration but rather a lot of rumble.

Charles
 

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Discussion Starter #3
Thanks Alfa Charlie

Your reply has given me somewhere to start although I asked my mechanic about this and he said he thinks it is the wheel bearings. So up on the jack this weekend to see what I can see.

Paul
 

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71 Berlina 74 GTV 17 Giulia Q4
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You won't necessarily feel much play in a rear wheel bearing and your description fits. You can jack the car up with the rear axle supported by jack stands to keep the car on the springs put it in 4th or 5th and about 3000 rpm. Have a broom handle and place it on different parts of the car that arn't moving:) and listen with the other end up to your ear. You can isolate where any strange noises are comming from. Changing rear wheel bearings on an Alfa is about the most pita repair on the whole car which is why you really want to make sure that is indeed the cause. The u joints are easy to check, just grab each end and rock back and forth, any play and they should be replaced. Congrats on the new car! photos?
 

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I agree with charlie and gigem not your mechanic. Meaning check and change your u joints first. Easier and cheaper. I have had to change ujoints on 5 of my cars. Changed rear wheel bearings on 1 1750 GTV, I think the 2000 GTV with LSD is way more difficult to change rear wheel bearings.
 

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Discussion Starter #6
2000 GTV rear noise

Thanks Gigem I will post some pictures soon.

Brad sorry can you clarify, Charlie thinks it may be in the driveshaft and Gigem I think agrees with my mechanic on the wheel bearing theory?

Paul
 

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The broom handle diagnostic technique works well for both scenarios.
Be careful or send videos.
 

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Check those u-joints and the center bearing first. I prefer a long screwdriver as a "stethoscope", It seems to transfer the vibes better.
 

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Discussion Starter #9
2000 GTV rear noise

Thanks for everyone's input. I have not had a chance yet to jack the car up and have a good look at the items suggested. But a strange thing happened today. I filled the fuel tank up for the first time and with the extra weight over the rear end the noise and vibration was still there but noticeably reduced. Hmmmmm
 

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The added weight likely changed the drive shaft and u joint angles for smoother operation. I still vote for u joint replacement.
 

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I concur with Brad 100%; u-joints.
 

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Discussion Starter #12
Centre bearing support

I have been under the GTV today and checked the universal joints which do not have any play in them and look OK ie no rusty streaks coming from them etc. The front doughnut also looks OK with no movement.

I found that the centre bearing support has some movement in it. I would say it will move up and down about 3 to 5mm. I presume as these are rubber they have some movement?

How much movement is correct in the centre bearing support?

Thanks.
 

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Hi Paul,

Yup, the central prop shaft bearing should be floating somewhat, don't know exactly how much. The u-joints should as well pivot smoothly. If they pivot heavily to the point where they appear to be almost frozen solid, such a setup would cause the prop shaft to rotate excentrically and vibrate.

Charles
 

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Has anything been done to the drive or rear end? A really easy cause of this vibration is mis-phasing of the u-joints. All you have to do is slide the spline out and install it wrong and you get vibration. Gubio replaced? etc.

The yokes on each end of the drive shaft for the u-joints should be exactly parallel. Otherwise you get vibration.

Robert
 

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Robert, this is where a shop drawing of ujoint alignment would come in handy. I agree with you.
 

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71 Berlina 74 GTV 17 Giulia Q4
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The other day I put two drive shafts on my vise with the jaws open a couple of inches just enough to lay each shaft in between the jaws. Put a level on the rear yoke and turned it to level. Then put the splined end on and each of them were about a half a spline off. ie, the short spline end was not level with the other end. I thought they should line up? I found the arrow on the short female end, it's by the grease nipple but for the life of me could not find the other arrow on the actual driveshaft. Has anyone ever checked this close?
 

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Here's the picture. Note that the yoke (#25) forward of the sliding splines has its axis about horizontal; the yoke at the rear of the driveshaft (#28) has its axis exactly parallel. Mis-setting the spline can shift this relationship.

Robert
 

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Robert, Perfect picture. I wonder how many splines there are. If an even # it could be assembled 2 ways if an odd# there is only 1 right way to put it back together.
 

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next time someone has their driveshaft off I'd be interested to know if the yokes when lined up are exactly level with each other. As I said I tried two and they were about a half a spline away from being in the same plane. In other words it's impossible for them to be exactly lined up. I'ts interesting that the arrow on the female spline is at the grease nitpple which is 90 deg from the axis of the yoke. Like I said I never could find the corresponding arrow on the long shaft even using a magnifying glass.
 

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If half a spline out you should rotate one part about 180 degrees and it should line the yolks up exactly, assuming there are an odd # of splines. I am sure the 2 yolks should be exactly in the same plane.
ps just checked a spare driveshaft even #, 16 splines, 2 yolks are pefectly lined up. 2 ways to put together correctly. except for original balance.
 
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