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Discussion Starter #1
My 74 GTV has a body vibration at about 35 and 65 mph. It is speed related and not rpm related. The drive shaft look OK (everything is tight) and I put new tires on. The engine in new. Can the differential case such a vibration? How can I further isolate the problem?
thanks for all you help in the past.
Joe.
 

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Did you change something and that's when the vibration appeared? Did it come on all of a sudden or slowly?
If road-speed related, it's generally in the drivetrain (driveshaft, tires, wheels, axle). If rpm-related, in the engine/trans combo. But this greatly understates the complexity of the issue, which has been covered a lot here. Driveshaft, donut, u-joints, trans and engine mounts are all suspects.
Andrew
 

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Discussion Starter #3
Did you change something and that's when the vibration appeared? Did it come on all of a sudden or slowly?
If road-speed related, it's generally in the drivetrain (driveshaft, tires, wheels, axle). If rpm-related, in the engine/trans combo. But this greatly understates the complexity of the issue, which has been covered a lot here. Driveshaft, donut, u-joints, trans and engine mounts are all suspects.
Andrew
The motor mount are good as are the u-joints, donute and center support bearing. The vibration was there before and after engine rebuild.
I looked for missing balance weights on the drive shaft and none appear to be gone.
There is no noise coming from the rear axles when being driven.
My next thought is to remove the rear axles.
 

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It's no different from the new tires?
1. I'd lift the car and spin the tires to see that they're round/flat in plane.
2. I'd remove the entire driveshaft, including donut and hardware, and give it to a known, reputable shop to check for straightness and balance (Alfas are very poor in this regard as the years go by for some reason). Look at all of it carefully on removal, or have someone you trust who knows what to look for look at it. Front bushing, matching "ball" on back of trans shaft, sliding spline, condition of u-joints, lots of things can be involved.
3. I'd confirm the output yoke nut on the trans is tight.
4. I'd confirm the pinion flange on the diff is tight.
5. Get the driveshaft back, and reinstall per the marks you made before removing it.

That's my process.
Andrew
 

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try removing the driveshaft and rotating 180 degree's...they are indexed for alignment (the arrows are faint..but they are there)
 

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Actually, the great problem is when you have the rear u-joint 90 degrees out. easy to do. The front and rear u-joints must be in sync.

Robert
 

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I've never had success with the 180 change, or adding hose clamps and moving them around as Pat Braden used to urge. I have had enough bad shafts over the years that I just bite the bullet, remove the thing, and figure out what's wrong. Get the driveshaft right from the outset, drive sanely, and it'll be good forever.
In my experience the key culprits are (1) wear in the front bushing and associated flat spots on the output shaft, allowing the driveshaft to "centrifuge" off-center around the ball on the output shaft, (2) straightness, and (3) balance. A driveshaft shop that is not used to this kind of shaft can make it worse, not better. A friend in San Diego just had such an experience on his Super, with weights added making it far more out of balance.
Andrew
Andrew
 

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If it really is engine RPM dependent, not road speed, it's not the drive shaft or anything after the clutch.

If it is road speed, another issue that hides pretty well is wear of the "olive" end of the TX output shaft. This fits in a bronze bushing in the front of the drive shaft, and should be greased occasionally. It wears out-of-round and can vibrate.

Robert
 

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Discussion Starter #9
When the engine was out I inspected the bushing in the fron drive shaft and fitted it to the transmission and saw no play and I did grease it at assembly. The only reference marks I saw on the drive shafts was where to two shaft attach and I saw none at the differential. I believe the drive shaft only attaches in two positions at the differential.
Does anyone think the differential could cause the vibration?
Thanks for all you inputs, it's always appreciated.
Joe
 

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Here I am chiming in again; I've never had a diff cause vibration. It's always been donut, driveshaft, trans or motor mounts, exhaust.
Not impossible of course. Did you spin the tires? If an axle shaft is bent it'll show as tire out-of-plane rotation.
Andrew
 

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There are always two u-joints. Check to be sure they are on the same axes. The sliding spline joint always has an alignment mark so that the u-joint pivots on each end of the drive shaft are parallel.

Robert
 

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Vibrations

I had similar problems on my spider ( 2600) when I stripped the drive train and fitted a new donut. Everything was replaced as I had found it so no reason for new vibrations to have started. What I did in the end was losen all the 6 bolts on the donut to finger tight, jacked up the rear of the car and ran the engine in gear ( slowly) to allow everthing to line up . Then I tightenned the bolts and all is now fine betwen 0 and 100 Mph no vibes. It looks like I had tightenned one bolt at a time on the donut and pulled it out of line. Worth a try?:)
 

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Discussion Starter #13
I did not know that the spline had a refernce mark and will remove the shafts and check the alignment. Also I will do the donut as mentioned by Redmerlin.
Thanks for all your help.
Ciao
 

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Discussion Starter #14
Can anyone recommend a shop near Orange County, Calif. that can isolate and/or fix the vibration problem?
 

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No problem....
West Coast Ballance shop
On S. Grand in Santa Ana
714-542-4173
if you need your driveshaft ballanced
Also they ballanced all of the rotating parts in my 1750 motor
 

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Rare, but Could Be Differential

. . .
Does anyone think the differential could cause the vibration?
Thanks for all you inputs, it's always appreciated.
Joe

Yes, though rare in the annuls of Alfadom, I just had this come up on a Super. The vib was speed related coming up above 97 kph quickly and especially under neutral drivetrain load conditions (clutch in, feathering the gas, going downhill and holding speed coasting, etc.). It arose and got worse over many hundred km's driving on a freeway with a heavy load and driving over 110kph. The car had not been pushed for several years.

While the diagnosis is not complete due to translation issues and some more testing, they tightened the bolts that retain a ring to a gear in the differential. The vibs magnitude reduced abut 50% but they said there was damage form driving in this condition and it would need further servicing (or replacement). The bottom line: something was loose in the differntial. Could have allowed bearing or gear wear.

This was after a complete driveline refurbishment* of everything but the guibo (which was good) which made no difference at all in the vibs. (*Work done: rebuild u-joints, replace rubber support, replace bearing and carrier, replace nose bushing, dynamically balance the half-shaft). Other things considered were blister or out-of-round tire, wheel balance weights missing, wheel bearings, shaft installed out of phase, circlip backed off on u-joint caps, loose bolting, worn u-joint journals. Not considered: engine/tranny/clutch as not RPM related.

I have had guibo failures (goes catasrophic quickly when a crack grows and throws a segment), nose bushing wear (faint and grows slowly), wheel bearing (speed related, for me at ~65mph, like the diff), and u-joints (most typical). SO it can indeed be the differential but highly unlikely. Some have said they only fail if they've been fiddled with as they are complicated to reassemble and adjust properly. Hope this helps.
 
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