Alfa Romeo Repair: Coast-down vibration, rear rotors, gtv 6


Question
Dave,
Just recently acquired a 1984 Alfa GTV 6.
Car has 66,000 miles and I got all records since new with the car. Car runs strong and smooth when accelerating up thru the gears, and runs smooth at steady speed. Problem #1 is a vibration when coasting down in any gear. If depress clutch, the vibration goes away. Problem #2 is shudder on braking which seems to come from rear which may be rear rotors, or could it be related to #1?

Answer
Hi,

Vibration is very common in the transaxle cars.  I have an 84 and an 83 GTV6 and they both feel completely different.

My guess is that you have worn mounts on the transaxle.  Most probably the rear mount but it's usually best to change all three.  When you depress the clutch on decel, you take the load off the transaxle from the engine and the vibration goes away.  You get the same type of torsional loading when you brake so it vibrates then also.  There is very little loading at cruise, so it runs smooth.
Replacement of the two front mounts can be done without special tools, but without the proper puller, the rear one is a real pain.

Other common causes of driveline vibration in these cars can come from the driveshaft donuts or "Giubos".  These are rubber universal joints and over time they crack and split.  That's not your problem in this case, because it would vibrate based solely on engine RPM, since the drive shaft turns at engine RPM all the time.  Those donuts usually weaken from age and pop at very high RPM from centrifugal force.  You will know it when it happens.  Usually, only one section pops out and you can keep revs down and drive as far as needed until you can replace it.

You can look at your rear rotors, but I doubt if they are causing this problem.

Good luck,  if I can help you further, let me know.

daveM