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Discussion Starter · #1 ·
I just recently got my GTV6 back from DV mechanics. He rebuilt the engine and serviced the driveshaft with all new guibos. I've been doing some electrical clean up recently (just redoing a lot of questionable **** the PO did) and got the stock exhaust system reinstalled.

Today was the first day I was able to take it out on a little errand and I noticed that every time it hit 4k rpm or higher there was a semi-violent rattle coming from the driveline. Enough that I could feel it in my right arm.

Any ideas on what this could be?
(I'm hyper paranoid that it skipped a tooth for some reason.)
 

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1977 Alfetta GTV 2.0
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Maybe the guibos are not aligned properly?
 

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Discussion Starter · #3 ·
Maybe the guibos are not aligned properly?
I would be V upset if that were the cause.

I suppose the exhaust could be hitting the driveshaft now that it's there, but I think I would've noticed that on the drive home from the exhaust shop.
 

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Well they are hard to line up right? But I suppose a shop specializing in them should do it right
 

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Take it back.
 

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Check your left and right transaxle mounts. I wrote a long post about this very problem some months ago. The current transaxle mount are NOT made for Alfettas or GTV-6s, they are made for Milanos and have an extra 3mm thick doubler plate welded to the bottom of the mount. I had an annoying driveline vibration for years even though I had replaced all of the mounts for the engine and transaxle and the flexatalic joints in the driveshaft. It got so bad that we wouldn't drive the car long distances... Anyway, dumb luck lead me to a long since closed GTV-6 website that talked about driveline vibration issues. I check my mounts and sure enough they had the doubler plates. I cheated to go on an event by shimming the entire transaxle crossmember down using 1/8" thick washers (1/8" = 0.125" * 3mm = 0.118") but when I got home I removed the mounts and cut off the doubler plates and put everything back together.

The books and web-site say the transaxle mount are for all transaxle Alfas but they are WRONG. I checked an old GTV-6 and several Alfettas I have and none of them had the doubler plates. I couldn't believe 3mm of deflection would cause that much vibration but it did. Once I lined everything up correctly the driveline is as smooth as glass at any RPM.
 

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I just recently got my GTV6 back from DV mechanics. He rebuilt the engine and serviced the driveshaft with all new guibos. I've been doing some electrical clean up recently (just redoing a lot of questionable **** the PO did) and got the stock exhaust system reinstalled.

Today was the first day I was able to take it out on a little errand and I noticed that every time it hit 4k rpm or higher there was a semi-violent rattle coming from the driveline. Enough that I could feel it in my right arm.

Any ideas on what this could be?
(I'm hyper paranoid that it skipped a tooth for some reason.)
I had this problem years ago on a GTV6 right after a guibo service. The shifter rattled around 4,000 rpm. It was the center driveshaft support bearing going bad.
 

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Discussion Starter · #9 ·
Check your left and right transaxle mounts. I wrote a long post about this very problem some months ago. The current transaxle mount are NOT made for Alfettas or GTV-6s, they are made for Milanos and have an extra 3mm thick doubler plate welded to the bottom of the mount. I had an annoying driveline vibration for years even though I had replaced all of the mounts for the engine and transaxle and the flexatalic joints in the driveshaft. It got so bad that we wouldn't drive the car long distances... Anyway, dumb luck lead me to a long since closed GTV-6 website that talked about driveline vibration issues. I check my mounts and sure enough they had the doubler plates. I cheated to go on an event by shimming the entire transaxle crossmember down using 1/8" thick washers (1/8" = 0.125" * 3mm = 0.118") but when I got home I removed the mounts and cut off the doubler plates and put everything back together.

The books and web-site say the transaxle mount are for all transaxle Alfas but they are WRONG. I checked an old GTV-6 and several Alfettas I have and none of them had the doubler plates. I couldn't believe 3mm of deflection would cause that much vibration but it did. Once I lined everything up correctly the driveline is as smooth as glass at any RPM.
This is good info! Even if it ends up not being the case it's good to know for checking any parts I order in the future.
 

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I suspect that the propshaft centering bearings are not seated properly, worn out, or damaged. There are little spherical bearings at center and rear Giubo. The front uses a spherical bearing with barrel nose at flywheel/crank. The middle and rear are particularly difficult to seat and it is easy to knock the outer race off during Giubo replacement especially with the newer Giubos which seem to fit a little too tight on the outer race of these bearings. I've had to use a brake hone to open up the hole to allow proper fitment. The Giubo will retain shape well enough at lower RPM to be tolerable, but without proper centering the propshaft can shake violently at higher RPMs. I've dealt with this issue many times and the shaking begins abruptly and becomes violent shortly thereafter. Hopefully you can catch it early enough before damaging the propshaft. The cars that I've dealt with this issue on required replacement of the propshaft as they were badly damaged at the bearing location and were not economically repairable. Also, expect that the Giubo (especially the rear with its 3 ear rigid structure inside) may require replacement if the trauma was significant enough.

A cracked or broken clutch housing could cause similar issue.

If it is mostly RPM related and not load related...I'd check these areas out. It will require removal of the propshaft.
 

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Discussion Starter · #12 ·
I suspect that the propshaft centering bearings are not seated properly, worn out, or damaged. There are little spherical bearings at center and rear Giubo. The front uses a spherical bearing with barrel nose at flywheel/crank. The middle and rear are particularly difficult to seat and it is easy to knock the outer race off during Giubo replacement especially with the newer Giubos which seem to fit a little too tight on the outer race of these bearings. I've had to use a brake hone to open up the hole to allow proper fitment. The Giubo will retain shape well enough at lower RPM to be tolerable, but without proper centering the propshaft can shake violently at higher RPMs. I've dealt with this issue many times and the shaking begins abruptly and becomes violent shortly thereafter. Hopefully you can catch it early enough before damaging the propshaft. The cars that I've dealt with this issue on required replacement of the propshaft as they were badly damaged at the bearing location and were not economically repairable. Also, expect that the Giubo (especially the rear with its 3 ear rigid structure inside) may require replacement if the trauma was significant enough.

A cracked or broken clutch housing could cause similar issue.

If it is mostly RPM related and not load related...I'd check these areas out. It will require removal of the propshaft.
Oh goodie!

I talked with Dorian just to confirm that everything in the driveline was new, which should mean the centering bearing as well. I want to confirm that it's not the exhaust system interfering with the driveshaft, before I bring it back to him.

Any suggestion on how to do that without having to stick my face near the rotating shaft while the car's on jackstands?
 

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Put a (video) camera underneath the car and then turn the car on. Film until it makes the noise, shut the car off, pull out the camera and watch the video.
 

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Joe,

Let me clarify. I'm talking specifically about the centering devices which are at each joint location; each of these devices is a spherical bearing is less than an inch in diameter. There is also a center support support with carrier bearing; this sealed radial ball bearing is closer to 2 inches in diameter. Most propshaft services replace the 3 Giubos, center support, and carrier bearing. The centering devices are typically not serviced as they should basically last forever if properly installed.

This thread has outstanding information and photos: http://www.alfaclubvic.org.au/forum/index.php?topic=7349.255

My opinion: the car needs to be elevated or lifted anyway to inspect a number of things to troubleshoot this condition and make corrections, I suggest just going straight to get it evaluated.

Photo below shows the centering device, credit from other thread linked.

Automotive tire Rim Gas Auto part Automotive wheel system
 

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Stealing another photo from the highly detailed thread that Rob posted, look how close the gearshift rod is to the driveshaft. When I had a similar issue many years ago, the vibration was caused by an imbalance in the driveshaft that caused the gearshift rod to resonate loudly around 4,000 RPM. One way to tell is to hold your hand on the shifter while going through the RPM band when the noise appears. It sounded like the the car was going to fall apart, but was caused by the driveshaft flexing enough to nick the gearshift rod at certain revolutions. If you can feel the shifter start vibrating when the noise starts, you found the source of the noise. In my case, it was a worn center donut, but anything along the drivetrain could cause the problem.

 

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Discussion Starter · #16 ·
This is great info!

Rob, that thread is a massive help thank you!

I think I started to feel the vibration in the shifter before I heard it. It feels and sounds worse under load, but you can still sense it when the car's stationary, in neutral, and revving.
 
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