6 Cyl Center Donut

[Warp]

My '84 GTV6 has been acting strange. Wobbling shifter, grinding noise on touching
shifter in first. I replaced the front transaxle mounts but no improvment. Pulled the exhaust and found half the rubber connection in the rear engine mount was bad. Pulled the driveshaft since I decided to get the bellhousing out to change the engine mount and I found the center donut I replaced barely 1000 mi ago was trash. It was so bad the bolts
were hitting the driveshaft yoke and both yoke and bolts were getting eaten up. What surprised me most was that the donut seemed to not be solid rubber, but have layers of fabric or canvas inbetween rubber layers. Is this the right center donut for the GTV6, or
did deteriorating rear engine mount cause the center donut to die a very early death?
TIA!

[116_Veloce]

I've had the same problem with a donut but after many many years on the car. Even then it didn't show the symptoms you refer to, it was just worn.

Fabric? Peeling layers? Unheard of, I really don't know where you got that donut! Even if there are oil leaks and dirt it should never come to this.

Get another one. Very strange story.

[Warp]

I attached a pic of the destroyed donut. Interesting to see the construction I think.

[116_Veloce]

I've never seen a donut made like this so I'm not sure it's OE. I don't know too much about the V6s but I'm used to see donuts in solid rubber.

Very strange part. Try calling Alfa Parts in CA 510-5259435, and ask them about this flex joint.

Is the drive shaft support and bearing OK?

[Warp]

The support and center bearing are good. After consulting with several people
I've about decided that I didn't have the centering bearing inserted into the end
of the front shaft. From now on I think I'll be assembling the center donut with
both halves out so I can see the parts better.

[ossodiseppia]

WOW! That is the first time I've seen one like that. That's definately not designed to take a lot of torque. I think you are lucky that the centering bearing didn't get destroyed. Looks like a tractor part

[Little Italian]

Nope. You would have never gotten the rear doneut into it's race on the transmission unless the ball race on the center donut together. I took a drive shaft out just yesterday and saw the same cloth interior. Part of the vulcanization process - just like nylon tires. I looked closely at a original center donut I have been keeping on the parts shelves to compare the construction. The old OME part was just starting to show fabric. The problem is balancing.
All the GTV-6 & Mialno propeller shafts are dynamically balanced. Pretty hard to find someone to do this. There is a lot of stuff on the GTV-6.org site about this.

Best to get all new driveline parts and get the assembly balanced as a unit.
I'm thinking of building a Balancing rig using a large piece of channel or I -beam, four pillow blocks, a multi-shieve pulley and electric motor, all bolted to the Channel. Then build a support to hold the center bearing out of angle iron with all-thread support -welded to the center of the channel at the right point. Use a chalk to mark the rotating assembly - marking the high spots. Weld pieces of sheet metal to the opposite side, trimming as necessary to get
conter balance. By changing the belt to smaller shieves, I can make adjustments at different speeds.

I read somewhere on the net , one ounce of out-of-balance is equivalent to rotating a sixteen pound bowling ball on a rope one foot long at some rpms(?).

With a 1800 rmp electric motor and a 2:1 pulley, I can check at 3600rpm, 3:1 pulley 5400 rpm, and 1:2 900 rpm. Threespeeds should do it. Ofcourse precautions for safety need to be taken - some heavy strap guards.

Then one could also get a magnetic sensor (coi) lattached near to the rig and monitor the voltage change caused by the induction to find the essectric points.

Sounds like a Service to be offered to Alfisti. What do you think guys?

[Warp]

[quote=Little Italian]Nope. You would have never gotten the rear doneut into it's race on the transmission unless the ball race on the center donut together. I took a drive shaft out just yesterday and saw the same cloth interior. Part of the vulcanization process - just like nylon tires. I looked closely at a original center donut I have been keeping on the parts shelves to compare the construction. The old OME part was just starting to show fabric. The problem is balancing.
All the GTV-6 & Mialno propeller shafts are dynamically balanced. Pretty hard to find someone to do this. There is a lot of stuff on the GTV-6.org site about this.

I've replaced the offending part and the other two donuts since I last wrote here. I came to the same conclusion about the bearing but was at a loss as to what caused the destruction other than a defective part. I had spent some time balancing with an extra nut and two screw clamps and thought it seemed acceptible. When I went to dissasemble the axle I commited the untimate (?) sin. I forgot to mark the driveshaft halves! I had put different colored tape on
all the bolts/ nuts up to then but it was late at night and OPPS! Things turned out for the better though. I looked and looked at both parts of the driveshaft for some previous markings. It seemed any I had put there before were gone but I noticed numbers stamped
lengthwise on the tapered back end of the front half and a large dimple in the weld bead for the tapered part on the front end of the back half. With no other marks I lined these up and
believe it or not, the balance is perfect. I still have a mysterious rattle from somewhere though. I told myself it was the passenger seat but holding the seat back still doesn't help.
Any ideas what this could be?

[Greg Gordon]

The rattle can be caused by a loose pinch bolt. It has to be really tight!

[Alfisto Steve]

That donut is the 60522066 thin version used in some GTV6/Milano set ups. I have two new ones of that type if you need a new one. The wide one is 60521649.

Also are you sure you have the 60521636 spherical bearing in center shaft? It is same size/part number as one that goes on rear into transaxle yoke. It goes on the ball end of shaft and is what aligns two shafts so it will run true. I don't have anymore of these left but www.difatta.com may have.

[mtnbkgtv6]

Alfisto Steve, I need new donuts for my '82 GTV-6. You have a couple? I would be interested.

Thanks,
Aaron

[Alfisto Steve]

Aaron,

I have new set of front, mid and rear donuts plus grease seals and believe I have new center support bearing (not spherical mentioned above), thin locks nuts, etc. I should have wide and narrow center donuts too. I have to hold inventory and get back to you on exactly what I have left. Since I have sold my GTV6's and Milano I have some stuff I can move out of my spare parts for these types.

Later,

[Warp]

Quote:

Originally Posted by Greg Gordon The rattle can be caused by a loose pinch bolt. It has to be really tight!