Driveline vibration at 60+ mph

[supercub]

I've been experiencing a vibration at highway speeds in my '66 for a while now. Stock '65 40hp engine and stock transaxle. Engine runs smooth with no misfiring. Seems to be driveline related. The vibration starts in at around 60mph. If I shift to neutral and let the rpms drop it smooths out, which should eliminate wheel or brake drum balance issues. I thought maybe the pressure plate was out of balance since I did replace the disc and pressure plate about 1500 miles ago. It had this vibration with the old clutch too though. If I leave the car in neutral at 60mph and rev the engine there is no vibration. To me this would seem to rule out the engine/clutch. Match rpms and let out the clutch again at 60 and the vibration returns. I'm beginning to think that the front trans mount may be suspect. It's still the same mount I put in 15 years and 110k ago. I replaced the rear mounts a couple years ago but didn't do the front. When I shift into 2nd and 4th gear, the shifter jumps forward a bit when I let out the clutch, so the front mount is probably on the way out. Would a worn front trans mount cause such a vibration? Something else?

[zerotofifty]

A wobbling shifter is a symptom of the nose cone rubber mount failing.

Grab the tail pipes (make sure they is cold) and lift them up and down. If you see excessive movement of them relative to the body or bumper, that is another sign that the nose cone rubber mount is shot (assuming the tail pipes are not loose to the muffler)

There should be nearly zero up and down movement between the pipes and the body if the rubber mounts is good, If you see movement, well that is an issue

Note that there are two stud sizes used for the mounts to the tranny tail cone, 8 mm and 10 mm If I recall correctly. Early trannies used the smaller. But note, that sometimes over the decades, folks have drilled out the tail cone from the small size to the larger size, in which case you MUST use the larger stud rubber mount. do NOT use undersized studs in the larger holes, else you will be doing the job again, maybe even having to replace the tranny tail cone!!!
So before ordering a new nose cone rubber mount, get under the car and ascertain what diameter studs you have, or better still remove the retaining nuts and observe that the stud is a tight fit in the tail cone, just in case some one installed a small stud rubber mount in a large holed tail cone


If you install a small stud mount in a big holed tail cone, the studs will move and oval out the soft magnesium tail cone holes.

So measure your tail cone hole size before ordering a new rubber mount, get the correct mount!!!!

You need to pull the engine to do this job, remove the tranny cross bar from the two chassis horns but you can usually keep the tranny in the car if you use jacks to push the tranny via the axle tubes backwards to give clearance to remove and install the rubber mount. after you have pulled the motor and the tranny crossbar (the cross bar is what the two rear rubber mounts be bolted to.) The factory books tell us to remove the axles tubes from the torsion plates, which means wheels and brake drums all need to be opened up, a lot more work.
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Sorry About That Chief.

Give Peace a Chance.

Words to live by.

[Eric&Barb]

With the engine out would be good to see an image of the flywheel and pressure plate in situ. Each should have lightening/balancing drill holes, but balancing was not done down to a gnats arse equivalent. So if you have the heavy sides of both parts lined up it can be felt, especially at highway speeds.
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[zerotofifty]

PS If the mount is on its way out, get on it soon and fix, cause when the mount finally totally tears, the Bug will be near undrivable. This cause the motor / tranny will pivot on the bell house mounts, the motor going up and down with acceleration or slowing, and when the motor moves, it moves relative to the throttle cable, so you end up with the engine surging, then going to idle causing the car to buck like a bronco, making driving "interesting" Give it a little gas and she will surge in rpm.
Happened a while ago to a friend of mine, as a temporary fix until he could get the new mount we did this to make it drivable...

the board (a 2x2) was wedged between the bumper and tail pipes, this pushed the tail pipes down about as far as they can go, the nose cone lifted up, this prevented the engine from rocking while driving, the tape around the bumper and wood helped hold the assembly in place. He ran like this for a week or so, the throttle cable had to be adjusted to compensate for the engine down configuration, but at least it was held in place with out the motor shifting up and down as he drove.

So when that mount totally tears away, you will need to rig something up to hold the engine in place until the mount is replaced.
_________________
Sorry About That Chief.

Give Peace a Chance.

Words to live by.

[supercub]

[supercub]