Hello all...I recently posted about a vibration I'm having at 30 and 60mph.
I have some new information to share and some more questions.
I purchased the hub centering rings from Chris Foley and they made no difference.
Today I took the car to my mechanic's shop and we put it on a hoist and I ran it up to 70mph. The shake/vibration was still there!! So, it's obviously NOT in the front end. Mechanice says he's pretty sure the shaking stopped when I put the trans in neutral and turned off the engine. Although that could be a function of the speed reducing also.
So, where to look now? Flywheel? CV joints/axles?
Car is a 74 2.0 liter.

Thanks as always...
Mike

Probably not the first place to look, but many people converting 914s to electric power have reported vibration which turn out to be caused by aging transmissions. Rebuilds I think have generally solved the problem.

Any large mass which is rotating at high rpms can be the culprit. Can you eliminate some components from consideration? What if you rev in neutral to the rpms you'd run at 30mph and 60mph? What about with the clutch pedal depressed?

Just thinking out loud...

S

Good thoughts...NO vibration when revving in the garage. Must be something in the trans or CV joints and shafts....
Mike

Add to that: Flywheel and clutch, motor mounts, cooling fan etc.

How about shifting into neutral at the vibration speeds, that will elimnate a few more possiblities, just coast down with the engine at idle speed.

Yup...clutch and flywheel are on the "suspect" list.
Motor mounts look new. Cooling fan unbalanced? Would that shake the whole car?
Mike

Jack it up with one rear wheel on the ground and the other above the ground. Doesn't matter which one. Put it in gear. The wheel above the ground should turn and the one on the ground should remain motionless. I say should because if it was modified then both could turn but check carefully in first gear. As long as it is still in first gear and the wheel is turning slowly, you can check the tire/wheel combo for out of round. I place a 2x4 next to the tire for a visual reference. Don't place it in front of the tire or it could get pulled under and fired out the rear. Then run your speed test at 30 & 60. If we get a vibration from one side and not the other, I'm looking at CV's and/or their shafts. If there is no difference start working your way thru the tranny. BTW, you have had a 4 wheel alignment by someone that knows these cars, right?

How can you tell? They are a bitch to get to with the motor in the car.

Tranny mounts?

Sir Andy....to be honest, I'm not sure. I was driving the car while it was on the lift and my mechanic was under it. He said the motor mounts looked new and the tranny mount was fine. That's all I have to go by...maybe the P.O. changed the mounts while chasing the same problem?
Mike

There are a few bearings inside the transmission that will continue to vibrate even if you are in neutral.
Not sure how to diagnose this without testing each system.

Mounts...motor and transmission
Fan, blades missing, mounted properly
Alternator (ditto)
Pull tranny...
Flywheel balannce along with Pressure plate
Pull gear stack...replace broken bearings.


You know, you may want to dump the tranny fluid into a very clean container and fish for brass....that is what breaks apart on the bearing cages.....
never know...
Rich

How about front wheel bearings? Make sure theyt aren't loose. Pull on tire top and bottom while jacked up of course and see if any play. How old are tires/ possible flat spot or warped rims?

If the clutch and or flywheel was imbalanced wouldn't this be more related to engine speed instead of vehicle speed. If the flywheel was not balanced very well then your motor would cause the vibrations at higher rpms. sounds like it would be either chassis or as previously stated here that your trans might be causing the issue. If in doubt check balance of tires and check your rear trailing arm mounts, and get the alignment checked in your driveway with some strings just so you know its within spec. Have you ever replaced the trailing arm bushings on your car?

his test on a lift eliminates both the front end bearings and the rear trailing arm bushings.

Agree, most likely not the flywheel...but all other rotating mass is suspect.

Rich

Thanks Rich...here's a related question...
Is it possble to get the drive shafts out without removing the heat exchangers?
How do you guys normally do this?
Mike

yes, you can pull the gear stack in the tranny with the motor in the car and only the muffler removed.

To remove the drive axles and CV joints,,,,remove the inner bolts, then remove the large outer nut and hit the axle with a hammer (put a piece of wood on the axle tip)
Could good smacks should gt it free.

Never set the car down on the bearing without the axle in place..it will ruin the bearing.

Rich

Sorry...I wasn't clear.
I was asking if it's possible to remove the Axle shafts without removing the heat exchangers. Is there enough room to get them out using your method?
Cheers
Mike

Yes ...

Thank you Sir...I think that will be my next chore.
Mike

I had a similar problem with my 914. It turned out to be the outer surface on the rear wheel hubs not being perfectly clean, this is where it meets the inner of the disc brake. The hub had been (badly) painted and the inner of the disc was not clean either.
After cleaning up the vibrations were gone.


/Lars S

I had a vibration in my car recently and the problem turned out to be the transaxle mounts. They looked fine but were sagging from age. This caused the bump stop to hit under certain conditions and it would tend to keep hitting from the rebound and you would feel a vibration in the seat of your pants and in the shifter. New mounts cured it completely.

You can see where the steel bump stop plates are worn and marked from hitting the rubber stops on the mount.

Click to view attachment

Thanks gents...obviously I have a few things to investigate.
Cheers,
Mike

I'll bump this in case anyone has any ideas....
Thanks,
Mike