Hi all,

I've recently gotten my 914 running under battery power! 200 miles on it so far, up to 70 MPH without topping out. I've got several electrical issues on the low voltage side, but my biggest issue is vibration from the transmission. With the little electric motor instead of the larger gasoline motor, vibrations in the transmission at about 3,700 rpm tries to shake the car apart. Given how quiet the car is at lower speeds, I really want to fix this problem.

I am looking for a shop around LA that can do the following:

Minimum:
- Rebuild the transmission/differential to make it quieter (the gears whine loudly, especially when down shifting)
- Try to balance the parts to minimize vibration
- Grind the teeth off the flywheel (no starter)
- Balance the flywheel (attached to the electric motor)

Goal:
- Drop the gear ratios*
- Dynamically balance the motor/flywheel

Any advice?

Thanks.

* At 70 mph I was still in 3rd gear so I don't need the upper gears much, but it is hard to start quickly on steep hills with the weight of the batteries (~1,000 lbs of lead). If I drop all the gears such that the current ratio in 3rd becomes fifth and then drop the others accordingly, I can drive it as a 5 speed and have much better torque on steep hills.

If you have vibration problems that are so bad it feels like it "tries to shake the car apart" I would probably look other places than bad balance of the transmission. The very small diameters of the shafts and their rotating masses makes this unlikely especially cropping out of the blue. More common would be some misalignment of the new electric motor to the transmission due to a off center adaptor plate or an unbalance condition of the flywheel/pressure plate which have much higher rotating masses. Now if you simply need a trans rebuid, why not greyhound it to Dr Evil to let him work his majik?
For balancing the motor flywheel I would bet any electric motor rewind shop could do this for you.

AS far as a vibration goes, check your CV joints. Worn and failing CV joints can give you this type of vibration.

Steve

The Electrical motor is balanced when manufactured...if it was not it would explode on the first use.

You do have a different power equation at this point...you are capable of producing full power in a split second and this full torque can and will beat up all the stuff mentioned above.

For a vibration look at the wheels, tires, alignment, motor and tranny mounts, and CV joints first.

If all of those subsystems are fine start looking at the transmission, flywheel, clutch and mounting adapter.

Finally the transmission will break with a full load of torque applied from an electric motor...its the weak spot in mid engined cars.

If and when you pull the gear stack out, take a look at the intermediate bearing for the two shafts...these bearings, and especially the pinion shaft bearing are well known to die..they break apart.

If you are curious, pull the drain plug and dump the gear oil into a clean tub and sift through it for brass pieces...you wont find them with a magnet..if you run the gear oil through two layers of window screen you should find the larger pieces..
If you see brass, its time for a rebuild.

Rich

I wasn't implying the electric motor was unbalanced as it was, but may be after the addition of the flywheel and clutch. This may be a moot point as some electrics don't use flywheels/clutches.

To do some home diagnosis he could first run the motor flywheel up to speed uncoupled from the trans and see if it vibrates. Also could run up to speed the motor/flywheel and trans with the CVs disconnected to see if the issue lies there.

Check with T H O M A S herein.

I am intrigued with this issue..

Think about all the vibration and noise that you eliminate by removing the IC motor...so now there are a whole new set of issues that may have been there before but you can finally hear them and feel them...

I wonder if certain sub systems are left at a spec that is just tolerable...

Rich

Your problem sounds very interesting,, I have a couple of ??s for you. My guess is a badly balanced tire.

Did you ever run the car with gas when you first got it? Was the problem present then? I've seen badly balanced tires shake the heck out of a car at certain speeds.

Can you put the drive wheels up with jack stands and try 3700 rpm again with tires off. This would definately eliminate the wheels as a potential problem.

Where in LA are you? I'd love to see your car and shoot some BS.

-Rob

Thanks for the comments everyone. I'll try to answer a few questions:

1) Yes, I am using the stock 5-speed with the stock clutch. The flywheel is bolted to the electric motor.

2) With the clutch pedal in, I can spin the motor up to above 6,000 rpms without much vibration. Above 6k, it starts to shake a little (which is why I want to better balance the flywheel)

3) I do not think the vibration is in the wheels or the axles because it is dependent on the speed of the motor, not the speed of the car. If it is vibrating hard at 3,500 rpm in 1st, shifting to second makes the car silent. No change in tire/axle speed.

4) Because I use the upper half of the engine compartment for batteries, the motor is wedged into a very small space. I do not have room for the motor mounts. My electric motor is hard mounted to the stock engine bar. I replaced the transmission mounts with new ones - the old ones were badly cracked.

5) I suspect that some part of the transmission is shot. When I slow down using the motor as a brake, there is an awful whine from the back-end of the car. For a car that is silent most of the time, it is embarrassing to have pedestrians looking for the problem from half a block away.

6) I'll drain the transmission fluid and look for brass. Good idea.

7) Yes, I bought the car to convert. The engine was struggling, but I drove it about 1,000 miles to make sure that the rest of the mechanicals were strong enough to justify the time and money I was going to spend on it. Shifting was sloppy, but it looked to be just bad (or missing!) bushings. I now think it was more than that.

8) At least two other electric 914's are having trouble with vibrations in the transmission. Check this blog for details of the best documented one:

http://914ev.blogspot.com/

Here is the post where he first replaced his transmission with a rebuilt one and the vibrations stopped:

http://914ev.blogspot.com/2008/01/yay-less-vibration.html

The picture there shows you what the motor looks like attached to the transmission.

9) Pictures? Yeah, I am in trouble with friends, family and coworkers for not posting any. I would rather be working on it than documenting it. Once I get the last bugs worked out and clean up some of the hacked 12V wiring, I have promised to post a video tour of the car. I'll post that here when I do.

I do have a short page on the "EV album" that describes some of what I've done to the car:

http://www.evalbum.com/1241

The picture is the one the previous owner took to sell the car.

Thanks again

Thanks for the comments everyone. I'll try to answer a few questions:

1) Yes, I am using the stock 5-speed with the stock clutch. The flywheel is bolted to the electric motor.

2) With the clutch pedal in, I can spin the motor up to above 6,000 rpms without much vibration. Above 6k, it starts to shake a little (which is why I want to better balance the flywheel)

3) I do not think the vibration is in the wheels or the axles because it is dependent on the speed of the motor, not the speed of the car. If it is vibrating hard at 3,500 rpm in 1st, shifting to second makes the car silent. No change in tire/axle speed.

4) Because I use the upper half of the engine compartment for batteries, the motor is wedged into a very small space. I do not have room for the motor mounts. My electric motor is hard mounted to the stock engine bar. I replaced the transmission mounts with new ones - the old ones were badly cracked.

5) I suspect that some part of the transmission is shot. When I slow down using the motor as a brake, there is an awful whine from the back-end of the car. For a car that is silent most of the time, it is embarrassing to have pedestrians looking for the problem from half a block away.

6) I'll drain the transmission fluid and look for brass. Good idea.

7) Yes, I bought the car to convert. The engine was struggling, but I drove it about 1,000 miles to make sure that the rest of the mechanicals were strong enough to justify the time and money I was going to spend on it. Shifting was sloppy, but it looked to be just bad (or missing!) bushings. I now think it was more than that.

8) At least two other electric 914's are having trouble with vibrations in the transmission. Check this blog for details of the best documented one:

http://914ev.blogspot.com/

Here is the post where he first replaced his transmission with a rebuilt one and the vibrations stopped:

http://914ev.blogspot.com/2008/01/yay-less-vibration.html

The picture there shows you what the motor looks like attached to the transmission.

9) Pictures? Yeah, I am in trouble with friends, family and coworkers for not posting any. I would rather be working on it than documenting it. Once I get the last bugs worked out and clean up some of the hacked 12V wiring, I have promised to post a video tour of the car. I'll post that here when I do.

I do have a short page on the "EV album" that describes some of what I've done to the car:

http://www.evalbum.com/1241

The picture is the one the previous owner took to sell the car.

Thanks again

If you need a rebuild John Williams at Otto's in Venice Beach has done 2 901s and 1 915 trans--for 3 different cars I have had. They have all worked very well. He is the man and can get it done correctly and quickly. He has lots of racing experience and can advise on gearing too.