• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Vibration at 35mph - cause, thoughts, HELP?

Share this page

lbc_newbie

lbc_newbie

Jedi Warrior
Offline
My car is experiencing a vibration at 35mph or so. It worsens if you try to go any faster. The mechanic's thoughts on this are that the drive shaft is at a severe angle causing the u-joints to bind. I have a 78 Midget with a 1275 and Datsun transmission. We recently installed the rebuilt motor (it was pulled and installed with the tranny). Has anyone experienced anything like this? Could there be an alignment issue with the way it was re-installed? The suggestions are to look for a lower transmission rear mount and install wedges at the axle. I found the 2 degree wedges at Summit and I'm wondering if I need 2 or 4 degrees. Do I need to pull the engine and trans to install a lowered rear mount? The other thing he noted was that the yoke is bottomed out on the rear of the transmission leaving me no play for the suspension. Potentially causing bearing wear. My first course of action will be to take the drive-shaft to the shop for evaluation and shortening. Thoughts on how much I should shorten it? The U-joints are an unknown. They flop around loosely when the drive shaft is out of the car. Not sure if they are supposed to be firm. There is no lateral slop in them. This is never-ending. All I want to do is drive my freakin' car.
 
When did the vibration start? Has it always been there since you installed the Datsun transmission or was it smooth originally and then started vibrating after driving for awhile?

I doubt the drive shaft angle would be a problem in these cars are the amount of suspension travel is small. Possible, but seems unlikely to me.
 
Other questions: Does the vibration stop if you push in the clutch above 35mph? If so, the vibration is engine/transmission related. If the vibration continues, it's speed related: i.e. wheels, rear end, drive shaft. Another test is to drive to a speed so it vibrates and then shift into neutral. Does the vibration stop of continue?
 
What type clutch did you use? Is this a Rivergate conversion using the stock 1275 clutch cover or a Morriservice using the Datsun clutch?
 
The flywheel must have been drilled/tapped and pinned to mount the Datsun pressure plate. If this was not aligned properly, you will have an engine vibration. That's why I suggest you do a couple tests to isolate the cause of the vibration. Are the mechanics that suggested drive shaft angle fixes aware that you've installed the Datsun gearbox?

I'm in process if installing a Datsun gearbox using the Datsun pressure plate. I've been wondering about having the flywheel/pressure plate balanced before putting it together.
 
I would suspect driveshaft imbalance. I have found spridget driveshafts to be fairly fussy. I have a pile of them and only 1 or 2 that are good. Had a good one till I went to fit new U joints and forgot to mark the flanges, Its now in the bad pile.
KA.
 
lbc_newbie said:
The other thing he noted was that the yoke is bottomed out on the rear of the transmission leaving me no play for the suspension. Potentially causing bearing wear. My first course of action will be to take the drive-shaft to the shop for evaluation and shortening. Thoughts on how much I should shorten it? The U-joints are an unknown. They flop around loosely when the drive shaft is out of the car. Not sure if they are supposed to be firm. There is no lateral slop in them.
Click to expand...

Your driveshaft is too long - I missed this when 1st reading your massage. Have it shortened and balanced by a driveshaft specialist company. I had a driveshaft altered and balanced when I raised by Jeep, it was expensive, but absolutely necessary. It the driveshaft length is your only problem, you should be able to feel it hitting the transmisison when going over a bump. I'd also install new U-joints just because they are cheap.
 
I'm with Colin. Do the shaft first to see where'yat. You gotta do it anyway. I wouldn't think angle is a big deal, unless the 1500 engine mount points are substancialy different then the A series points. What did you use for engine mounts? Had to have custom stuff fabbed up? Does the tranny mount cock everything over to one side? That's the only thing I can think of for angle.

A new custom shaft cost about $300 here, including new joints.

Get to 45 MPH, put in neutral and kill the motor; coast down and see what happens.
 
There is a driveline shop in Totem Lake, west of 405, south of 116th, before Tacoma Screw.

When I ran my shop, I got it all done there.
 
kellysguy said:
Where'yat on this? Any progress?
Click to expand...

I took this to Drive-shafts Northwest, a reputable company up here in the NW. They did not have anything even close to the front U-joint. It's a Datsun yoke with the MG rear flange. Speaking of the flange, they determined it was shot, so I'm in need of one. I have a line on one from a friend here in town, so I'll pick it up and take it in. They also mentioned the rear U-joint is bad. So, most likely the cause of the vibration. The front U-joint is OK, so no worries on that.......yet. Thanks for all the help on this, much appreciated.
 
Can't they make you a custom shaft with all new juice?
(full Datsun up front and MG out back)

Sure, it's alittle $$$, but it'll be a done deal and alott easier to deal w/ down the road......if you drive it that much.
 
Awesome, sounds like you are getting closer now!
 
Back
Top