Sudden drivetrain vibration - more info upd

Hi all,

A friend has a Gen II Hemi-powered 1970 Barracuda, with Keisler 5 speed transmission. This car has been on the road for several years now, with no issues. Yesterday, he ran it through the gears, up to 4000-5000 rpm, and a fairly severe vibration started happening. He hasn't done any driveline work on it recently, nor changed tires/wheels, or anything like that. He crawled underneath to look for anything obvious, found a slightly loose nut on one of the transmission crossmember bolts, and tightened it - with no change. I suggested he check for a missing drive-shaft weight, or wheel weight. Any other ideas on what could cause this to happen? Thanks for any suggestions.

Edit more info: he says it seems to be speed-related, not rpm related. It starts at about 85 mph, 4000 rpm in 3rd gear, gets worse as speed increases.

Roger

Bad U joint. Engine issues.

I'm with Stumpy bad u-joint.

Check for loose wheels. You never know. Beyond that possibly universal. Loose pinion nut on the center section? You said speed related. So also look for missing wheel weight.

I wouldn't think a u joint would suddenly go bad to the point of causing a severe vibration unless it lost a c-clip etc.
I would look more at the tires themselves (belt separating?), age or balance. hard to diagnose looking at a monitor
keep us posted

Thanks for the suggestions so far - I'll report back on whether we find anything.

Get the rear axle on jack stands and run it up to the speed he claims the worst vibration.
Try it in a low and a high gear to narrow the problem to rpm or speed related.

If it's speed. Remove wheels but leave drums on and bolted down.
Remove drums.

Keep in mind an out of round tire can shake a car but not vibrate.

I suppose he checked wheels to see if one has spot in which it's noticeable a wheel weight came off? Also kind of PITA but if he has a spare he could check one-by-one driving car with spare tire.

Just to add another angle to this (no pun intended).....i have the kiesler tko 600 in my 68 b body on the street, and my goid friend runs one in his 71 E body. In both cases, we each have viabration issues at higher speeds. His being much worse than mine. Mine starts at about 75 mph and higher. I chased this around and have all new parts. I have checked bith cars, and in each case, the transmission is installed almost touching the tunnel. We cannot get the rear of the transmission any higher and this causes the trans to driveshaft angle to be less than optimal. It is pointing downward quite a bit. This is also the case in his car. Pinion angle is off and this has been causing a viabration. In order to set the rear angle equal and opposite, the rear would have to be setup pointing up like 6 degrees. We both race around the streets and that is asking for trouble with yokes and ujoints for us. So, we just live with it. The kit could have been more thoroughly engineered with proper dr shaft angles in mind. My opinion.

Maybe this is the cause of viabration he has. Have him check his trans, driveshaft, rear angles.

Had a VERY similar issue w/ my cuda a couple years ago. It was a bad U joint.

If it seems "speed" related start looking at tires (physically swapping/rotating F to R, side to side to see if the vibration moves from F to R/side to side) to determine if a belt broke, or weights are missing, look at the U joints, replace if needed, wheel bearings/axle bearings, rotors, etc....

You need to shim the rear axle between the spring and the housing to get the correct driveshaft angle. Drive shaft angles depend on the alignment of the centerlines of the pinion shaft and the center line of the motor/trans. What that relationship may look like from under the car makes no difference. it sounds to me like the front of the motor is sitting too high, which is causing your vibration issues. If you can't raise the tail of the trans high enough to get the correct drive shaft angles, you have to rotate your rear axle to get the correct numbers. You will also have to modify any traction additives accordingly.

As it is now, you are getting the vibration because you are trying to bend the driveshaft every 1/2 revolution. When the driveshaft angles are correct, and the traction assistants are adjusted correctly for the "new" rear axle position, everything will play much better together. Gene

Several years ago, Hot Rod magazine[ before TEN canceled most of their paper magazines], they did a fix on I believe an E body with the Keisler m/t swap to stop the vibration. Along with some revamping of the mounting the main fix was a new drive shaft with I think a c/v joint up front. This was needed to get around all the messed up angle issues. Was good after that.

Am I reading this right? Your transmission to driveshaft angle is 6 degrees?

Hi all,

Thanks a lot for all the responses, and sorry for taking so long for this update. My friend finally got the car to a driveline shop to have everything checked out. The U-joints were fine, but both ends of the drive shaft were slightly out of balance. The shop straightened and re-balanced the shaft, and the situation has improved quite a bit. Now, in 3rd gear @ 5,500 rpm, under load at 100 mph, there is no more vibration. However, there is still a slight vibration in 4th gear @ 4,500 rpm, under load at 100 mph. His angle at the rear of the transmission is 4-5 degrees, so the shop thinks there may still be some binding at that joint.

Special thanks to CKessel for the reference to this Hot Rod article. My friend really likes the idea of a front CV joint, on an aluminum drive shaft. He will likely look into that.

Moparts to the rescue again!

Roger

Your problem is you, and your friend, needed to cut the tunnel to get the engine/trans at the factory installed angle. The first time I saw a kiesler trans swap the engine was leaning so bad that the fan was maybe a 1/2 in from the radiator at the bottom and 2 plus inches at the top ... that told me all I needed to know about their no cutting install claim.

A pinion should never point up and 6 deg is too much.