Rear End Shimmy

[healeynut]

CHA CHA CHA! No, I'm not talking about Christina Aguilera!


I have a very mysterious rear end shimmy at all speeds, whether in gear or out of gear (so I don't think it's a bad U joint or anything like that).

When going slow it feels like one of my rear wheels is out of round. It is somewhat severe and getting worse... to the point the car shakes quite a bit at speeds over 40mph. I can feel the shimmy in the seat of the car even doing 10-15 mph.

I have checked for oil leaks around the rear hubs (there are none) but I don't expect any because I had just tightened the spline lugs on both sides just about a month ago. No oil is leaking, so I know the lugs are tight.

I have a BJ8 with Cape's rear disc brake conversion kit, so it can't be drums out of round. I've looked at the discs closely and they don't seems to have any scoring so it doesn't appear that the hub is loose, but it is hard for me to confirm.

There is no noise or whining of any sort, so I don't think the rear hub bearing is bad.

The only thing that I can think of is the hub's octagon fixing-nut has come loose somehow and the rear hub bearing is now sitting in a slightly offset position.

Any other thoughts before I start ripping the rear end all apart?

 

[Randy Forbes]

I'd swap the wheels front for rear to eliminate them as a source, them resume the diagnostic process, as required.

 

[Dave Richards]

See "Weebles Wooble" post this forum June 11, same subject, exact same problem, excellent replies.

 

[Johnny]

Hello Alan, on the first drive after restoration I had a similar "shake" at the rear. Discovered I failed to tighten the "U" bolts on the rear springs. Might check both sides and the shackles as well. Double check shocks also.

 

[BobHorvath]

U joints spin in and out of gear. My hub extension nuts were super tight and the extension was still moving on the hub. I detected it by applying the ebrake while the rears were off the ground. Rotated the wheel, clunk, clunk. Replaced the nuts and the clunk went away. My symtom was a hop and it too went away. I checked the run out on the tires before and after no change.

 

[Johnny]

U joints spin in and out of gear. My hub extension nuts were super tight and the extension was still moving on the hub. I detected it by applying the ebrake while the rears were off the ground. Rotated the wheel, clunk, clunk. Replaced the nuts and the clunk went away. My symtom was a hop and it too went away. I checked the run out on the tires before and after no change.

Sorry Bob, I don't follow you here. Could you elaborate a littly more?

 

[BobHorvath]

I wanted to point out that if the u joints are the cause it would manifest in or out of gear. The spline nuts as you referenced, if not seated properly can cause an out of round condition. If you jack the car up, apply the e-brake and attempt to spin the braked wheel and hear a clunk you might have the same condition I had

 

[jmepmn]

HealeyNut,
Several years ago, the front pinion bearing on my 100 started to wear severly, even ate a shim or two.
The car would do exactly what you describe but only under deceleration.
Don't know if that helps, but you can tell by grabbing the pinion flange where it attaches to the rear u-joint and see if you can move it side to side or up and down. Should be no more than 1/16th" movement.
Good luck

 

[healeynut]

mine is more constant... i get it all the time, decelleration, acceleration, coasting... the car is osscillating when under power between 1500 rpms and 2000 rpms... so ?? will have to get into it... thanks all for the great ideas.

 

[Keoke]

Switch the wheels like Randy suggested .---Keoke

 

[healeynut]

Hi All -

I thought you'd like to know that I focused on the right rear wheel because that's where it felt like the shimmy was coming from.

Jacked up the right rear wheel and spun it... saw it immediately... the belts in the tire have started to separate inside the tire... can't see anything except the tire is warped!

That's what I get for driving on 15 year old tires. Time for new shoes for the BJ8!!!

 

[Dave Russell]

Hi All -
That's what I get for driving on 15 year old tires. Time for new shoes for the BJ8!!!

Actually, way past time!!
D