I am no expert, but I had a similar problem. It turned out that when I had my front drums balanced they weren't doing it while attached to my hubs. After repeated attempts to fix I had them balanced as one unit and it solved the problem. I am sure you have done all this but I just thought I would throw it out there. Good luck...I know what you are going through

 

I posted with a "shaky car at high speeds" post today, but have not nearly as much fixing as everyone spoke of here. Is there a type of mechanic one takes a car to that will solve this problem without all the trial and error? I'm not a mechanic, just a happy classic owner.

 

I'll bet you have a bent rim. I should have thought of that before because it happened to me. I had my wheels balanced and they (Alton's Tire; big in the Northwest) didn't notice it was bent at the time. I took it back a few weeks later and explained the problem. It was after that they discovered (not sure how) that one of the wheels was bent and needed to be replaced. That cured the vibration. I was suprised because they were fairly new rims and had no defects visable to the eye.

 

Nah... it's done it through 4 different sets of tires/rims. Its' always the same regardless of rim diameter, width, tire height, width, tread pattern, whatever...

Getting the outer bearings swapped out tonight. Will post results tomorrow... keep your fingers crossed!! I found one retainer quite "smashed" - no telling what kind of abuse the mechanic might have put the bearing through to make that happen!! The new bearings are silky smooth compared to the 39 year old stock unit though...[X(]

 

OK. Replaced both back outside axle bearings. Found one to be the WRONG type. Outside dimensions were correct but the race was not centered in the width of the bearing. Anyway, we cut them off, since this was easiest to do. They were both DRY. Absolutely no trace of lubricant, but the insides were clean, shiny, smooth and in no way defective. Put the new ones on using a proper press.

Test drove the car. SMOOTH up to about 68 (Gained 10 MPH!!). Now when the vibration starts it is at best maybe 1/3 the magnitude, and comes in and out as I'm going down the road. (Possibly affected by road surface??) This tells me the vibration is definitely in the back end. The shocks are NEW, so at this point I'm starting to think that this is maybe some kind of natural "resonance" that is just part of the car. I've had some buddies ride with me and say it's "not that bad".

Anway, it's WAAAAYYYY better than it was before. I have some "wheel hop" when cornering and running over bumps - the *** end feels like it wants to jump around, and I SWEAR both rear wheels want to come off the ground. At this point, I'm thinking maybe a sway bar on the rear end would help keep the back wheels on the ground, and possibly alter or ELIMINATE the "resonance" that seems to be happenening at high speed.[&:]

 

here's a thought!! When I took off the old springs and put new ones on, lots of stuff was just flaky rust and crunchy rubber residue. I was looking through a mustang catalog and it showed "spring pads, upper and lower". When I put mine together, I didn't have anything like that, so the spring is right on the perch and bolted up solid. I just ordered some of these "isolation pads". Think this will make any difference?? It might raise the axle a little bit, changing the angle of dangle, no?? Anyway, everything else has made little or no difference, so my search for the final solution continues.

 

hello, i havent read the posts. but i recently had this problem. i was told that i had a warped rim. i had it rebalenced several times, bought new tires and wheels. but the vibration wouldnt stop. took it back had them pull the rear wheels off and re balance them again. same thing. then i went looking for stuff. i found that the gas tank only had about half the bolts and they were loose! replaced and tightend the bolts and the vibration quit! it was simply the gas tank vibrating.

 

ya bent rims will make it seem like you have alot of problems

 

I have the exact same problem in my 68. It starts vibrating at about 55. I am about to pull my hair out.

If you want to check if it is your drums, try putting it up on stands and running the rear with out the drums or tires on remember not to hit the brakes or put it in park until it stops. Mine still vibrates so I know its someplace forward.

 

Well what happened with your vibration? I know you said you had the driveshaft rebalanced, but what about the pinion angle? The pinion angle being wrong can cause vibrations at higher speeds.


sorry for digging up an old post.