My sons '68 XR7 with c4 and 8 inch rear axle has a bad vibration at about 65 to 70 that seems to get worse with speed.
The car has a rebuilt C4, including the rear bushing in the tail shaft.
The universal joints are new, and I have even substituted a different drive shaft to eliminate that possibility.
The tires and wheels have been balanced and rebalanced and I have also substituted front for rear, and that made no difference.
The vibration got worse for awhile and I replaced the rear brakes and it seemed to get a little better. The old rear shoes actually had cracks in the lining (probably do to age).
I can put the car up on jack stands and it seems to not vibrate, but them there is no load on it either.
Has anyone ever had a bad bearing or axle that would do something like this? I am about to rebuild the rear end as it is the only thing left that I can do.
1.May have a bad shock 2.Driveshant may be to short(I had this problem caused by the Diff.Yoke being wrong ie.too short) 3. Bad Tie rod end or ball joint. 4. Could be the condition of the highway (So ca. roads are good for this).
Check for a bent rear axle too. I had a 73 Mach 1 with the same problem. Drove me nuts until I found it. I couldn’t feel the vibration through the steering wheel but hand on the floor you could feel the car vibrate. Started to vibrate at about 60-65 mph and smoothed out over 80 somewhat. Smooth as silk after I put a new axle in.
Don, we are going to rebuild the front end, but I don’t feel any vibrations in the steering wheel. I think the drive shaft is ruled out, but I will do some measuring and see. That is a good point that I had not considered. I was on I10 around Palm Springs and pulled over because I thought I had a flat… turned out to be a strange pattern in the road surface that went for miles.
FFR, I had not considered a bent axle, but that makes a lot of sense. how do you check an axle?
Bill in my case the axle was slightly bent at the outer wheel hub where the tire bolts on. The car had been hit in the qtr panel and replaced and my guess the axle was also bent as a result.
Dial indicator mounted on the brake backing plate. Rotate the pinion yoke and see how much endplay the axle has. should have very little to none.
A carrier bearing going bad can also mimic some of the symptoms you’re expressing, but I’d check the axles first.
Yeah, you can have twist that doesn’t shear the splines, but results in a harmonic type vibe. The runout will be okay, but the axle itself will be off.
You might pull them and give them a look when you can. That’ll give opportunity to pull the third member and check the carrier bearings, naturally.
has the motor and or trans been out, replaced etc? I ask because if an improperly balanced flywheel, harmonic balancer, torque converter etc. will cause the shakes.
Are the wheels the OEM steel variety? If not, are they bolted up correctly?
I have experienced some insidious tire problems in the past. The shop swore they were perfect yet I had a bad shake. It wasn’t till I showed them a lousy wear pattern and they could tell a belt was pulled that they would replace the tire.
The wheels are cast aluminum Shelby style 16". I have rotated them and no changes also I have looked at run out and they look true. The way things are going, it will be after the party before I can tear it apart.
My approach would be to put a known good set of tires and wheels (oem steel type) on the vehicle and give it a test drive. Surely the list of cars in your sig are outfitted with good tires and wheels to choose from.
xr7g-- coming from a master-tech for nearly 16 years i can tell you a vibration at high speeds can be caused by, and most likely one of the following (in order of likeliness) :
#1 tire balancing of course (no brainer) or bent rim #2 reason: a tire that have a very slight steel belt separating (look for a small area with a more wear that the opposite spot 180 degrees around IE a flat spot
3- outer axle bearing bad
4- inner bearings/ diff issue / pinion bearings
5- u joint bad or over tightened (very common, most are like 12 lbs torque)
6- bushings but not likely
its not a brake issue, or you’d mainly feel it at braking only (ok 99.99999999999999% of the time)
Thanks, I did not realize that you could over tighten a U joint… That I have to check right away. I need to start rebuilding axles as a regular part of doing these cars, I just hate the smell of old gear oil.
oh yes, standard chevy 4x4 is 12 lbs, you can do that with your pinky, if its reefed on it will fail very premature if its been changed recently. I always start with the very old or very new Mechanical CSI
I had the same thing and it had a rebuilt tranny, I swapped to a manual and the vibration was gone, I was thinking it was in the torque converter, my vibration had a rythym (sp) to it
Mechanical CSI 