More on vibration

[Brad Thomas]

Still losing my mind...along with others. To answer a few questions the car is an original BB 4-spd car. All engine and trans mounts are new. Balancer is good. Changed entire clutch system and even replaced the transmission using the one out of my 68 Camaro. I did notice a few things playing with it again after giving up. I can run the car up to 4500 rpm ( and hold it there ) in 1st,2nd,3rd...totally smooth. As soon as I shift into 4th, the car wants to tear itself up. Play with the clutch and it gets better. So I'm lost. Doesn't seem to be an rpm issue...doesn't vibrate at rpm in 1st,2nd,3rd gear. Doesn't seem to be a mph issue as 4500 rpm in 3rd should keep the speed near close to the same at 3000 rpm in 4th.
Today it wasn't there at all. It was like a brand new car. Would pull to 4000+ rpm and be totally smooth. Of course that's only because I had a passenger trying to help me with it. After I dropped him off and returned to the freeway it was back. P.S. It's for sale.
You do hear a clunking noise in the back of the car occasionally, like something is shifting. Usually noticed when backing up, or just starting to go forward after backing up. I've always said it seems like something is moving in the rear of the car. I've done nothing more than lift the car to change oil, hit the freeway and it's gone. Pull off, hit the Circle K for a drink, get back on the freeway and it's back. Nothing changed other than backing up and hearing a clunk. Is there anything in the rear of the car that can move causing it to "clunk". From my drag racing days I would swear that maybe the pinion angle is changing...either vertically or horizontally. Is this possible? Bushings or control arms ??? Not a U-joint issue as I have changed those more times than I can count.
Thank you

[Andrew Strauss]

Re: More on vibration

Have you checked differential stopper[what I call it].The bushing that cushions the movement of the diff when accelerating?

[Mike Cobine]

Re: More on vibration

Obviously, if it is for sale, then I'll offer you $5000 since this car is obviously haunted.

Actually, a lot can move in the rear suspension. There are many pieces bolted together, and if they get loose, things move a lot.

Now that you mention all of this, my '67 coupe would vibrate like crazy if too much was loaded in the rear, or if there was someone sitting in the back (they were collector items back then).

The problem was not so much that the rear was moving as much as the rear luggage body panel pushed into contact with the rear crossmember.

The solution in my case was to use two rubber stoppers about an inch thick and about 2 inches in diameter. I put them between the crossmember and the body, to isolate it from making contact with the metal.

It could be that you have the differential crossmember making contact or the front of the differential could be loose enough to lift up and hit the body in the tunnel.

[Brad Thomas]

Re: More on vibration

Thanks Andrew / Mike. When you say the differential crossmember possibly hitting the body I assume you mean the per-say crossmember frame the diff. is mounted to??? And...how can the differential "move" to make contact with anything? I thought it was solid mounted. Andrew mentioned a stopper? Is there a bushing on or around the diff? Something you can see from under the car, or is it something the car needs to be on a lift for?
Is there anything I should zoom in on under the car? I know the camber on one side is way, way off, but I have corrected it over and over and while it doesn't stay, it doesn't fix the problem.
Thanks guys...we may be getting somewhere

[Roy B.]

Re: More on vibration

OK sounds to me that the rear pumpkin support RUBBER DONUT is worn (soft) allowing the pumpkin (ring and gear housing ) to move up and down, Because you said when just starting to back up or going forward you hear a clunk.
Which also will cause the rear end to shake now and then, as you stated

[Tracy C.]

Re: More on vibration

Brad,

Check this part for wear...

good luck

[Jean C.]

Re: More on vibration

Brad,
In an earlier note, I believe you mentioned that the vibration sounded as if the pinion shaft could be interfering with something as it rotated.

Referring to Tracy's photo, if one of the two bolts securing the center section support (specifically the forward one directly over the letter "s" in Tracy's comment on the photo) shears, the pinion shaft will move upwards on acceleration as the center section rotates around the axle axis and the pinion shaft/u-joint will contact the bottom of the floorpan. Doesn't exaclty produce a vibration but more like a chain saw destroying fiber glass. Don't ask me how I know about this but you may want to check all the bolts in the rear end plus the rubber bumper that Tracy pointed out.
Best regards,
Charlie

[Bill Stephenson]

Re: More on vibration

Brad,

-------When you say the camber is way way off and you have corrected it over and over, it sounds like you might have a broken C-clip inside the pumpkin. That would allow the stub-axle to move in and out way too much. Clunking might originate from this area. You can check for this extra in and out movement pretty easily with a friend. Just have someone move the top of the tire in and out and watch the stub-axles movement. Tiny bit of movement is OK, but no more. Hope this helps.............Bill S