I have a 66 convert with a 327 and a 4 speed. I am getting some sort of chattering/vibration coming from under my seat. Its not clutch or fly wheel they are new. It seems worse when driving slower. I am not mechanical so I am try to get at least a lead of where to start looking. It is under the car. Suspension?,Differential?___???????????? . Any common problems that might give me a start. I know this is tough with out seeing but I also know that there is a lot of experience out there. Thanks for any help you can give. Mike

 

Could you describe it more thoroughly? Did this condition just start to occur -- like right after that clutch/flywheel change? Does the frequency & pitch of the noise vary with on vehicle speed only, or does engine rpm a dependant variable?

I have had parking brake springs break & come apart inside their drum within the rear rotors. That will make a grinding, crunchy noise that you can actually feel & hear more pronounced at low speed/low noise conditions. Get the rear wheels off the ground slightly & rotate each by hand -- you'd hear & feel it.

 

is it constant or does it only happen under acceleration?

 

When seated in a Vette, your butt is very close to the rear wheels. While they are not "under the seat", they are very close. The rear wheel bearings and the axle drive shaft u-joints are both problematic areas that I would probably check first.

 

Only comes when accerelating slow. engine rpm does not affect. seems to smooth out if going a little faster 3000 rpm and up. I know this is tough not seeing or hearing. Just trying to get a start. Does feel like under drivers seat towards rear of seat. Mike

 

I think that you might be right. If a wait a month or so until the weather changes and cant drive it will I do any extra damage or worse yet will I break the car. thanks Mike

 

As you say, it's tough to diagnose something like that long distance. The things that can actually break and cause extensive damage are those I mentioned earlier, wheel bearing and u-joints. From your last description, I am thinking more along the lines of perhaps wheel bearing. Usually, they can be heard at low speed, and when they get really bad, you can hear some grinding and popping.

Lift the rear of the car safely and get a good grasp on the top and bottom of the tire. See if there is any "wiggle" from top to bottom. There should be very little or no decernable movement of the tire. Also, visually inspect the u-joints. Frequently, a failing joint will be leaking a rust colored powder from one or more of the ends.

If you discover anything that isn't like it should be, repair it immediately. A failed u-joint can do a lot of damage under the car. A failed wheel bearing can do a lot of damage as well, and they have been known to cause the loss of a wheel. You can imagine what the loss of a wheel at speed might do in terms of damage to the car and to the occupant(s) of the car.

 

new clutches and throwout bearings also can fail, Just lost a throwout bearing with less then 1000 miles on it since it was replaced. Mechanical things, even new can and do fail.

 

Not sure of you geographic location, but try this. Find a long stretch of road,(maybe down hill) have a friend with you, get up to speed and shift to neutral. Listen for the sounds. Along with the good observations above, what is the history on your ownership. Have you or the previous owner, (if known) done any work on the rear spindles or u-joints? If one side is bad, it may be money well spent to have the other side done at the same time. I can say from personal experience, Bair's in Linesville PA. is the best and most accomodating. They will send you a specially constructed box to ship them in. Spindle rebuilding is a VERY specialized process requiring very special tools, something left to those who have considerble experience. Good luck!

 

See if it's the exhaust.
Right underneath my driver' side seat, my pipes are secured with c-clamps - right where the middle electrical ground is located. The rearward exhaust pipe fits into the forward pipe, and is secured by a c-clamp. Even though the exhaust clamp is tight, if I bottom out, sometimes it will cause the rearward pipe to slip from the grip of the clamp, and I will get a rattle.

I have to loosen the clamp, push up on the rearward pipe, which causes it to push further inside the forward pipe, and back into the area where the clamp secures it. Once tightened, no more rattle.

May or may not be the cause of your problems, but is an easy fix, and worth a look.

Good luck!

 

I had a similar problem last year... the vibration was actually Posi clutch plate chatter. It was most apparant when driving slowly - pulling out off first and turning.... the fix was easy (for once).... suck out the old diff lube and replace with the GM diff lube and a bottle of GM Posi Additive (put the additive in first, then the new fluid).