C3 - BB 68 motor mount movement with respect to the frame - is mount broken

[Dale P.]

I recently had an occasion where I was lifting on the driver's side of the engine and noted MOVEMENT of the engine with respect to the frame. the section of the frame where the motor mount is attached. At first I thought I was just seeing things. So I actually placed a jack under the motor (toward the driver's side) and actually placed some lifting pressure under that side of the motor. I was surprised to see that I noted a good 3/8 - 1/2 inch of dead vertical travel of the motor from the frame until it stopped. The frame never did move at all, and I really didn't want to apply any more lifting pressure. I didn't note any movement on the pass. side during any of this.
So the question is "Is this normal movement or do I have a suspect motor mount

I guess the last piece of data is that I have a really bad clutch chatter, that is what I was doing under the car to start with. The other day when I backed the car out, I happened to have the hood up.. I noted that the engine seemed to have a fair amount of shake while I was releasing the clutch and it was chattering.

What are the thoughts of the tech guys out there? Did I accidently find my clutch chattering issue?

[Dick W.]

Re: C3 - BB 68 motor mount movement with respect to the frame - is mount broken

Left motor mounts were a problem in that era. They were subject to breaking, hence the first major safety recall. The clutch chatter would/could be consistent with worn motor mounts

[Dale P.]

Re: C3 - BB 68 motor mount movement with respect to the frame - is mount broken

So Dick, do you agree with me that the movement I described if definitely not normal? I would expect NO movement of the engine with respect to the frame.

[Dick W.]

Re: C3 - BB 68 motor mount movement with respect to the frame - is mount broken

I would expect to see minimal movement. I suspect that the rubber either is in the process of separating, or has separated from the metal.

[Michael G.]

Re: C3 - BB 68 motor mount movement with respect to the frame - is mount broken

Time to replace the mounts. Like Dick says....there should minimal movement of engine. The fact the engine moved up during jacking and frame didn't budge is a definite indication left side motor mount is done. Replace both.

[Dale P.]

Re: C3 - BB 68 motor mount movement with respect to the frame - is mount broken

any suggestions on type ( stock, or urethane). I guess I'll do the transmission mount at the same time. Looks like the exhaust manifolds have to come out to get to the mounts. Gee doesn't look like fun.

[Joe L.]

Re: C3 - BB 68 motor mount movement with respect to the frame - is mount broken

any suggestions on type ( stock, or urethane). I guess I'll do the transmission mount at the same time. Looks like the exhaust manifolds have to come out to get to the mounts. Gee doesn't look like fun.

Dale-----


I suspect that when you remove the motor mount, you're going to find that it will come off in two pieces. One of those pieces will look like the attached photos. This mount was a genuine GM mount (note GM part number on the side).

As far as what to replace it with, ALWAYS use stock-type rubber. Unfortunately, the GM mounts are discontinued and they were the best ones available. As far as I know, the "only game in town" these days are foreign-manufactured mounts. Just how good they are, I do not know. Usually, the metal components of these mounts is a little thinner than GM and, to some degree, they appear "crude". But, they might be OK.


DSCN2895.jpgDSCN2896.jpgDSCN2897.jpg

[Michael G.]

Re: C3 - BB 68 motor mount movement with respect to the frame - is mount broken

any suggestions on type ( stock, or urethane). I guess I'll do the transmission mount at the same time. Looks like the exhaust manifolds have to come out to get to the mounts. Gee doesn't look like fun.

This is not that difficult of a job. I've never removed the exhaust manifolds to remove motor mounts. You'll need to safely support the engine. I've used a bottle jack and block of wood under the oil pan to support engine during removal. Stock style mounts should be sufficient.

[Dale P.]

Re: C3 - BB 68 motor mount movement with respect to the frame - is mount broken

In looking around for a set of replacement motor mounts (ZIP, Eckler's, Paragon) I noticed that on my 68 Big Block the parts diagram references a "Y" shaped "shim" as it is called - that goes between the mount and block. I don't think mine has it installed. I can only assume that it was removed way before I bought the car. So now I am wondering if the mounts are even correct for this car. secondly wouldn't not have the shim in place position the engine itself lower in the engine bay? wouldn't this also then cause stress on the bell housing - assuming the transmission is in its correct position? Gee this is turning out to be like solving a mystery.

[Joe L.]

Re: C3 - BB 68 motor mount movement with respect to the frame - is mount broken

In looking around for a set of replacement motor mounts (ZIP, Eckler's, Paragon) I noticed that on my 68 Big Block the parts diagram references a "Y" shaped "shim" as it is called - that goes between the mount and block. I don't think mine has it installed. I can only assume that it was removed way before I bought the car. So now I am wondering if the mounts are even correct for this car. secondly wouldn't not have the shim in place position the engine itself lower in the engine bay? wouldn't this also then cause stress on the bell housing - assuming the transmission is in its correct position? Gee this is turning out to be like solving a mystery.

Dale-----


Does your car have air conditioning? The motor mount shims were used only on cars with big block and A/C.

[Patrick H.]

Re: C3 - BB 68 motor mount movement with respect to the frame - is mount broken

In looking around for a set of replacement motor mounts (ZIP, Eckler's, Paragon) I noticed that on my 68 Big Block the parts diagram references a "Y" shaped "shim" as it is called - that goes between the mount and block. I don't think mine has it installed. I can only assume that it was removed way before I bought the car. So now I am wondering if the mounts are even correct for this car. secondly wouldn't not have the shim in place position the engine itself lower in the engine bay? wouldn't this also then cause stress on the bell housing - assuming the transmission is in its correct position? Gee this is turning out to be like solving a mystery.

Corvette Central is now reproducing correct motor mounts:

http://tech.corvettecentral.com/2011/02/introducing-correct-c2-c3-motor-mounts-from-corvette-central/

http://www.parts123.com/parts123/yb.dll?parta~dyndetail~Z5Z5Z50000050g~Z5Z5Z513092~P13.95~~~~S3VI0YL3J424231119750B~Z5Z5Z5~Z5Z5Z50000050G

That should make it easy to decide which ones to get.

[Richard M.]

Re: C3 - BB 68 motor mount movement with respect to the frame - is mount broken

Dale, the factory recall mounts had a safety interlock feature that limited engine movement if the rubber separated you might look for some of them, also good time to check the rear transmission mount. Your lucky you haven't busted the fan shroud. Richard