I really need some help on what could be causing a nasty vibration in my 66 coupe (Stock 302/C4). I posted a while ago and got no hits, please help. I recently changed out the rear mount on my C4 because one of the studs was missing, apparantly sheered off. I replaced it with a heavy duty poly mount. I also had the u-joints replaced as it was obvious they were worn out. Ever since, I have picked up a nasty vibration from about 1500-2000 rpm. It feels like a cavitation of something in the C4, the whole drivers compartment vibrates and it wasn't noticable with the wasted mount in place. It vibrates when moving and when sitting in N or P revving the engine. The harmonic looks to be in good shape and the vibration is barely noticable in the engine comapartment. I really have a gut feeling it is in the torque converter or the tailshaft of the C4 but was hoping someone else out there has run across something similar before. My "trusted" mechanic said to just put an original style of mount back in because he couldn't figure it out, but that seems silly as it doesn't take care of the source of the problem. Any help to focus my efforts would be a big help. Thanks.

Big Nate

 

If it does it while parked or nutral its not in the drivetain its in the engine. have you had any engine work done.

 

might be the tranny shaking. With the loose mount, you couldn't really feel it, but now it's all tight, you can feel it. something off balanced????

 

No, no engine work. I think the vibration was there all along, I just couldn't feel it due to the busted mount taking up the slack. There really is no noticable vibration in the engine compartment, just inside the car, especially near the front of the tranny. I really don't think it is the harmonic or flywheel, but it could be. The engine runs smooth as silk, no smoke, smooth idle, great power and even compression throughout.

 

on a chevy the torque convertors have balancers on them. I dont know about fords though. i'd stick with something off balance. maybe the convertor or flywheel.

 

check to c if the torque converters bolts are tight

 

Listen to your "trusted "mechanic. put a stock mount back in. Why do you need a heavy duty poly mount? This is just transfering more of the engine vibration to the cabin.

 

Well, obvioulsy the stock mount isn't that great or it wouldn't have failed on me in the first place with an essentially stock configuration. I have a new stock mount ready to put pack in, but it just seems like I'm not addressing the real, yet unknown, problem. It isn't "regular" engine vibration, feels like something is off balance. Thanks for all the input, once I figure it out I'll be sure to share the results.

Big Nate

 

Hmm, I guess 40 years out of a trans mount means it isnt great?? Come on. How often do you wear out a trans mount? Im sure carrol shelby didn't change them to heavy duty ones, and his cars managed quite well. Mine new mount has given me 4 years of service with no signs of a problem.
That said, from the info you have given, the vibration only became noticeable after you replaced your worn out trans mount, and U joints. You have also said that you get the vibration when standing still, so that rules out the U joints. Logic now says, It has to be caused by the new mount. Its not a big job, just put in a new stock mount and see how it goes.
Also give the car a tune, so its running as smoothly as possible.

 

The mount is less than 3 y/o. I have a new factory type mount but am hesitant to just put some lipstick on the pig and leave it at that. The engine is tuned and running smooth as silk, not a tuning problem. I checked the torque converter nuts and noticed the flexplate has some signs of wear. I know I am looking for a zebra in a bunch of horses here, but the vibration just feels to severe to be anything normal or simple tranfer of forces due to a stiffer mount. Once I have chased my tail for a while troubleshooting this, I'll be happy to say it was just the stupid mount and the guys at my shop and fast66 were right all along and I am just a paranoid freak.

Thanks

Big Nate