Hi, I just bought a 66 mustang coupe 289/C4. It needs a lot of work but I love it. Im pretty good at pickin the problems out when they happend and pinpoint what it is..but this one has me kinda stumped. The thing is pretty smooth up to about 45 50 mph and if im not giving it any gas at all its nice and smooth but i can BREATHE on the gas and the car just shakes like crazy.. i was thinkin engine mounts? or maybe tranny mounts? Am I going the the right way on this or is it something different PLEASE help thanks!![>:]

 

Certainly start with the easy stuff first and motor mounts and trans mount are easy and relatively cheap. Don't go the urethane route; they're too hard and you'll continue to have vibration problems.

 

After the mounts, then check the U-Joints. If they are tight, then take off the drive shaft and take it to a machine shop and have them check it for balance. If it is balanced, then you may have either a worn out rear or tranny.

 

does it still shake if you drive it at 50 any shift it to neutral? or only when you are giving it gas?

 

Even before all that I would check the tire balance.

 

Check the trans bellhousing to engine bolts and the trans to bellhousing bolts. C-4's are one of the only auto trannies that have a detachable bellhousing. I had a similar problem with my T-5, 2 of the 4 trans to bellhousing bolts backed out and teh other 2 were finger tight [], and it would do the exact same thing. I replaced the 2 that were missing and tightend up the ither 2, I loctited em just to be sure.
As far as diagnosing vibe probs, if the shake is in the steering wheel check for vibes in the front end (worn parts or bent rims, out of balance tires), if you feel the vibe in the seat or the floor board its coming from the rear (or anything attached to it).
-P.

 

NO it doesnt shake at all unless im giving it gas.

 

Let's get it fine tuned - it doesn't shake when braking? Does it shake at any speed? Does it shake more severe at any given speed?

going by your words - we're only shaking under a load. With that - we've gotta look at load sensitive areas.

Mounts ( Motor, Trans, Rear Axle ) U-Joints, Rear end ( both pinion and axle bearings ), Wheel lugs.

As was suggested, start simple and move from there. I'd suggest Drive shaft as well, however, it should vibrate at any speed, not just under a load if the shaft was out of balance, etc.

I'm going to guess mounts - but I'd not completely rule out Pinion bearings.

 

Then that indicates it's in the driveline. Check those U joints and the other things we mentioned thatare in the driveline from the motor back.

 

There so many things this could be that ---------well , it's UFO's .

Ball of dirt inside the tire, U-joint, dirt on rim,. bent rim., Idiler arm, pitman arm. tire rod. Steering box,. loose lugs, ETC.