Hey all,

I just bought a 68 mustang coupe with the straight six motor and three speed manual tranny. I have a vibration in the frontend when I hit 35 mph in third gear. It's only when I'm excellerating that it vibrates if i let off the gas the vibration stops. If I hit 35 in second the vibration isn't noticeable. I'm new at restoring, especially frontend work, so go easy on the technical terms please..;}

 

If it only vibrates when you accelerate, then you most likely have a broken motor mount.

 

well then its probably not a front end issue.

Im thinking engine or transmission (something that is related to power)

If the car is totally smooth with no issue at or above 35 but as soon as you apply power it vibrates then the issue is related to something that transfers power.

Is the engine totally smooth from 1000-4000 rpm in neutral? (if yes then probably not the engine balance)
If its great in 1st and 2nd above 35mph for 2nd but goes to pot in 3rd then it could be an issue with 3rd gear.

I would also check U joints on the drive shaft and rear wheel bearings (might as well check the fronts too)

Let me know if you find anything new.

Gun

Ps when your at say 45 and its vibrating bad in 3rd the vibration goes away instantly when you put in the clutch right? Its probably a trans issues.

 

I have some vibration through 1st and 2nd but third just really starts shaking the car. It's a bit smoother now that I have all cyl. firing (most of the plugs were solid carbon) as soon as I let off the gas in third it smoothes out. I don't dare take it over 35ish because of the shaking.IS a broken mount obvious or is it something you need to look closely at, I ask because just looking from the fender they looked solid.

 

Get a chunk of lumber and put between the jack and your oil pan. Start jacking up the motor, and if you have a broken motor mount it will be apparent.

 

might as well check the rear axle bearings and look for any type of runout from the rear wheels (do they run true) I just got through replacing my rear axles because I had .015 runout at the axle hub. Thats not much but boy what a difference new axles made.
p.s .002 to .005 is tolerable upper limits for axel runout. Might as well look into that.

Gun

 

I recently had a similar problem, turned out that I had the wrong u joint for my new rearend.