I have looked through all the previous postings, but I didn't see this one. In a 1968 Camaro big block 540 with motor plates running a powerglide, there is a vibration right at the finish line felt only in the throttle pedal. The car handles fine, and the 1/8 mile times are consistent. The car runs 5.60's at 122 MPH. Any suggestions?

too many possibilities for anyone to say for certain. I would check engine and trans mounts, drive shaft u joints and wheel balancing first if you don’t feel it in the steering wheel. Could also be on the rear suspension, is this a 4 link?

Don't ignore a vibration.

Much more information will help....

Is this the peak RPM moment?

Do you match that RPM earlier in the run with no vibration?

Under load, just coming off the throttle, or upon decel initiation?

Travel limiter(s) on the engine / trans?

High RPM ignition breakdown, carb getting lean, or siphoning fuel out the vents into the engine?

Changed anything before vibration manifested??

Some good leads to follow up on. This is a ladder bar suspension, double adjustable rear coilovers, and double adjustable front shocks with coil springs. A collar was added to the drive shaft yoke to read driveshaft rpm. Dana 60 rear so the collar had to be to the yoke. Hard to believe the collar could change things, but it could be possible. The vibration occurs at wide open throttle about 40-60 feet before the finish line. I think the next thing to do is remove the collar and see what happens.

sounds like you found the source of your vibration.

How many sensor lugs are on/in the collar?

4 lugs with 2 clamp screws. The collar clamps down with maybe only a few thousandths space between the two parting edges.

Is your throttle pedal linked to the carb by a cable or a rod? If it's a rod, then that is a direct mechanical connection from the pedal to the power train, so that would make sense if anything is out of balance in the engine, trans, driveshaft. Cable would seem less likely to transmit vibration, but perhaps still possible if under tension at full throttle. Sounds like you are on the right track to eliminate a possible cause.

rev limiter ??????

quote:

Originally posted by FootbrakeJim:
Is your throttle pedal linked to the carb by a cable or a rod? If it's a rod, then that is a direct mechanical connection from the pedal to the power train, so that would make sense if anything is out of balance in the engine, trans, driveshaft. Cable would seem less likely to transmit vibration, but perhaps still possible if under tension at full throttle. Sounds like you are on the right track to eliminate a possible cause.

Jim,
FYI, I drive an engine dyno with a cable (22 feet) to the carb and I can easily feel when an engine has a vibration. My "guess" is an engine vibration.

Joe

quote:

Originally posted by Joe C:
A collar was added to the drive shaft yoke to read driveshaft rpm. Dana 60 rear so the collar had to be to the yoke.

Not sure why you have to have the collar on the driveshaft yoke with a Dana 60, I ran a Dana 60 with the collar on the pinion flange. just took a local machinist a little time on a lathe to make it fit.

quote:

Originally posted by Joe C:
A collar was added to the drive shaft yoke to read driveshaft rpm.

Did this vibration happen right after this collar was added? I would look for a bind right there. Technically you took up yoke length.

I guess the first thing is the reason you feel it in the throttle pedal is your foot is pushing as hard as it can on the floor/stop. Do you not feel it in the seat or shifter?

Rest assured, that vibration is all over the car but he “feels it” in foot

Going to add my two cents here. Have you considered tire/wheel balance? Most of our slicks are bubble balanced, probably not the best way.

I have shock sensors on the rear of my car. I can see the vibration on the top end even though I can't feel it.

Just a thought.

I thought those of you who responded to my question about the vibration would like to know if it has been cured. Yes, it was the addition of the speed sensor collar around the transmission yoke. The driveshaft was rebalanced with the collar on the yoke and the vibration is gone. Thanks for all the responses. Several of you identified that as the potential cause.

That's why I had asked you how many sensor lugs were on the collar. Had several customers collars be out of balance over the years. It always worried me that the lugs could be out of 90 degree relationship to each other. Seemed that would cause timing issues.