I am running a stock flathead 8 and 3 speed in my 51. When i get to freeway speeds, sometimes it runs smoothly but other times vibrates. If I step on the clutch and release it, the vibration changes and in a few tries I can usually get it to engage without vibration. I suspect the pilot bushing but don't want to go in blindly. Anyone have experience with this?

 

I have the same situation and cure on a 56 with a y block/3speed combo... just like you, i can settle in it with a press or two of the clutch pedal at speed.

I also suspect my pilot bushing...(or even lack of!) and will investigate when i pull the transmission for an OD swap...
I also suspect this was from previous owner work...

i also thought it could be a worn input bearing or collar, but no confirmation.

 

Don't rule out U-joints, I've had that exact situation when the front U-joint is shot. It will be obvious if so.

I'd be surprised if it's the pilot bushing, you'd have massive chatter on take-off if it was that bad. There just isn't much mass to cause vibration if the input shaft is misaligned. It would also be RPM dependent, not speed dependent.

 

U joints or drive line angles I check first.

Kevin Bigwin

 

if your going down a straight road at a constant speed/rpm and you press the clutch pedal in/out and can get a vibration to change.

1. it's good chance it's in the clutch assembly, (pilot bearing included) i've seen this problem fixed with a new clutch/pressure plate, pilot and throwout bearing replacement, but i can't say which one it was.

2. like the others, could still be other driveline imbalances. worn anything... alot of the time driveshaft vibrations show up as, growing noise/feeling when accelerating hard from a stop. and your most able to feel around 45 to 50 mph. fyi, u-joints, yokes etc... can all be good but your angles are alittle out of phase due to worn tranny mounts or sagging leaf springs......

(accelerating hard can pitch the pinion up alittle causing the u-joint angles to change)....

 

Thanks, I will check the u-joints. The drivetrain is pretty much stock and sitting about right so I doubt it is alignment. I do get some vibration variation at lower speeds with higher rpms but not as noticeable as at 50 - 60 mph.