mattdel

the reason it's getting worse is because with the pedal pushed in, the driveline is now only spinning from the inertia of the rear wheels. with the clutch engaged(pedal UP), the entire driveline is now under pressure from the motor, reducing any vibration because there is active torque in the line.

think of spinning a basketball on your finger. as long as you keep it going with your other hand, it will continue to spin fast and smooth. once it begins to slow and you're no longer applying continued speed to it, it wobbles and dances around.

94mustang94

any suggestions to what it might be. and why it just now statred this the tranny and rear have been done for months

mattdel

tailshaft bushing from not properly addressing the length of the driveshaft issue with installing a 3550 transmission. they make the spacer for a reason.

94mustang94

how likely is it that the tailshaft busing went bad. is this common for 3550s?

mattdel

its common in any transmission where the slip yoke is barely hanging onto the splines.

94mustang94

well its only 5/8ths of an inch so there is still a fair amount in the tailshaft but i guess that 5/8ths really makes a difference?

AdderMk2

yes.. it does.

thats why the spacer exists

94mustang94

i was told by the guy that i got the tranny from said if i wasn't running to strong of a gear like 4.30's or more i would be ok w/o the spacer but it seems thats not true

Jfsram

The driveshaft balance must be better than perfect for a steep gear like 4.30's.

94mustang94

tailshaft busing good, spacer installed and i drove it around for like 10 min with no problems. i thought the vibration was gone and then it came back. this is crazy any suggestions