77 Bronco Driveline Vibration

[muddog75]

I am having trouble figuring out this vibration issue. Here is a little history of the problem.
Started when i changed from 3.50 to 4.56 gears. Didn't notice vibration with 3.50 gears. Vibration is high frequency and it resonates at 60mph about every 2 seconds. RPM's are about 3k. It has a 3.5" suspension lift. Listed below is what i have done to trouble shoot.
tires are balanced (35")
driveshaft has been checked for balance
checked dana 20 output shaft for slack, its good
added 6 deg shim to correct pinion angle
u joints have been checked and are good
if i leave it in 2nd gear (c4 auto) and run it to 3k i do not feel the vibrations.
Only feel it in 3rd at 60

 

[svastano]

Who changed the gears out? To me sounds like the pinion has too much slop.

 

[Tugross302]

Curious because I may have the same problem. Did you lengthen your driveshaft? I haven’t checked mine to make sure there is more than 1 1/2” inserted where the driveshaft connects

 

[Tugross302]

Sorry. I meant “if” you put the lift on at the same time

 

[muddog75]

a rear end shop did the set up. i installed the 3rd member

 

[muddog75]

the driveshaft is aftermarket. it has plenty of engagement

 

[muddog75]

lift was already on there when i bought

 

[DirtDonk]

Is the vibration still there when you decelerate, or just let off the gas? What about pushing the clutch in and keeping the engine revving for a few seconds? Go away, or come back?
If an auto trans, flipping it into neutral changes anything?

What type, model, size and age are the tires? What size wheels? How much tire pressure?
And just so we know... Got pics of your rear pinion angle? Even though you put the shims in, and they usually line you up perfectly, you never know.
A friend has an original '76 Ranger he bought new and we ended up installing the shims backwards to correct the wrong angle that the dealer did out of ignorance.
My friend had needed the rear end warrantied back in '76 when there were just a few thousand miles on the truck. After that, even though he did not notice a vibration, he went through rear u-joints to the tune of one every 4,000 to 7,000 miles. For 40 years!
Turns out the housing was tilted upward too far and the six degree shims pulled it back down where it should be.

Sorry for the long and seemingly unrelated story. I know it's not the same as yours. Just showing that there is still room for oddities in our world of Broncos.

Paul

 

[sprdv1]

Who changed the gears out? To me sounds like the pinion has too much slop.

yeah, definitely might take it back to have it checked out thoroughly...