vibration

[melmount]

Jacked the truck up tonite in the rear. I have been having a vibration at 38mph. It still did it when jacked up. I tried 3 different wheels sets on the back. All were the same. Just had the driveshaft balanced.
The weird thing is i can hold it at 38 then barely give it more pedal. It jumps
to approx 43mph. Feels like i let off the brake. But no brakes were on. Odviously a motor skip would not bounce the rear end up and down.
how do i know what it is??
thx

 

[bigrigr]

Any lift on it? What about the trans mount? Is it nice and tight? Try lubing the slip and splines on the driveshaft, I've seen many fords w/the coating on the splines worn off. Ford thought they were smart and dipped the splines in a non greaseable coating to take the place of grease. It works ok for a short period of time, but eventually it will need grease. I've even had to go sofar as to take the slip and splines apart to get enough grease in it to lube properly. Good luck.

 

[DaveBen]

Tranny??

Dave

 

[melmount]

drive shaft came back from a driveshaft shop. It got balanced and checked. I lubed it before installed it. Its all balanced and straightened.
How would the trans cause this shake? The rear end starts to bounce at 38mph. You can see the wheels go up and down? No lift just a front level kit.
Dave i dont understand how the trans can do this?
thx

 

[JLDickmon]

drive shaft came back from a driveshaft shop. It got balanced and checked. I lubed it before installed it. Its all balanced and straightened.
How would the trans cause this shake? The rear end starts to bounce at 38mph. You can see the wheels go up and down? No lift just a front level kit.
Dave i dont understand how the trans can do this?
thx

balance the tires
AND REPLACE THE REAR SHOCKS

the damping valves are worn out.

 

[DaveBen]

Dave i dont understand how the trans can do this?
thx

I don't either. I was just fishing. Something is out of balance.

Dave

 

[BIG JOE]

did you Index (mark) the D-shaft before you took it out ? So it went back in.. the same postion.. in relation to the Yoke(s) ?

 

[DaveBen]

I think Big Joe has it. Turn your drive shaft 180° and reinstall it, now drive it. Vibration should be gone.

Dave

 

[melmount]

the shaft came yesterday from being balanced. Its installed exactly as the guy there directedme to. He marked it while balancing it. I have checked injectors, uvch, ohm'd everything. I replaced the tc. All I can think of is the rear has a bent part or loose. It clunks every time i come to a stop or reverse to drive etc. I tried 3 different sets of back wheels too. It also did it before i sold the dually wheels. I have to think its the rear itself?? Any thoughts?

 

[BIG JOE]

No matter what the guy said ? Mark the D-shaft & Yoke, disconnect the D-shaft and turn it 90*. Try that. Try another 90* 'til you get back to the mark... if that don't fix it.. at least you've eliminated the D-shaft being out of balance with the drive-train.

It's worth a Shot.

Then, I'd go with what JLD sez: New (upgraded) Shocks.



Joe