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I have a 95 F150 and it has a 6" Lift. The whole time Ive had the truck is has had the lift and this vibration. It Vibrates when you left off the gas, but only at speeds above 80Km/h. Drives smooth anything below 80. The Faster the you go the worse it gets, and I would say doing about 100 km/h you notice the vibration all the time (not only when coasting).
I have checked and changed every U joint of the Rear Driveshaft, and it seemed to help slightly, but certaintly did not fix the issue. Tires have been balanced and double checked.
That is where my knowledge and experience stops, and I am looking for advice, or links to other threads on this topic.
I suspect the lift could have something to do with it, and the diff. The rear diff is just spaced up with blocks. I assume the Pinion angle would not change if the front and back was lifted the same, so I dont think that is the problem. I dont think its possible to install the rear lift spacers wrong because they sit on the metal plates on the axle housing, and are held down by U-bolts. I have tried loosening the U-bolts to adjust one side, but nothing even moved. I tried adjusting one side because it appears it could be at a slight angle compared to the other side. But hard to tell.
I dont really know how to check the diff angle, so if anyone is willing to chime in I am willing to try anything. I tried rotating the yoke when I had the shaft off from the diff, and it moves about 1/4" turn, which I believe is normal.
Would a worn manual transmission cause vibrating when coasting? Or am I right in suspecting the Diff as the Culprit.
This is my first post here, so thank you, and looking forward to some brilliant responses
Ujoint angles, phasing or driveshaft balance.
I've had a car where Ujoint angles were marginal and it would vibrate when you lifted on the top end about 120 mph.
Thank you very much, this gives me something to start looking at. I had the driveshaft out for putting in a new/used transmission. I never marked the shaft and it got bolted back up however it fit, so I will look into PHASING, and existing markings and weld seams. I will just start by trying to turn the driveshaft and rebolt it to the yoke.
Would the lift increase U joint angles? I am thinking if the front and back was lifted the same, then the u joint angle would stay the same... If my thinking is mistaken, then I am thinking It is going to be very difficult to fix this problem. I will have to find some sort of custom driveshaft with more u joints to reduce the angle I presume.
Last edited by TheEnduroist; 02-09-2017 at 07:51 PM.
Reason: Spelling
Any lift will change the ujoint angles unless the diffs were tilted to accommodate for the lift. There is no way I'm aware of to maintain a stock angle without tilting/rotating the difs. Is a 6" enough to cause a problem? Someone with more experience than me will have to answer that.
OK. Now looking and thinking, of course a lift will change the anlgle of the diff. The diff is still the same distance from the ground but everything else is higher, making an increased angle. Feeling foolish.
With that aside, I have inspected the u bolts and lift blocks for the diff, and blocks on the rear diff are tapered to tilt the diff accordingly, and they are both facing the right direction. I loosened off one side of the U-bolts because something didnt look right, I hit it with a hammer and tightened them up again, and after driving it today it didnt seem as bad as I remember...Might try doing that again.
But I am thinking it still could be the free transmission I put in, or the pinion bearing, not sure, and dont know how to check those.
Thanks for the continued ideas, I will keep posting my updates as long as people are helping.
Still nothing is figured out.
But I think it vibrates all the time pretty much.
Thinking it could be the manual transmission, is there anything to check there without pulling it apart?
Now I am thinking its the rear driveshaft angle based on these posts and talking to other people I eliminated the most of my other assumptions. As far as I know there is no way to fix it affordably, my plan is to drive it until SHTF and then do it all over again.
02-09-2017, 05:11 PM
Vibration when left off the gas pedal
