I just lifted my 2000 F150 Extra Cab, 7.5 inches with a Fabtech kit. 33.5's on 16" rims. Leveling blocks in the rear came with the kit. I noticed a shimmy in the rear at 45 and 65 MPH. I asked the dealer whom I bought my new rims and tires from to check the balance of the rears. They did and said that they are true. To get to the root of the problem, I rotated them front to back and vice versa. Still got the shimmy! Rules out the tires and rims due to my steering wheel being dead solid with no vibration. Now, I have noticed and have heard the pinion angle on the rear end actually shift upwards or downwards slightly depending how Im facing on a slope. I know this is not good and am assuming that this is related or causing the shimmy. Is my problem due to weak leaf springs and would helper springs fix the problem?

 

Still having this problem. Wanted to bring it back to the forefront. Please help! Sucks!

 

i have never run into leafs causing my shimmy issue. however shocks, and wore out tierods up front have. give the front a shake down (been aligned recently?) i had noticed my RF cupping. i gave it a few adjustments with the eyeballs and a level and i noticed my shimmy had gone away for a while. i have wore inner tie rods.

 

take a pic of your pinion angle and post it up so i can see it.
Your allowed 1* of tolerance either direction before shims would be needed.
Have you checked the drive shaft bolts to make sure there tight.
Have you had the drive shaft rebalanced? Could have slung a weight off which would cause a rear shimmy.

I just noticed that you just installed the kit. Did you install the driveshaft spacer, If not then the driveshaft is to short and needs to be lengthened, It's eating up your output shaft bushing and seal

 

Klitch, if you notice I said "Rules out the tires and rims due to my steering wheel being dead solid with no vibration". This was because I swapped the tires front to back. The shimmy is still in the rear.


slowrunner, thanks for the input. I have not done these things. Ill take a picture of the pinion. Also, I did notice that my drive shaft is "pulled" out a bit from the tranny. The only thing is, wouldnt Fabtech tell us that we needed a driveshaft extender? Ill check the drive shaft bolts also.

One thing that I do remember is that when I was messing with the rear end, it accidentally came off the jack that I had holding it up. So for about a minute the rear end was hanging off the end of the driveshaft!!!! The reason it hung was due to me not removing the middle crossmember yet, so the driveshaft was hanging on that and had the rear end on its end. Couldnt that have bent the driveshaft slightly?

 

If that is the factory aluminum driveshaft then yep that rear axle weight got yea.
Those axles weigh alote for that drive shaft to hold up, heck even a steel shaft would have been knocked out of balance.

As for the space at the front of the driveshaft at the yoke, the rule of thumb is there should be know more than 1" of visible yoke showing.

 

i didnt mention but i should have. i was watching the rear of my truck bounce, but my issue was actually up front.

 

I will take pictures tomorrow to confirm slowrunner. But I think youre right. Just from memory, I think it is more than an inch of yoke showing. Expect pictures soon. Thanks for all the info slow and klitch.

 

Ok, I have pics and they dont look good


yolk spacing



Notice the tranny fluid dripping out.




How's the pinion angle look? This is with the truck setting at a very slight pitch. To the right is the higher pitch of driveway.

 

Your pinion angle does not look bad, BUT your driveshaft is to short, and that trans fluid in the pic hanging from the output shaft housing and all over the exhaust pipe is a bad output shaft seal, more than likely caused by the drivshaft being to short and not fitting inside the bushing far enough, hopfully it has not damaged your Bushing yet.

 

Where could I pickup a driveshaft extender? Also, if the bushing is bad, how much do you think that might cost? Damn, I thought Fabtech would tell me, unless they thought it was for a standard cab.

 

As for the Drive shaft spacer, I thought all Fabtech kits 6" and over came with them, especially on a 7.5" lift, i would call fabtech, they have the spacer.

The output shaft seal would cost $150 here where i live, and i don't know how much the bushing would cost, I do know that the output shaft housing has to be removed and the old bushing pulled out and the new one pressed in. The seal is easier, take the drive shaft off, take a flat head screw driver and wedge the seal out carefully so that you don't damage the seal seat, Then just tap the new one in working in a clock wise motion around the seal until it is all the way in.

 

Well, I talked with a Fabtech Technician and he said that he has the same truck. He told me that the reason that a driveshaft spacer was not included in the kit was because with the 7.5 inch lift, a spacer is not needed. He said that with the spacer, the problem gets worse. I dont understand how. He says that more than likely, the leakage is due to the mileage of the vehicle and not the lift. He also said that he has a Ford with the same year and he had the same problem with the output shaft seal. Is this guy lying to me?

 

My drive shaft sticks out at leat that far 06STX but no vibration ,I would try the spacer and maby ballacing the shaft , dont fix the leak until you solve the problem. good luck

 

Yea he is, As you add lift to the rear of the truck, the driveshaft is pulled out of the output shaft housing, the higher the lift the more its pulled out, Its like 1/4" for every 1.5" of lift. once the drivshaft is slipped out far enough, the yoke will not be inside the bushing or worse is going in and out of the bushing as the suspension moves up and down which would damage the bushing, Hense the reason for the spacer, its used to put the driveshaft back into the housing at factory specs.