I understand how lowering the truck changes the pinion angle, that is why I suggest getting a kit that supplies shims. Actually you adjust it upward, by installing the shims. (Thick part of the shim toward the rear)

Here is the thing though, some folks that have installed shackles with out shims, have noticed a vibration at varous speeds. When I was looking for mine, DJM did not have shims available with a kit.

I wouldn't want to install a new set of shackles, develope a vibe, and not have any shims to correct it, then have to go through the hassle of finding the ones I needed.

Spend the extra $ and get a kit that supplys shims, install them if you want/need to, either way...they are right there in the box, and you truck never skips a beat.

https://www.f150online.com/forums/sh...ckle+vibration

 

If lowering the rear raises the pumpkin up why would you want to raise the pumpkin up even more by putting the shims in backwards?

 

Lowering with drop shackles lowers the front of the diff. By placing the shims (with the thick edge toward the rear) in CORRECTLY, they cause the front of the rear diff to point upwards.

Think of it like this....

When you unbolt your shackles, and push up on the leafs, what happens to the front of the diff? There is only one direction it can go, down. Essentially, that is what you are doing when you extend the length of the shackle.

 

If you lower the differential, you are raising the truck. If you raise the differential, you lower the truck. There’s no two ways about it.

 

I did the 2 inch shackles and I wanna drop the back another inch or two.... F'in ford gave me on helluva rake....

 

kbldawg:

jpdadeo is right on the money with this one. Shackles installed at the rear leaf spring mount will lift the leaf pack at this point (near the bumper), pivoting it about the front mount. This will lift the differential while rotating it downward at the same time. To rotate the diff back in line at this position, the thicker end of the shim must go towards the front.

Doing the opposite way would likely double the incorrect pinion angle, and you would be much more likely to get a vibe.

Don't take it from me, here it is straight from DJM:
DJM pinion shims

 

I think we will all agree that buy extending the rear shackles, the rear of the leafs are raised, which in turn lowers the rear end, while at the same time pivoting the front of the diff downward. Do we agree so far?

OK, if the front of the diff is now pointing lower than stock, we need to bring it back up.

Where is the pivot point? The axle, right? The leafs are bolted to the frame, so they will not move once they are tightened. So...if you match the flat sides of the shim (thick end rear) to the leafs, and axle which direction is the front of the diff, going to rotate?

https://www.f150online.com/forums/sh...t=pinion+shims
https://www.f150online.com/forums/sh...ighlight=shims

 

The point that is being overlooked is the fact that the pumpkin itself is going up 2”. The axle pivots in the center of the leaf spring and the rear of the spring must be raised approximately 3” in order to raise the center of the leaf 2”

Yes, the pumpkin does tilt down slightly on the pivot, but it’s minimal compared to the pumpkin directly going up 2” thus changing the angle.

Drive shafts aren’t supposed to be straight at the U-joint. Proper angles should be equal. This pic shows the angle off by 1 degree. If both angles were 9 degrees, it would be right on the money.

 

jpdadeo,

First, I'd like to say thanks! It's refreshing to actually disagree with someone without name calling, flaming, and cheap shots. I appreciate that.

I called Ground Force Tech Support today, and spoke with Dan. (724-430-2068) I simply asked him this...."Which direction does the thick end of the shim face (front or rear of vehicle) with your 2" Lowering Shackle Kit?" I explained to him, we had a difference of opinion and stated that DJM instructs their custmers to install it facing toward the front. After some time looking up my kit, (about 45 sec.) he told me it needed to face rear, and explained the reasoning behind this.

I turned right around and called DJM and asked them the same question, spoke with Mike (310-538-1583). He says that the thick edge of the shims point forward.

Did the same thing with Belltech, spoke with Eric (800-445-3767). They agree with Ground Force, thick edge of shim faces rear.

What does this tell me? Mike is wrong! hahahaha J/K.

All, I can say is this....

A. Mechanically, it makes more sense to face them to the rear.
B. I have installed mine per Ground Force Instuctions, and have no problems what so ever.

Regards,

 

I can see the logic behind both applications. Actually measuring the angles would be the sure-fire way to set it perfect. I doubt it’s exact from the factory, but close enough to function without vibration. I’m glad I didn’t need to shim because I’d probably would have screwed it up. That’s good info you got by making a few calls.

 

i ordered the groundforce today. i'll install it when i get it back from the dealer for the 8th time