Vibration 19-25MPHs after lowering shackles

[SS1LE]

So I installed M-3000-HB lowering shackles on my 2022 Lariat FX4 5.5 foot bed stock 20" wheels Powerboost (not max tow). Now I am feeling a vibration mostly during breaking between about 19-25 MPH. I haven't fully tested it out because I do not drive that slow very much. I do not remember it before the install, and my wife noticed it when she just drove it, she thought she was over the line and the lane centering was yelling at her.

Has anyone else had issues with drive shaft vibration around these speeds after the lowering kit? I was sure if I should look into some shims and/or just live with it.

Before the install I had about a 3" rake, now it is down to around 2".

Sponsored

 

[SALEEN961]

I would start by measuring your driveline angles to verify if you need to adjust the pinion angle after installing the shackles.

 

[93dpscoupe]

If you have a 3-spring pack, then you probably wont be able to keep them. Even with a 2.5° shim, the vibration just moved from low speed to high speed.

 

[SS1LE]

I will have to check what it has. If it is three springs I think the third is a very small helper spring.

Is it just an annoyance or an actual issue?

 

[93dpscoupe]

I dont want to risk premature failure of a u-joint or pinion bearing

 

[SS1LE]

I dont want to risk premature failure of a u-joint or pinion bearing

I checked, and I have two springs and a helper spring. I am not sure what max tow springs look like. I know my truck window sticker does not show the max tow package, it does have the tow technology package.

 

[SALEEN961]

To give you a point of reference, my truck has no vibrations from 0mph all the way up to the speed limiter. My u-joint angle at the slip yoke is roughly 0.2° and the u-joint angle at my rear diff is roughly 1.4° with my truck sitting in park in my driveway.

I don't have an assistant available right now, but if I were to put my truck in drive to load the driveline and rear suspension a little, I would expect the pinion angle to rise slightly and bring the u-joint angle at my rear diff down to roughly 0.4° which would closely match the angle of the other u-joint.

 

[FirstFord]

Most other threads and forums would suggest that the issue is likely the "new" pinion angle, and shim(s) need to be added.

For what it's worth (if you find any value to this information), I measured my pinion angle, and it is at 3° from the Ford factory (Scab, 6.5' bed, 4x4). I measured, because I too plan to lower the rear of the truck, except I was going to use the method of removing the 4x4 axle block instead of adding lowering shackles. I measured the pinion angle first to establish a "baseline". My plan was to measure the pinion angle again after I removed the block and compare the two to see if there is any change. If there is, then I will know not only that I need to shim the pinion, but how much. This was my reasoning.

 

[SS1LE]

I ended up ordering a digital angle guage and went ahead and ordered some 2.5 degree shims. I unfortunenty do not know what the pinion angle was stock. It also seems like they are all over the place with these trucks. I guess there is about a million different minor variations.

 

[SALEEN961]

I ended up ordering a digital angle guage and went ahead and ordered some 2.5 degree shims. I unfortunenty do not know what the pinion angle was stock. It also seems like they are all over the place with these trucks. I guess there is about a million different minor variations.

The pinion angle itself doesn't really matter because both u-joint angles change when you lift/lower the truck. You want the running angles of your u-joints to closely match each other when the driveline is loaded in drive. If you take measurements with the truck in park, setting the pinion 1° nose down from the point at which the u-joints angles are equal usually gets you pretty close to the desired angles when the driveline is loaded.

 

[SS1LE]

I installed some 2.5 degree shims this weekend and seems to have fixed everything. The low speed vibration went away and I did not feel anything up to 75MPH or so. It has only been a couple days but my MPG seemed to have also improved by 1-2 MPG.

It would be nice to have it a bit more level, but if I do I probably will just raise the font a bit, I do not want to mess with the rear anymore. The Powerboosts have a crazy rack.

Sponsored