I've tried a few different things to fix this issue, but no luck. I removed the flat blocks in my CCSB fx4 and have a vibration at around 50-60mph. There is no vibration with the blocks installed. My first question is does the 2wd truck, which doesn't come with blocks, have something else different with the driveline? Is there a shim or something under the transmission mount in the 4wd models that isn't present in the 2wd models?

Pinion measurements with and without the blocks are basically the same, with the pinion angle about 2- 2.5 degrees more shallow than the output flange angle which makes sense because it's compensating for torque lifting the pinion and making the angles match. I tried a 1 degree shim to move the pinion upwards (thick side to the rear of the truck) and this actually seemed to help a little somehow, but still isn't perfect. With the pinion pointed upwards 1 degree, the vibration is still there but not quite as bad. I'm assuming without the blocks, there is less leverage on the leaf springs and likely less pinion lift under load. If I'm really on the throttle with the 1 degree shims, I have no vibration detected. If I'm trying to just maintain 55-60, that vibration is noticeable.

I was damn near 100% sure that nothing needed to be done with flat blocks, but this is bothering me. Am I doing damage with some vibration? I reinstalled the factory blocks and hate the rake and bed height. Braking and turning is noticeably worse with the blocks in too. I don't really want to lift the front because I plan on keeping the stock tire size and don't even like the space between the rear wheel and the bed with the blocks. I think the only other shims I can try are the 2.5 degree shims, but that just doesn't make sense to me on paper.

 

Heh there.......what device are you using to measure the angle ?

 

I have a cheap magnetic digital inclinometer that seems to work fine frankly (e.g. The side of the filing cabinet is 89.9 degrees). I put it on either flange to measure. I'm frankly at a loss here and just hoping some small level of vibration (seems to be almost oscillating) is okay in terms of longevity.

 

Try to use a machined surface......use the shaft itself then the machined part of the pinion if you can get to it / rotate to different spots....I used this method on our 9" when racing, but found an expensive digital one gave more repeatable results trying to get the suspension right. A couple degrees can be make an issue sometimes, at least that is what I found.
Hopefully someone who has done this on the same truck can expand on this for you.

 

Thats the funny thing. Everyone who has done this doesn't seem to have issues removing blocks. If i add the 1 degree shim and get within about a single degree of difference, it still has a little vibration. Im very hesitant to keep adjusting upwards because as I understand, its desirable to have a degree or so of difference so the pinion is slightly downward pointing relative to the transmission to account for axle wrap.

By simply removing the blocks, I'm:

1. reducing the driveshaft angle
2. not changing the pinion angle (i think i measured like a 2.5-3 degree difference as it comes from the factory)
3. Reducing axle wrap by reducing the mechanical leverage, which might mean I need to point the pinion up slightly. I think the 1 degree shims might have helped just a tad, but I can't get a 1.5 degree shim right? Open to shim recommendations btw.
4. Running my brain in circles because this seems to either be a problem unique to my truck or its something I have extreme sensitivity towards.

 

Maybe this is not helpful but for the sake of the discussion.
In the past there always needed to be a pinion end angle for the joints to work...... the exact number was not that important so long as there was an angle....we used 2-5 for automatic cars and up to 7 for stick. Also that said I have no idea what the factory spec is for an f150 like yours.That doesn't really apply here just an example from the cript LOL. Different trucks with different rear springs and loading will all show different results imo.
This is the reason I have not done this yet, I want to because like you the high back end angle seems high for my use, but sometimes folk don't reveal all the bits so to speak. Check back on some older threads, I think there was some mention of what angle worked. I wonder of there is a kit from somewhere with the correct shim in it.

I will be very interested to hear what your results are.

 

Remember you are also changing the relationship at the trans end, may not be much, nevertheless. I agree I have read others don't have a problem so they say. You would think that changing the box loading would create the same situation. Have to ponder that a bit, think of springs flattening, hangars moving etc.....are you sure you got the u bolts tightened properly so the rear end is aligned ? Past that I can't guess, sorry.

 

Man this has been a while ago but measure the angle of the u joints on each end of shaft. They have to be very close to matching to play nice. It has something to do with a gyro effect, imagine having 2 wheels hooked together but at different angle and spinning, 2 gyro angles fighting each other may be where your vibration is growing Jim

 

To give you a point of reference, my 2021 CCSB 4WD 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 will also add that many of the magnetic angle finders you find at hardware stores don't seem to give very repeatable results. The "clinometer" app I downloaded on my smartphone seems to do a pretty good job of giving accurate and repeatable results.

 

I had the opposite measuring success.
I found my dangling needle to be very repeatable, and the apps, not so much.
I could not get my tool to lay perfectly along either flange, rear had a buttress, and for the trans I laid an angle along flange and gauge in angle - transferring line to where I could get it.

I also found the differences is what counts: trans to shaft, shaft to trans, and all have to be same direction.
Trans lower going to rear, shaft lower going to rear, and the hard one to visualize, rear lower going to rear.

Apparently each joint requires 1/2 degree for rotation of needles.

See https://spicerparts.com/calculators/...gle-calculator