Hmmmmm….I had that same vibration right before I put new springs. Maybe it fixed mine with the new springs maybe it sagged the rear down and had the pinion angle messed up.
Don't they make some adjustable engine and transmission mounts?

My advice was based on what is considered “correct angle theory” not on any success I have had over twenty years chasing my vibration with varying pinion angles. ☹️

7* Down on the transmission sounds excessive for a T5 swap. It should be around 3.5* Down. Use the wedge shaped shims to bring the pinion up to an angle of about 2*-3* Up. The pinion usually needs to be slightly less Up than the transmission is Down to account for "pinion climb" during acceleration.

I agree that 7 degrees down seems like a lot. I am at 4.5 down.   Another 6 degrees down on the driveshaft, after the engine is already 7 degrees down also seems like a lot. My driveshaft is 2.5 down. What motor mounts do you have in the car?   You might want to think about getting some Ron Morris adjustable mounts to lower the height of the engine to reduce that downward angles a bit.

But as to your specific question, this is a good article that should be helpful.

https://www.diyford.com/ford-restomod-rear-suspension-guide/

You can easily check your angles yourself. TREMEC makes a good app you can download to your phone or you can just use an angle finder.  The TREMEC app works pretty well, but I find that the buttons on the side of your phone can throw things off a bit, but that may depend on which phone you have and where the buttons are.

To find your angles, take a reading off something that is parallel with the crankshaft (I measured from the 6 o'clock position on the harmonic balancer), then take a measurement off the driveshaft, and then take a measurement off a flat spot on the diff that is parallel with the pinion.  Once you get all of those angles, then you can figure out what, if anything, you need to adjust.

Those measurements make more sense than your 1st set and are pretty close to mine.  I have not had my car at highway speeds yet, so I don't know if I have any vibrations with my set up. Will test that on my next test drive. 

I am by no means an expert on this but have been looking at this as I have wondering if I am going to have to go through the same exercise.

My understanding is that ideally you don't want the working angle of either u-joint to be greater than 3 degrees and you want to have the working angles of both u-joints to be within 1 degree of each other.

Do you have any ability to shim up the trans a little bit to reduce the tail shaft angle at all?   

For sake of discussion, let's say your tail shaft is 4.5 down.

If your driveshaft is 2.4 down, I would say that is ok because there is apx. 2 degree difference in those angles, which is less than the 3 degree recommended max working angle.

The next angle to look at is the pinion. At .8 down on the pinion (and I assume you mean the front of the pinion is facing down towards the pavement), with a 2.4 down on the driveshaft, the total working on the u-joint is 3.2, which is over the magic number of 3.

So, if you put a 2 degree shim under the rear axle, it would change your pinion angle to +1.2 degrees up and then change the working angle of the rear u-joint to +1.2 up (2.4 down on the driveshaft plus the 1.2 up on the pinion).

Now keep in mind that ideally the goal is to have the working angles of both u-joints with in 1 degree of each other. With a 2 degree shim under the pinion and other measurements as described above, that should get you there because each u-joint will have a working angle under 3 degrees and the difference in the working angles is within 1 degree of each other, i.e., +/- 2 on the front joint and 1.2 on the rear joint.

The other thing to keep in mind is that when you put a 2 degree shim under the axle it will probably also reduce your driveshaft angle a little bit since the pinion will now be higher than it was before, so the above calculations may be off a bit, but I think a 2 degree shim would be a good place to start.

Appreciate comments from others as well.

Last edited by Chaplin (4/27/2021 7:31 AM)