Hopefully someone can answer this one...

2001 SuperCrew with 4r70w trans, 1-piece aluminum driveshaft and 9.75 axle.

I picked up a slight shudder/vibration and noise at 40-45 mph after dropping the rear with 2" shackles and SVT coils...overall drop 1 1/2". I did some research to find out if shims would solve the problem and was shocked at what I found.

Driveline specialists say it is extremely important to make sure:
1. the relationship of the output flange on the trans and the input flange on the axle should be parallel.
and
2. the minimum angle between these flanges to the driveshaft ends must be at least 1 degree with no more than 3 degrees. The minimum 1 degree angle is required to permit dispersion of grease within the u-joints and to permit the needle bearings to wear evenly.

So...I went to Home Depot and picked up an inclinometer...a circular level with a magnetic flat base and measured the angles.

Output flange on trans is angling down (to the rear) 2.5*
Driveshaft is angling down (to the rear) 2.6*
Pinion input flange is angling down 2.5*

I have a 0.1* angle between the DS and the trans and a 5.1* angle between the DS and the pinion.

My goal is get the pinion flange almost up to parallel to the trans flange. Will I achieve this with 4* shims between the springs and axle, taking into account that I also need to increase the angle at the front? Also, I have no stock shim...just a 1/4" flat stock steel spacer.

On a side note, I did notice that the stock pinion angle seemed to be angling down quite a bit even before the drop. There seems to be quite a few owners who develop shudder, vibration and noise with no change or even a slight change in suspension drops or lifts, while others do not have any problem at all.

 

I had a 2001 ext cab lowered 3/4 and had to use a 6 degree shim this left me with a small vib at 55 under hard take offs normal driving it was hard to feel a 8 degee would have probily took it all out.

Dale

 

IF all you had where 2 shackles 2 degrees would probily get rid of it . with just the shackles I needed no shims. 4 would deff. get it if you did not go to much.

 

I developed a vibration under hard acceleration after I installed the Roadmaster Active Suspension which required removing the overload leafs (nets about 1'' of drop). If you look closely at the factory shim on your truck you will see that it probably is a 1 or 2 degree shim(you may have to remove it to see this). The vibration lessened with time.

I just finished installing a Western Chassis 3/5 deluxe drop with a 6 degree shim and finally removed the vibration after adding the last 1" with the rear shackles. I first tried 3" with the spring hangers and 1" with shackles and the vibration was severe as was the angle of the diff.(pointing down) even with the 6 degree shim. So I switched the spring hanger to the 2" position first and removed the drop shackle and used the factory one with the 6 degree shim and still had a slight vibration. Adding the last 1" with the drop shackle finally corrected the vibration.

I also swapped my leaf springs side-to-side because the driver's side was always over 1" lower than the other side (and still is about 3/4"after the swap). The arch was likewise when I compared the leafs while off the truck.

You may need the 6 degree shim.
https://www.f150online.com/galleries....cfm?gnum=1666

 

Thanks guys for all of your feedback.

I've calculated a 4.5 degree angle change going on a right triangle measurement:
Driveshaft length - 80 inches
Difference in height between the trans and pinion flanges 5.25 inches.

Did a little math to calculate the angles and came up with 9 degrees. Divided by 2 (4.5) to keep a somewhat equal angle on the front u-joint and the rear u-joint for balance, but only move the pinion up 4 degrees which allows a half degree down angle on the pinion to take torque into consideration.

I'll get the 4 degree shim, install it and post my findings.

Man...those stock rear pinion angles are really wacked. No wonder most of the SCrews have problems.

MR2X75: Do you a SCrew? I see you had an SCab in the past. I think theres a big angle difference between the Scab and the SCrew being that the Scab has a longer driveline. You'd have to see my pinion to believe it. If you had a 6 degree but couldaused an 8, then my 4 degree should be in the ballpark.

HiOSilver'01: Holy Moly...you sure went through some changes with yours to get it right huh? Frustrating to beat all hades I bet! So right now, you're at a solid 3/3 drop?????


Thanks again!

 

hey just checking to see if you got things worked out.

Dale

 

mr2x75:

I spent this afternoon determining the size of shims needed.

I jacked it up, pulled the wheels, loosened the u-bolts, jacked the front of the axle flange up level (rotated 2.5 degrees from where it was) and inserted some 1/4" x 1" flat stock between the spring perches and the existing 1/4" flat spacers which are located directly under the leaf assembly. After inserting the 1/4" flat stock as far as it would go, there was an open space behind this shim that measured out to be 5/16" which equates to ~4.5 degree shim.

I tightened up the u-bolts, slapped the wheels on and re-measured my angles:

Pinion flange = 0 degrees (flat)
Driveshaft = 1 degree down (towards rear)
Trans flange = 2.5 degrees down (stayed the same of course)

Ideally, I need to rotate the pinion up 2 more degrees to get the pinion flange closer to parallel with the tranny flange and equalize the angles on the front and on the back of the driveshaft to the respective flanges.

Now I just have to find some 6 degree shims...nobody around here carries them and Summit is back ordered.

I took it for a test drive and it was smoother, I did not get the slight thunk when starting out from a stop, and no more vibration or noise at 40-45 mph. The angle change I did apparently allows the spline to move more freely.

I also had to shorten the end links on the rear Hellwig.

Still not done with this...when I do, I'll post my final measurements.

 

Area 52

Yes, it was frustrating to say the least.

I think everything has about settled in over the last week. The front only measured 2 3/8" lower the day I installed the front drop but is lower now. Will post some new pics soon. I haven't measured again but front should be 3"and rear 3" + 1" from taking out the overload leaf.

 

HiO,

The drop looks really nice. I bet the Roadmaster really smooths out the ride compared to stock.

That trans support crack looks nasty. I'm surprised the Ford mechanics didn't catch it. Do you have the 4r70w trans and how many miles on your truck now?

Kevin

 

Kevin,

The Roadmaster does help smooth the ride and reduce sway ( the main reason I bought it since SCrew's don't come with rear sway bars). It also reduces wheel hop very well. If you decide to get one make sure to get the heavier duty version that they recommend for Expeditions - the sway reduction seems to diminish some a week or so after adjusting the tension on the springs. The
truck corners very well after the drop though.

I too have the 4r70w trans. and 36,582
miles as of today.

Glad to see you figured out your angles

 

UPDATE....UPDATE....UPDATE:

I finally received my Belltech 4 degree* axle shims and installed them yesterday. (I was previously using some 1/4 inch flat stock spacers on the back side of the spring perches.)

I reversed the stock 1* shims (which previously I thought were flat) and slipped the new 4* shims in between the leaf pack and the stock shims. By reversing the stock 1* shims and adding in the 4* Belltech shims, I was able to rotate the pinion angle almost 6 degrees upward. The pinion flange is now just below parallel of the tranny output flange to permit a slight upward rotation under load, and I have enough of an angle on the front and rear of the driveshaft to permit the proper lubrication and wear on the u-joints.

With the addition of the 4* shims, I barely had enough threads left on the stock u-bolts though when I cinched down the leaf packs onto the axle.

Again...no more "grrrring" sound or vibrations at 40-45 mph, and...and...and...no more driveline thunk starting out from a stop.

My driveline is now set up just right!