Leaf spring perch install

[Billw69]

I’m replacing the spring perches on my B1, wondering if their surface should be parallel to the pinion angle or do I need to include some angle? Seems to me that parallel with the pinion would allow the use of shims to accommodate driveline geometry? Suggestions.

Thanks

 

[mjlan]

If it was me I would locate the perches so that no shims were needed to get the desired pinion angle.

 

[Billw69]

Makes sense. I looked over an axle out of a ‘71 staggered shock car today at a friends shop. Using a magnetic angle finder I was able to determine the perch’s have an approx. 10-11 degree difference from the pinion angle. This makes sense knowing the leaf springs are not level at the attach point of the perches due to the arc of the leaves .

 

[Stanglover]

I could well be wrong, but I think the pinion angle should be 3 degrees.

 

[tony-muscle]

At the end of the day you want the pinion angle to match the transmission output shaft angle within 0.5 degrees during normal driving to reduce the chances of vibrations. The transmission shaft angle is the same as the engine angle. For reliability you don't want the angle between the u-joins (drive shaft to pinion) to be more than 3 deg. However, up to 5 deg it would work but you start losing longevity. This is all what I remember when I researched this topic back in the day when I redid my whole drive shaft.

In my not-stock car the engine and pinion angles are at about 4 deg +/- 0.5. I had to use shims on the springs to fix the pinion angle.

 

[Billw69]

Thanks for the excellent input!
I’ve been chasing a driveline vib that occurs north of 65mph. It’s not harmonic but I see it and hear it in the shifter lever. Since I have the winter I decided to take off a welded on set of locating plates (welded on the top of the perch’s) from the axle housing. This car was a dedicated drag car in the early to mid ‘70s. The plates were a quarter of an inch thick and had a locating hole for the leaf spring drilled in the middle. After removing the plates, I discovered that the original perch holes for axle location on the leaf springs had been elongated significantly, indicating to me that the U-bolts obviously weren’t snug, and the launches on the dragstrip had elongated the holes into slots. I also found two shims one on each side that were welded underneath the rear of the added plates, these were welded on the back part of the perches and brought the pinion angle nose down. they're about a quarter inch thick also adding to the shims which placed about a half an inch pad on the rear of the leaf axle housing perch over the stock configuration.
When I measure the angles of the perches compared to the angle of the pinion, they are parallel. I believe the angles should be different and I’m interested in finding out what drawings might indicate those two lines should be. when I measure other stock axle housings for the 9 inch I find about a 10 or 11° difference between the angles of the pinion and the perches as stock.

If any of the experts have any input it would be greatly appreciated.

At this point, I intend to reassemble it as close to stock as I can come up with, then drop the car on the wheels and remeasure the driveline angles in the hopes of eliminating that vibration

Thanks, Bill

 

[tony-muscle]

Thanks for the excellent input!
I’ve been chasing a driveline vib that occurs north of 65mph. It’s not harmonic but I see it and hear it in the shifter lever. Since I have the winter I decided to take off a welded on set of locating plates (welded on the top of the perch’s) from the axle housing. This car was a dedicated drag car in the early to mid ‘70s. The plates were a quarter of an inch thick and had a locating hole for the leaf spring drilled in the middle. After removing the plates, I discovered that the original perch holes for axle location on the leaf springs had been elongated significantly, indicating to me that the U-bolts obviously weren’t snug, and the launches on the dragstrip had elongated the holes into slots. I also found two shims one on each side that were welded underneath the rear of the added plates, these were welded on the back part of the perches and brought the pinion angle nose down. they're about a quarter inch thick also adding to the shims which placed about a half an inch pad on the rear of the leaf axle housing perch over the stock configuration.
When I measure the angles of the perches compared to the angle of the pinion, they are parallel. I believe the angles should be different and I’m interested in finding out what drawings might indicate those two lines should be. when I measure other stock axle housings for the 9 inch I find about a 10 or 11° difference between the angles of the pinion and the perches as stock.

If any of the experts have any input it would be greatly appreciated.

At this point, I intend to reassemble it as close to stock as I can come up with, then drop the car on the wheels and remeasure the driveline angles in the hopes of eliminating that vibration

Thanks, Bill

I would focus on the pinion angle rather than the perches. Find the appropriate shim to match the pinion angle to the transmission angle as close as possible within 0.5 degrees if you can with the car loaded. Now I know that for drag racing they would have the pinion angle lower to compensate for when the axle rotates. That said, there are different setups. So again, for cruising you want the transmission and pinion angles to be close. If you are drag racing or have a lot of power upgrade to thicker axle U bolts and box the areas where the perch is welded to the axle. You can read here my Q and A from a couple of years ago: https://7173mustangs.com/threads/leaf-springs-u-bolt-recommendations.32765/
Boxed perches: https://7173mustangs.com/threads/mu...hread-1971-m-mach-1.19381/page-13#post-338446