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

 

[Sheriff41]

Have you checked your tail housing bushing? Vibrations at higher speeds are usually due to loose or worn parts in the driveline.

 

[Billw69]

Thanks for the input guys. That gives me a great starting point and it’s where my focus has been. Before I started this project. I drove it over a pit and measured the driveline angle at 3° down and the pinion angle at 3° down. My question would be these angles need to cancel or can they be positive positive or negative negative depending on how you look at it? If there’s a requirement to offset angles, that makes perfect sense to me regarding u joint function.
Regarding the tail shaft bushing on the transmission I’ve had the trans rebuilt, and I also had the driveshaft balanced at the same time. Unfortunately, the Business that did the driveshaft balance lost my driveshaft …… that’s a whole Other story, so I got a brand new one which could be considered good since it’s certainly straight. I also assumed that when I take my transmission in to a reputable business for a rebuild that they would change the bushings to the input as well as the tail shaft, again that is an assumption on my part. I’ll look into it.
I’ve been using an app on my phone as a digital angle finder, seemed to work pretty good. In the interest of leaving no stone unturned I bought a digital magnetic angle finder and will be using that going forward.
My plan is to clean up the surface of the exiting perches that are in the stock location, weld up the holes and redrill them to eliminate the oblong shapes. Then reassemble, put weight on the wheels and recheck my angles then.

Here are some visual aides

 

[tony-muscle]

Thanks for the input guys. That gives me a great starting point and it’s where my focus has been. Before I started this project. I drove it over a pit and measured the driveline angle at 3° down and the pinion angle at 3° down. My question would be these angles need to cancel or can they be positive positive or negative negative depending on how you look at it? If there’s a requirement to offset angles, that makes perfect sense to me regarding u joint function.
Regarding the tail shaft bushing on the transmission I’ve had the trans rebuilt, and I also had the driveshaft balanced at the same time. Unfortunately, the Business that did the driveshaft balance lost my driveshaft …… that’s a whole Other story, so I got a brand new one which could be considered good since it’s certainly straight. I also assumed that when I take my transmission in to a reputable business for a rebuild that they would change the bushings to the input as well as the tail shaft, again that is an assumption on my part. I’ll look into it.
I’ve been using an app on my phone as a digital angle finder, seemed to work pretty good. In the interest of leaving no stone unturned I bought a digital magnetic angle finder and will be using that going forward.
My plan is to clean up the surface of the exiting perches that are in the stock location, weld up the holes and redrill them to eliminate the oblong shapes. Then reassemble, put weight on the wheels and recheck my angles then.

Here are some visual aides

The angles have to cancel so the vibration "cancels" each other. Since the transmission is down the pinion should be up. However, I am talking about the transmission shaft canceling the differential pinion. Not the drive shaft.

 

[mjlan]

Holy crap those spring perches are trashed!

To add to the great info that Tony is providing, the representations of the relative angles of the tailshaft housing and the pinion centerline are when the system is loaded, which tends to rotate the rear axle up. If you are racing the idea is to bias the pinion CL down a degree or two to account for the climb under load since the car will spend the majority of its time operating in this condition. If you are not always operating in this load case then its debateable how much joint life biasing the angles will provide, so most just set them up as the graphic shows in a static condition.

As for verifying the trans tailshaft bushing wear- if you feel any movement (up-down or side-side, rocking etc.) in the drvieshaft slip yoke when you slide it into the trans then you WILL have a vibration. Either the busing in the tailshaft housing is worn out or the OD of the slip yoke is worn.

 

[Billw69]

Well as they say: a pictures worth a thousand words. Those diagrams are incredibly helpful thank you. I can easily check the play on that driveshaft slip yolk into the tail shaft since I haven’t removed the driveshaft I just suspended it.
Based on what I’ve been given, I intend to remove the shims from the perches, clean up the surfaces, light welding to fill in the elongated holes and then re-drill them. Then I’ll reassemble it, put some weight on the wheels and remeasure the angles.
Question: how critical is the size of the hole in the perch in relation to the bolt head in the midst of the leaf springs? Should that be a tight or snug fit or is a little slop acceptable? I’m assuming it translates to alignment issues if it’s way out. what would be considered “way” out
Thanks for the invaluable input Tony. The diagram and your links are a great deal of help!

 

[Billw69]

Thanks Matt for your note as well, makes perfect sense now!

 

[tony-muscle]

Well as they say: a pictures worth a thousand words. Those diagrams are incredibly helpful thank you. I can easily check the play on that driveshaft slip yolk into the tail shaft since I haven’t removed the driveshaft I just suspended it.
Based on what I’ve been given, I intend to remove the shims from the perches, clean up the surfaces, light welding to fill in the elongated holes and then re-drill them. Then I’ll reassemble it, put some weight on the wheels and remeasure the angles.
Question: how critical is the size of the hole in the perch in relation to the bolt head in the midst of the leaf springs? Should that be a tight or snug fit or is a little slop acceptable? I’m assuming it translates to alignment issues if it’s way out. what would be considered “way” out
Thanks for the invaluable input Tony. The diagram and your links are a great deal of help!

Good question. I don't know the right answer but every time I have installed springs the holes are bigger than the nut on the spring. I think they are meant to be loose so the perch aligns itself while the U bolts are being tightened around the axle. That's why you want to tighten the U bolts in steps. But again, I could be way off.

 

[Billw69]

Sounds good, glad I’m not the only seeing that.
Thanks Tony

 

[giantpune]

Also worth noting that you don't want to make the input and output parallel while the car is stationary. When you are actually driving the car, the rear end squats and the rear axle housing rotates (wraps). The way you are using the car and the type/firmness of suspension play a role in how much the rear axle's position will change. 4 link will have less wrap than leaf springs. Traction bars on leaf springs will also have less wrap than stock.

Copy paste from QA1.

Many drag racers adjust their pinion angle to optimize operating angles for maximum power delivery when the car is under power. The less operating angle in the u-joint, the more power will make it to the rear tires. By compensating for pinion rise in their static pinion angle, racers can minimize pinion angle during hard acceleration. Ladder-Bar and 4-link suspensions offer a lot more control of the axle, and therefore the pinion. But drag racers will still set up the pinion angle to compensate for the rise. According to Pro Stock chassis builder, Jerry Bickel, ladderbars require ½° of pinion angle. A 4 link requires 1-2½°. Vehicles with leaf springs can require 6-7°.

For a good visualization of non-parallel u-joints, there are some silly lego videos. You can see how the non-constant velocity joints stack up.

 

[turtle5353]

When I did mine, I removed old rearend. Put it on jack stands and got the yoke 100% level. Then placed angle finder on old spring perches and recorded number. Then did same thing with new rear end and weld perches on to match old numbers. Figured the factory perches should be in correct angle.