Dr. Diff Spring Relocation and 2" lift springs... Question about Pinion Angle

[glitch340]

Okay... So while pulling the transmission out to rebuild it on my '73 'Cuda, I decided to throw some 2" lift springs in the back. While removing the originals I had several front spring hanger bolts break off due to some rust issues. So I decided to get Dr. Diff's 1" offset hangers and 1" offset shackles...

Here's my question...

My plan was to grind off the old spring perches, mount everything up and check the pinion angle with weight on the springs. Then tack weld the new perches in place, remove the rearend again and bring it down to a local welding/metal fab shop to run a good bead on the perches. Then I realized that'll be a LOT of extra work. So my question is with only 2" of lift, is the pinion angle going to change significantly? or can I just take the rearend down to the shop now and have them match the new perches to the old angle and weld them on, then mount it back under the car and if I need to maybe add a shim???

Any help is greatly appreciated. I have angle finders and all sorts of stuff to find pinion angle, but I wonder how acurate a person can actually be with them, but that may come from my surveying background where we like to be within 5 seconds of an angle. So would it be better to keep the stock angle even with the 2" lift springs?

[glitch340]

Also... What's the best thing to do with the sway bar? Can it be bent slightly? Should I build a new bracket for the links? Can a B-body Swar bar be used instead? Is there one made specifically for this purpose?

[Killer_Mopar]

Also... What's the best thing to do with the sway bar? Can it be bent slightly? Should I build a new bracket for the links? Can a B-body Swar bar be used instead? Is there one made specifically for this purpose?

  I read on here that it could be bent, however every time I tried it - the bar just sprung right back. Due to its size I couldn't get it to seat in my 20 ton press, so I tried a come-along and a trailer hitch....pulled it a good 8-10 inches and it sprung right back. I was thinking about going further but didnt want to chance the bar breaking and scratch the truck. Im probably not going far enough, but something about seeing steal spring that far doesn't sit easy with me. I'll revisit it this weekend if I get a chance and report my findings....

[dutch]

I would not try to bend it. Usually these bars are made of spring steel and they are hardened after bending so you will have a pretty good chance to get cracks... visible or not... 
If you want to bend it, the best way is to have it annealed, then bent and hardened again.  ( this could take some time to figure out unless someone knows exactly what steel grade was used...)
building new brackets would be my first choice.

[glitch340]

Okay, I was leaning toward new brackets. I'll start having a look at those. Any idea on pinion angle? Should I cut the old perches off and mount everything up, then tack the new one's in place, remove the rearend and get them welded, and mount it up again? Or should I just have the shop weld the new ones in at the same angle as the old ones?

[challydust]

Good luck with tryin to find a straight answer on pinion angle anywhere....im goin through this now and have had 8 differrent answers oh how or where to measure angle....I wish i could help you...but no one seems to agree on one perticular method.  Only thing i gathered was if ur angle is too steep....the car would be tough to roll in neutral, or u get a bad vibration....or take out ur tailshaft bushing.....good luck

[HP2]

I'd say start with the original angle, put it all together and see where you come out.

On the sway bar, a B body unit will work if you want to retain the stock appearance. You can also alter the link ends so long as the bar does not interfere with your tires. Another option is to go with an under axle unit.

[ericindc]

Honestly, I come from a Jeep backgrouns, I dont think a 2" increase is going to be enough to cause problems.  Even on Jeeps (much shorter wheel base), a 2" lift doesnt mean you need a pinion angle change.  I agree that you should just put it together and see if you have issues. 

[glitch340]

Thanks for the replies guys!
I think I'll go ahoed and remove the rear end and have the shop put the new perches at the same angle. Then when I'm mounting it all back together I'll measure the pinion angle and trans/tailshaft angle and see how it does. If it doesn't seem to be working right I'll go ahead and throw in a shim.

[Changin Gears]

If you want to see what the pinion angle with 2" lift is, jack the body up 2" and measure.

The easiest way I have found to measure the pinion angle is off the flats of the u-joints.  I space out my angle finder with a socket off a u-joint flat pointing down, rotate the drive shaft 90 degrees and repeat.

This works on the front u-joint also.

Assuming a 50" drive shaft, a 2" rear change, means about 2 degrees of pinion angle change:

inv sin(2/50) = 2.3 degrees


I would just bolt it together, measure it, then change if needed with spring angle shims.

[glitch340]

Yeah, I think I'll bolt it all together and change it with shims if needed. As for your formula, I don't know if I agree with it. That's what I was thinking to begin with, but then though about the lift, it lifts the body of the car 2 inches relative to the rear axle, but that actually changes the angle because it's pivoting around your front wheels, therefore you're not raising the transmission a full 2 inches, but you're changing the angle of the transmission compared to the rear axle. I think the same formula would work if you took into account the wheelbase and the location of the transmission.

[Changin Gears]

The front wheels have nothing to do with this.  If the axle moves down 2", the back the the drive shaft moves down 2".  The front of the drive shaft hasn't moved up or down at all.  This all uses the body as the reference.  This is all correct because the pinion angle has nothing to do with the angle of the ground.

[glitch340]

Yeah, I thought about it again, and you're right. Sorry. I didn't mean to sound like an ass, I've had a long day and when I sat down to calc the angle change it wasn't making any sense. I kept picturing the diff staying at the same angle relative to the car frame, etc. and was figuring that the angle wouldn't change because it's just going to make the angle on each end of the driveshaft increase slightly. But considering the pivots of the leaf spring, it will change the angle of the diff slightly. I need sleep. Thanks for all your help everyone!

[larry4406]

Regarding the sway bar, one of the resto threads here or on moparts had detailed pictures where the mounts were cut and splayed apart, metal plated welded in, and a 2nd hole added.  After paint they looked pretty convincing and kept the sway bar as-is.

[glitch340]

Yep, I've got that one bookmarked! I'll be doing mine the same way