2" lift shackles WILL lift your van 2"s - leave it to the ex

[moonbuggy]

Myth buster Moonbuggy says.........YES; hello? are we stupid......NO, hello! O.K. so here's the scoop, stock spring hangers are 4 1/4 in.'s from center to center of mounting holes (he said mounting ). the INSTALLATION holes on the 2in. lift shackles are 7 1/2in.'s from center to center. making a 3 1/4 in. improvement of lift at the rear shackle and 2 in.'s at the axle. now about pinion angle ,................... THAT is relative to drive shaft angle, not "Level" or transfer angle..........so, need not put so much thought into that with only 2 in. lift at shackle.

[loopie]

now about pinion angle ,................... THAT is relative to drive shaft angle, not "Level" or transfer angle..........so, need not put so much thought into that with only 2 in. lift at shackle

I get your humour ...and love the red. Nice

About pinion angle...the tranny end of the driveshaft angle is set. The distance from the rear leaf spring center pin to the front spring eyelet and the spring perch on the axle is set (and determines the pinion angle and is a fixed pivot point of the rear axle)) and the stock setup have these two angles one and the same....Or else you may experience driveline vibration.
They have to match. The typical tranny end angle might be -3*...so the diff pinion will be +3*...any vibration caused by being 3* out of balance gets cancelled out. 0*...Smooth ride.

Extend the shackle....it will change the angles at both ends of the driveshaft but more so at the pinion than the tranny. Lets guess the tranny end is now at -3.5* but the pinion is at +4*...you've just introduced .5* that will cause vibration somewhere in the rpm range of the driveshaft.

[moonbuggy]

Ah yes, the "Loop Effect", so will the shims offered at say; olv work to counteract that, they offer 2 and 4 degree pinion shims?

[chevy57bert]

so lets present the people with a solution.
to what degree is the pinion angle changed with 2 in."s of shackle lift and, is there a set of shims available to off set the difference?
now some people probably have "just done it" . that is put in shackles with out addressing p/a. so... does it vibrate?

[Dirk]

Well I dug up the old calculator and threw some math at this question.
Theoretically you get 2.2 degrees of increased pinion angle for every inch of lift, that would result in 4.4 degrees for a 2 inch lift.

For those of you that would like to know the math please PM me and I'll try and explain it.

[Gary]

Nice.

[Dirk]

Thanks Gary, I figured with all this talk about lifting and cracking springs I'd give it a go on the old calculator and find out what the actual changes would be.

I would like to know if this change in pinion angle would be within tolerances or if it would be necessary to readjust the pinion angle to what it was before the lift. Off course it would be best to stick with the non lifted specs but just for kicks & giggles I would like to know the tolerances.

A little side note, please do remember to reposition the bump stops as the standard location would not be sufficient in case of bottoming out the suspension.

[Gary]

You know Dirk I don't know what the tolerance would be.For me it is a save bet to restore the pinion angle to stock.Can't forget the range the rear end goes threw driving down the road which the stock spec allows.No re-welding needed.Just the proper shims which is easy to deal with.Doing that insures no problems.

[Dirk]

I totally agree Gary, better safe than sorry!
I was just wondering what the tolerances would be on the pinion angle, just for kicks.

[Lumpy]

If you lift it with rear shackles, and then use shims, which way do you install
the shims? With the thick end FORWARD and the thin end REARWARD?
Thereby cancelling the angle created by the shackle extention?

Or do you put the narrow end of the shim FORWARD to try
and reduce the angle of the rear U joint?

Doing the former would appear to make both the Trans to driveshaft
AND the Diff to driveshaft angles equal. I"m thinkin' that's a good thing,
both angles equal. That would probably wear out U joints faster than
stock, but at least both angles are "balanced". Having the two angles
different seems like it would invite vibration and tend to wear bigger,
more expensive parts, like transmissions and differentials.

Am I looking at it the right way?


Lump

[loopie]

That's exactly right Lumpy:)
Thick end of the shim to the front to tilt the pinion down. Matching the angles at both ends of the driveshaft(assuming a guy used the correct shim spec).
Yes, lifting any vehicle increases the working angles of the ujoints involved...but in my experience and that of friends over the yrs with moderately lifted vehicles...a reduced service interval on the ujoints is very minimal. So far apart and so cheap that it really doesn't come up as an issue of concern:) It's really only a notable concern with shorter wheelbase vehicles than our vans...Toy's/Jeeps/Suzuki's...

[Dirk]

Readjusting the pinion angle should in theory result in zero extra wear on the U joints.
You reset the angle to the original position thus canceling out any adverse effects of the lift.

Lump, your first thought was right.

[Gary]

Readjusting the pinion angle should in theory result in zero extra wear on the U joints.
You reset the angle to the original position thus canceling out any adverse effects of the lift.

Lump, your first thought was right.

Times two Dirk.

[kennyj]

Lumpy,
Here's a little experiment/demonstration... take one of these u-joint swivel adapters and put an extension on each end; rotate one end smoothly in your hand while holding the other end and change the angle between them. You'll notice the driven end starts to turn unevenly; it accelerates and decelerates each 1/2 turn of rotation, and it's not a subtle amount. If you add a second swivel and match the angles, the change in velocity is cancelled out and the second driven part turns smoothly.

Driveshaft u-joints do the same thing; if there's any angle between transmission and driveshaft, the driveshaft changes velocity twice in each rotation. An exact matching pinion angle cancels out the velocity change so the pinion is driven at a constant rate. Constant velocity joints (CV joints) don't have this anomaly.

[Lumpy]

So what's a CV joint, exactly?

I've had them on front wheel drive cars.
Looks like 2 u-joints back to back.


Lump

[loopie]

http://en.wikipedia.org/wiki/Constant-velocity_joint

[Dirk]

There is one thing that keeps bugging me.

The lift shackle is 3.25" longer than stock.
Stock springs are a total of 54" long, the axle is located 26" from the front of the spring which leaves 28" towards the rear.
Simple logic says 3.25" is not enough to get a 2" lift at the axle, a 2" lift at 26" should be a 4.15" lift at 54".

[vangogo]

I recently put shackles on the rear of my '99 Astro...and yes it does vibrate (ALOT). Deep rumble when I touch the accelerator. I had it inspected by a tire shop and driveline shop, just to rule out other causes. Shopping for shims today.

[Bread Van]

Vangogo please let us know which shims you install and if they improve the vibration.

[vangogo]

Welp, I decided to go a different route. After eye-balling my van and its perfectly level stance with the 2" shackles, I decided it needed a bit more lift to the rear (giving it a slight rake). My springs have always been a bit saggy, I decided I might as well pull them out and re-arc them, and it only made sense to have them beefed up to do the entire 3" lift (opposed to 1" re-arc plus 2" shackles). So the spring shop did the work this morning, now I have 3" lifted springs in the back, stock shackles once again (and I will probably post my barely used 2" lift shackles for sale soon). The new leaf springs corrected the pinon angle and got rid of the vibes.
I was also previously using the Hellwig 815 helper springs with the shackles, (to compensate for the saggy leafs) and noticed that the vibration with the shackles alone was not that bad...but when I added the helper springs it became very noticeable.