Wheel Hop Problem

[Ronk]

I'm having a wheel hop problem in my '73 Challenger.  It was really bad this summer whenever the tires broke free.  I figured since I am going to be installing a more powerful motor this spring than the 383 I have now, I had better try to get a handle on this.  I ended up replacing the shocks (completely shot) and leafs.  After that it was still doing it just a hair less, but was still pretty violent.  I went with KYB shocks and the MP XHD springs.  Replaced all the spring and shackle bushings as well.  The pinion snubber is set about 1/2" to 3/4" from the floorpan.  Tires are BFG T/A radials.  I was thinking the clamps on the front half of the springs might help, but was looking for your opinion on what is causing this or what I can do to fix it.  Thanks! 

[brads70]

Pinion angle? Shocks? Maybe try setting the pinion snubber farther away from the floor?

[Strawdawg]

snubber is often set around 3/4-1"  Half inch is pretty common at the track....  wonder if the body is getting kicked up and unloading the rear by some means?

kinda doubt it would be the pinion angle unless it is way off....purpose of putting some negative angle to it is to have it straight under power to maximize power transfer instead of wasting in in a bind condition.

[Moparal]

Make a pass with your snubber off and see.

[Strawdawg]

also, does the car have Sure-Grip?

[Ronk]

Pinion angle? Shocks? Maybe try setting the pinion snubber farther away from the floor?

Not sure what the pinion angle is, I'll have to go pick up an angle finder.  It rolls pretty easy in neutral.  Shocks are brand new KYB's.  I thought the old shocks might have had something to do with it because after I took them off I could compress them and they would stay compressed.
 

also, does the car have Sure-Grip?

It does have a SureGrip.  I'll try taking the snubber off and take the car out for a spin as soon as the snow goes away.

[Strawdawg]

check the length of stripe on both sides

[femtnmax]

Everyones comments are right on target.  Wheel  hop is caused by too much/not enough U-joint angle. One U-joint cap is going real fast, the opposite is going real slow...thus causing the hop hop hop.
I have to ask...Did you install the XHD springs on the correct sides of the car???  The right hand side, passenger side has the short leaf (at the bottom of the leaf spring stack) facing forward.

[Ronk]

check the length of stripe on both sides

If it didn't hop so bad I could leave a stripe.   

I have to ask...Did you install the XHD springs on the correct sides of the car???  The right hand side, passenger side has the short leaf (at the bottom of the leaf spring stack) facing forward.

I just check the spring orientation.  The left hand side has 6 leafs with the shortest one on the bottom being of equal length on either side of the axle tube.  The right hand side one has 6 with the bottom one cutoff right under the axle tube and it is facing forward.  Glad they are in right.   

I guess I lied about the snubber.  I got my memories mixed up (should have checked).  It is a non-adjustable one and it is sitting 2" from the floor pan.

I just got done figuring out the angles but I'm not sure my math is up to par.  I raised the car up on jack stands under the suspension so the car had all its weight on the suspension.  It wasn't completely level like it would be while sitting on the ground.  Does that make a difference?  Do I have to grab a reference angle from somewhere?  I used a magnetic angle finder set on a socket on the u-joint caps.  It looked like the transmission was angled down 4.5 deg.  The driveshaft was angled down towards the back .5 degrees.  The pinion was angled up 2 degrees.  From reading other threads I gather that the pinion is supposed to be pointing down instead of up.  If I did the measurements wrong, please let me know and I will get new numbers and post them up.  Thanks for the help so far.

[brads70]

I always set the pinion down 3 degs. Up is not so good. I'm more familiar with stock car racing than drag racing but 3 degs is where we start?

[Cooter]

Well, there's always slapper bars....

[femtnmax]

I guess I lied about the snubber.  I got my memories mixed up (should have checked).  It is a non-adjustable one and it is sitting 2" from the floor pan.

I just got done figuring out the angles but I'm not sure my math is up to par.  I raised the car up on jack stands under the suspension so the car had all its weight on the suspension.  It wasn't completely level like it would be while sitting on the ground.  Does that make a difference?  Do I have to grab a reference angle from somewhere?  I used a magnetic angle finder set on a socket on the u-joint caps.  It looked like the transmission was angled down 4.5 deg.  The driveshaft was angled down towards the back .5 degrees.  The pinion was angled up 2 degrees.  From reading other threads I gather that the pinion is supposed to be pointing down instead of up.  If I did the measurements wrong, please let me know and I will get new numbers and post them up.  Thanks for the help so far.

Does not matter that the car is not level...reference is to relative to the drive shaft "tube", then the angle to the pieces on each end beyond the u-joints...sounds like measuring off the u-joint caps might work, but there may be too much slop in the socket...suggest remove pinion snubber and measure off that big flat surface where the snubber bolts to the rear differential.
Brads70 is correct...pinion should point down NOT up.  That way when you accelerate, the "down angle" changes to "less down" or none.  Shim axle housing to have correct initial degree angle, then that is where the pinion snubber comes into play, the snubber stops any further amount of pinon angle change by making the rotating pinion/differential actually lift the back of the car thu forcing the tires into the pavement.   Keep at it, your getting there.

[dodj]

Well, there's always slapper bars....

They're just wrong...

[Ronk]

Well I remeasured with the car on the level garage floor, just so I have a better feeling of the measurement while it is on it's tires.  I came up with 2* down on the driveshaft and 0* on the pinion off of the yoke.  I couldn't fit the gauge up on the top of the snubber mounting location with the snubber removed.  I went over to our local 4x4 shop and picked up a set of 4* shims to throw on there.  I'm assuming the 4* shims should get me where I need to be.  I hope this works!!  I'm having longer u-bolts made to accommodate the shims as I only have 2 threads showing on the end of the u-bolts as it sits.  I'm planning on installing all this tomorrow on a lift at the auto hobby shop on base.

My other question is do I need longer spring pack bolts to hold the shims in place or will the shims fit in there just fine?  I noticed on my old set of springs that the bolt that holds the spring pack together is specialized on the side where the axle mounts sit.    It looks like a rounded off dowel.  I unfortunately did not pay too much attention to how all that fitted together when I replaced the springs.   The shim is 3/8" in the center where the dowel would go through and the dowel is 5/8" long.  It seems to me that 1/4" sticking out of the top for where that dowel needs to locate on the axle is too short.  What do I do here?

Thanks everyone for all the help so far.  As soon as I get through this I'll let ya know how it turns out.

BTW, had slapper bars on a 1971 Roadrunner and I hated those things.  Worked great for traction, but they drug on everything and just didn't look right.   

[femtnmax]

RonK - sounds like the shims may have too much angle to them.  What is the shim thickness on the "thin" end of the shim?   I'm asking because the 3/8 inch thick at the center sounds like a lot.
Do you know the angle of the shim.
If I try and figure out the angle of the shim, here is what I have:
Assume the shim is 4 inches long.
Looking at the shim from the side, thin edge to the left, thick edge to the right.  Half way along the shim at the center hole the shim is 3/8 inch thick (thats .375 inch), and the length from center hole to thin edge is 1/2 of 4 inches=2 inches.
 
Assuming the shim is very thin at the "thin" edge, and 3/8 thick at the center hole in the shim.
So the Tangent of the angle formed is .375/2=.1875
The inverse function of tangent is Arctangent.  Solving for angle "theta" = arctangent .1875

Now go to internet, handy arctangent calculator:
http://www.rapidtables.com/calc/math/Arctan_Calculator.htm

The answer is 10.6 degrees.  This is WAY too much angle.
My assumptions may be wrong.  If they are close, then you need much less angle, which would mean a thinner shim so you would not have to worry about the amount of leaf spring center bolt sticking out of top of leaf spring stack.  Do some research to find what correct angle should be, although 2 degrees difference between driveshaft and pinion does not sound like too far off.
If the car is has an auto transmission, see if you can powerbrake it, and have a friend off to the side of the car and take a picture of driveshaft/pinion gear...is pinion now pointing parallel with driveshaft, or maybe pointing above the driveshaft?