I have a 67 442 Sport Coupe with an M21 and a posi rear axle. It is rotisserie restored and completely stock except for having the w30 profile camshaft and 205 70-14 radial tires. The rear springs were not a great reproduction so the rear is a bit higher than it should be, by maybe as much as an inch.

When I stand on the throttle in first gear as the tires start to break loose they start hopping. It will hop so violently that I broke the original P housing 3.55 rear end (longer more emberressing storey). I happened to fall across a P housing 3.90 axle so I went through that one and installed it. New upper control arm bushings in the diff and rechecked all the rest. Same thing.

As background, I'm old and have held an Auto Journeyman's ticket for longer than I care to mention. So I do have a pretty good grounding in the subject. I know to tighten bushing through bolts in their normal sitting position. I've checked for looseness back and forth from the engine to the diff. All engine and trans mounts are new and tight. All cross member bolts are tight. I know that for the 442 the rear upper inner control arms go in the upper holes in the frame.

The significance to the being old part mentioned above is that I knew these cars in the 70's. I'd been away from this stuff for a long time and I bought this one to restore because it was pretty much identical to one a friend had back in the day and I loved that car. And that car never had an issue with wheel hop. And guys back then used to put air shocks on and jack up the rear end to fit wider tires on and that angle change didn't cause issues.

So, am I missing something? Or is this perhaps a result of better tires than the old F70 14 bias ply tires you could smoke off like nothing back then?

Steve g

 

What shocks are you running? You need to transfer more weight to the rear axle.

 

I have off the shelf name brand gas filled shocks. Back in the day we used an 80/20 or 90/10 shock up front to shift the weight to reduce wheel spin. I know if I eliminate wheel spin I eliminate wheel hop, but I'm wanting to find out why the wheels hop. With or without the shock change my recollection is that these cars never experienced the hop way back when.

Thanks for the input.
Steve g

 

From what I have seen,when guys tried to lift the car with air shocks,they got wheel hop.I saw one so bad,it broke the pumpkin,ripping the axle tube right out.
Getting the rear of the car down would be a good start.
As for the holes in the frame for the upper control arms,the lower set would give the rear suspension better geometry,moving the instant center toward the rear.
Do you have stock OEM style bushings in the rear control arms?

 

They make anti-hop bars which move the aft end of the upper control arms up a few inches.

 

I have anti hop bars and air bags of course with disconnected sway bars for racing only,The bars go back for street driving and a ho racing suspension from Malibu racing in California the edelbrock bars are supposed to be the real length just do some home work on those and I have no wheel hop and plenty of traction on 9.75 street slicks more on my sticky mickeys at 10.5. I also have kybs for a all around compromise period. new suspension packages can be expensive just think it thru first.

 

Wheel hop can be caused by a few different things. The suspensions ability (inability) to hold the wheels from any lateral movement during hard acceleration has a direct effect on hop. In theory the wheels need to be rigidly fixed in the chassis. On a race car the suspension bushings would be solid or spherical bearings. But on a street car this is not a good solution as ride quality would be greatly compromised. Try putting an air bag in one or both of the rear springs. The passenger side first, then the other side, then both. Then play with the pressure in both bags. They might like different psi verses inflating both to the same psi?
Have you played around with tire pressure and contact patterns?
Ladder bars might be next???

Wheel hop is very dynamic. Everything from road surface, tire compound, tire wall design, wrong spring rates for the application and worn suspension to thermal dynamics can contribute to it. Basically it’s the grip, no grip, grip cycle that your experiencing. This will cause the axle to "wrap" by way of shifting the wheels back in forth in the wheel well (the caster is moving back-n-forth). If the axle can be held from any lateral movement (caster) in theory it should eliminate the hop (that’s primarily what ladder bars are designed for but don’t jump to that solution yet).
So if everything is up to snuff in the suspension then you've covered the basics. Now try the other things I mentioned, beginning with the simple one, tire psi/contact pattern. From there add a bag in one or both rear springs and play with its inflation psi. The bags usually do the trick. A stiffer higher quality gas filled shock such as KYB or Edelbrock would be next, (IMO) not coil-overs, though some have had favorable results using them.
Have you tried playing with the pinion angle at all? Try a few degrees either way from where it is now after adjusting tire psi.
Moog or Eaton should be able help you dial in a spring rate for your application.

Caution: Use the “smart approach” to trouble-shoot a problem. Change one thing at a time and keep tract of those changes until the problem is solved. That way if you need to go back to where you started you’ll know exactly where that was. This also helps pin-point the root cause of the problem.

IMO I’d do it in this order (cheap & easy to expensive)
1. Tire psi
2. Bags
3. Shocks
4. Springs
5. Ladder bars
6. Different tires
7. Pinion angle (with adjustable uppers)
8. Spherical control arm bearings
9. Sell the car and buy one with out wheel hop (kidding ha-ha)

Get back to us and let us know what solved this for you.

Steve...sorry I had to edit this. I wrote this up for someone else a while back and saved it because the problem comes up from time to time and I didn't want to retype it from memory. I figured it applied to your problem with out thoroughly proof reading it again. The OP that I originally responded to had adjustable uppers. This allows easy pinion angle adjustments.

 

I cured wheel hop by installing all new bushings and boxing the lower control arms. I used the anti hop bars but they put too much down force on the center section of the rear end and I bent an axle tube.

 

Raising the mounting points like the no-hop bars do,is the same effect as using the lower set of mounting holes on the frame.Just not as drastic. It brings the imaginary intersection point of the lower control arms with the upper control arms rearward,improving the instant center.
The South Side Lift Bars achieve the same thing by lowering the mounting position on the axle,thus bringing the intersection point rearward.
If your car has the stock control arms,then the pinion angle should be in the stock location.

 

Sometimes the cure can be as easy as a 50#bag of sand in the trunk.

 

I've also heard a man hole cover will do the same thing. Seriously, I read it in carcraft.

I do like the post by MrMorland very scientific. Good place to start if some weight in the trunk won't do it. Lot of variables.

Ya know, I've ran air shocks a long time and know their limitations. But wheel hop has never been a problem for me, it was usually the road surface in question. I like the idea of an air bag, just never tried it.

 

Thanks to everyone for the input. I guess what puzzles me is that of all the cars we played with back in the day, these cars with their four link suspension were the least trouble and most forgiving of change. The greatest issues were with spring wrap on leaf spring cars.

The side to side oscillation of traction is interesting, but why did the w30 cars not have springs of different rates side to side? They made some pretty good rear tire torque with 4.33 gears. Is there a tire compound/size that would have created this in an off the shelf car back in the day?

A little more information, I do have the original boxed arms, all bushings are stock rubber and new. Shocks are KYB and are new. Tire pressures are even at 30 psi.

I'm really leaning to the ride height/arm angle theories at the moment. My front ride height is high limit correct at 10" measured at front of door. Spec is 9 1/2" +1/2 and -1. The rear is off over 2 inches. I am just shy of 12", spec is 9 3/8" + 1/2 and -1. I'm not sure if going to the lower holes will be enough to confirm the cause. The lower holes for the upper arms are used for cars with ride heights from 9 3/4" (coupes, sedans 10) to 11 3/8" for a wagon. I'm going to try it to see if it makes a difference of any kind to determine if we're on track. Weighting it down to get the angles correct will affect the traction and wheel spin, so I don't know if testing it that way will help.

Ultimately I intend to get the ride height corrected anyways. I'm a little frustrated that the new springs that I bought from a custom manufacturer in Kansas (can't remember who) turned out to be so far off. Where does one go to get the 442 only springs that will be correct? Is it a crap shoot all over or is there a reliable source for this. Wrong height after spring changes seems to be something you hear all the time.


507Olds, the story of the broken centre and tube torn out, that's exactly what happened to my nice original SJ axle. So now I'm scared whitless to "test the theories".

One other thing, can you guys keep your eye out for an orange 25 tooth muncie speedo driven gear. having trouble locating one.

Thanks again,
Steve

 

The driveline angle is off,like the others have said.

 

Like 507 said, lower the rear end, make sure the front mounting of the upper arms is in the lower holes.

 

For springs check out MOOG or Eaton Detroit

The following engineering specs are what you need to know for your specific application.

Wire Diameter.
Installed Ht.
Free Ht.
Load Rate
Load Capacity

They will have this OEM info and can make you a set inexpensively if not in stock. They do custom springs as well per your application.

Sounds to me like someone sold you a cargo coil- variable rate spring?