Wheel hop on deceleration...what causes it?

69merc · 08-31-2009, 08:20 PM

When I'm open tracking my Cougar, I am getting wheel hop on real hard braking. What is the cause? I have 5 leaf rear springs, KYB shocks, and Caltracs.

Thanks for your help,
jim

MedievaL · 09-01-2009, 12:43 AM

I'm not a suspension expert but I would guess it is the same thing that causes wheel hop during acceleration, only in reverse. the caltracks prevent the rearend from twisting during acceleration but does nothing to stop it twisting the other way during heavy breaking?

Scottem · 09-01-2009, 05:22 AM

Rear wheels locking up at all? Both wheels hopping or just one? Lug nuts tight? Any irregular wear on the rear brakes or tires? Are the U-bolts tight (not stretched or bent)? Have any bad belts in the tires? Inspect hardware that holds the rear end to the car? Leafspring bushings good? Rear sway bar need adjustment?
What is the suspension set-up in the rear of your car? May be time to get a stronger set of leaf springs (different rate). Car isn't sagging on one side is it? Are those KYB's up to the job of holding a Coog going through its paces?
Maybe have someone video tape your runs and re-produce the problem on video and post it up here!

http://www.axlewrap.activesuspension.com/
http://ateupwithmotor.com/terms-and-...uspension.html

GT289 · 09-03-2009, 01:01 PM

I think the Cougar has the unequal spring segment
lengths- front axle length is different from the
rear distance? If so, that makes for an interesting
harmonic. My feeling is that you're
too stiff in the rear. I'm not crazy about the
valving on the KYB shocks and the bump/rebound
ratios on many rear shocks are not even close
to correct- KYB also has this issue.

If it's any consolation, even a perfectly set-up
early Mustang or Cougar will have a slight
tendency to axle hop on decelleration when using
various race tires....on some track surfaces.

ex-Global West GM
1991-1994

69merc · 10-23-2009, 04:04 PM

The leaf springs are the mustangs plus 5 leaf reverse eye. I don't understand what you mean about the unequal lengths? I agree the shocks could be better. But I am debating on changing the rear leafs to a maier racing type with most of the leafs before the axle. Is it worth it trying it? Or just better shocks first?
Thanks for the help.

silverblueBP · 10-23-2009, 04:33 PM

Are you not rev matching on your downshifts? or is it hopping before changing gears?

I have 4 1/2 leaf Mustang+ springs with Koni shocks set at halfway and have never had any hop...on street tires or R comps.

69merc · 10-23-2009, 11:37 PM

Its hopping before changing gears (two places at the track I run at....one place is a hard brake zone at 120 mph and the other is a hard brake at about 70 or 80 mph). Maybe it is the shocks? Could it be the rear sway bar?
Thanks for the input.
jim

Comic · 10-24-2009, 08:54 AM

To much rear brake.

Another thing that contibutes to this: soft front springs/stiff rear springs

When the car dives into the braking zone the rear is unweighted causing the rear brakes to lock up.

Shocks /tires really do not add to the issue

silverblueBP · 10-24-2009, 10:24 AM

What rate are your front springs?

69merc · 10-25-2009, 11:45 AM

The front springs are Mustang+ 620's. I've dialed some of the rear brake out, maybe I should dial all of it out? It obviously happens when the car is really diving. So, different shocks or rear springs wont help? Does a rear sway bar contribute to this?
Thanks again for the input,jim

silverblueBP · 10-25-2009, 03:04 PM

I'm running the same springs up front, no rear sway bar or traction bars (panhard bar), full rear bias on the rear stock drums and a running weight of 3,050 lbs.

I have never heard anything good about a rear sway bar on these old cars on track. I have an adj stambar that's keeping the mice company out in the barn!

69merc · 10-25-2009, 05:05 PM

I guess I will try running without the rear swaybar and take some rear brake out. My Cougar weighs a bit more (about 3400 lbs) than your 66, so that may cause more diving.
Thanks for the help....I love your 66 and the video's you post.
jim

silverblueBP · 10-25-2009, 05:11 PM

Keep updating this post with your changes and what happens!

JohnTheTruckGuy · 11-03-2009, 09:32 PM

More "rebound" damping in the rear shocks will help. Rear axle is a big, heavy mass, and it'll oscillate (which translates into "hop") at a low frequency (compared to other suspension components). More rebound helps a LOT.

I run double adjustable shocks (Koni's, modified by Truechoice) in the rear, specifically so I can have separate handles on compression and rebound. Short-bodied Penske single adjustables in the front. Not cheap...but effective.

69merc · 11-04-2009, 11:42 PM

Thanks for the help JohntheTruckGuy! I was looking at better shocks to help my hopping issue and it sounds like that is the first thing to upgrade. I was looking at the new bilsteins, but maybe a koni adjustable it the way to go. Do the single adjustable koni's adjust the rebound?
Thanks again for the help!