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Author
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Topic: Help! I think I found out why my slicks are spinning but how do I stop it!
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70coupe
Gearhead Posts: 357
From: Toronto,Ontario,Canada
Registered: Aug 2000
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posted 09-05-2002 07:31 PM
  
I was watching some video in slow motion of my car as it launches. What I noticed is the rear tire is doing a sort of hop. I cant feel it from inside the car because it gets close to hopping but doesnt actually come off the ground. When the wheel gets loaded up and as the slick wrinkles,I can see the rear end do an up and down twice rather than take the transfer of weight from the front end. Does this make sense and how can I fix it. I believe this is whats causing my 60' to be inconsistant due to tire spin.------------------
351c 4v clsd heads
60'1.619
1/8 [email protected]
1/4 [email protected]
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capri man
Gearhead Posts: 3385
From: doerun, ga.
Registered: Nov 2000
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posted 09-05-2002 08:05 PM
your front suspension could be pulling it back down. what kind of front shocks are you running?------------------
mike r
racing is real
everything else is just a game.
81 capri-7.51 @89mph 1/8
1.54 60 ft.
http://prestage.com/site/site_display.asp?SiteID=141
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70coupe
Gearhead Posts: 357
From: Toronto,Ontario,Canada
Registered: Aug 2000
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posted 09-05-2002 08:09 PM
I'm running 70/30 front and 50/50 rear shocks. It doesnt look like the front end is being pulled down on the video. It looks like the front rises gently but the rear axle hops up and down a couple of times. The rear axle is hopping even before the front end is all the way up.
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Just Strokin
Gearhead Posts: 754
From: Tuscaloosa, Alabama
Registered: Dec 2001
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posted 09-05-2002 08:24 PM
Sounds like axle/spring wrap-up. You can try stiffening the rear shocks or maybe clamp the front of the springs or traction bars/cal-tracs?
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70coupe
Gearhead Posts: 357
From: Toronto,Ontario,Canada
Registered: Aug 2000
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posted 09-05-2002 08:29 PM
I have traction bars and the front of the springs are already clamped!
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kid vishus
Gearhead Posts: 4538
From: middle of NC
Registered: Oct 2000
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posted 09-05-2002 08:51 PM
Just a couple of random thoughts. What brand of shocks are on the rear? Perhaps they are either too stiff or too short. Even though they are a 50/50 shock, they might be a stiff 50/50 shock that isnt letting the rear of the car seperate to plant the rear tires fast enough. My granada was real sensitive to the stiffness of the rear shocks. And on your rear springs, since the fronts of them are clamped, are the rear unclamped to let them seperate so they dont try and "s" shape the spring on launch? Just a couple of thoughts. [This message has been edited by kid vishus (edited 09-05-2002).]
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70coupe
Gearhead Posts: 357
From: Toronto,Ontario,Canada
Registered: Aug 2000
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posted 09-05-2002 08:54 PM
They are clamped on front of the axle and unclamped behind. The shocks are Lakewood's front and rear.
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jsracingbbf
Gearhead Posts: 1677
From: Batesville,MS. , U.S.A.
Registered: Mar 2002
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posted 09-05-2002 10:43 PM
When I used to foot brake race my 70 mustang with leaf springs I remember it doing the same thing. I found out the shocks were fully extending on the rear. I had to install shock extensions to keep them from completely pulling apart. I don't know if this is your problem but you might check it.
Jerry
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Rustang
Gearhead Posts: 471
From: Clarion PA
Registered: Nov 2000
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posted 09-05-2002 10:49 PM
When I first got into the elevens, my car would hit the tires so hard it actually threw the tires off the pavement. It would lift the front wheels a little, then up would come the rear ones. People watching said it actually would have all 4 wheels in the air. It would porpoise back and forth a couple times, then go down the track. It was a blast to drive, but didn't 60' real well! This was with stock leaves and slapper bars. It's been about eleven years, but I remember taking a few leaves out of both sides(the previous owner had about seven leaves in each side), putting about 90psi in the right rear air shock and none in the left, made sure the snubbers were resting on the spring eyes, and made clamps for the springs. You wouldn't think so, but making the rear springs softer actually helped the porpoising problem. I also learned to use the clamps to vary the rearend lift. I think you'll find clamping the springs behind the rear of the axle will have the greatest affect on controlling body lift.  This combo eventually got me into the 1.50's. The front suspension was stock with worn out front shocks and swaybar left on. ------------------
'68 mustang 351 clevor- 10.92@124
'67 Stang, 351W -11.18@118
'69 351C Torino-14.90@100
'78 Pickup 351W-15.56@88
'79 Pickup 460 ET=??
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70coupe
Gearhead Posts: 357
From: Toronto,Ontario,Canada
Registered: Aug 2000
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posted 09-06-2002 06:53 AM
I thought you wearn't supposed to clamp behind the axle only in front?
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Rustang1
Gearhead Posts: 110
From:
Registered: Nov 2000
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posted 09-06-2002 11:35 AM
Think of it this way, when you push down on the car the main leaf will press against the other leaves and increase the spring rate. When you launch and the slapper bar works, the main leaf arches away from the other leaves. So now you need to increase the spring rate in the opposite direction. By not having them clamped, you only have the spring rate of the main leaf preventing lift. Clamp them, then you will have increased spring rate to fight body lift. The portion of the leaf spring assembly behind the axle is longer than the portion in front of the axle, and is what does most of the "springing" on a typical vehicle. Especially when for racing you bind down the front portion to act like a lever instead of a spring!
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67Coupster
Gearhead Posts: 179
From: Fortson, GA, USA
Registered: Oct 2001
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posted 09-06-2002 02:25 PM
I had to clamp the rear of my leafs to try and slow down the hit to the tires. Mine was hitting the tires then bouncing back up and spinning. It knocked a full tenth off my sixty foot time. Still doing it some just not as bad. I also set my Rancho shocks on #5 setting.------------------
James
67 Coupe
393W, 4 Speed,
7.07 @ 98MPH 1/8
1.52 60'
'66 Fairlane 500XL
Daily Driver
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Buster
Gearhead Posts: 780
From: Orlando
Registered: May 2002
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posted 09-06-2002 05:52 PM
I also had the same problem. It looked like all 4 wheels lifted off the ground... A friend of mine, a drag racer for many years, tried to bounce the front end... Way to stiff, he said. He also suggested to replace the rear springs. I replace the front shocks 90/10's & rear springs and it stopped... it did look cool before thought, lol. but not good for the 60' times. btw, at this time I don't have the rear clamped yet... [This message has been edited by Buster (edited 09-06-2002).]
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steve'66
Gearhead Posts: 6522
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 09-07-2002 11:22 PM
I tried one clamp in the middle of the rear today. The front 1/2 was already clamped, I'll let you all know how it works next week. Best 60' last Wednesday was 1.509 with the Rancho's set on 3. SteveW
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70coupe
Gearhead Posts: 357
From: Toronto,Ontario,Canada
Registered: Aug 2000
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posted 09-08-2002 05:45 AM
Thanks Steve, I would appreciate that.
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TomP
Gearhead Posts: 4812
From: Delta BC Canada
Registered: Dec 99
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posted 09-08-2002 12:45 PM
It sounds like it's maybe the same thing my car did at first...if the rear suspension is topping out too violently. In my case i have Thunderbolt type traction bars, work like a ladder bar but mount high at the front pivot. These things force the rear tires down violently.Shocks topped out hard and would lift the rear tires. The leaf springs simply hold the car up. The fix came from... Butch Leal! He was running a Chivverlay Pro Stocker a dozen years ago and i asked him what they did back then. He said in S/S trim with skinny slicks it wasn't a problem, but with the 10" slicks they used in A/FX they added a second pair of rear shocks. Sure enough if you look at the pictures of his car in the Feb. 64 Hot Rod you can make the brackets out! Instead of doing exactly that, i found out what the shocks are rated at, pounds-wise.... Monroe Gas Magnum truck shocks were twice the extension stiffness as any car application shock (600lbs i think?) The ones for the front of a 79 Ford 4x4 fit and changed the car completely. It still rises quick, but plants the tires.
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70coupe
Gearhead Posts: 357
From: Toronto,Ontario,Canada
Registered: Aug 2000
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posted 09-08-2002 01:15 PM
Well,I was under my car for about 1/2 an hour looking at my rear suspension and noticed right away that all my bushings in the rear end are cracked and rotting out on the edges. I have shackles on the rear of my 70,I'm not sure if they all came like that but those bushings look ruff as well. Should I replace these even though I know there fine inside the springs (they rot on the outside edges). I looked at my rear shocks and they have small rings on them to show how far your shocks are extending. There is still at good 2" or so at the top. I also noticed on my traction bars there are 2 tabs that stick out by the snubber with holes in them. Could I put a U bolt in there over the spring just after the eye and tighten it up a bit? ------------------
351c 4v clsd heads
60'1.619
1/8 [email protected]
1/4 [email protected]
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