Last October my car began spinning off the line every pass when footbraking...it does not spin off the transbrake...wth?...the car was in need of suspension work anyway so we put new AFCO double adjustables out back and singles up front...we also found the four links were all bound up so we took everything apart and cleaned it all up and everything is working properly again...we set the rear shocks at soft and the front kinda hard per AFCO...this was back in december...yesterday I tried to footbrake for the first time since we did the work...damn if it spun again on both passes...I am talking 16 and 11 numbers high on the 60' for both passes...I did lower the launch rpm from 3000 to 2800 on the second pass...oh yeah, I leave at 3400 on the brake...

Obviously something is amiss so I am asking if y'all have any ideas why it will spin off the foot but not off the button...clearly the same problem is still there from last fall...

I have a mild bracket car...79 Monte with a pump gas 496 running 6.50 to 6.60...I have 14/32 slicks running 11.6 lbs in them...5:13 gears with a glide...

Thanks everyone...

I am gonna guess you aren’t hitting the tires as hard foot braking it. Adjust rear shocks all depends on how four link is set up, does the rear squat or separate from rearend on launch?

I’m fixin to start running a 14/32 have no idea on pressure but that sure sounds like a lot

I am running 9 lbs in both 32x13.5Wx15 and 32.5x16x15 on my car running 5.2x-5.3x haven’t tried higher but going to this year.

I would try loosening the fronts up and see if it helps.

try setting rears 2 clicks stiffer on bump [compression] to help tire stay applied

What is different between leaving off the TB and foot braking? If you hook off the TB and spin off the foot brake, that's what you have to figure out - what's different?


The only things I can imagine are the suspension is pre-loaded differently when leaving off the TB, and/or the converter behaves differently at 3400 as opposed to 3000 or 2800.


Try foot braking with the converter stalled to 3400 (same as your TB rpm) just for fun, see what happens.

What size & condition (amount of wear) are your slicks, and how old?

Suspension is loaded when launching from the foot. Also the tires are "hit" a little harder when launching from the brake. Both can make a difference.

On the tire pressure thing---my car runs 6.40--.50s and never turns a tire at 13 lbs air with 31X14 Hoosiers. weighs 3000. As for the spin mine leaves flat as a flounder off the foot but picks up the fronts about a foot off the button. But it don't spin.

fuzzy,set the rear tires @7lbs.

Loosen the extension up more on the rear, get video and get the body to tire to separate a little. I’d guess it’s just not hitting the tire hard enough. You may even need to shorten the IC to get it to work. Video is your best tool on this. Also if your tires are on 14”-15” rims at your et I’d say air pressure is about right. Again video will tell all.

This message has been edited. Last edited by: regal,

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I asked what the rear does because if it squats and you want to adjust rear shocks for more bite then you have to stiffen compression to hit tire harder but if the body separates then you have to loosen rear extension so it can push rearend down faster. I think I got that right.

What does car weight and what spring rate on rear?Too stiff a spring can cause issues.

quote:

Originally posted by dtye:
fuzzy,set the rear tires @7lbs.

I run 8lbs in a 2000lb roadster 14x32 Hoosier. At 7lbs it starts to quiver the tire. Lower and it will rattle pretty good. I guess every set up needs something different but I would be surprised if going down was the answer although he didn't state which brand, stiff or soft sidewall or if he had tubes and that does matter.

it seems something has changed for sure,for it to be off that far in sixty makes me think something could be off in motor or trans preventing it from getting enough hit to plant plus being down on power to get a loss that big. check all simple things timing stall or drop back and ect

Thanks for all the replies...the car weighs 3240 with me in it...I run 11.6 lbs. since it hooked great and every time at that pressure...I began at 8 lbs. and kept going up in 1/2 lb. increments...this year I am going up in 1/10 increments...still hooking fine off the brake, of course...

Yes, the rear squats on launch...I had someone stand 20' behind me on my last footbrake pass on Saturday and he said it left great as far as that goes...

I am not sure of the spring rate in the rear but when we put on the new AFCO's we also put new coil overs from AFCO to match...as y'all know we had to do four corner weights of the car with and without me in it and measure travel before AFCO sold me all the shocks and sprinngs...

Yes, I have 15" rims...my slicks have only 31 passes on them...my converter won't let me foot at 3400 rpm...it will push through...I might could get to 3200 on a good day...lol...

I think 11.6 lbs. is a lot as well but it leaves fine at that pressure...btw, I made my first footbrake pass last weekend at 10.5 lbs...it spun like crazy...I went to 11.6 lbs. on my second pass...my car was running 6.59-60 off the brake that day...off the foot I went 7.02 first pass and 6.90 second pass...lower pressure was worse...sheesh...

We will try some adjustments at the track this Saturday and see what happens...very frustrating......

If the back is squatting then you need to tighten the compression to get more bite if you are trying to fix it with shocks.
If it picked up that much going up one pound on the foot then I would go up two more pounds and see what happens. Tip toeing up on pressure takes a lot of runs and you are far off as far as what it will run on the brake so I would take big swings at it.

The indicators that say the car hasn't nearly enough anti-squat in it, is the tire pressure the OP has found through trial and error works best, is four to five psi more than the tire dimension calls for. That and leaning on the converter 3000 plus rpms foot braking. Look at the youtube video in my signature, that's how you want to look. Skip off the starting line and get up on the tire. Rethink your 4 link, shorten - raise it up as regal said. You'll run less air pressure when it's right and have no need to lean on the converter.