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Heavy Braking Front End Travel

45
27
Exp. Type
HPDE
Exp. Level
3-5 Years
NJ
Hey All,

Having an issue I can’t seem to fix. Under heavy track braking (120mph +), the front end of my car tends to go right and then left quite a ways. It really has limited my ability to threshold brake and maximize the GLoc R16s. I’m running MM Road and track springs with Koni yellows. Set the fronts to half a turn from full still and the rears half a turn from full soft. Appreciate any insight/thoughts from the group on this.
 

Mad Hatter

Gotta go Faster
3,557
2,079
Santiago, Chile
I do. BMR brackets and I’m currently using the middle hole.
Dont remember how low the MM springs lower the car, but try in the upper hole. I found that a LCA angle of 2.5degrees was more or less max angle for me... And if you want more squat, then 0 degrees would be a good place to start. To much LCA angle really does affect your high speed braking, among a slew of other things...

TMO has a long squat thread the deals with it in detail.

As Bill mentioned it could be the rear pads, or even worn LCA bushings. Or all of the above....
 
45
27
Exp. Type
HPDE
Exp. Level
3-5 Years
NJ
Dont remember how low the MM springs lower the car, but try in the upper hole. I found that a LCA angle of 2.5degrees was more or less max angle for me... And if you want more squat, then 0 degrees would be a good place to start. To much LCA angle really does affect your high speed braking, among a slew of other things...

TMO has a long squat thread the deals with it in detail.

As Bill mentioned it could be the rear pads, or even worn LCA bushings. Or all of the above....
I’m on R10s in the rear. Bill, what are your thoughts there?

I just inspected the rear LCA bushings and all good there. I’ll mess with the LCA bracket hole as you mentioned and see if it improves at all. It’s tough to validate any of these changes away from the track though. Do you have a link to that other thread? I’m on this site nonstop so I might’ve seen it already haha.
 

Bill Pemberton

0ld Ford Automotive Racing Terror
5,336
3,805
Exp. Type
W2W Racing
Exp. Level
20+ Years
Blair, Nebraska
I run R18 G-Locs up front and R10s in the rear, as I am a super aggressive braker! I think your set up is good and I know I am asking simple questions, but often I have found when selling customers who did mods to their cars ,the answers are often things we assume are difficult and they end up being simple. So your pads appear not to be a culprit and as silly as it may sound , how is the car aligned ? Did not see anyone ask this and to make it a bit more exact , asking not just how it is aligned , but when was it done last?
 
486
588
Exp. Type
Time Attack
Exp. Level
Under 3 Years
SoCal
I run R18 G-Locs up front and R10s in the rear, as I am a super aggressive braker! I think your set up is good and I know I am asking simple questions, but often I have found when selling customers who did mods to their cars ,the answers are often things we assume are difficult and they end up being simple. So your pads appear not to be a culprit and as silly as it may sound , how is the car aligned ? Did not see anyone ask this and to make it a bit more exact , asking not just how it is aligned , but when was it done last?
Great question Bill, this is where my thoughts were as well.

OP, I see you have the MM adjustable outer tie rod ends - were these setup properly using a bump steer gauge? It almost seems like a toe alignment issue, and with it changing on suspension compression would make me suspect the bump steer settings.
 
3,203
2,965
Start simple, are the tire pressures all correct and within a couple of pounds (hot) side to side?
worn parts is the next check. Turn the nannies off, and check alignment front and rear using the adjustable panhard bar, look at the bumpsteer, and check the shocks and see if you have a dead one.
All that aside, IMO, you're going to find something going on at the back of the car. These cars need tons of ride height, which means that any movement should be linear (which is pretty much impossible). so any change of factory attachment points can have unintended consequences.
Here's a pic of a Roush car at Daytona, you can see the suspension movement.

nvhCcRrl.jpg
 
45
27
Exp. Type
HPDE
Exp. Level
3-5 Years
NJ
Start simple, are the tire pressures all correct and within a couple of pounds (hot) side to side?
worn parts is the next check. Turn the nannies off, and check alignment front and rear using the adjustable panhard bar, look at the bumpsteer, and check the shocks and see if you have a dead one.
All that aside, IMO, you're going to find something going on at the back of the car. These cars need tons of ride height, which means that any movement should be linear (which is pretty much impossible). so any change of factory attachment points can have unintended consequences.
Here's a pic of a Roush car at Daytona, you can see the suspension movement.

View attachment 64775
Thanks all for the replies.
I had an alignment performed before this past weekends event at the Glen where I experienced this issue. I’ll have some time this weekend to tinker and will report back.
 

Norm Peterson

Corner Barstool Sitter
831
616
Exp. Type
HPDE
Exp. Level
5-10 Years
a few miles east of Philly
What condition are the front control arm bushings in? Particularly the big hydraulic rear ones?

Heavy braking puts big rearward forces at the ball joint, which is going to rotate the entire arm (as seen in plan view) rearward as the rear bushing does its compliance thing. I can't see that not affecting toe, or necessarily being symmetrical where the net right side plus left side balance each other out dynamically.


Norm
 
45
27
Exp. Type
HPDE
Exp. Level
3-5 Years
NJ
What condition are the front control arm bushings in? Particularly the big hydraulic rear ones?

Heavy braking puts big rearward forces at the ball joint, which is going to rotate the entire arm (as seen in plan view) rearward as the rear bushing does its compliance thing. I can't see that not affecting toe, or necessarily being symmetrical where the net right side plus left side balance each other out dynamically.


Norm
I recently installed the Boss 302 S/R arms with the Ford racing bushings and Howe extended ball joints. Actually replaced them just prior to the event where I had this issue.
 
Not sure I can point you in the right direction, only tell you how I solved what sounds like a similar problem. As I came up through the HDPE program, my braking was always smooth and firm. Of course no where near threshold, but I had lots of confidence in my braking. But as part of my effort to get better, I went from Hawk HP+ front and rear to a very aggressive Hawk HT-10 front and rear. That is where by problem started.

The car started to feel loose under braking, and one day while trying to chase down my buddy, I did a big swap under braking coming off the back straight at UMC to a hairpin. It made for some dramatic video. Luckily I went two feet in and the corner had plenty of run out. Lost the corner, saved the car kind of thing.

That led to about two years of trying different pads, different techniques to try to get my braking mojo back. Lap times stagnated. So I decided to go back to the basics, go back to a pad set that I knew would only be slightly more aggressive than my HP+ days. For the last year I have been running Hawk Blue fronts and HP+ rears. I know not a popular combination here at TMO.

Everyone on this forum will likely think I am crazy, but the step back has worked. It allowed me to work on my technique with a familiar feel to braking. The car feels more planted and as I have stuck with it, my braking has improved greatly. Lap times have dropped. Five personal bests in the last 5 sessions works for me.

I have a personal theory, that others can feel free to chime in on. I think that the ABS logic in my car could not keep up with the very aggressive pads, having been engineered for street use. Going back to a much less aggressive pad put me back in the happy place for my ABS and allowed me to work on the loose nut behind the wheel. Again, just a theory.

I hope you get it figured out because I know what you are going through!
 

Norm Peterson

Corner Barstool Sitter
831
616
Exp. Type
HPDE
Exp. Level
5-10 Years
a few miles east of Philly
I have a personal theory, that others can feel free to chime in on. I think that the ABS logic in my car could not keep up with the very aggressive pads, having been engineered for street use. Going back to a much less aggressive pad put me back in the happy place for my ABS and allowed me to work on the loose nut behind the wheel. Again, just a theory.
I tend to agree, without knowing if it's simply the 'mu' or if it's more about modulation and release characteristics. Or if it's something I don't even have a clue about.

My car was fine with various Carbotech formulations up to XP12/XP10 on the OE 12.4"/11.8" brake sizes. But I did experience some instability after I put the 14" (Ford) front brakes on (G-loc R10s up front, XP10s out back). Had the ABS take itself offline a couple of times after the 14" swap as well, but I don't remember which issue came first. Should have been paying more attention, I guess.


Norm
 

Bill Pemberton

0ld Ford Automotive Racing Terror
5,336
3,805
Exp. Type
W2W Racing
Exp. Level
20+ Years
Blair, Nebraska
Honestly Norm , G-Loc 10 up front is not enough pad in my estimation. I run R18 front , R10 rear and I recommend most folks to use a 16 up front , especially if going to fast tracks. Either way, the brakes on all my Bosses and the GT 350 worked quite well with some kind of stagger and a lower max. temp pad in the back.

PS note; all G-Locs or Carbotech pads should be purchased pre-bedded in my humble opinion.
 

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