Heavy Braking situation

[Sesshomurai]

Hey guys,
So I swapped out my front pads to HP Blue track pads. Rears are still HP Plus with a few track days on them.
During some heavy straight braking I noticed the back end getting a little "light and squirrelly" during braking.

Is this considered "wheel hop"?
Or is it a consequence of the rear pads overheating or being worn compared to the new fronts?

The car is lowered, but I have yet to put the adj rear LCA's and relo brackets on. This Friday.

Thanks for any tips.
D

 

[pufferfish]

It's likely due to the additional bite on the front axle completely unloading the rear. I had similar conditions when I ran a lesser pad in the rear.

 

[F.D. Sako]

when you brake hard, the front end dives and the rear end gets light.
you can remedy the issue in a couple of different ways.
1. you can stiffen up the front shocks a little bit, that should eliminate some front end dive.
2. you can change rear brakes with more aggressive compound
3. you can play with the brake bias with a proportioning valve.

on the corolla I like to have light rear end, because it helps the car rotate more during trail braking. but i understand it could feel unstable during high speed braking, especially with the speeds the boss can get up to.

so, i would start with number 1, if that doesnt help and it throws the car off-balance to your liking during cornering, then your second best option would be number 2.

I would highly recommend that you replace both of your pads with more aggressive compounds. HP pluses overheated pretty quickly for me, even though they kept stopping good, they destroyed the rotors... HPS's were even worse on the rotors once overheated. Maybe next season get track dedicated pads.

wheel hop is experienced during acceleration, not braking. When u accelerate fast from a dead stop, or a very low speed, you will feel the rear wheels hopping and skipping until full traction is achieved. Wheel hop usually happens when at a drag strip, it's less common at a road course.. from my experience at least.

 

[Sesshomurai]

Hey guy,

when you brake hard, the front end dives and the rear end gets light.
you can remedy the issue in a couple of different ways.
1. you can stiffen up the front shocks a little bit, that should eliminate some front end dive.

Did this already with sportline springs. Dampers set to 5. 4 in rear. Maybe go to 5 in rear?

2. you can change rear brakes with more aggressive compound

Got a set of HP Blues on order.

3. you can play with the brake bias with a proportioning valve.

on the corolla I like to have light rear end, because it helps the car rotate more during trail braking. but i understand it could feel unstable during high speed braking, especially with the speeds the boss can get up to.

Yes. I also like a slightly lighter backend for throttle steering and the boss is great at it, especially with trackey.

so, i would start with number 1, if that doesnt help and it throws the car off-balance to your liking during cornering, then your second best option would be number 2.

wheel hop is experienced during acceleration, not braking. When u accelerate fast from a dead stop, or a very low speed, you will feel the rear wheels hopping and skipping until full traction is achieved. Wheel hop usually happens when at a drag strip.

Gotcha. Cool. Thanks for the tips! Didn't see you Summit this weekend!

 

[CaliMR]

You mean the Hawk Blue? It is a pretty big step up from the Plus. My Spec E30 runs Blues and RA1s all around and it will get a little squirrelly under threshold braking but not much worse than the Boss does on stock pads/tires. A lot of people I know run a more aggressive pad up front than back, if the wiggle is pretty minor and is only on really hard braking then it is probably not a big deal though personally I would run the same pad all around. But as Sako said, you can play with the shocks too but based on my tire wear the regular Boss shocks are under damped at 5 in the front anyways, and the rears seem to be about right at 4, at a high speed track with a good surface. But with the rears at 4 the car doesn't feel right to me, so I run 5/5 and just try to not look too close at the wings on the tires.

But the real reason I am replying is to warn you about the brake dust from the Blues. It is nasty. You need to wipe it off pretty quick or it sticks really bad, and can eat the finish on the wheels. If it gets wet, it gets like cement. I have tried many different cleaners to get it off my track wheels after I did a rain weekend and it just will not come off, plus it turns to rust which can be bad for the bits under the car that it also sticks to. If you want to keep your car nice, I would switch to something like EBC or PF which are not supposed to have the same corrosive dust issues though I have not tested them yet. But if it is a straight up track car and you don't mind the wheels being a pain to clean, they are great pads.

 

[Sesshomurai]

Thanks for those tips! Much appreciated. Yeah, I put the Blues on after the first track day Saturday. The plus's were worn down and WOW what a difference.
I think with the more aggressive pad and nose dive from that, the rear is lighter and I've noticed that.

I intend to put full coil overs on next race season, but wanted to see if I read what was happening correctly.

With the metallic pads, yeah, can rust, etc. I didn't think of that so more maintenance needed for sure. I guess spraying brake cleaner is not a good idea
since it eats through paint finish?

 

[CaliMR]

I haven't tried that, but if you search google there are a lot of discussions of ways to get it off. Best advice I have is treat it like Gizmo from Gremlins, clean it that day (before midnight lol) and do not let it get wet. If you leave the pads in for street use, that isn't really an option. My street wheels for the E30 are basketweaves... I am not even trying to clean them. But I know guys who race Mustangs and use PC and a couple other brands, you don't need to stick with the Hawk pads. I'm trying out EBC pads next on the E30. Also the Blues are rotor killers, on the E30 I get the same life out of a set of rotors as I do a set of pads.

 

[Grant 302]

The car is lowered, but I have yet to put the adj rear LCA's and relo brackets on. This Friday.

Thanks for any tips.
D

Put the brackets on. IMO, this is the *main* reason to put the brackets on a lowered road race car. Not the only reason, as they should also help traction on exit/acceleration.

With the sportline's 1.5" drop I think I'd use the lower hole on the brackets if you have two settings.

Without the brackets, all and any of the rear braking force will have a component of lift for the back end until the front LCA joint has been lifted past level with the rear LCA joint. Past this point, and coupled with the front braking, it continues to lift the rear higher and starts unloading the rear axle and exaggerates any brake dive.

Brackets aside, if your front brake dive is well controlled, then I *think* you would fix this by proportioning more to the front.

Please report back your results after you get the brackets on.

 

[VoodooBoss]

Put the brackets on. IMO, this is the *main* reason to put the brackets on a lowered road race car. Not the only reason, as they should also help traction on exit/acceleration.

With the sportline's 1.5" drop I think I'd use the lower hole on the brackets if you have two settings.

Without the brackets, all and any of the rear braking force will have a component of lift for the back end until the front LCA joint has been lifted past level with the rear LCA joint. Past this point, and coupled with the front braking, it continues to lift the rear higher and starts unloading the rear axle and exaggerates any brake dive.

Brackets aside, if your front brake dive is well controlled, then I *think* you would fix this by proportioning more to the front.

Please report back your results after you get the brackets on.

Interesting. I'm new to live axle suspension mods and I'm curious if this will solve his issue.

 

[ArizonaBOSS]

Suspension mods, brake pads, blinker fluid etc aside, the easiest way to alleviate this issue is to get on the brakes smoothly and progressively not to upset the balance of the car so much. Think of it like shooting--squeeze the trigger, don't yank it. Same thing with the brakes--squeeze down on them firmly, don't just JUMP on them.

 

[Sesshomurai]

The car is lowered, but I have yet to put the adj rear LCA's and relo brackets on. This Friday.

Thanks for any tips.
D

Put the brackets on. IMO, this is the *main* reason to put the brackets on a lowered road race car. Not the only reason, as they should also help traction on exit/acceleration.

With the sportline's 1.5" drop I think I'd use the lower hole on the brackets if you have two settings.

Without the brackets, all and any of the rear braking force will have a component of lift for the back end until the front LCA joint has been lifted past level with the rear LCA joint. Past this point, and coupled with the front braking, it continues to lift the rear higher and starts unloading the rear axle and exaggerates any brake dive.

Brackets aside, if your front brake dive is well controlled, then I *think* you would fix this by proportioning more to the front.

Please report back your results after you get the brackets on.

Thanks Grant. Ordered the BOSS S MUSTANG REAR LWR CTRL ARM RELOC BKT Make: Ford | Part#: M5650A, but not sure if it will arrive before Friday when I'm having adj sway bars and adj rear control arms put on. Might have to find another seller to speed ship them.

 

[Sesshomurai]

Suspension mods, brake pads, blinker fluid etc aside, the easiest way to alleviate this issue is to get on the brakes smoothly and progressively not to upset the balance of the car so much. Think of it like shooting--squeeze the trigger, don't yank it. Same thing with the brakes--squeeze down on them firmly, don't just JUMP on them.

That too yes. There was one turn in particular where this happened and I thought to myself, sh*t am I gonna lose the back end braking in a straight line here?!?
Although in a speed event, its not always possible to be graceful with the brakes. I'm not yet advanced enough to get into brake diving during laps, but when I get to competitive racing,
it will have to be done in some situations.

Ok, I'm overnighting the BMR relo brackets[1]

[1] http://www.americanmuscle.com/bmr-lca-relocationbracket-0512.html

The Ford ones seem out of stock.

Incidentally, this is also why I put the wing on the back, but this wing flexes too much so I ordered a carbon fiber wing that is taller to help keep the rear planted.

 

[PeteInCT]

Suspension mods, brake pads, blinker fluid etc aside, the easiest way to alleviate this issue is to get on the brakes smoothly and progressively not to upset the balance of the car so much. Think of it like shooting--squeeze the trigger, don't yank it. Same thing with the brakes--squeeze down on them firmly, don't just JUMP on them.

+1 - and Amen ! If you're close to or are invoking the ABS then you're probably unsettling the suspension too much. I've taken a number of lessons from some pro's (not that it helps ;D ) and the #1 thing they concentrate on to lower your lap times is braking technique - both application and release. Peter Argetsinger (great instructor and former pro, http://peteargetsinger.com/bio.html ) stresses brake release techniques probably more than anything else, reason being the more settled the chassis is when you enter a turn the faster you can move through it. In his words - just pretend you have a full glass of beer on the top of the dashboard... ;D

 

[F.D. Sako]

Suspension mods, brake pads, blinker fluid etc aside, the easiest way to alleviate this issue is to get on the brakes smoothly and progressively not to upset the balance of the car so much. Think of it like shooting--squeeze the trigger, don't yank it. Same thing with the brakes--squeeze down on them firmly, don't just JUMP on them.

+1 - and Amen ! If you're close to or are invoking the ABS then you're probably unsettling the suspension too much. I've taken a number of lessons from some pro's (not that it helps ;D ) and the #1 thing they concentrate on to lower your lap times is braking technique - both application and release. Peter Argetsinger (great instructor and former pro, http://peteargetsinger.com/bio.html ) stresses brake release techniques probably more than anything else, reason being the more settled the chassis is when you enter a turn the faster you can move through it. In his words - just pretend you have a full glass of beer on the top of the dashboard... ;D

These two statements aren't the same thing tho. What you're saying Pete is correct. Once you get to a certain level of driving, you're supposed to "jam" on the brakes up to the limit without loosing traction, and then progressively take your foot off as you turn in.

When you first start driving, all instructors are going to teach you to be smooth. Once you are starting to squeeze that last tenth from your time, then the instructors start changing their approach. By practicing initial hard braking and progressively releasing the brakes, you can achieve late braking. But of course there are exceptions... Not all corners are the same and not all tracks are the same, and you don't want to upset the balance of the car, which ArizonaGT was saying. But Darren you know what you're doing, so keep doing it the way it feels right to you lol.

 

[ArizonaBOSS]

+1 - and Amen ! If you're close to or are invoking the ABS then you're probably unsettling the suspension too much. I've taken a number of lessons from some pro's (not that it helps ;D ) and the #1 thing they concentrate on to lower your lap times is braking technique - both application and release. Peter Argetsinger (great instructor and former pro, http://peteargetsinger.com/bio.html ) stresses brake release techniques probably more than anything else, reason being the more settled the chassis is when you enter a turn the faster you can move through it. In his words - just pretend you have a full glass of beer on the top of the dashboard... ;D

Yep--release technique is important too; if you "pop" off the pedal the front of the car unloads, reducing front grip which could cause understeer when you are trying to turn in or mid-corner if you are trail-braking!

And FDS, I disagree, you can be smooth and be fast. There is a difference between jamming the pedal for all it's worth and quickly (but progressively) getting onto the pedal.
Take a look at this video of Joe Foster in a 302R at VIR, even on the very high speed braking zones the car is not getting out of shape. He gets on the brakes fast and firm but not so hard that the car is wagging around.
[youtube]OcvIN5N9a8o[/youtube]

For me personally it took the ABS module in our race car to fail before I really learned how to use the brakes. That was an eye-opening experience.

 

[CaliMR]

+1 on smooth release, but that is not what causes OP to be squirrelly while braking

 

[PeteInCT]

Not implied, that's the brake application being too abrupt. I'd run the front shocks at 5 if they are not already also...

Here's a good general link on brake bleeding. Doesn't cover speed bleeders but other than that it's good for those new to the topic. Not sure if it says anything about multi-piston calipers, so in the case of our front brakes you should bleed the inside pistons first (one closest to brake line).

http://www.stoptech.com/technical-support/technical-white-papers/bleeding-brakes

 

[Grant 302]

Not implied, that's the brake application being too abrupt.

Personally, I don't think it's the rate of application on a straight that is the issue. On a straight it shouldn't matter. I believe it's total braking force given the current setup. If Darren got on it at the same rate, but a little less...there wouldn't be an issue. With the brackets, odds are that Darren could drive it the same as he did and not get squirrelly.

Joe F has the brackets on his car, and is not lowered as much as Darren. Please trust me, the brackets will fix this issue.

And to be clear, I understand that smoother is better. But there is a hardware issue/limit here.