Pedal feel during track use

[94shodriver]

I have had a lot of success using my C5 set up on the track, having taken 4 full track days to wear down the pads to 2mm in spots and plenty of life left in the rotors. However, the pedal feel leaves something to be desired. Basically the top half of the travel is very good with good linear bite to pressure. After about a moderate amount of braking, if I apply more pressure as if to brake as late as possible, then the pedal feels mushy on it's way to the floor until I get ABS activation and the pedal comes almost all the way back up. I don't recall when the car really developed this issue as I don't use it consistently enough. I flush the fluid every year and did it just a month ago, as well as bleed before each track day. I have used the ABS activator to flush the ABS block, but not as recently. I'm running Raybestos ST-43 pads up front and Stoptech street performance in the rear. Every other car that I have used the ABS in under hard braking just pulsates at the point of lock-up, not pushing the pedal back up in travel a significant amount. I'm thinking air in the ABS block, master cylinder or cooking the pads, but pad wear rate does not indicate that. Thoughts?

 

[RonPorter]

Particularly on my SHOs, more so than the others, pad choice seemed to make the biggest difference in pedal feel.

Second biggest difference was when I got my Motive Pressure Bleeder 12-13 years ago. I get a firmer, more consistent pedal than I have with other, previous methods like a vacuum bleeder, the two-man method, etc.

Regardless, the SHOs just never got the pedal feel that I've enjoyed on the other cars I've tracked.

 

[jayro]

^^^^^ I second this. The Motive Bleeder works great. It actually takes longer to set it up than it does to bleed the brakes.

What brake/suspension mods do you have?

I am running stage 1 (96 upgrade) brakes in the front, stock rears with bias plugs and stainless lines all around. Front pads are Carbotech XP10 and rears are stock autoparts brand (I think Duralast Golds). With this setup I was able to out-brake most of the cars I was on the track with and had no fade or boiling issues (I use Valvoline Synthetic DOT 3/4), but my pedal feel hs never been what I want. They grab fast and stop well, but I get more pedal travel than I would like when braking hard. From talking to others, I think this is just the nature of the set-up. I have changed my master cylinder 3 times and bleed the snot out of them with no change. I have read that upgrading to a different setup, like Cobras, will fix this.

Is far as he ABS feel, I am not sure. I know I can feel it when my ABS kicks in, but I am not sure how to describe it. I do feel it in the pedal though.

What is your braking technique?

 

[94shodriver]

Hear is my write up for my set up:

http://www.shoforum.com/index.php?threads/c5-corvette-calipers-under-slicers.126616/

I'm running Thunderbird SC rear vented rotors with modified Cobra brackets in the rear, similar to the Gen 1 setup, but no knuckle or caliper change necessary. Of course stainless braided lines all around. With the 12in cobra set up I was cracking rotors almost every day! My local track is notoriously ******* brakes.

I have used the Raybestos ST43 pads using both setups and I seem to recall better feel earlier in the car's career. I have a pressure bleader that I will use next time as well, which will be before I go back to the track. My calipers are due for a rebuild. If that doesn't do it, I guess I will move on to the MC. I plan on using Colbalt pads next time, used them on other cars with good success.

My braking technique is slightly early (I would brake later if the pedal would support it) with trail braking until good rotation is achieved. Then roll on the throttle as the slip angle is still up. Left foot when possible.

 

[jayro]

Hear is my write up for my set up:

http://www.shoforum.com/index.php?threads/c5-corvette-calipers-under-slicers.126616/

My braking technique is slightly early (I would brake later if the pedal would support it) with trail braking until good rotation is achieved. Then roll on the throttle as the slip angle is still up. Left foot when possible.

I read through your brake setup thread. Since you stated that the pedal feel was good at hat time, then it has probably changed. I would start with bleeding everything really well including the ABS. Then move on to the MC (as you said). I was thinking about the Cobra setup, but was told to only do it if I use the bigger rotor due to the cracking issue in the smaller one. I am sticking with my setup currently......the peddle feel is not confidence inspiring but the car does stop very well,

It sounds like your local track is very ******* brakes. Do you ever have any fade issues? Are you still running brake ducts?

With your technique, when you say slightly early does that mean less braking force applied as well? You have the Gen 3 subframe, correct? What other suspension tweaks do you have? I know the sub-frame is supposed to reduce nose dive, but other items could further reduce the weight transfer and keep your rear ABS from kicking in.......though this really doesn't address your pedal feel issue.

I miss the track....gotta make it out here soon.

 

[94shodriver]

By slightly early I meant less force applied earlier to corner entry.

I've got sub-frame connectors, konis, eibachs, polyurethane, 22/26mm sways with rod end links in the rear and a few other things I forget about. Nose dive is bad because of the spring rates, probably more from tail lift than dive actually as the front is on the bump stops at ride height.

Another factor I came across is that my calipers have spread about 0.050" from ID to OD on the pad swept area. Probably because I neglected to swap pads inside to out often enough. Oh well, I'll have to upgrade to C6 calipers that are said to be another 25% stiffer.

 

[jayro]

By slightly early I meant less force applied earlier to corner entry.

I've got sub-frame connectors, konis, eibachs, polyurethane, 22/26mm sways with rod end links in the rear and a few other things I forget about. Nose dive is bad because of the spring rates, probably more from tail lift than dive actually as the front is on the bump stops at ride height.

Not sure how it would affect pad life, but I had always heard to have the best braking performance you want to brake hard for a short period, rather than lighter for longer. Things don't get as hot this way plus you have longer between your braking period....though this maybe small enough that it really doesn't matter.

Are your Eibachs cut? I am running uncut Intraxs and I am not sitting on the bump stops, but my car is also lighter. I haven't noticed a lot of nose dive even with the stock subframe.

This is at a 90* turn at the end of a straight, though I am sure I am off the brakes at this point even trail braking into the turn.

 

[94shodriver]

I've heard the short/hard braking thorey as well, though I don't believe it too much. Physically you have to disapate the same energy regardless of distance, only speed differance matters. I think dragging the brakes matters where you keep the pads in contact with the disc longer allowing heat to flow back into the pads. Same reason why you don't set the parking brake after a session.

Eibachs aren't cut and bumpstops are junkyard parts, from when I put my konis together. I only noticed when I was taking measurements for my yet to complete coilovers.

I'll try to post some video from my last day when I have some time.

 

[RonPorter]

Yes, hard and short on brakes definitely gives them more cooling time. Boiled fluid that people experience seems to be one of two things: Either the fluid wasn't recently flushed, and/or they do streetbraking of long & soft rather than short & hard. I believe it gives the pads more cooling time.

 

[bpd1151]

Experience seems to be long & soft rather than short & hard.

Gee, I don't know there RP.....

I kind of like embracing both concepts of "short & hard" as well as "long & soft".

He he he

 

[RonPorter]

HAH! At any rate, "HOW" you brake makes a hue difference. There are some well known SHO folks that still boiled fluid with the high $$$ brake systems because they don't brake properly. Spending more $$$ than the cost of Valvoline DOY 3/4 at any parts store is a waste for a 20-minute track session. If you boil that after a fresh fluid flush, it's your technique that sucks.

 

[94shodriver]

In my case the fluid didn't boil even when the pads were down to less than 2mm. Maybe I should have described my technique on that day as medium and softer instead of as hard as possible and unfortunately short, haha! Regardless I think my issues were related to the calipers spreading and/or air somewhere in the system. I'll report back in a year when I get back on track.