whosurdaddy

So, this is the 2nd time in the four years I've had this car over about 50 track days that I've had to replace piston seals due to some kind of air ingestion.

My C6Z is largely stock and I've even been running PS2's. It took the whole first year in 2006 to get the brakes right as no one had the proper pads or airflow mods to sell at the time. However, the subsequent two years were great with a few changes and I felt like I had solid braking. One of those changes was replacing Calipers (at the time they were not much more expensive than the re-build kits).

Now, this year, I've moved into R-compound tires and I'm back to ground zero again. Since my most recent track day, and after a good solid bleed, I find my pedal going easily to the floor.

Before I go and replace piston seals or the whole front calipers yet again. Anybody have any commentary that I should consider?

AU N EGL

StopTechs or an APRacing brake set up.

JRitt@essex

At this stage it sounds like you're going to keep pouring money into, and wasting time on, a system that will never meet the demands you're placing on them. I normally encourage people to try everything else first before going with a complete brake upgrade...pads, lines, good fluid, good ducting, etc. It sounds like you've done all of that already. The R compounds are only going to pour more heat into your system.

You need calipers that were designed to handle that level of heat, along with heavy duty discs that were designed for the same.

I'd recommend talking to Gary at Hardbar. He just released a new system for T1 racers designed to handle the issues you're facing:http://forums.corvetteforum.com/auto...brake-kit.html

If you keep replacing seals, discs, etc., you still aren't solving the fundamental issue of those components not having enough heat capacity in their design for your needs. You'll keep cracking discs, incinerating pads, boiling fluid, and wasting time trying to hold it all together. I know bleeding brakes between every session is no fun!

JDIllon

Jeff is right, your never going to solve the problems with the stock brakes. You have been pretty lucky to run as many events as you have with relatively few problems. If you want to make the change slowly? you can put a BBK on the front and run stock rears. There are quite a few guys here in Florida doing that and have had pretty good luck with that setup. The best plan would be to move to complete BBK Stoptech, Brembo, Wilwood, AP One caution before you make the change, besure you check the price of replacement components IE: Pads, rotors, rebuild kits. JD

whosurdaddy

Yeah, thanks for the feedback though I didn't want to have to spend all that money. Is it possible that I'm experiencing a different problem?

Anybody else seen a situation where you do a bleed, have a nice hard pedal, then (with no track time) a short time later it starts getting soft?

AtomicZ

How far down are you running the pads.

10% left - 20% left - a third? more - less

whosurdaddy

I through them out at 2 or 3mm remaining. Most recently, I had fresh pads just before they started getting soft on their own

longdaddy

it is definitely possible that you are sucking in air elsewhere.


are you seeing air come out immediately if you bleed right after this happens? can you see any brake fluid where it should not be?

whosurdaddy

No leaking that I can tell. I certainly don't see any puddles

LEAVINU

Sort of off topic but what's the deal with "J" hook design rotors now? I'm seeing them everywhere but not sure how the design benefits over a standard slotted design.

whosurdaddy

I think alternate shapes vs standard straight cut slots are useful to reduce heat and pad wear

JRitt@essex

When you cut a slot or drill a hole in a disc, you do a couple of things. The first is to impact heat transfer. The area around the slot or hole acts as a cool spot when the disc heats up. This is not ideal. Ideally, heat is distributed uniformly around the disc so it can be hit with cooling air that is pumping through the disc, radiate outwards away from the disc, etc. Cool spots create stress risers, and increase the propensity for the disc to crack. They also cause the face of the disc to distort unevenly.

When you have the slots oriented like below, there are big gaps of hot and cool spots on the disc inner and outer faces.

/ / / /

During extensive R&D testing the J-Hook design was found to create a constant pathway of evenly distorted material on the face of the disc. That's why the hooks are arrayed the way they are. They are spaced out as evenly as possible both around the circumference of the disc, as well as from the inside edge (where the hat attaches) to the outside edge of the disc, with a slight overlap to promote even heat distribution/distortion.

The even heating of the disc also helps get a nice even transfer layer of pad material on the disc when you bed them in.

Also, every slot or hole on a disc has an edge for the pad to grab. The more leading edges, the greater the bite. That's why a drilled disc has more bite than the J-hook disc, which has more bite than a straight slot disc, which has more bite than a plain face disc without any holes or slots.

If you run a J-Hook and a standard straight slot disc back to back (all else held equal), you're going to notice more bite with the J-hook. Because of all of those leading edges, you'll also notice more whirring/scraping noises like you would a drilled disc. So, the tradeoff is slightly more NVH...but the benefits are more even heat distribution, less propensity to crack, cleaner pad material transfer during bed-in, and more bite.

In other words, for this type of application it's a no-brainer to use the J-Hook slot pattern, and a very beneficial feature to have.

C5Lion

I run Hoosiers and have so for the past 2 years or so. I have stock calipers, stock cooling and run race pads like Carbotech XP12. To me the stock brakes hold up pretty well. Once in a while after 5 or 6 hard laps in a row the pedal might get a little soft. This just happened at Laguna Seca.

I have always wondered how much harder some guys run where they say you must upgrade the calipers. I would not call myself the fastest driver at the track, but I do OK. I know the track makes a difference to in terms of how hard you have to use your brakes.

For those that have switched, how many hard laps are your running per 25 minute session or in a row. With traffic these days at tracks it is hard to get a lot of clean laps so usually I will do a 70% lap and let the brakes cool.

rbl

I agree and think it is beyond foolish to spend big bucks for no good reason, especially if you're just doing track days. Changing out some seals, while a PITA, is tons better than wasting money. The Corvette brakes (with good pads) are PDG right out of the box and you'd be very hard pressed to out drive them.

dfinke23

Have you bled since the pedal went soft? Any bubbles?

John Shiels

Do you have spindle ducts?

longdaddy

you need to figure out where the air is (if it is air indeed), the most basic test is how many pumps until you see a bubble in the bleed tube and which caliper does it.

another thing to try is go into the wheel wells and clean everything especially calipers and brake lines. then drive the car and see if you can find traces of brake fluid anywhere as the pedal gets softer. you are not looking for puddles - rather for damp/greasy spots. pay special attention to bleed screws and brake line fittings.

i would definitely try to troubleshoot/isolate the issue before replacing the piston seals - otherwise you are going to go through 20 seals without being 100% sure if it will even help

some upgrade calipers just to have access to cheaper and thicker pads.

geerookie

I had a very similar experience and never had any air inthe system. Turns out the master cylinder seals were letting fluid bleed between chambers thus producing the soft pedal but no air bubbles.
It's easy to replace and not too expensive, about $130 if I remember correctly.

AtomicZ

I had to rebuild a set of Brembo GT 6 pot brakes. It was explained to my by Doug Rippie that I was running my pads too low. This was doing two things. First - when the pad gets down to the thickness of the backing plate or less, too much heat is being transferred from pads into the caliper. Second - the pistons are being pushed too far out to do there job.

I now only run pads down to 1/3 of the material left and then switch them out. Seems to have fixed my problems.

whosurdaddy

This is interesting. How did you diagnose this problem? Is this a DIY job or do i need to bring it to a real mechanic?