whosurdaddy

I am looking for feedback on this problem.

I noticed an increasingly soft brake pedal during the last two track days (at Summit Point, which is fairly rough on brakes). When bleeding I noticed increasing amounts of fluid discharge on the caliper and even evidence of fluid flying out of the rims where it no doubt dripped off the caliper. The location of the leak appeared to only be the inside bleeder (by looking at the location of the ruined paint and associated grime build up).

I would run 10 strong laps with a solid pedal, then start noticing the pedal getting soft quickly. It would return to solid again when it cooled a bit. I would think this is just pedal fade but it came on quick and there was discharge.

I recently had my brake fluid flushed at a Corvette shop (a sponsor) and I use Modul RBF600 and Carbotech XP10's with R-compound rubber. I've got front air ducts. This is all on my 2006 C6 Z06.

I've never encountered this problem and am hoping it was just the result of some sort of failure on the valve itself or dirt that prevented it from seating properly.

Thoughts or recommendations? I'm going to VIR this weekend and need to make some decisions - do I replace the whole caliper (which has seen some 20 track days)?

davidfarmer

I would bleed them again and actually torque the bleeder screws. GM recommend 106 IN-lb (NOT ft-lb). You might want to try and pick up an extra bleeder to swap out the leaking unit. There is no reason your caliper should be damaged unless someone overtightened the bleeder and damaged the threads.

davidfarmer

a couple more notes. Are you actually losing fluid.... ie are you "topping off" the master? If not, it could be fluid that was spilled during the bleed that is just flying off.

Also, there is a chance you are cooking those XP10's. Pads, like tires, have a heat range, and if you go beyond the heat range, the pad loses friction, but usually comes back once it cools down.

2000BSME

I had a recent drip on my banjo connector. I tightened it up a tad and it seems to have gone away. Had that same symtom that you did though, brake fluid on inner wheel.

whosurdaddy

Right - pad overheating is a reasonable observation and may be happening also. I was previously limited to street rubber and only have XP10's - I need to step that up on the next set.

Do piston seals fail?

John Shiels

How do you know it came off the bleed screw? Why would it be good for 10 hot laps then no good and then good again? Take out the bleed screw and inspect it or switch it with another wheel. Could the piston seals be leaking?

whosurdaddy

Good questions. You must know how brake fluid destroys paint when hot, so you could follow the trail pretty easily after pulling the wheel off. The trail led right to the left front inside bleeder valve. Plus there was quite a bit of grime that built up around that valve versus the other one because it spent time being wet.

davidfarmer

sounds like you indeed have a slow leak, but I don't think it is related to your soft pedal. Get a new bleeder, and get some hotter front pads.

Seals do fail eventually, but unless it is damaged during service (like pushing a piston back in that is contaminated with something really abrasive), they should last several season of DE use.

John Shiels

Get some SRF

whosurdaddy

You know, I've resisted moving to SRF because its so expensive and my fluid gets so dirty so quickly. I like the idea of bleeding to keep it all clean - whether I need to or not. Moving to expensive SRF would make me think twice, unless there is something magic that I should know about.

whosurdaddy

Come to think of it - in two track days I've burned through 1/2 of my front pads. I am getting virually no brake squeal on track at all - so maybe its just a pad material issue. Thanks.

jaa1992

My C4 was the same way - after a track day lots of grey fluid.
I was flushing every other event. Bit the bullet over the winter and replaced the master and all 4 calipers. Now even after CMP i'm not getting that much grey fluid using the cheap valvoline brake fluid.

I'll switch to SRF the next flush since I fixed the problems with the fluid discoloration.

Z11409

Factory (PBR) bleed screws are soft-replace with a steel bleed screw.

davidfarmer

if you switch to a steel bleed screw and some moron over-torques them, you will ruin your caliper.

Also, if you were boiling your fluid, your pedal won't come back. You are having a pad issue. Stick with affordable fluid until you boil the fluid. If you are an efficient braker (ie you don't brake to "settle the nose", touch the pedal at every little bend in the track, and DO compress your brake zones) you shouldn't need SRF in your car. The 14" rotors and OEM calipers (especially with ducts) have adequate thermal mass.

John Shiels

magic was for me It works better and last longer.

Pos a picture of the pads.

RX-Ben

The only reason to get SRF over the reasonably priced alternatives (Motul 600, Wilwood 600, Brembo 600) is the wet boiling point. SRF has a slightly lower dry point than the others listed. ATE has a lower boiling point, and since David knows what he is talking about, I'd stick with his advice. I like the Motul stuff b/c you can easily spot discoloration, which I found useful as I wanted to make sure all the old fluid got out of my braking system, incl the abs pump (used car- clutch and brake fluid were black).
If you flush regularly (every few months or more if needed) and don't change your brake fluid in a downpour, wet boiling point should not be a factor in your brake fluid choice. Here is a good primer on brake fluids -
http://www.stoptech.com/tech_info/wp...fluid_1a.shtml

John Shiels

So, you say, “I’ll just run my hot rod down to my dealership or mechanic and ask them to replace the fluid with AP 550.” Two problems here. First of all they won’t have it and won’t know where to get it. Second and more serious (after all you could supply it yourself) all dealerships and most independent mechanics use pressure bleeders. These devices certainly speed up the process of brake bleeding, but by forcing the fluid through tiny orifices using pressurized air, any air left in the partially filled system will be forced into the fluid solution. Quadruple Damn!!!!

how long does it take for fluid to absorb moisture and get to the wet point?

Seems very small amounts of moisture can cause boiling.

What happens when you boil the fluid and get gas bubbles which lead to compressibility and then it cools? Is it like water boiling and when it cools the fluid would be less compressible? Then you have a hard pedal after it cools?
If you read the papers is seems that pressure bleeders are forcing air into the fluid unless they have a separate chamber for the air.

I have used Motul and others before and they cannot hold a candle to SRF and were in worse shape in less than half the time so now you can cut the price in half of SRF. I went through two sets of SL6 thick pads and never changed the SRF or bleed one drop for kicks and it was 999 track miles to be exact. The cost of running a car all added up SRF is a drop in the bucket. I thought Lou / LGM was nuts as he campaigned to get me to use it. I mean you look at the can and say 69 bucks! Worth every penny in performance and saved labor in bleeding.

Zenak

OK Read here on how to start your set up:
http://forums.corvetteforum.com/auto...e-learned.html

Comments on your problems:

1.) im amazed on how often a shop "oops" and lets the reservoir get oo low in a bleed and gets some air into the system they "flush out the oops bubble" but air gets into the ABS. You will need to do a GM Tech II unit ABS bleed to fix this. You will look for demons all day long and never find them without the fluid hot enough to expand the ABS bubbles.

2.) unless you are doing rolex 24, Motul is just fine for HPDE dont waste your $$$

3.) change your stock lines to good after market SS lines, preferably ones without banjos like the DRM ones

4.) if you are on XP10 without brake ducts you are insane. You will destroy your rotors, calipers, boil fluid, etc. quantum makes the best kit, if you need an after market duct DRM is my fav

5.) SS bleed screws - i like speed bleeders since i can then bleed solo without any pressure Bull sh-t that does force air into the fluid or moisture or both. get a motive bleed bottle and you can do both fronts in under 15 minutes solo including taking the tires on and off jacking etc. buy AN EXTRA speed bleeder while there. If you ahve a failure, you have a back up waiting!

6.) change your pistons from the aluminum ones in the calipers to the SS ones from DRM. The DRM ones insulate the fluid form the brake pad heat, the aluminum is a heat sink that pushes the heat into the fluid causing boil.

Hope this helps.

John Shiels

You can buy a one-way valve for 8 bucks and bleed by yourself and have no speed bleeder problems or air forced into the fluid.

whosurdaddy

Thank you for the recommendations and discussion. I'm guessing I'll be blowing through my XP10's (I do have ducts and SS lines) soon, so I have a new pad formulation on the way.

Carbotech calls it XPS and tells me they're designed for enduro use. Properties are similar to XP12 - they just last longer and cost a couple extra bucks.

So, I figured I'd give them a try and see how it goes.