brake pedal goes to the floor

[Gabe O.]

I have a 92 Civic that my friend/teammate and I race in Honda Challenge (H2). This past weekend we encountered some brake problems and we're trying to diagnose what's causing it.

 

We have Wilwood Dynalite calipers on the front http://www.wilwood.com/Calipers/CaliperProd.aspx?itemno=120-6806 , with Hawk DTC60 pads

Integra LS/GSR calipers in the rear, with Stoptech high performance street pads

ATE Blue brake fluid

No ducting

94 Integra RS prop valve

91 Civic EX sedan 15/16ths master cylinder (purchase new as a reman unit from Checker/O'Reilly)

stock 92-95 Civic brake booster

Stainless steel lines

 

^ we've ran this setup for every H2 race in 2012, 2013, and the first 2 race weekends of this season with zero issues....ever. 100+ degree track days in the Arizona summer. 3 Hour endurance races. You name it.

 

Prior to this past weekend's race we put in new brake pads in the front and rear. Unfortunately we were not able to get our usual Hawk DTC60s in time and had to go with some Wilwood Polymatrix B pads for the front.

 

Saturday's practice and qualify sessions were uneventful. However about halfway through the 30 minute race on Saturday, my teammate lost pressure in the pedal and had to repeatedly pump up the brake pedal before arriving at his braking points to get any braking effort out of the car. We hadn't flushed the fluid in awhile and figured that we had just boiled the fluid. So Saturday afternoon, after the race, we flushed the ATE blue fluid out and ran an entire 1 liter bottle of ATE gold through the brake system. I took it out for 2 consecutive HPDE sessions in the afternoon to try and duplicate the same type of heat that you would see in a race to see if we had solved the problem. The brakes worked fine and pedal pressure felt very solid.

 

Sunday's practice and qualify sessions were trouble free. However about halfway through the 30 minute race on Sunday, I noticed that the pedal was getting a little softer than normal. Since I didn't have anyone around me I tried to nurse the problem and stay off the brakes wherever possible so the problem did not get as bad as what we experienced the previous day. About 22 minutes into the race, we had a transmission problem that forced me to pull off the track immediately and coast to safe spot. About 10 minutes after I parked it, the race was over and the safety truck came out to tow me in. They hooked up the tow line to the tow hook on our car and when I went to apply brakes to create tension on the tow line, the pedal sank to floor. I had to repeatedly pump the pedal to create any pedal pressure and finally just used the ebrake to maintain tension on the line while they towed me in. When we went to push the car on the trailer, the pedal pressure came back and feels normal again.

 

So....my theories are:

A) the Wilwood polyB pads are not sufficient for our setup and overheating, which is in turn transferring the heat to the caliper/fluid.

B) the brake MC (purchased new as a reman unit, 2 years ago) needs to be replaced

C) the brake booster needs to be replaced

 

Any help or ideas are appreciated.

[DrunkenMonkey]

Some things I would check:

 

1. Is the fluid level dropping in the reservoir? Check for leaks throughout entire system.

2. Look at the fluid in the reservoir and bleed some out of the calipers in a clear bottle and check the color to see if it still looks fresh. Not the best test but it will give you an idea of what the fluid has gone through. Especially if one caliper has much darker fluid than the others, it might indicate a problem with that one generating more heat.

3. On the Wilwoods I use, there are 4 bleeder valves on each caliper. When bleeding the brakes, make sure to only bleed from the top bleeder valves and start with the inside valve first then the outside valve. Sometimes the valves are known to leak a small amount of fluid when hot. After bleeding, I usually have to tighten them down again after a hot session. Wilwood also sells replacement valves if that becomes a major problem.

4. Check the pads you used to make they were the same thickness you used before.

5. Check break lines for and wear or bulging. You may have someone press the pedal while looking at them.

6. Inspect calipers to make sure they are not seized and the seals are working.

7. Pull the MC off and bench bleed it to see if everything is working and to make sure there is no air in the lines. Put it back and test again. MC aren't incredibly expensive so it might not hurt to have a spare with you next time you are at the track.

[Lucid Moments]

I used to use the PolyBpads with super blue fluid in a heavier Car with more power and never had that kind of problem so I think it is not likely to be the pad. Be damned if I know what it is though.

[ILIKETODRIVE]

Not the booster meho. Opposite effect if that were the case.

 

Master cylinder is a possibility but unlikely. With the car parked, off, and cool, the pedal would/should travel excessively and/or sink while attempting to hold pressure.

 

Pads possibly not being up to snuff and possibly causing excessive heat transfer possibly causing fluid poopness in the calipers also a possiblity possibly possible

BUT

the issue I had for about a year was slight fluid leakage/seepage from the bleeders on my front calipers. I would get slight pedal sinkage about halfway through races but basically my pedal would kinda go to a 7/10 rating vs starting the race with a 10/10 rating. I thought it was due to not tightening enough or intermittent based on tracks but it was strictly that the calipers needed to be tossed.

[AZELISE]

You boiled your brake fluid in both cases. The reason your fluid boiled is because too much heat was transferred to the fluid. One option would be to either not race at WHP East because of the heavy braking with insufficient cooling time . Or, figure out a way to keep so much heat from transferring into the fluid. Your old pads might have had a thicker metal backing plate (or different material) that prevented as much heat transfer to the piston (and then to the fluid). So, switching pads might solve the problem. Cooling ducts for the brakes will get rid of more heat and keep it from heating up the fluid as much. Titanium or stainless steel shims between the brake pad and the piston will insulate the piston and reduce the heat transfer. Last resort: bigger calipers that have more surface area to better dissipate the heat.

[ILIKETODRIVE]

So go back to DTC60s, add shims, and check for any seepage/leakage.