Honda CRX Brake Pressure

[darthmonkeyIT]

Based off my other post regarding brake problems with a 1990 Honda CRX Si I am investigating the brake performance to identify the failure mode. Or more importantly verify that there was a change or improvement after replacing a part.

I am curious if someone knows the optimal or normal un-boosted and/or booster brake pressure on a four wheel disc Honda CRX Si? I have a brake pressure gauge and have measure my un-booster pressure at around 650 PSI stomping on the pedal. I have seen reference to needing 1200-1400 booster pressure to stop a car but this was a generic reference.

A friend found a chart in his manual that listed the brake pressure balance front to rear which including what peak values he should be seeing. I do not have my manual on me at this moment so I am not sure if it is even in there.

Thought I would ask here to see if someone has some data regarding the CRX brake system.

Did a search and did not easily see a topic on the subject so I made a post for future references.

-Sean

[sackdz]

Hi darth, this may be old news, but, 650 psi is way too high. It makes perfect sense tho if the gauge units are kPa (~95psi) unboosted. Most modern brake systems will have locking pressures 75-150 psi on dry asphalt with street tires. The increased grip on race tires is counteracted by higher mu pads as well, so that range is still more or less accurate, perhaps shifted up a bit. I don't think there's any way to achieve 650psi unboosted without bending/breaking something.

I followed your other thread with interest since I was having similar issues.. checked everything except the booster. I'm at the point now where I either need to locate a pushrod adjustment tool or use other means. Did you happen to get your hands on one?

Regards,
Ed

[sackdz]

I have to correct myself, it was me who had my units crossed.. I was thinking in bar but wrote psi. 75-150 bar is normal locking pressure. So your numbers seem reasonable, but I would have expected you could get higher than 650psi unboosted if you stand on the pedal.

[darthmonkeyIT]

The booster change ended up fixing my brake problems.

Car off pressure was a function of air in the lines. After some more bleeding at the rear T joint and brake bias I ended up seeing pressures in the 1100+ psi triple pumped and stomped.

The bad booster showed some interesting problems. I would pump the brake and stomp on it spiking up to 1400 psi. Then the pressure would bleed off around 50 psi a second until settling at around 900 psi. This was an indication that booster was unable to keep pressure on the brake system properly.

After replacing the booster I was starting to see 1800 psi pumped pressure with it dropping maybe 50 to 100 psi after a few seconds. A quick un-pumped punch was in the 1400-1500 range with little to no bleed off.

Seeing as I have no completed two double race weekends and a test day with the new brakes I am going to declare the booster the culprit.