brake pedal sinks on my 2nd gen

Ok. I own a 1990 Acura Integra LS 5-speed 2 door hatchback, intake and exhaust. The usual 4 wheel disc, non-anti lock brakes. Ever since my friend owned this car, it has a problem of the brake pedal sometimes sinking slowly to the floor, but not at a high rpm. This problem is not constant, I can usually go a week of having excellent braking, then all of a sudden the pedal starts sinking to the floor, usually after the car has been drivin all day, then the problem leaves as quickly as it came about. I’ve been asking around to everyone I know that knows anything about cars, and everyone tells me it’s a vacuum problem, which makes sense. I checked all the hoses for holes/tears/splits, and I made sure they are all connected tight. My haynes manual tells me that I have a vacuum modulator, Autozone tells me a vacuum modulator OR vacuum pump, is not required on my car. I also blew into the hoses both ways, that passed also. So now I’m stuck in a quandary, and I have no idea what I should do next. I don’t have a vacuum pressure gauge, or vacuum hand pump, being I am flat broke. If anyone out there knows for sure what is wrong, how and what to fix, and what tools I’ll need, I will GREATLY appreciate the help…Oh yah, it’s not my brake pressure/air bubbles because the problem would be more constant, and wouldn’t matter if the car was hot cold or whatever. The problem has been worse since the weather has been hotter. (I live in IL and its been around 80 Degrees the past two days, rather than the usual 50-60 Degrees. I think this might be a helpful hint to someone that knows what’s going on with this problem.)

its the brake master cylinder. get that changed asap!

mine did the same thing years ago (4 i think) and I didnt change it for a while…until the pedal sank all the way to the floor and i lost all braking while I was cruising at about 25mph down a 45 degree 1 mile driveway…and had to pull the e-brake to stop. needless to say…the wheels locked and i spun around about 4 times before i came to stop about 3" away from a hillside. so yeah…might want to change that as soon as you can. :smiley:

yea i had that problem with my 240sx. check the brake master cylinder, brake booster, and check for leaks near the master cylinder. :slight_smile:

definitely master cylinder. If it starts sinking start pumping the pedal. I’d get that changed out asap.

I used to get that when my a/c was on. It’d just sink to the floor when I’m at a stoplight. It didn’t happen all the time… maybe once a week. I don’t remember the last time it happened.

get that new m/c in & don’t forget to bench bleed the sonofabitch …

The master cylinder gets my vote too. :dance:

ok, im going ot replace the master cylinder within the next week, thanks for the help guys. ill keep you posted after im finished, and im sure as hell going to bench bleed the m/c, i do all my work by the books… <3 Haynes manual, haha.

suggestion, DO NOT DRIVE IT until you get it fixed. i lived 1:15 from work when mine started doing that. i was half way home on the day it totally went out. i almost slammed into the rear of the car in front of me.

its VERY dangerous to drive it when the m/c is out. i lived in a small bumfucked town where noone had worked on an acura before lol. it took them a week to fix. they had trouble finding the parts.

The head mechanic at NTB told me it was the master cylinder too. He said something about the fluid by-passing the O-ring…? To replace the m/c would cost around $300.

btw, what is bench bleeding as opposed to regular bleeding?

bench bleeding is where you pump the master cylinder with a screwdriver. You have plastic/rubber hoses that usually go into the brakelines to go back into the reservoir until there are no air bubbles.

make sure they lube up first.

even at the dealership a new MC is $170. sounds like that mechanic needs to learn what KY is.

The following is directly from the Tech Service Bulletin that Acura issued on this topic.


Model(s): 1986-95 Acura Vehicles
Group: Brakes
Bulletin No.: ASN 0295-03
Date: February, 1995

If a customer complains that “the brake pedal sometimes sinks while
I’m holding the car at a stop,” there 's usually nothing to worry
about. You’ve probably experienced it yourself When the A/C cycles on
and off, or as electrical loads change, engine idle speed drops
momentarily, then the ECM compensates and raises it back up. These
changes in idle speed change the amount of vacuum available to the
brake booster, which, in turn, changes the brake pedal height.
If you’re asked to evaluate this symptom, make sure the A/C and all
electrical loads (including cooling fans) are off. If the brake pedal
height still changes, test the master cylinder:

  1. Start the engine, and let it warm up to normal operating

  2. Sharpen one end of a piece of welding rod, hold it next to the
    brake pedal pad, and push it through the carpet to the floor.
    See Fig. 1.

  1. With the engine running in neutral, depress the brake pedal lightly
    (about the same pressure that’s required to keep an A/T equipped
    car from creeping).

  2. Mark the pedal height on the welding rod with a felt tip pen. Hold
    the same pressure for three minutes (this is very important), then
    mark the pedal height on the welding rod again.

  3. If the pedal sinks less than 10 mm in three minutes, the master
    cylinder is OK.


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