boorah623

Hey Guys,

About a week ago, I was driving down hill and had to stop suddenly as the car in front of me did so. I noticed that the brake pedal hit the floor but the car was still moving. It eventually stopped but I decided I probably needed to replace my brake fluid. Just a week before, I had an oil change done and they recommended this so, that's at least 2 data points suggesting so.

So, last weekend, I got busy and attempted this myself. After reading a bunch of posts and watching a few videos, here's what I did:

- Removed as much fluid as possible from the master cylinder using a turkey baster
- Refilled it with Honda DOT 3 (although the bottle was kinda warped)
- Took off each wheel starting with driver's front working clockwise (car pointed at 12 o'clock) until driver's rear--this is the order described in the service manual; seems to contradict most other sources that suggest farthest wheel to closest
- I had my assistant pump the pedal 5 times, hold on the 5th, and I opened the bleeder screw and had the fluid flow out through a clear tube
- This tube went into the bottle that held the old fluid I drained from the master cylinder
- I then closed the screw and had my assistant release the brake pedal
- Did this until I saw clear liquid and no bubbles--about 4-5 times at each wheel
- Rinse and repeat, ensuring that master cylinder always had sufficient fluid
- Here are a couple of pictures of all the fluid that came out




Given the color of the fluid that came out, I thought I should have a big improvement. However, after all that, I feel like it hasn't really improved the situation. The brakes work but if I need to stop suddenly, pressing the brakes down hard doesn't immediately stop the car--it feels like it grinds a bit still and comes to a stop. Basically, there's no "bite".

I am thinking that maybe I introduced air into the system? I think when I used the turkey baster at the master cylinder, I may have taken out too much. Could I have introduced air into the master cylinder? If so, how do I even get that out?

There's also a chance that the first wheel I did, I had not closed the bleeder screw tightly before progressing on. I had to go back and tighten this. Perhaps I just need to do this process over again?

Any chance maybe the fluid I got was bad? The bottle was warped (I bought 4, all 4 were like this)--is this normal?

What do you guys suggest?

thoiboi

Don't worry about the 'warped bottles'. They come with vacuumed in a sense to introduce as little air in them as possible due to brake fluid being hygroscopic (absorbs water)

i think ink either some brake line is bad introducing air into the system, or you just need to redo the bleeding procedure (you're doing it right.). Did you make sure the master cylinder was full at all times?

bbsitum

I had before 7 years acura legend and replaced master cylinder 4 times till figure out i have to bleed it. You MUST bleed master cylinder separately till sure it is not air in it. Harbor freight have a handy cheep mc bleeder that can do it. I would not believe bleeding master cylinder through lines.

MarcDavidoff

That fluid does look pretty bad but sounds like you did the procedure correctly. You may have a failing master cylinder or possibly brake booster. If it went to the floor before you did the bleeding, that would indicate an issue that bleeding won't likely resolve. Usual when pedal goes to the floor it is the MC going bad. On cars in the 70s and older master cylinders used to go bad all the time. I remember replacing them every few years on my old Torino.

Skirmich

Did you made a travel stop for the brake pedal? this is KEY because if your assistant hold the 5th pump and you opened the drain plug on a caliper the brake travel will bottom out to a mechanical stop which is BEYOND the intended brake pedal travel.. This will hurt the Master Cylinder O-Rings and introduce a gap between the various stages of the Master Cylinder pressure piston.

By your description I also agree this is a Failing Master Cylinder.

bbsitum

Imo if is new MC should be bench bleed, not bad. Notice that exist expression "bench bleed MC" and it is for reason. I figured it out at 4 MC beck then.

08KBP_VA

Failing master cylinder is usually validated under slow pressure to brake pedal for instance but under hard direct pressure it works fine. I agree that bleeding the brake you didn't introduce any air since behavior was present prior to bleeding. Check each hose and connection to calipers too

boorah623

So, I feel like what you described is the opposite of what I'm experiencing--for me, slow pressure works, hard pressure doesn't respond as well. Let me try to describe in more detail:

Prior to brake fluid replacement: the brakes always seemed to work and would apply brake pressure on the car and would generally have bite--I never really hit bottom and never really had a problem. But on that one time going down hill and needing to stop quickly, I hit bottom and the car rolled a bit.

After brake fluid replacement: the brake pedal is definitely more stiff and I can put my foot down hard and it won't hit bottom (at least very difficult to do). I can feel brake pressure applied when using the pedal. It's just that when I press the pedal hard down, it's not "biting"--the car still rolls a little. It's like the brake pressure at max isn't quite tight. So, this part is still the same as prior to fluid replacement.

So, is that a failing MC? I'm hoping not because replacing the MC sounds like a chore. :/

boorah623

Hey Skirmich, yes my assistant did not press the brake down to the bottom--just held steady pressure when I released the bleeder.

justnspace

iTrader: (1)

sounds like you are now hitting the limits on your tires.

Yikes

My Acura had the same problem described in the OP.

Turned out to be a failed brake booster.

Best of luck.

08KBP_VA

Yes my experiences were direct opposite and sure enough replacement of master cylinder was the cure.

Inspect all 4 brake hoses for leaks and brake lines if they are ok try turning vehicle off, the brake pedal should remain firm. However, if you push the pedal lightly and it sinks to the floor, the master cylinder has an internal leak. If the brake pedal is fully depressed and feels unresponsive or spongy, this is the result of a malfunctioning master cylinder. Also note another symptom of a bad brake master cylinder is contaminated brake fluid. Brake master cylinders use rubber seals which can break down and wear out over time. When they do, they can contaminate the brake fluid and will turn it into a dark brown or black color. Check all bleeder screws too.

And while my replacement was on a different vehicle and little easier to access it really wasnt that bad at all. The biggest thing to remember that will save you a lot of pain and suffering is to be sure to bench bleed the new MC before installing.

boorah623

Thanks for all the responses guys. Based on the feedback here, it looks like it's either the master cylinder or the brake booster... or maybe both.

So, I'm still trying to figure out which one exactly. I've been reading a lot more on how brakes work in general and testing different checks. I also dug this up from the service manual:





Here are my findings:
Functional Test 1. Pedal does not sink -- pass
Functional Test 2. Pedal does sink -- pass
Functional Test 3. Pedal does not sink -- pass
Leak Test 1. As soon as I turn off the engine, the pedal rises -- so this is a fail
Leak Test 2. I couldn't tell if this was working correctly, the pedal seemed to be in the same position each time -- inconclusive or fail
Check Valve Test. I haven't done this yet, will do it in the morning.

So, based on these results, I think it's more likely that the booster is faulty, right? What's confusing is that Functional Test 2 passes suggesting that the booster is OK, but then Leak Test 1 fails suggesting that it is not OK.

Maybe I should just take it into a shop...

01acls

To restore the positive firm hard brake feel to the brake pedal you need to activate the abs unit. Bring your car up to speed so that you can lock all four wheels to activate the anti lock braking system. That should firm up your pedal. Find a long straight stretch of road with a loose surface and lock the wheels at speed. A wet road will work also. Be careful and safe.

If the pedal hits the floor then replace the master cylinder.
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boorah623

It's been a while but closing out this thread. Remember I had tried the following:

I took my car to a local shop. They diagnosed the problem as bad vacuum hose. They said when they hooked it up to a vacuum it worked perfectly so definitely hose issue. I was a little suspect of this because of my tests, but anyways, they said about $90 to replace the hose.

Well guess what, they got the hose, put it on, didn't solve it. They then replaced the booster and used the new hose too ($500 all in). Afterwards, it brakes like a champ. So, it wasn't the master cylinder or my brake flush problems--it was the booster (and possibly the hose). Was able to engage the ABS and everything afterwards.

bbsitum

Tanks for letting us know. Believe or not I use my own old treads at forums to figure out current problems. Basically I use forums like recording books for my past problems.