dpine

We overhauled my brothers brakes over the summer. The brake overhaul consisted of replacing master cylinder (bench bled), prop valve (4040), brake lines, front brake calipers and going from rear drum brake to rear disc.
The problem is the brake pedal never gets firm and stays that way. The best way I can describe it is similar to brake bleeding with the pedal, after you tighten the bleeder screw you have to pump the brake to get back pressure.
My problem is once I do this (pump the brake pedal until firm) after a few minutes the brake will become spongy again and have to be pumped up again.

Since we replaced so many parts at once I have put a few bottles of new fluid through the brakes and bleed them to get all the air out but it seems as if the pumping of the brake pedal is some how enjesting air into the system.

The master cylinder is a reman'd unit so it could be the problem. I dont know at this point so I a looking for some help.

thanks

slowcivic2k

Ford F150 ABS systems are prone to this type of problem, particularly the RWD variant. If you want an answer, you better review the requirements for a post like this. Start with what you drive. More information = more results.

dpine

95 civic, I seemed to have left that out.

slowcivic2k

1: Check for fluid leaks, including a change in master cylinder level. This would indicate a hydraulic leak into the booster.

2: Check for the proper brake cylinder size per wheel with the master cylinder you are using. If you expect an enormous caliper to apply with little compliance with a factory master cylinder, you are mistaken.

3: When you install any wheel end part, it is wise to tap gently the housing of the caliper or wheel cylinder to dislodge any air that may be in those components.

4: Like I said before, if you want a good solution or starting point, give us information. Right now, the information you have supplied requires a half-assed solution.

Let me help you out:

1: Is the car currently 4 wheel disc or disc drum?
2: What master cylinder are you using?
3: Does the car have ABS?
4: When was the last time the brakes worked correctly?
5: What repairs have you attempted to correct this problem? Did you bled it, and if so, how, and in what order?

If you can add to this list I applaud you, as I have made my point clear.

dpine

As stated in my original post I did convert the rears to disc brake as well as changed out my prop valve to a 4040 unit, new steal brake lines, new front caliper (94-up integra sized). However I did leave out MC size.
To answer your questions
1)4 wheel disc brakes
2)replaced the 13/16 MC unit with a 15/16 unit from a 92 civic ex sedan.
3)no ABS
4) before all of the said items were swapped out/replaced

5)I have bled the system per what I have read online (RR,FL,RL,RF). Yesterday I swapped back to the old 13/16 MC. B bench bled it and re bled the line again. I am still have the same issue.

I have checked all possible connections and cannot find any leaks or dampness at all. I will look at the manual online tonight to see what it calls for to test the Brake booster and booster check valve though I think the check valve and booster are ok as they were the only things not replaced.

walters474

There could be that nasty air bubble in the proportioning valve which is beneath the master cylinder. After letting my master cylinder dry as I was flushing the brake fluid, I had a spongy peddle. Flushing two qts. of B. F. did not help. I decided to crack the flare nut, for the upper circuit of the proportioning valve assy., pushing the peddle, I heard air hiss with signifigant improvement. I did the same thing with the bottom circuit and the brakes became excellently firm. The bottom circuit can be accessed from the bottom. Doing this with the most accessed flare nut of each circuit worked. Celebration time after that.
96 Accord, non ABS.

B serious

iTrader: (1)

The two-man, pumping and holding method only works for teh pr0nz.

There are more effective ways to bleed brakes. Try using a bottle and a vacuum line. You move a lot more fluid and can bleed the brakes more effectively. Plus, you only need 1 person. Spend a lot of time flushing through each line. You'll need at least a LITER of fluid to flush all the bubbles out if you removed all the stuff you did.

A better bet is to buy 2 liters. Most of the time, you won't be very efficient at bleeding the bubbles.

Also...does all your caliper bracketry move freely? Any stuck pins?