Braking Issue

[maroman88]

Not Fbody but for the 95 Impala.
When I bought the car, the pedal would randomly drop pretty low. Replaced the master, twice, replaced the booster, I've bled the thing numerous times. I had the proportioning valve apart and it's clean as can be. ABS works fine.
Still getting the same results, and can't pinpoint a condition causing it to happen, totally at random hit the brakes and it's either fine or sinks almost to the floor. Doesn't pull, stops straight as can be.

I did notice very minor seepage today where the plastic tank sits on the master? But the problem has existed with 3 different masters lol.

I'm stumped.

[The_Bishop]

Have you ever had the brakes bled with the ABS pump run? Might be random pockets of air in the ABS pump/block.

[maroman88]

Yea that's what I'm thinking, but every search turns up that there is no bleed procedure for it, just says to bleed system normally. I took the car out in the rain for ABS testing purposes and it does work lol.

[The_Bishop]

Yeah, that's how I bled the abs block in my '98. Don't have a scan tool that can activate the ABS pump.

[townsend]

GaryDougs program "Scan9495" can actuate the abs block to bleed it. you can download the program for free and just need the obd1.5 to usb cable from obd2allinone dot com.

also ill try to find the proportioning valve upgrade i had on my impala. the impala has the same master as the drum brake equipped cars which makes the brakes very vague, with the prop valve barbell swap it was night and day, brakes felt almost like fbody brakes on my 96 impala ss after. it was like 60 bux and its just the prop valve barbell, but fixes the bias issues

[V]

This may not have any real relation to your issue but here is something I dealt with on my daily driver, an '08 Mazda 3....
Nephew owned the car and rear ended someone. He blamed it on the brakes, his mom said it was he driving style. Anyways, Insurance totaled it, and I bought it back to make my daily or to flip it. When I drove it right after the accident, I noticed the brakes were very very soft and very low, so I could understand they might have been to blame. They worked, but something wasn't right, even with abs kicking in when called for. I replaced the master and booster, also new rear calipers(rusted badly) and no real change. Upon doing research online, I found out the abs units, mainly the electronic modules, have issues. Those are not sold by themselves, only attached to the abs pump/block. OEM was the only option and over $1200 for the part(+dealer charge to program module to car). Instead I found a company in Canada the fixes the modules. Cost about $300. I sent it out and they said there were some common faults that they fixed but based on my description of my problems and no actual ABS codes coming up on the car, my main problem was with the abs pump/block. I put just the repaired module in and still had the issue. I searched Ebay worldwide and found a New Old Stock complete ABS block in england for $400. Listed for a focus but same part number, my module actually had the ford logo on it. I eventually received the NOS part and swapped the electronic modules since mine was programmed to the car and would avoid a dealer visit/charge. I then looked up how to bleed the abs system and read that I needed a special scanner or needed go to the dealer. Some said to just drive on gravel and slam on the brakes. I decided to try the old school way, kept the battery disconnected as I manually bled them, with my father-in-law working the brake pedal. I then drove the car to see how it was and it was 100% fixed. The pedal was back where it should be and the brakes were super responsive. Its been over a year now and the brakes are still great.


So... maybe its a faulty abs block even though it appears to be working?