E34 Rear Brake Failure (some questions and a confession)

[hoodsstalker]

Hello everyone, I own a 525i a/t with about 134k miles on it.

the problem i've had with my bmw is one that i caused, so before i ask what i can do let me tell you what i did to cause my problem. it was around march when i was in the parking lot of pep-boys, i bought a small quart of valvoline steering fluid and ATS fluid for my steering wheel and transmission that had been acting up on cold mornings. i popped open the hood and looked for the steering fluid resevior, in my ignorance and foolishness i poured almost the entire quart into the brake fluid resevior(that little circle icon to represent the brake looked like a steering wheel at the time). oblivious to the error i had just made i went about my daily tasks and about two days later i began noticing a considerable decrease in the firmness of my brake pedal. Almost a week later, i informed my dad about what i had done and showed him were i poured powersteering fluid. he quickly pulled out from his tool bag a tiny rubber pouch with a metalic tube attached to it and vacuumed out a large portion of the powersteering fluid that i had poured into the brake fluid resevior. he said hopefully it hadnt entered the lines enough to clog the system and cause the ABS to fail. about a month went by and i still had decreased braking firmness. about a month later the braking ability of the car was fairly poor, so i decided to replace the front and rear brake pads which is when the problem immobilized the car. i went on to the bmwe34website and printed out a step by step tutorial on replacing the brake pads. the front brake pads came out and i installed them effortlessly but when it came to the rear brakes i had a problem. on either side the caliper and piston would not reset far enough for me to fit the new replacement pads. i went online and read step by step on bleeding them. in the tutorial it warned that if air would slip into the lines while bleeding i could have complete brake failure. while i was bleeding the brakes the pistons and caliper moved all the way and allowed me to reset, i was extremely excited. i then took the car for a test run, and the rear brakes failed to engage. i didnt know what to do and a friend suggested taking it to a shop to have it vacummed by the machine they have at the shop. i had the process done twice and still the rear brakes failed to engage. in conclusion the mechanic as well as my father formulated that the problem lies in the master cylinder. if i were to buy the master cylinder online and attempt to install it myself would it be difficult? would that fix my problem? whats the price of the job im looking at? being that my brakes are ABS does that make the issue more complicated or is there something i'm over looking? i havent driven the car in over 4 months because fo this problem , any suggestions or advice would be greatly appreciated
thank you for your time.

[BillionPa]

replace the calipers too.

and the rubber lines.

the fact that you were able to add a quart of anything to the brake reservoir means it was probably sucking air into the cylinder at that time.

and the fact it was so low means either the grommets on the reservoir going to the cylinder were badly leaking or one of the calipers is leaking.

do the following:
remove all calipers
drain all fluid
remove cylinder
blow out all lines with compressed air
install new cylnder
replace rubber lines all around
install new (rebuilt) calipers

i doubt that trans fluid in the abs unit would cause it to fail, as auto trans valve bodies are pretty similar. but you will have to bleed it REALLY WELL to make sure there isnt any left in there.

invest in speed bleeders, and bleed one caliper a day for about a month.

if your brakes are still boned after new cyl and calipers you will need to find a replacement ABS unit, but hopefully all those parts will fix the problem.

you may not need to replace all the calipers, but it would be a good idea to rebuild them and do a very thorough check with a scope on the inside checking for any sign of corrosion around the piston area.

[silver-e34]

more than likely the trans fluid softened the rubber parts on the brake system making them swell up and clogging the rubber lines or making the caliper pistons leak.

it shouldnt be that hard to diagnose the problem simply remove the 2 rear brake lines at the inlet of the abs unit and pump the brakes to see if you have fluid pressure if you have no pressure or very low pressure than its your master if pressure is good then the next step is remove 2 rear brake lines from the outlet of the abs unit and do the same test no pressure=bad abs unit if you have pressure go to the rear calipers and disconnect the lines at the caliper and run the same test if the brakes arent engaging it usually lack of pressure = air in the system,leaking lines/calipers,bad abs unit,pinched lines,intrusion in the lines,either way these tests will help you determin where the problem is.

worst case scenario you will have to replace all rubber parts on the brake system

[hoodsstalker]

so in the worst case scenario how much can i look at spending?

[silver-e34]

if you go to a junk yard and get everything there you might get a good deal maybe $400 for everything and the 4 rubber hoses get new those will run you about $20 each so you are looking at $480 minimum