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Old 06-20-2019, 05:34 PM   #1
crap GC 99
Scooby Newbie
 
Member#: 413457
Join Date: Feb 2015
Location: Oklahoma
Exclamation New calipers and MC.. now no brakes

I have a 1999 Impreza L.. which had original calipers and master on it with 230k miles. Brakes had been real weak for a long time but I just drove around it. Finally got a little change in my pocket, and decided to replace the FR caliper that had a minor leak and a rough looking piston.

well, the brakes improved dramatically! But, I could tell the master was weak because they would fade/fall with the master cyl test (car off, pump and hold, etc). happy about the improvement with one caliper replaced (Autozone caliper) .. I decided to do the master cyl and other caliper also. Since then, very very soft and low pedal. probably 20% normal braking power. I tried my best to bleed and rebleed. and finally took it in to a pro mechanic. The rear drum pistons and pads were replaced by a pro hoping for improvement, but.. he couldn't get the brakes to perform any better (at all). He was stumped and just gave up after a few days of bleeding and getting nowhere. Zero leaks anywhere.

I did notice the banjo bolts on the Autozone calipers have smaller heads. IDK if the bore is smaller or not.. but smaller seems like it would yield more pressure not less. (but might make bleeding harder)

and.. no. I didnt' bench bleed the master. I thought I could do that on the car (I don't hve a bench/vice).. but there's no way to move the lines off the master to bleed in the car. they can be loosened, but not backed off etc.
also, I had to take the FR line off and attach it to the MC before installing the MC because it just would not catch the threads in the car. i topped off the MC in the car and gravity bled it to start. i put a board behind the pedal when i used the buddy method.

I keep looking at the master which is tilted up a few degrees.. and thinking air is trapped in the front of the master. it's a 4 port master btw. Two on side and two on bottom. the Front top has an 'S' mark above it. does that stand for 'Service' as in .. bleed here? I've considered parking the car on a decline to move the alleged bubble to the rear.

any ideas? my bleeding tricks and the mechanics have so far failed to fix my dry MC install fubarsky.


Looking forward to any assist. Thanks in advance.
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Old 06-20-2019, 11:46 PM   #2
jamal
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Member#: 71875
Join Date: Oct 2004
Location: Montana
Default

You could try sort of doing a bench bleed in the car. Leave a bleeder open, pump brakes for awhile, have someone keep the res topped off. Do this on one caliper on each side as there are two circuits in the MC. This is a good way to flush fluid as well, it generally doesn't pull much, if any air back into the caliper when you let off but I like to do a standard bleed on each corner after to make sure.

But, yeah, if air is in the top of the mc bore above the ports, it's pretty hard to get out without having it off the car.

Or maybe your new MC is junk.

Or your "pro" isn't a very good pro.

Last edited by jamal; 06-20-2019 at 11:52 PM.
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Old 06-21-2019, 10:13 AM   #3
crap GC 99
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Member#: 413457
Join Date: Feb 2015
Location: Oklahoma
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Thanks for the reply!

the MC is from Subaru OEM. It's possible I ruined it.. but i'm telling myself it's ok. Does seem to hold well, but hard to tell bc pedal is soft in general.

"Leave a bleeder open, pump brakes for awhile, have someone keep the res topped off. Do this on one caliper on each side as there are two circuits in the MC."

So you're suggesting to bleed the two front calipers (separately of course)… using the " bleeder hose submerged in fluid" method?

Another bit of info.. the pedal seems sometimes firmer and sometimes weaker. a few times it's felt quite firm and I thought "ya! at last" but when the engine is on, the booster kicks in and the pedal goes to the floor. The brakes will slow the car, but will not bite and 'stop' the car.

oh btw, do you ever bleed the proportioning valve? the mechanic said it seemed to be 'overactive'.. whatever that means. activating on mild pedal i guess. ..

I"ve tried to bleed the MC a few times .. with partner in the car on the pedal and opening the top front 'S' port etc same as if it were a caliper. fluid is coming out.. hard to tell if there are bubbles or not.

Last edited by crap GC 99; 06-21-2019 at 10:16 AM. Reason: added bit about bleeding MC at the end
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