i've had problems with the brakes on this car (late 1988 base) since i got it. the brakes will bottom out before they lock up and replacing parts only makes it worse!

let me say that i do brake jobs all the time at the garage and none have been 1/10th as daunting as this.

i have put on a NAPA rebuilt master cylinder (changed nothing), newer booster bench tested with a vacuum pump and guage (made the brakes jumpy), abjusted all pushrod clearances, and bled the **** out of the whole system! i'm talking 2 of the big bottles through the pedal/assistant method and the vacuum method.

the most recent thing i have replaced was the power booster. i adjusted the clearance between the pushrod and master cylinder at 20 in/hg, put it on and bled it. the pedal bottoms out with ease and i still can't get full braking. it feels stranger than ever and is VERY sensitive. if i tap the brake the car jolts. if i try to adjust it any further the brakes drag and i can't get over 60mph.

i've been pulling my hair out all day and have finally conceded to miss tomorrow's autocross...

 

Did you check to see if the brake pads are frozen to the caliper? That usualy causes a soft pedal condtion (much to the contrary of what people think). Also, if your brake hoses are starting to deteriorate, one of them can be bubbling up or something. Im just saying, don't conclude that the problem neccesarily in the master half of the system.

 

i've replaced the pads several times and am using high quality semimetallic pads i got from BAP/GEON with some orange sticky anti-sueal. they aren't frozen to the caliper.

the only things i haven't replaced are the calipers and the proportioning/bypass valve. i suppose it's possible that the reman master cylinder is garbage... but i'm not losing any fluid.

 

It DOES sound like a bad master cylinder. I know its not very likely but it is possible. You could return it and get another and see if that gets it done. Sucks to miss race day. good luck.

 

yeah, it was cheapo napa reman. i might snag one from one of our suppliers at the garage.

i mean... what else could it be? the booster is good, calipers work, and i've got no external leaks.

 

Replace Master

 

coicidentaly, if you replaced the break master vac hoses, you may have introduced yourself to potential issues. The short elbo vac line contains a vac check valve. Without the checkvalve, you will have no power breaks.

 

good idea, but this is not the case. i had a line i made and put the stock check valve into. there is now a stock line on there.

the power booster is obviously not the problem. the brakes are just harder to press when the booster is bad. in this case, the brakes are easy to press, but i don't get full action.

what is happening the pedal bottoms out (not on the floor, i'm guessing the MC is bottoming out) before i get full braking and lockup.

 

i bought a brand new tokico master cylinder (for $42.00 thru work ), set the booster rod clearance to about .1 mm and put it in.

i then proceeded to bleed the master, then all 4 corners starting with the furthest from the MC. the better part of a large bottle of fluid was put through the lines.

i'm pretty confident there is no air in the system, but the brakes are still squishy. i can get a little squeal out of the tires now, but it still bottoms out before lock-up.

is it possible that there is a line ballooning out or something? i would think i'd notice a swollen soft line while bleeding the brakes and having someone pump them.

i don't think i can count the times i've bled these damn brakes on both hands!!!

 

i missed this, i'm going to check for swelling today if i have time... i got a free sonic cleaning bath

 

yeah, the lines are good... even used a caliper to see if they were swelling as a whole. initially i was looking at the and feeling them all voer while i had someone pump the pedal.

 

my car is doing the exact same thing. i've spent all weekend cleaning and painting calipers and now after bleeding alot they still go to the floor. my master is the original so i wanted to see if there was an upgrade available. i know my problem is not lines because they are all new stainless. good luck.

 

tip: when bleeding master cylinder, do not push pedal all the way to floor.

doing so will kick up dirt thats built up in the m/c over the years and destroy seals, requiring new master cylinder.

 

good point tho

 

I had problems with proportioning valve, always felt spunge. It can stop up or bleed by. Good luck

 

I have the same problem. I thought it was just shitty workmanship at the place I got it done at....guess not :-/ btw alexdimen where do you work at, I wouldn't mind finding someone decent to do brake work.

 

the name of the shop is PARADISE GARAGE (yes, i hear, "another day in paradise..." alot. it's between main and cary on allen street, 14 S. Allen. right in the fan. the boss is in the middle of re-doing the floors, so we only have 2 lifts right now. swing by if you need anything. we're usually a good bit less expensive than other places.

i think there may have been two rotary cars in there in it's entire existence. my own and another person's a while back that had flooded (surprise). i'd love to see another, since i know the FC N/A pretty well now. getting to know the FD currently.

as far as the car goes: the brakes are still weird! the response is fast and crisp, but it still doesn't feel right... too soft and after it grips initially it doesn't really get that much better, then bottoms out. i bled from the proportioning valve and got what looked like aerated fluid out of one fitting.

i'm really contemplating taking the car somewhere where they have a really nice bleeding apparatus and test equipment if i can't figure it out.

 

i was responding to rob86

 

I had the same exact problem.

Try pressure bleeding the system. Get a spare master cylinder cap and attatch piece of 1/8 in. copper to the vent hole. Then hook to a small air regulator set at 10 psi. This will force the fluid through and the air out. I did this and got a bunch of trash out. You can bleed all day long and not need a helper!! It did fix the problem.

 

sounds like a good idea. did you just crack all the valves open or do one at a time?

 

pressure bleeding did nothing. i actually let the resevoir get too low once and got a little air in the lines. i bled that air out and it feels the same. there is no air in the lines, so it's got to be something else.

 

could it be a tiny leak? testing would be easy: with the car running you will feel the pedal bottom out, then slowly go lower after that. also, try this test with the ebrake on and off, sometimes it leaks where the e-brake attaches to the caliper.

 

i don't think so. when i say the pedal bottoms out it's not like it just gets stiff. i mean it's squishy all the way down and then there's nothing. i'm almost sure it's the MC bottoming out. the wierd part is that the car does brake, just not all the way and of course it feels funny.

there's no way for me to do that test because there is no resistance bulding up. even if it did leak down there would be no way for me to detect a difference.

i'll double check back there though, but i've had the wheels off so many times now and haven't noticed any leakage as of yet. the resevoir is still full as well.

i thought i would mention that i was braking coming off of an exit ramp and the brakes suddenly became extra grippy at the end of the ramp and almost felt right again. this was while i applied basically even pressure the whole way down.

the other thing that confuses me is that the pedal feels perfect without the car running. i had my buddy at the auto-x press the pedal while the car was off and he said it felt the same as his FD. bah!

 

first, are the rotors re-machined? if old rotors are not flat on the braking face and new pads are put on then the brakes cannot sandwich into the valley until they are fully broken in which can cause spongy brakes in which case you can just go do some highway speed "oh-****" emergency stops and see if the brakes eventually come to life.

if the rotors/pads are not the problem then the caliper slides could be crapped up or frozen which will cause the pads to not fully grip the rotors and also cause a spongy pedal, remove the calipers and check all of the sliders and re-grease them.

if you still cannot find the problem then you can begin isolating the problem by using some clamp tools on the rubber lines to each of the calipers, if you have all 4 lines clamped off to the calipers and the pedal is still spongy with the car off and booster bled down then more than likely the issue is within the master or differential pressure valve(proportioning valve), since you replaced the master more than once then logic would assume it is ok and the proportioning valve is the fault. if the pedal is hard with the calipers clamped off then remove themone by one while checking the pedal feel to see where the problem lies.

good luck.

 

new front rotors and high quality pads all around. the rear rotors could use machining soon, but are not horrible. no lips or grooves.

calipers are well lubed. however, i've noticed that the grease i've been using gets kind of gummy after a while. it's CRC synthetic brake grease from autozone. i need to get something better, but with fresh grease there was no difference.

the clamp method sounds like a great idea and i probably won't even have to take off the wheels.