These brakes truely do hate me *long*

[p00t]

I’ve been living with this problem now for almost a year. First 50% of brake travel does nearly nothing (has a tiny bit of spongy pressure however), at half way the pedal pressure appears. It’s not rock hard but fairly stiff at that point... it feels like how the top travel of a normal brake system is. It feels like the entire action of the brake system was slid down to half pedal (I hope you understand this). I can even lock up the front wheels when braking, so there’s good pressure in there.

s13 1993 fastback, non-ABS

***************************************************Chain of events of me ruining my brake system (I think?):

10/03: Stock brake system, nice stiff pedal. Brakes work fine, some screetching at low speeds from one of the rear wheels. After examining the problem, previous owner didn’t install the LR pad correctly (didn’t line up the nub on pad with hole in caliper). All pads still had decent life left except for the dragging LR. Have cash to burn, so hey why not do a little upgrade.

Ordered Brembo Blanks F+R and MetalMaster Semi-Metallic Pads F+R. Recieved brembo rotors and PBR brand semi-metallics... Maybe I was jipped, maybe I wasn’t... heh. New shims and clips as well.

11/03: Did the install and flushed the brake system with motul 600RBF. I thought it was a Dot5.1 but its a full racing fluid.... doh... doesnt comply with Dot specs! Had some early bedding in concerns which everyone helped me with. Brakes worked properly after fully bedding in, real crappy when cold during the first 500 miles of use. Improved after a while though (pads behave properly for semi-metallic now, and I have no problems with them).

Heres an old post of that event: http://nicoclub.com/zerothread?id=42669

Every thing seems OK in Brakeland.

3/04: Rather than type out the whole situation I’ll link you to my old post:

http://nicoclub.com/zerothread?id=56459

Thread sounds a lot like this one eh? Sigh… I *assume* that the Motul RBF fluid soaked up fluid or something… but its strange how it just appeared at a light all of a sudden. I flushed it with some generic DOT3 stuff, didn’t help. From this point on the brakes have felt the same… spongyness and all till this day.

12/04: Pedal feels a little softer then before, so I figure I’ll rebuild the MC, maybe the Motul killed the seals? Maybe the old brake lines are bulging and adding to the spongy pedal? Well let me take care of that:

I rebuilt the MC. Installed SPL SS brake lines. Installed speed bleeders so I wouldn’t have to recruit someone for the pedal pumping (every one hates it). Bled the whole system with Valvoline Syn Fluid, 3L worth of it. Used the LR, RR, RF, LF sequence the FSM recommended, no bubbles visible from bleeders when done.

Unfortunately pedal is the same… with the 50% mark being more firm (because of the lines).

********************************************************************

The only thing I can think of at this point is the brake booster. However:

*There is no hissing noise from the booster. (not leaking).*There is only a small RPM drop when brakes are applied (no vac leak).*I still have full assist from the booster.

Article on Zilvia describes how to get rid of some of the top spongy feel to the brake pedal. This is done by adjusting the output rod on the brake booster:

http://www.zilvia.net/faqs/arc...r.asp

My brake system has stock MC and calipers…. Why would I have to adjust the booster now after 100k miles of it being fine? What could have changed if the booster is at fault? I am worried that the brakes will drag if I readjust it, since there is a little bit of pressure in the top 50% of pedal travel.

Does anyone have any insight into this problem? I'm completely lost at this point.

[s13sr20chris]

i have not yet read your links(got to go to work). i reccomend at least checking the brake pushrod adjustment. should not be it but check anyway. make sure all the pads are installed right(im sure you did it right) and make sure the caliper slides actually slide. will talk more with you about this later.

[navysnail]

i think i understand what y our saying, mine kinda do the same thing, like if i press it when the engine is off to get rid of the vac in the boster and make the pedal reall stiff, it has like 1mm of play, but with the engine running and the booster working, it has like 3cm of play, i cant figure out when to adjust it though, with the booster working or not. i just decided to play it safe instead of burning up my pads

[p00t]

I dont understand what could have gone wrong inside the booster to do this (if it is the problem)... but as soon as the garage is vacant I will play around with it. Yes sr20chris I did install the pads correctly, notches on the back are lined up.

One interesting thing that keeps coming up as I google for info is that when one line fails pretty much all MCs have a failsafe action. When one line has no pressure one of the pistons in the MC will have resistance while the other will be easily pushed by the rod. The feeling in the pedal is strangely...exactly like what I am experiencing.... pedal will be be soft till 50% then you will get pressure. This how-stuff-works animation shows what I am trying to describe. Go to the last two animations, one is for a normal MC, and then one one with a leak. http://auto.howstuffworks.com/master-brake1.htm

When one circuit fails the first piston must travel all the way to the second till it touches and forces the other piston to move. Hopefully NISTECH's experience can come into play here: What symptoms are typical of a failing proportioning valve? Is it possible that this internal valve is broke and not allowing one circuit to build pressure? I rebuilt the MC pistons seals only cause they are only $10, so i wanted to try that before a $80-100 MC (which is still a blind stab at the problem). Any info in reguards to this?

I appologize for the huge page of text, just trying to offer as much info as possible so I can hear everyones 2 cents on the whole issue. Big Big thanks to all who make it this far in the thread.

[s13sr20chris]

how is your braking performance? does your rear end lock up way before the front? or vice versa? will one end not lock up at all? how about sliders/pins? did you check them. my 240 came with locked up pins. that was not a problem until i messed with the brakes one day. then all of a sudden i have half a pedal of "slack" travel before it catches. i ended up putting used caliper slides on it from the junkyard.

[p00t]

how is your braking performance? does your rear end lock up way before the front? or vice versa? will one end not lock up at all? how about sliders/pins? did you check them. my 240 came with locked up pins. that was not a problem until i messed with the brakes one day. then all of a sudden i have half a pedal of "slack" travel before it catches. i ended up putting used caliper slides on it from the junkyard.

Slides...hmm no i didn't consider them. What should I be checking for? Check to see if they are excessively lose? I know I can shift the front calipers around on them alittle... maybe 1 mm (this is looking at the outside face of rotor and pushing the caliper body in, out, left, right. No play in the rear, but i have never taken them out and inspected them.

What did you do when trying to fix the "locked up" issue that caused the brakes to have problems? Did you just work them out and lube them, or did you sand them down?

In my entire ownership of the car I have only been able to lock up the front.

Thanks Chris!

[s13sr20chris]

ok, my car sat for 3 years before i bought it. during that time the caliper slides rusted stuck. so the brakes are ok. one day i go to inspect my calipers to see if they need rebuilt and i find this out. i did not have time to pull the whole torque member(caliper bracket) and heat them up. so what do i do? i beat the crap out of them with a sledge hammer to try to free them up. no good. they are still stuck. what i did not know was that i had moved them in some. i put back together and figure i need to spend more time with them when i can. when i go to drive the pedal is just like yours. i take it back apart and realize what happened. with the slides moved in slightly the pads, caliper, and rotor have all this extra space. this space should get rid of itself but the slides wont move. the result is the piston has to take up all that space before the brakes work.

i ended up getting a couple of calipers from the junkyard and slapping on new blank rotors(my work) and hawk hps(tirerack) front and rear. when i was done i worked some magic on my old slides and they freed right up.

[Texas240]

yup. I had the same problem you had (except i didn't throw so many parts at it) it was the power booster and master cyl. as you've already rebuilt the MC, the pB... well, that's my .02 anyway