It may have been covered but I'll post this anyhow as it may be the answer to your prayers.

I bought my car as a rolling body and the master cylinder had stuffed seals and leaked down the front of the booster. I had it honed, sleeved and re-kitted. Deleted the monstrous abs pump. Had one hell of a time bleeding the brakes and they were never quite right. They always felt a bit flappy, sensative when the car is running, though they did stop the car.

Drove it for a while then parked it up for a couple years

Pulled it out the garage. No brakes, foot to the floor. The master had bit the dust again. Pulled it. Kitted again. Struggled to bleed it or so I thought, flappy pedal, sensative while car is running, though it did stop. Car off hard pedal. Car on, soft. Car running, put foot on the brake, shut off car and pedal raises instantly.

Now everyone will say check the check valve. Fully functional and flowing the right way. I say it's the booster to every one I talk to as I did the first time the car was on the road. "If the booster failed it would be rock hard pedal. There's no way you would get a soft pedal. Impossible. It'll be bypassing in the master" everyone will say. Pulled the booster. Brake fluid leaked out. The rod slopped around like a **** in a sock. Second hand booster goes in. Trumpets sound, the heavens part, a choir of angels sing and I for the first time since owning my fc have fully functioning, real feel brakes.

 

I have see plenty of threads where they bleed and bleed. go through multiple m/c. Calipers. Pads and rotors. Then they fit a suby or 929 m/c and booster and the problem goes away. They never swapped the factory booster. Was this the issue? When the master goes bad it leaks into the booster destroying the rubber seal and who knows what else. Not sure how exactly it causes the soft pedal?

 

..you may need a smaller Sock Ben..sounds like a personal problem..hahhahahahha!

 

I'm kinda surprised that faced with a master cylinder that leaked into the booster, it took so long to suspect the booster would be a problem.
Anyways, what you fixed was malfunctioning hardware but having done so (and congrats on that success), it's still likely you have a "soft pedal" because that's baked into the basic specs of the system.

 

more often than not it is the reverse, i have seen plenty of stiff pedal FCs with malfunctioning brake boosters or booster line leaks. oddly enough those owners never complained, but when i drove the cars and had to stand on the pedal to stop relatively quickly, i felt unsafe.

soft pedals are usually simply due to air in the system. bleeding the system is a fine art. if the pedal isn't tapping the floorboard with your weight into it, then i doubt you even have an issue.

 

I always did but when you are told by brake specialists and mechanic after mechanic it's not you listen, for far too long. Especially when you give up yourself and send it in to be rectified. It comes back slightly improved but still sloppy and they tell you its fine. And I'm left standing there

No normal pedal feels soft to me after what I experienced. (Very hard to do stand stills with a pedal that feels like tissue paper) Haha.

 

firstly, i find a stock FC has a much different pedal feel than a new car, the FC has less effort, but more pedal movement than an average new car, which can feel odd these days. the FC is really linear though, so once you get used to it, its quite nice.

second, the FC's tend to have mushy pedals, and i've seen a few reasons for it over the years. the booster can certainly be one of them. the other is what i found on my car, the brake booster pushrod to master cylinder clearance was way off. the stock spec is 0-0.2mm of clearance, and mine had like 2mm of clearance. it doesn't sound like much, but the pedal is a 5:1 ratio, so by the time it gets to your foot its half an inch (13mm), which is totally obvious.

 

Being generous, the best I can say is these people seem incompetent.

Having deleted the ABS, there are only three components in the system- the calipers, the master cylinder and the booster.
The calipers are simple- if the pistons move and it's not pissing fluid, it's good.
You had the master renovated...it could be bad still, but unlikely.
That leaves the booster...the booster that had brake fluid drooling down it's face and is the last major part of the circuit: but let's NOT check it because of... reasons, I guess?

I never adapted to the longer stock pedal travel- I didn't think the FC brakes were bad but the feel always seemed "off".
You exactly describe how hydraulics work- the FC has a relatively small bore master cylinder (and a smaller, single diaphragm booster), so it requires less effort but must travel further. Increase just the master cylinder bore and the travel decreases linearly but the effort increases. Add a larger booster and effort decreases again, while still requiring less travel.

 

Oh you're preaching to the converted sir. The first time, years ago after all the carry on it was livable. This time it was worse. My brakes are finally mint. I did check it this time despite all these fellows telling me it's fine and the general consensus on here being fcs have crap feeling brakes. I posted this because I've read too many threads( not just on here) about mushy brakes. Poor chaps who have been through several master cylinders, bled their brakes every which way you can, replaced calipers, get told what they have done could still be the problem, do it all again, finally they swap to a 929 m/c and booster or suby combo and hazaah it's fixed but they never put it down to being the booster because everyone (yourself and i excluded) will still say failed boosters cause hard pedals, period. Or it was the master, you were just unlucky on the 3 you swapped for example.

 

Baaaaahahahaha I somehow missed this!

 

how can a failing rubber diaphragm cause the pedal travel and effort to be less than it is supposed to be?

a failing/failed booster to me causes the pedal to be harder, i cannot mentally imagine a scenario where a failing booster can overdo its job. clokker is right in one aspect, if you had fluid leak into it, it should have been replaced or at the very least cleaned out immediately following noticing the leak. i see masters leak all the time, rusty boosters with snail trails dripping down them, but i still don't suspect the booster to be bad, because the seals inside the booster are immune to brake fluid, for the most part. the steel parts may rust and then compromise the booster but i haven't seen it yet.

the only physical way i can picture a booster overdoing its job is if the displacement of the fluid is allowing the booster to collapse easier, making the pedal effort less. siphon out the fluid, done.

i didn't bother because what are you gonna do, replace it with an OEM booster for like $500? replace it with an unknown booster from a junkyard? or "upgrade" it with one from another car? i think the FC brakes feel fine, after driving the car for a decade you kinda get a feel for it...

most people are full of crap, and they bleed the brakes again after a few weeks of the car sitting and along with their booster replacement, probably coincidentally fixing the issue. a mushy pedal is almost always quite simply air in the system. i use a vacuum bleeder and never have any issue with bleeding the brakes.

 

. Haha. The only thing I did on Saturday was replace the booster and my pedal was instantly fixed. So I have no great explanation of the physics behind how the failed booster causes an over boosting feel but it did.

 

If changing your booster 'solved' your soft pedal, then your adjustment rod was off and corrected by the new booster...

A failed booster means it's leaking vacuum, which means it is not providing as much if any assist.. This equals a very hard pedal and diminished brake performance.


I mean it's nice that you fixed your problem, but don't parade around the forum essentially implying that other - very intelligent - people are wrong or that you can't explain it.

 

thanks, i felt like he was totally ignoring what i said. well, actually he was.

travel adjustments are one possibility, air is another, but a failing booster means the opposite of his symptoms.

 

Sorry for parading about the forum and being an *******.

Just so you know a cracked internal hub or destroyed reaction disc inside the booster (from say brake fluid leaking inside the booster eating the rubber disc/valve which explains the floppy pushrod. ) can cause my issue of maybe poorly described as soft pedal and should have been called overly sensative pedal feel.

 

Sorry for parading about the forum and being an *******.

Just so you know a cracked internal hub or destroyed reaction disc inside the booster (from say brake fluid leaking inside the booster eating the rubber disc/valve which explains the floppy pushrod. )or missing/dropped reaction disc can cause my issue of maybe poorly described as soft pedal and should have been called overly sensative pedal feel.

 

Floppy pushrod? That extends from the front of the booster into the master? Any booster I've ever dealt with has had a 'floppy rod'

I'm sorry, but I don't buy it. Never, ever have I heard of, had, or seen a booster fail and cause a soft pedal. Here are some things that will cause a soft pedal..

- misadjusted throw rods
- Air in the system
- leaking master or sticking Caliper, slides, or pads
- no-leak internal seal failure in master
- Overheated or worn hydraulic fluid

Good day. :-)

P.S.BTdubs, soft pedal and sensitive pedal do not align...

 

complete causes

 

http://www.ausrotary.com/viewtopic.php?f=4&t=178847&view=previous describes my symptoms exactly. And I thought I had also. Will need to pull my old booster apart (if they are designed to come apart otherwise it'll be cut off wheel. ) see if reaction disc is in place and not perished from the fluid getting in.

 

Pulled the rod. As suspected no reaction disc. Shook the booster but no rattle. Must have been wedged in somewhere as i tipped it up the other way and dull rubber rattle rolling around.




Couldn't get it past the spring so pulled the booster apart. Not that hard actually. Full of fluid and....at the top you'll see the disc.




Here it is next to the rod piston should be in behind it down the hub where i shone the light in the first pic.

So I never claimed this was the only way you could have a soft sensative pedal but yes this can happen. Yes this is an issue with the booster. Yes this was remedied by replacing it but I now know I could have fixed the original booster. And no amount of bleeding or rod adjustment will help. I hope some one learned something today and hopefully this helps someone some day and maybe saves a potential unnecessary cost.

 

RotaryEvolution and Acesanugal. I never said the causes and effect examples you gave were incorrect information. In most cases you are spot on and that's all the help someone will need and I know you're a wealth of knowledge among the 2nd Gen community but you were feeding my frustration (which accounts for my replies, sorry) as I knew I had an oddity on my hands. Their responses and like from mechanics and so on are my "reason" Clokker that I didn't immediately go for the booster as to most it was very black and white unable to be the booster and in 99 percent of cases this is true. I may have given a less than ideal description in the title. Soft, sensative almost zero feedback pedal though I never mentioned spongy. Now with my pics and digging deeper into what my instincts told me we find another possible fault within a booster causing the complete opposite to a failed diaphragm. All I wanted to do was share my experience to help someone who may stumble across it. Something to tick off the list when you've tried everything else and you're about to set your fc ablaze.

The job of the reaction disc is as I understand it, chime in if you can better describe it or I'm wrong on some thing, is as you apply force to the pedal you force the rod applying pressure to the master cylinder, the reaction disc is compressed receiving force back from the rod. it transfers part of it back to the pedal which results in pedal feed back or resistance. The more it's compressed the more feedback you get through the pedal.

 

oddly enough my fc had the same issue with leaky brake master and sloppy pedal feel. instead of bothering with any of my tiny stock na stuff i went with clokker's subaru legacy master cylinder and booster setup. i wanted something a little beefier since this will be my track car and it was easy to source a nice used unit from the junkyard. i still have my old booster laying around somewhere so i could check it out to see if it was in fact the missing reaction disc when i have some free time.

 

Yeah no idea how it fell down but interesting to find. It came up while searching that there are other car forums where it was a more common issue than the fc community had experienced. But yeah I brought it up to save folks some money if it was their issue rather that hunting every other possibility. But if you are after a beefier set up anyway bin the fc stuff and go for it. Curious to see if it was.

 

Gave it a little shake before opening it up and heard something moving around. Popped it open and sure enough it wasn't where it was supposed to be. Glad clokker did that experimenting because this subie 1-1/16" master has some real stopping power paired up with the 4 piston calipers.

 

Nice! If I ever get a bit more serious down the track ill look at the subie combo as you can't buy the 929 stuff here.