Brake sponginess?

[majorscooby]

Right here's the problem guys, Really stumped!

As some of you may know i have been trying sort out my Subaru 4 pot brakes due to lack of power when braking hard.

At first i had just a re-bleed as the fluid was really old, and this did improve them slightly but i was still not convinced or had any confidence in them so i decided to strip them all down and replace all the caliper seals, boots and front pads etc, along with a repaint and de-rust. disc's also purchased on front.

So today Mr Crowman came over to re-bleed the system with me.
System was bled a fair few times from, passenger rear first, drivers rear, then passenger front and finally drivers front. also bled a second time round in a diagonal pattern after reading a few things on the net.

After we took the car out our initial thoughts of the pedal being spongy was that they need a good 300 miles brake in and but as we braked every second time round the pedal got harder and the brakes responded brilliantly, even getting the ABS to kick in which i never was able to do before.
But here's the problem, the pedal goes back to being spongy again once released and you carry on driving? its like fluid is letting by somewhere and it takes the second pump of the pedal to make the brakes work fine???

Have checked all around and have no leaks from anywhere, levels are stable in the reservoir and don't move, all i can think of is the master cylinder has a fault within it, ABS, Servo??, don't really know what else to check, pull apart or where to look?.

Any input would greatly help!

Might jack it all in and go and buy a white spec C

The one certain thing is that there is no air in the system .
As rich says if you press the brake pedal down until it actually does something then release and re apply imediatly the brakes are spot on .

With the car stationary and engine off , if you apply pressure to the brake pedal it goes slowly down over half way just as if you have a bleed nipple open .

[asperformance]

just out of stupidity you do have the caliper bleed nipples installed so they are at the top?? have seen this a number of times over the years and catches more people out than you'd think............

the other thing is have you checked and o/hauled the rear brakes also??

final thing would be that you have a leaky seal in the master cylinder and its drawing air........

Calipars up the right way.
Rear calipars are in great condition and have been overhauled also.
I personally think its master cylinder.

[C. J.]

Is there a valve in the vacuum pipe ?

Chris are you talking about the pipe that runs from servo Along the bulkhead over to the inlet manifold

[C. J.]

Yep servo end there should be a one way valve

Ok , rich will have to check .
Do they fail ?

[C. J.]

Not that I know but sometimes poeple change the hose and don't transfer them over into the new pipe

[majorscooby]

As martyn has said, yes to the calipers being up the right way and yes to the rears also being overhauld to! did them all as i had the time and patients.

Thanks for the ideas guys i shall have a look one evening, the only annoying thing is that its gonna need another complete bleed if i strip it all down again, but i WILL succeed!!!!!

Not sure what the master cylinder actually comprise's of or what to take apart but ill have a google and get the spanners out.

[C. J.]

Will take you 2 mins to check the valve is there . Give us a call if your unsure .
Me numbers on facebook

[majorscooby]

Originally Posted by C. J.

Will take you 2 mins to check the valve is there . Give us a call if your unsure .
Me numbers on facebook

Cheers chris, ill have alook tomo after work and give you a buzz on my findings!

[asperformance]

a missing vacuum valve would give you a totally solid pedal on first application which then got better, not a spongy pedal..........
and wont be affected at all when the engine is off by its very nature

I did wonder about the engine off thing.
It's hard to explain, but if you put your foot on brake pedal and put a steady not to hard pressure on it, the pedal goes down over half way until it stops. It feels exactly like you have a bleed nipple opened a small amount.

To be honest it has same feeling as if air was in system but we have bled the brakes very very thouruoghly , it's not like we are novices, I have renewed brakes on my scoob a few times with no problems.

[majorscooby]

Just doing a bit of digging on the net and found a sequence to do the bleed but different to what we found on the net this afternoon?? whats right and whats wrong and does it really matter??

The bleed order for the WRX/STI is Front Right, Rear Left, Front Left and Rear Right. ??

Also read something about bleeding the Master cylinder and also the ABS by activating it a few times on a loose surface then returning home to bleed again?? Apparently the dealers can do this in shop but im not paying there prices to check this out!

Its tucked up in the garage for the night and Tomo eve i shall check C.J's possible missing valve idea in a vacuum pipe then go from there. After that i shall do the crawl around to look for leaks that i know are not there but for peace of mind and all that nonsense its worth the glance.

If i was to change the Master Cylinder would a UK STI SPEC one of around the same year fit a JDM STI SPEC car?

[Scott.T]

Sounds like a cylinder issue.
You should be able to pump the brake pedal up hard when the engine is off.
Keep your foot on the pedal then start it and the pedal should sink a bit.

Also just googled this :
"When a brake master cylinder begins to go bad or fails, you will notice a soft or squishy feeling when you press down on the brake pedal. When constant pressure is maintained on the brake pedal (like when you keep your foot on it at a stop light), the brake pedal will begin to sink to the floor as the brake fluid leaks internally in the master cylinder. This is called "extended travel" when the brake pedal goes farther down than normal or than it was intended to. When this occurs you will have to "pump" the brake pedal to regain normal pressure and to keep the car from moving forward because the brakes are slowly releasing. The red brake warning dash light should come on to indicate low brake fluid, or excessive movement "travel" in the brake pedal.
You will not normally see the brake fluid leaking out externally of the brake master cylinder or from the wheel areas when this pedal softness occurs, so fluid level alone isn't an indication of a good or bad brake master cylinder. The fluid will usually not be low or in need of topping off…remember the leak is internal and the brake fluid is leaking past internal O-rings, so an obvious external sign that the master cylinder is "bad" is usually not existent. "

Scott that pretty much sums it up.
Good find

[majorscooby]

Tis a good find indeed and ill have a look tonight after work, but the only thing that gets me is im not sure i can get the pedal to travel to the floor with constant pressure. Perhaps i need to sit there longer as i dont think we gave it enough time to show this fault mart.

If i remember correctly its soft halfway down the stroke then hardens up mid way down and goes solid and stays like that.

( Back to the brake issue guys minds out of the gutters please! )

Then its straight back up on the pedal and down again and the travel is reduced with more braking power?

[andy-m]

most of the time the end of the piston/barrel in the master cylinder used during normal and gentle breaking would get used and therefore wear more than further down the piston/barel? maybe that would explain why your pedal gets down so far and then seems to stop?
just a guess though, i've never pulled one apart myself and had a look

[majorscooby]

Do i need to look along these lines??

Blimey, by time we finish mate, we will be experts .

[majorscooby]

How do you bleed the ABS part of the system?

Before i go buying anything im gonna need to clear it in my mind that there is no air trapped in the master cylinder or the ABS unit.

And im guessing there maywell be, after reading a few bits on the net with guys with the same second push symptom needed to get the required power all the answers a given as to trapped air in the ABS part.

[asperformance]

not sure exactly what age car you have but generally speaking only the earlier cars have an bleed nipples on the ABS pump............

[majorscooby]

Originally Posted by asperformance

not sure exactly what age car you have but generally speaking only the earlier cars have an bleed nipples on the ABS pump............

Mine is a 99 t plate JDM STI.

I have been looking on Evil bay for a new'ish or second hand master cylinder and there are a few on there for pennies and a few at £60 plus and im still leaning that way to replacing it as the first port of call to finding the fault.

Thing i would like to know is if anybody can help, would a master cylinder from a 2007 or a 2005 scoob fit a 1999 classic??

First thoughts from you ( and myself to me were ) "NO you stupid boy as their years apart" but the more i look at the pics the parts look identicle from the different models of cars.

Really hoping to get home ealy tomo and check a few things out, still haven't checked C.J's thoughts of the vacum valve missing.

[BIG"E"]

what about CJs mate Saj ?

Jap parts?

[majorscooby]

Originally Posted by BIG"E"

what about CJs mate Saj ?

Jap parts?

Has he got a web site E?

Jap performance parts Crawley

[Greig]

I'd Definatly check that vacuum hose, done exactly the same thing on Niges old car when we changed the hoses to blue silicone we didn't notice the valve and the brakes did the same
Easy fix tho

[majorscooby]

Originally Posted by Greig

I'd Definatly check that vacuum hose, done exactly the same thing on Niges old car when we changed the hoses to blue silicone we didn't notice the valve and the brakes did the same
Easy fix tho

Hmm, ill have to check but im sceptical as all mine look standard and untouched since its come from factory.

Sod it im going out now with grips and a torch to remove said pipe to see if its in there!!!!!!!! be back soon.

[majorscooby]

Ok im back and little white valve is there in the flexi pipe that connects to the master cylinder black booster bit. You can also feel it in there!

Just been sitting there pumping the pedal with the engine off and pedal is so soft then second pump it hardens but doesn't feel as solid as it should.

I left it for 10 sec's roughly and pump again and its back to being soft again??

Did notice i have a weeping nipple on the front and rear on the same side but its next to nothing, not enough i would of thought to notice through the pedal stroke and to change pressure, its just a bit of a wet smear. Will nip them up tomo!!!

Really need to get to the bottom of this and may have to resort to getting a pro to look!

Mate, if they ate definately weeping then you will need to just do a quick bleed of those two calipars then tighten them up . Be careful they snap off easy .
You sure the bleed nipples are not diferent from front to back and you got them mixed up . Just a thought

[BIG"E"]

Fingers crossed.


I hope this sorts things for you,

if not a trip to CJs mate in Crawley me thinks.

[majorscooby]

No i would say that they are all the same in length for sure as when i was cleaning them with a wire brush they were all layed out in the bowl and i would of noticed, but now im not sure if the tappered ends are different? Tomo, i will take them all out, check, and get the to do a quick bleed on each corner again sat morn.

[majorscooby]

Originally Posted by BIG"E"

Fingers crossed.


I hope this sorts things for you,

if not a trip to CJs mate in Crawley me thinks.

Yeah i think i may have to ask C.J nicely to have a look if i cant sort soon!

Just haven't really been able to have an enjoyable spirited drive yet!

[BIG"E"]

Originally Posted by majorscooby

Yeah i think i may have to ask C.J nicely to have a look if i cant sort soon!

Just haven't really been able to have an enjoyable spirited drive yet!

who needs brakes anyway?

what's the handbrake like?

Scooby Slayer reckons he only brakes 21 times on the ring

[scoobyslayer]

Originally Posted by BIG"E"

who needs brakes anyway?

what's the handbrake like?

Scooby Slayer reckons he only brakes 21 times on the ring

But 21 braking points with no brakes = 21 potential crashes Ian

[scoobyslayer]

Back on topic.
I assume the pedal was OK before you started if so it would be a big coincidence for the M.C to fail at the same time as you rebuilt the calipers dont you think?
If you at any time emptied the reservoir then I would stake my reputation (for what its worth ) on there being air somewhere in the M.C or ABS modulator.
I would pressurise the system and working away from the M.C crack all the unions one by one.

[majorscooby]

Originally Posted by scoobyslayer

Back on topic.
I assume the pedal was OK before you started if so it would be a big coincidence for the M.C to fail at the same time as you rebuilt the calipers dont you think?
If you at any time emptied the reservoir then I would stake my reputation (for what its worth ) on there being air somewhere in the M.C or ABS modulator.
I would pressurise the system and working away from the M.C crack all the unions one by one.

Sounds all pretty fair to me, I have had my thoughts that there is air in either of those components but never had the knowledge or ideas about how to get it out. but i shall give it a go.

There was a mention of a bleed nipple on the ABS modulator part on the early cars but unfortunatley this is not on mine. would of made things easier for sure.

[C. J.]

Have a vacuum bleeder if you need it but your need an air line to

[majorscooby]

Cheers C.J but i have no airline here!
Ill keep it in mind for sure and do some digging as to who has one to hand near me.

Would that 100% push all the air out if any was in there, even in the tricky ABS and MC parts??

[C. J.]

It pullsit out .
You can always drive over to us

[majorscooby]

Originally Posted by C. J.

It pullsit out .
You can always drive over to us

That would not be a problem.

YHPM.

[C. J.]

Snap

[majorscooby]

This may seem a silly question but what stops the pads / pistons in the calipers retracting back to far??

Was just wondering as the first pedal stroke still seems longer than the second, (even after c.j's bleed tis morn. which has improved it).
So i was thinking is this because im taking the slack up so to speak on the first push and then the second then feels normal?

Has any body on here got a classic with standard 4 pots that i can come and feel to get a comparison to mine!

Really getting ticked off now that i cant get a satisfying feel even with martyns and c.j's wicked help and efforts!

[BIG"E"]

Mate I think you've got to go and get your master cylinder sorted.

Sorry to hear its not sorted.














ps. you missed a nice meet.

[C. J.]

Think it's going to be more air & thought via text it's loads better ?

[majorscooby]

Originally Posted by BIG"E"

Mate I think you've got to go and get your master cylinder sorted.

Sorry to hear its not sorted.












ps. you missed a nice meet.

Well i have just looked at my M.O.T certificate and it runs out on wednesday and the tax at the end of the month!

So its gonna get the lot ripped off and bits changed (or thrown in the bin) untill i get to the bottom of it. i cant believe that i cant get a solid pedal when pumping with the engine off!?????

Sorry i missed the meet guys but im not really in the mood to show off my pride and joy till shes working and running propely.

I am 100% positive I had bled every bit of air out.
Is it possible air is getting back into the system , does the pedal feel sh ite again ?

[majorscooby]

Originally Posted by Crowman

I am 100% positive I had bled every bit of air out.
Is it possible air is getting back into the system , does the pedal feel sh ite again ?

It doesn't feel as bad but still not as hard as it should be!

Basically i should expect the pedal to feel the SAME with every push!!!!!!!!!! not soft then hard then soft again as i approach a round about at warp speed.

Orderd a servo and cylinder complete off ebay from a my00 jap import.
Second hand but looks double clean. I just couldn't stump up to getting a brand new one C.J after your wise words.

Its the thought of changing something expensive that may make no difference.

[asperformance]

only really two things can give you a soft pedal that firms on the second push..........

first is air getting past a seal in the m/cylinder or second you are suffering pad knock off (however this would normally only occur with the vehicle in motion as a reult of a duff wheel bearing, etc.)