Spongy Brake Pedal

[ferni]

So brake experts.. need some input...

I run Stock R33 GTR Brembo calipers... DBA5000 discs, braided lines, Removed stone shields, Master cyl stopper... with RBF600 fluid and DS2500 for street and DS3000 for track.

Everyday driving/street on the DS2500 the pedal is reasonably hard, good feel, and gives me confidence.

For track days i change pads from the DS2500 to DS3000, as soon as i get back in the car after changing pads, the pedal feels softer... a bit spongy... Now since the only thing i'm changing is the pads, You'd have to assume its the pads, or the pads not bedding to the discs properly... At the track the pedal is soft as well... so coming up to a corner i'm on the brakes much earlier than i should be at about half pressure, if i jump on them to hard the pedal just about hits the floor and i have to take a 2nd stab at it....

It's not pad knock off because i tap the brakes with my left foot before jumping on them for big stops....and even when i take a 2nd stab at them the pedal is never hard.

Now the weird thing is i found i had a hard pedal at one particular corner at Phillip island.... Turn 5.... not sure why... not a high speed stop really....

Now after the track day i put my Street pads back in DS2500 and the pedal seems to be hard again.... coincidence?

Options i have: Rebuild the calipers? Replace/reco the master cyl? Replace the Brake booster?

First thing i'm thinking of doing is putting a brand new set of pads in (i have a new set of DS3000 sitting in the box at home).... and see if the pedal is hard with those in....

Any input/suggestions welcome...

[Gts-t]

obvious question, do u bleed the brakes from more than one point after u change the pads?

[ferni]

No i don't bleed the brakes after i change the pads.

I bled the brakes about a month ago with new RBF600 fluid....

When i change the pads i just push the piston back into the caliper to fit the pads in... I don't crack the bleed nipple.

[Beer Baron]

I hope you have the lid off the master cylinder when you are pushing the pistons back in with the nipples closed. because the system is sealed and if you are pushing a piston back in that pressure has to go somewhere and often it ends up getting forced past a seal somewhere (master maybe) which can stuff the seals.

90% of the time spongy pedal is solved by bleeding the brakes. especially if your set of 3000s is more worn than your 2500s is possibly a reason why you are getting poor pedal.

[ferni]

Yep i Take the lid off the master cylinder....

But the pedal is now hard again when i've put my street pads back in - without bleeding.... and i bled them a month ago.....

[RBwhatever]

did you put any kind off brake goo on the back of the pads?

[RBwhatever]

I had a similar issue once.

http://www.skylinesaustralia.com/forums/in...p;#entry3195352

[Ant97GTR]

While I'm no expert....I'd try the new pads to see if there is a difference first.....if not try a proper bleed and then try the seal replacement kit.

I'm not sure why two sets of pads would have such a drastic effect on the brake pedal feel....would a big thickness difference matter?

[ferni]

Keymaker - No i don't use Shims or anti-squeel brake goo....

Both sets of pads DS2500 and DS3000 are about the same thickness, around 40-50%...

[Snowman]

I personally think you are just making excuses for not being able to run a 49.

[ferni]

I personally think you are just making excuses for not being able to run a 49.

haha yes lack of balls or lack of brakes? Probably about equal, i recon there is about 2 seconds to make up for my brake issues and another couple of seconds to make up for lack of balls..... Hopefully the brake issues i can fix easier than the ball issues

This link is interesting - http://www.zeckhausen.com/avoiding_brake_judder.htm

Talks about changing from street to track pads... not really related to a spongy pedal tho... but i do get brake judder as well sometimes...

[Roy]

At Sandown before Dutton when Juz was gettign used to the car she was gettign brake shudder pretty bad...a bit of housekeeping and change to the way the car is driven and next session they were good to go...

I think the real big hint to the problem is that in a bleep between corners when you have had big revs on board in teh same gear and you are braking from big rpm without a down change...see if anyone else thinks the brakes working well in this instance hints at the problem ????

[ferni]

Yeah i'm not sure if that was co-incidence or what, maybe it wasn't every time i went to that corner, but i just seemed to notice a hardish pedal at that corner, where as not really anywhere else....

I dunno, stupid brakes!

[Duncan]

Well....could be related to vacuum booster leaking or not working properly, and you only notice when you are pushing them hard.

vacuum boost (obviously) needs vacuum to work, you only get vacuum with a closed throttle.

do you left foot brake (ie throttle still open when on the brakes?) if so you may not have any vacuum in the boost and backup cannister so you get no assistance at turn 5. I have this problem at wakefield at the top of the hill - I keep throttle open through both right handers but never have any vacuum for the quick dab on the brakes before the second corner.

One simple thing to start with - make sure the 1 way valve on the way to the vacuum canister works (ie you can blow through it one way but not the other)

[ferni]

Yes i left foot brake to take up any pad knock-off and to make sure the brakes are still there before any big stops...

The one corner i seemed to notice a hard pedal was a good thing, when i say hard i mean hard and it seemed to stop well.. wasn't like it was a hard pedal and wouldn't stop.

I'm not sure where the one way valve is, but ill have a look - I don't have to remove it to check do I?

[blind_elk]

Valve is probably embedded in the hose - take the whole hose off to test.

Have you tried running the "street" pads, just to confirm it really is the pads, and not the fact that you are "racing"?

[ferni]

Running the street pads at the track? No... but i have run the street pads at DECA... Don't think i had the same issue there but i didn't really take much notice... I can't run my street pads at the track they will overheat.

PS. you have a typo in your signature blind_elk 'stoke week'

[blind_elk]

Running the street pads at the track? No... but i have run the street pads at DECA... Don't think i had the same issue there but i didn't really take much notice... I can't run my street pads at the track they will overheat.

Yes, but will you also have a spongy pedal? There are 2 major differences - the pads and the driving style. You need to eliminate 1.

Alternatively use the "race" pads on the street - is the pedal still spongy?

PS. you have a typo in your signature blind_elk 'stoke week'

DOH! thanks Edited September 25, 2007 by blind_elk

[Duncan]

there is an air line from the plenum to the brake booster, has a valve in the middle bascially on top of the booster. easy fix if that is the problem

[ferni]

Yeah the race pads are still spongy on the street....

Ok so what should i do with that Duncan? Pull the hose of from the plenum side and blow into it?