Master Cylinder spongy...
Thread Starter
Pro
Joined: Jan 2006
Posts: 643
Likes: 2
From: Alexandria Northern Virginia
Master Cylinder spongy...
All,
During my session on Saturday, my brakes were going pretty far to the floor to build pressure. So far that it threw my heel-toe rolling off a bit and I found I was making too big of a blip. I am sure I just need to bleed the brakes after the track event but it got me to wondering....is the MC a common go-bad part on these cars? Wondering if anyone has any experience with this part going out and what symptoms (other than leaking of course) anyone has had.
Thanks in advance,
Cassidy
During my session on Saturday, my brakes were going pretty far to the floor to build pressure. So far that it threw my heel-toe rolling off a bit and I found I was making too big of a blip. I am sure I just need to bleed the brakes after the track event but it got me to wondering....is the MC a common go-bad part on these cars? Wondering if anyone has any experience with this part going out and what symptoms (other than leaking of course) anyone has had.
Thanks in advance,
Cassidy
Burning Brakes
Joined: Feb 2005
Posts: 1,190
Likes: 0
From: Fayetteville AR
I dont race so I could not say what the long term effects would be. I dont have any problem with my MC and I been on this forum for years and never noticed any threads with problems with MC.
Tech Contributor
Joined: Oct 1999
Posts: 41,058
Likes: 9,821
From: Charlotte, NC (formerly Endicott, NY)
What you experienced is one of the signs of pad tapering in the front calipers. As the pads wear from bottom to top (as you are looking at them from the back of the caliper) they tend to taper considerably in the stock caliper. Replacing them with new pads will probably reduce pedal travel. Another thing you can do is swap the pads from the left to right calipers so the wear will reverse the taper.
You could have air in the system but your description really points to the very common pad taper issue. The taper along with piston knock back as you go through corners can produce a very long pedal. One thing you can do on the track is to double stroke the pedal when braking or as you travel down a straight after exiting a turn is to reach over with your left foot and tap the brake pedal a couple of times to get the pistons moved out. Here is a picture of a set of front pads showing the taper:
The taper you see here caused a considerably long pedal. These were new pads that had been burnished in before a two day track event with 4 20 minute sessions per day.
Bill
You could have air in the system but your description really points to the very common pad taper issue. The taper along with piston knock back as you go through corners can produce a very long pedal. One thing you can do on the track is to double stroke the pedal when braking or as you travel down a straight after exiting a turn is to reach over with your left foot and tap the brake pedal a couple of times to get the pistons moved out. Here is a picture of a set of front pads showing the taper:
The taper you see here caused a considerably long pedal. These were new pads that had been burnished in before a two day track event with 4 20 minute sessions per day.
Bill
Last edited by Bill Dearborn; May 12, 2009 at 01:08 PM.
Le Mans Master
Joined: Sep 2003
Posts: 8,847
Likes: 795
From: Longview Texas
I don't know how common it is, but I had to replace the brake master cylinder on my 2004 Z06 because it started leaking from the seal at the back of the cylinder.
You might check on the brake booster housing and see if there are signs that brake fluid has been running down below the M/C.
You might check on the brake booster housing and see if there are signs that brake fluid has been running down below the M/C.
Thread Starter
Pro
Joined: Jan 2006
Posts: 643
Likes: 2
From: Alexandria Northern Virginia
Thanks all,
I will check the pads and bleed the system this week. I have a feeling it just got too hot and I need to bleed the system. I will check the MC and booster for leaks but hopefully its something simple...
Cassidy
I will check the pads and bleed the system this week. I have a feeling it just got too hot and I need to bleed the system. I will check the MC and booster for leaks but hopefully its something simple...
Cassidy
Burning Brakes
Joined: Aug 2005
Posts: 1,057
Likes: 11
I am with Bill on this one, for the most part 
As the pads wear you get more knock back. As they really wear you get even more knock back. What I do to mitigate the low pedal is to do a double-tap going into the braking zone. The first tap moves the pads in close to the rotors, the second is you normal brake stroke. With practice, your passenger, instructor, imaginary friend, etc. will not even know you are double-tapping unless they are watching your right leg.
I prefer the double-tap vs. dragging the brake on the straight because it is easy to burn into muscle memory. Once burned in, you don't have to think about it and the technique works really well when there is only a little straight between turns.
You could also just slow down
As the pads wear you get more knock back. As they really wear you get even more knock back. What I do to mitigate the low pedal is to do a double-tap going into the braking zone. The first tap moves the pads in close to the rotors, the second is you normal brake stroke. With practice, your passenger, instructor, imaginary friend, etc. will not even know you are double-tapping unless they are watching your right leg.I prefer the double-tap vs. dragging the brake on the straight because it is easy to burn into muscle memory. Once burned in, you don't have to think about it and the technique works really well when there is only a little straight between turns.
You could also just slow down
Race Director
Joined: May 2005
Posts: 15,960
Likes: 21
From: West Norriton PA
St. Jude Donor '08
Also are you using rubber or steel braided brake lines ? As time goes on the rubber ones start to give.
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