brake pedal drops half way, then gets firm...confusion - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


Suspension, Brakes, Drivetrain discuss the wondrous effects of boost and your miata...

Reply
 
 
 
LinkBack Thread Tools Search this Thread
Old 09-24-2010, 09:05 AM   #1
Tour de Franzia
Thread Starter
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default brake pedal drops half way, then gets firm...confusion

My brake pedal drops about half way to the floor, then gets firm and its done this ever since I swapped in the turbo. I can pump the pedal up I have Wilwood front calipers, 1.8 rears (from a junkyard), wilwood prop valve, and nothing else special.

I've changed master cylinders, bench blead the master, changed front calipers, inspected rear calipers. I tried bleeding again last night with no success. I'm thinking about reverse gravity bleeding later today.

What are the chances of 2 bad masters?
Should I get a master rebuild kit?
If the calipers aren't leaking, what else should I look for?
Could it be the booster?

This is making me CRAZY!!! I've had this problem every single time and at my wit's end. Dear Lucifer, please help me!!!
hustler is offline   Reply With Quote
Old 09-24-2010, 09:15 AM   #2
Elite Member
iTrader: (1)
 
NA6C-Guy's Avatar
 
Join Date: Feb 2008
Location: Birmingham Alabama
Posts: 8,038
Total Cats: 43
Default

So it will build pressure back up when you pump the pedal a few times?
NA6C-Guy is offline   Reply With Quote
Old 09-24-2010, 09:54 AM   #3
Tour de Franzia
Thread Starter
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

Quote:
Originally Posted by NA6C-Guy View Post
So it will build pressure back up when you pump the pedal a few times?
Correct. I typically drive down the straights and pump the pedal with my left foot while at WOT to build pressure to it will engage at the top of the travel, so I don't think its the booster.

You can pump the pedal to bleed and the pedal is rock hard and sexy, then start the car and it drops half way to the floor. I suppose have I have old/bad master cylinders.
hustler is offline   Reply With Quote
Old 09-24-2010, 10:19 AM   #4
Elite Member
iTrader: (33)
 
RotorNutFD3S's Avatar
 
Join Date: Jan 2007
Location: Newnan, GA
Posts: 2,539
Total Cats: 29
Default

Quote:
Originally Posted by hustler View Post
You can pump the pedal to bleed and the pedal is rock hard and sexy, then start the car and it drops half way to the floor.
My '99 started doing this after I swapped a Sport Brake setup onto it, if you mean you push the pedal half way to the floor before you get resistance. I haven't figured out why (though it might have a lot to do with just vacuum assistance from the engine running), but braking is very strong, no loss of fluid, etc.
RotorNutFD3S is offline   Reply With Quote
Old 09-24-2010, 10:46 AM   #5
Tour de Franzia
Thread Starter
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

Mine did this after sport brakes, and currently with the Wilwoods. Maybe 949 is about to get more money; paging Emiliano Cervantistana and his revolution.
hustler is offline   Reply With Quote
Old 09-24-2010, 11:15 AM   #6
Senior Member
iTrader: (22)
 
Join Date: Oct 2007
Location: bay area, ca
Posts: 551
Total Cats: 19
Default

I had a small leak at the head of the stainless line going into the caliper on the TSE kit after some offroading at buttonwillow. Didn't find it till my next track day when 9 different spots decided to leak at the same time and the brake pedal did the same thing as you're describing. The fitting on the end of the line must have made contact with something because it was tweaked and no longer air/water tight. It doesn't sound like the problem you're having, but maybe it's worth checking the stainless lines.
orion4096 is offline   Reply With Quote
Old 09-24-2010, 11:20 AM   #7
Boost Czar
iTrader: (61)
 
Braineack's Avatar
 
Join Date: May 2005
Location: Chantilly, VA
Posts: 72,809
Total Cats: 1,780
Default

you have ABS?
Braineack is offline   Reply With Quote
Old 09-24-2010, 11:23 AM   #8
Tour de Franzia
Thread Starter
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

No ABS, no leaks anywhere, I've visually inspected every part and the only questionable leak lies at the "feet" of the master cylinder. I'm ready to put a stop to this because I'm tired of the chemical burns.
hustler is offline   Reply With Quote
Old 09-24-2010, 01:52 PM   #9
Elite Member
 
Join Date: Jul 2007
Location: Little Rock, AR
Posts: 3,109
Total Cats: 127
Default

pm bbundy about the master replacement. I remember reading a thread where he was experimenting with larger stock MC's that corrected the issue's of running larger brakes. I think they were from a 929 or 626 ask Bob.
jacob300zx is offline   Reply With Quote
Old 09-24-2010, 02:06 PM   #10
Moderator
iTrader: (11)
 
sixshooter's Avatar
 
Join Date: Nov 2008
Location: Tampa, Florida
Posts: 15,631
Total Cats: 1,559
Default

It probably takes x amount more volume to move the caliper pistons to the point of firm engagement if you are using larger bore calipers than stock. You might need to likewise increase the bore diameter of your master cylinder to compensate.
sixshooter is online now   Reply With Quote
Old 09-24-2010, 02:31 PM   #11
Elite Member
iTrader: (11)
 
Join Date: Feb 2009
Posts: 2,982
Total Cats: 10
Default

Quote:
Originally Posted by sixshooter View Post
It probably takes x amount more volume to move the caliper pistons to the point of firm engagement if you are using larger bore calipers than stock. You might need to likewise increase the bore diameter of your master cylinder to compensate.
I was thinking similar to this. If there is any increase in diameter of the fluid passage from master to piston, then you would see this. The current master cylinder piston only pushes a given volume of fluid regardless of the diameter of the rest of the system.

In other words......If we say the volume of fluid that is moved by a piston in a system with one caliper is 100cc.

The old system required 50cc to get firm pedal feel. The piston has to travel x distance to push this volume.

Now you changed systems and the new system requires 75cc to get firm pedal feel. The piston has to travel a greater distance to move 75cc than it did to move 50cc. Resulting in longer pedal travel before a firm feel.
miatauser884 is offline   Reply With Quote
Old 09-24-2010, 02:33 PM   #12
Tour de Franzia
Thread Starter
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

Quote:
Originally Posted by jacob300zx View Post
pm bbundy about the master replacement. I remember reading a thread where he was experimenting with larger stock MC's that corrected the issue's of running larger brakes. I think they were from a 929 or 626 ask Bob.
I'm interested in this but by the time I find the master, and booster, and make new lines...I've run out of time and give-a-****.
hustler is offline   Reply With Quote
Old 09-24-2010, 02:36 PM   #13
Tour de Franzia
Thread Starter
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

Quote:
Originally Posted by djp0623 View Post
Now you changed systems and the new system requires 75cc to get firm pedal feel. The piston has to travel a greater distance to move 75cc than it did to move 50cc. Resulting in longer pedal travel before a firm feel.
There is no gradual engagement, it drops half way with very little effort. I don't think Savington has this problem and we have identical hardware. Also, don't tons of people run the Goodwin or FM BBK with the stock master?

No one locally has a rebuild and the replacement master is $100...so I'm considering the Wilwood master if 949 has them in stock.
hustler is offline   Reply With Quote
Old 09-24-2010, 03:07 PM   #14
Junior Member
 
Join Date: Jan 2007
Location: EXTREME Southern Illinois
Posts: 281
Total Cats: 0
Default

Quote:
Originally Posted by sixshooter View Post
It probably takes x amount more volume to move the caliper pistons to the point of firm engagement if you are using larger bore calipers than stock. You might need to likewise increase the bore diameter of your master cylinder to compensate.
This, with maybe some pad knockback from worn wheel bearings or loose caliper sliders??
DammitBeavis is offline   Reply With Quote
Old 09-24-2010, 03:12 PM   #15
Junior Member
iTrader: (2)
 
Join Date: Feb 2007
Location: Santa Clarita, CA
Posts: 158
Total Cats: 0
Default

Mine has done the same thing also after bleeding numerous times. Stock calipers, no leaks, stainless lines, no ABS. I was going to change the master cylinder too.

In for details...
Chapman is offline   Reply With Quote
Old 09-24-2010, 03:19 PM   #16
Elite Member
 
Join Date: Jul 2005
Posts: 6,454
Total Cats: 80
Default

I have this same problem on my 97 M3 after changing the front BBK back to the factory brakes. Bleeding til my eyes bled didn't do squat. It's driving me nuts too.

I suspect it's knockback. I will try rebuilding the front calipers.
JasonC SBB is offline   Reply With Quote
Old 09-24-2010, 03:28 PM   #17
Elite AbsurdFlow Member
 
Laur3ns's Avatar
 
Join Date: Mar 2008
Location: Enschede, NL
Posts: 2,058
Total Cats: 11
Default

The larger pistons up front mean you will have more travel than ever before. In other words: in driving conditions you will never have the same firm pedal.

I've got the Wilwood master on the shelf, needs to go in still.
Laur3ns is offline   Reply With Quote
Old 09-24-2010, 03:28 PM   #18
Senior Member
iTrader: (6)
 
Join Date: Sep 2007
Posts: 1,085
Total Cats: 30
Default

Quote:
Originally Posted by hustler View Post
You can pump the pedal to bleed and the pedal is rock hard and sexy, then start the car and it drops half way to the floor. I suppose have I have old/bad master cylinders.
Mine did this exact thing after I swapped to 1.8 brakes, although I thought it was just me doing a shitty job of bleeding it

edit: maybe i'll try using a 2001+ master cylinder? any difference between in the part for miatas with sport brakes/regular 1.8s?
albumleaf is offline   Reply With Quote
Old 09-24-2010, 03:36 PM   #19
Tour de Franzia
Thread Starter
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

Quote:
Originally Posted by albumleaf View Post
Mine did this exact thing after I swapped to 1.8 brakes, although I thought it was just me doing a shitty job of bleeding it

edit: maybe i'll try using a 2001+ master cylinder? any difference between in the part for miatas with sport brakes/regular 1.8s?
You'll need the boost and the lines don't line up properly.
hustler is offline   Reply With Quote
Old 09-24-2010, 04:47 PM   #20
Tour de Franzia
Thread Starter
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

The Lotus crew reports similar issues and adjusting the pedal works. Any thoughts on pedal adjustment? The ability to build pressure at the top of the travel tells me not too...but this is a cost-free option.

Last edited by hustler; 09-24-2010 at 05:10 PM.
hustler is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Project Gemini - Turbo Civic on the Cheap Full_Tilt_Boogie Build Threads 57 07-19-2017 05:11 PM
Back to Stock Part Out!! Turbo Parts, MS2 Enhanced 01-05, Suspension, and MOAR! StratoBlue1109 Miata parts for sale/trade 16 10-02-2015 10:39 AM
Leaky Wilwoods mx592 Suspension, Brakes, Drivetrain 1 10-01-2015 01:45 AM
3rd Time's a Charm...hopefully. zephyrusaurai Meet and Greet 2 09-28-2015 11:59 PM
Another Alternator thread ihiryu General Miata Chat 9 09-28-2015 11:22 AM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 10:40 PM.