Soft pedal/Brake failure help.


Dave_Buky88

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Joined
Jul 20, 2014
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I have lost confidence in my car last year due to brake issues all season. For some u known reason on a few occasions I hit the brakes and there was nothing there as if the pad had moved and I had brake knock off, I decide to fit a brake prop valve to see if this sorted the issue. As the issue was very inconsistent I could not tell if this sorted it. Another issue I came across was when I blead all the brakes i had a really good pedal. When I then turned the car on, the pedal would go soft. I noticed the pedal does go harder after a few pups but then goes soft again when held down. I have now stripped my car ready for next year and noticed than someone has fitted what would seem to be a DC2 brake servo and I presume a bigger master cylinder. Could this be my issue or could there be an issue with the diaphragm inside? I really don't want anymore brake issues this year! Please advise as I have limited knowledge on these cars. Many thanks, Dave.

I have attached a few pics of my servo and master cylinder below;
 
you should be bleeding the brakes with the engine running with a servo system, the reason the pedal is going soft when you start the car is because you have vacuum assistance then.
 
i also noticed that the very first pedal pump i can hear a hissing air sound and when i release the brake pedal i hear a little squeak, is this normal? I have full Braided lines throughout the car that are fully sealed and no visible leaks from the connections. Do you think having a bigger MC and Brake servo could be part of the issue? thanks for your reply, Dave.
 
No the larger MC shouldn't make any real difference as for the hiss i have heard this in cars before its not a big deal, its the last of the vacuum pressure being used when the engine is off.

Before you go changing anything give the brakes a really good bleed with the engine running. If its still not 100% go for a drive and get the brake system hot and then bleed again.
 
cheers mate, its completely stripped at the moment so I just wanted to know if I should change anything now before it all goes back together as I imagine it will be a small pain if I need to do it after lol.
 
Only if you see and fluid leaking out of the master cylinder seal..

You'll have alot of bleeding to do after changing the master cylinder, what i usually do in that situation is just put the bleeding bottle on one of the back calipers, open the nipple and give the brake pedal a good 20 pumps with the nipple open just to get the fluid to the caliper and the worst of the air out. Do that with all 4 will get you 75% of the way there, just check the reservoir frequently you don't want it to run dry or you'll be back to square one again!

Good luck!
 
Thanks, I have no choice now anyway as the car is completely stripped so I will need to bleed the whole system from fresh. Il probably end up doing it to find out that the Master cylinder is goosed. I never thought of bleeding the car whilst the engine is on though so hopefully this might help. The method you said above is the normal bleeding procedure isn't it? I usually bleed the brake that is the furthest away from the MC working my way to the one on the same side nearest to the MC. so (NSR OSR NSF OSF). I do this until all the air is out of the system then repeat until I have a stiff pedal.
 
I don't use the traditional method of... Get someone to pump the pedal to build pressure then the other person releases the bleed screw and lets the fluid/air out... then while the pedal is held in the down position the bleed screw is closed.. then repeated

What I do and this seems to work fine for me every time (with the engine off) is...

- I use a brake bleed hose with a non-return valve fitted in line
- I start with the caliper furthest from the master cylinder
- Get a mate to work the pedal
- I release the bleed screw and tell him to keep pumping with full pedal strokes until I'm happy that that all the old fluid is through the line and that there are no air bubbles etc
- Then I tell him to hold the pedal down on the next stroke and I close the bleed screw
- Then top up the reservoir after each caliper is bled and that's it

This has always worked well for me
 
hi Spek9 thanks for your reply. this method is exactly what I do with the car. I think the issue could be to do with the bigger brake servo on the car causing a bigger vacuum and the pedal going soft when the car is on? The master cylinder is also bigger than a standard ek4 one. I have sourced a second hand standard size servo and master cylinder today so im hoping for a stiff pedal.
 
I think a bigger master cylinder should have the opposite affect and make the pedal firmer
 
I think it's more the servo that is causing the soft pedal. I might keep the bigger MC and change the servo to standard
 
I really doubt your servo is causing the issue, if it was over servo'd if you touched the brakes it would nearly throw you on the dash, the issue is air in the system, if you bleed the car as you were with the engine running it should be much better!
 
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