Please Help !! Brake System Probs

[Novette_71]

dear friends,

i have a problem with my brake system and it is killing me. i cannot fix it and i dont know what to do next.

my nova has :

- brembo 4 piston calipers front
- corvette C4 calipers rear
- brake proportioning valve in middle console
- brandnew booster
- brandnew wilwood mastercylinder
- stainless steel hoses D-03


i bench bleeded the master cylinder. i bleeded the whole system like you normally do it with a partner .... open caliper valve - push pedel - close valve - release pedal .....

problem is when you release the pedal you have lots of bubbles in the rear chamber of the master cylinder. i have no braking power on the rear wheels. if i jack up the car and go into D with engine running, the rear rotors rotate although i am on the brakes (a bit slower but they do rotate). my braking power was poor in general.

now i switched to stahlbus(.com) valves .... they allow bleeding the system without a partner so everything should be just fine. i even added these bleed valves at the master cylinder.

now at the calipers in the rear there comes pure bubblefree fluid out of the system. the master cylinder (see video 2 mentioned below) shows the same thing .... but still i have no braking power.

also bad is that the air that is released builds up an overpressure when i have the reservoir closed .... because when u open the wilwood cover, you hear how the overpressure is being released.

i tried bench bleeding, "bench bleeding" with MC installed in the car, reverse flushing the MC, old school bleeding with partner and new style bleeding with these special bleed valves ..... WTF.

anyone ever had such a problem ? can you check my youtube vids i am so frustrated. :( :mad:


http://www.youtube.com/watch?v=biiWK5kG1LU

http://www.youtube.com/watch?v=gim7We8N3j8

[Track Junky]

Have you tried to open your adjustable proportioning valve to allow more fluid to your rear calipers? Somebody please correct me if I'm wrong but I'm pretty sure you want the proportioning valve wide open when bleeding brakes.

[Novette_71]

yes, the valve was fully open.

what about this theory : when i release the pedal for whatever reason the resistence to suck in fluid from the reservoir is too high. an underpressure is build up and air is sucked in thru the rear rubber seal that is close to the brake booster.

these seals are conical so they are great to seal overpressure but maybe fail if an underpressure exists in the piston area of the MC.

the air gets into the piston chamber and because it is air and light immediately exists to the reservoir room.

but still that doesnt explain why the braking power is low, because when bleeding the MC there is no air coming out of the hose.

[Novette_71]

it is been 11 years since i started the restauration and the only thing missing is the cowl and good braking power and nice days without rain are not plentiful this year, pleeeeaaase any ideas are appreciated .....

[Track Junky]

Seems the problem is your rear brakes only, correct? If so, I would recheck the lines for any sort of material obstructions all the way through and check rear calipers also.

What about the brake rod to MC connection? Are you sure your getting full extension?

[Novette_71]

i just came in from bleeding the brakes for the 100th time.

status : each reservoir chamber has two holes, one small, one big. the piston i assume starts between these two. the big bore is for ventilation basically ?

so the bubbles come out of the big bore of the rear chamber no matter what and how you try to bleed.

when i turn on the engine and the vaccum is there i think the pedal goes down fairly far.

but i thought about the power on the rear brakes. i go to D (car jacked up) and apply the brakes i slow down the rear rotors to exactly zero but thats it. i dont have more power than to do that. so while driving the rear calipers have enough power to stop the wheels from pushing but not to really brake the car.

now my engine is fully done and delivers great torque. lets assume thats 450 ftlbs at my idle of 800 RPM. multiply that with 2 to 2.5 from the converter, 2.5 from first gear and 3.08 from diff. you have some torque at the wheel.

maybe it is just that the brakes in the rear are too small ? maybe it is not bad bleeding or air but just the size of that tiny corvette rear caliper ?

[JKnight]

i bench bleeded the master cylinder. i bleeded the whole system like you normally do it with a partner .... open caliper valve - push pedel - close valve - release pedal .....

problem is when you release the pedal you have lots of bubbles in the rear chamber of the master cylinder.

I'm not the most experienced tech in the world, and I don't pretend to know every way to accomplish a job, but your description of the two person bleeding method doesn't jive with what I've used in the past.

I always pump up the brakes with the caliper bleeder closed (three to four pumps per cycle), hold the pedal down, then have your partner open the caliper bleeder. The pedal pushes to the floor, you keep holding it until your partner re-tightens the bleeder screw. Rinse, repeat.

There is always the possibility that your master cylinder is defective or thrashed. These things tend to come defective out of the box more often than any car part I've worked with.

[Novette_71]

basically your technique is the same except you "preload" the system .... we had really good flow from the caliper screw and this method works fine esp since i have one way flow valves instead of a simple screw.

the MC is brandnew but i really think about replacing it .... which hurts (240 bucks) .... bought it long ago and left it boxed in the shelf so there is no way to send it back as defective.

i will have a test drive tom and see how it works. i just won an auction on bremo calipers for the rear ..... i think i just re-do half of my brake system to have it right.:yes:

[JKnight]

Ok, just wanted to make sure the basics are covered.

My dad had a defective wilwood master straight out of the box. That was about three years ago. Luckily he didn't have it long before installing and finding that it was dead on arrival. Frank at Prodigy replaced it for him and didn't seem too shocked that it was defective.

[Hydratech®]

This might help you nail down where the problem exists:

http://hydratechbraking.com/braketech1.html

:lateral:

[Vince@Meanstreets]

sounds like a master issue if you keep getting air from the master port...we get this alot if you depress the brake pedal all the way down on a dry or on an old master while bleeding. once you mess up the inner seal its trashed.

[Apogee]

Sounds like air...probably not what you want to hear. What did you do to bench bleed your master cylinder and how did you confirm that it was fully bleed? I normally plug both outlet ports and then stroke the piston...if it moves further than 1/8 to 3/16 inch before hydraulically locking and feels spongy, then you still have air in your MC. If you can get a firm pedal and it doesn't sink under steady pressure, then the MC is okay 99% of the time.

You didn't specify bore size, but that shouldn't keep you from being able to bleed the system. The rear C4 calipers have 45mm pistons, same as a C5/C6 setup, so while the caliper bodies may be small, they actually should work quite well assuming a Brembo 4-piston caliper with a piston area somewhere around 4 square inches.

Tobin
KORE3