brake problem

[Bill Grubbs]

Did you Bench bleed the master cylinder? If not it will be nearly impossible to get full pedal pressure.

[denny harvey]

i did bench bleed the MC,when bleeding the brakes,the fluid does not seem to come out in a fast stream..i will try to gravity bleed them today..the push rod hits the MC with the pedal about 3 inchs from the floor.car has all new brakes,lines.line-lock ,prop valve and MC,so i must not be getting all the air out or MC needs ck...also there are no leeks that i can find..thanks for input guys..back to the pole barn..man ohio is cold and windy..lol..

[Greg Hill]

Make sure the bore diameter of the master cylinder is the right size or you won't have much of a pedal. I would call Wilwood to find out for sure but I think it needs to be around 1&1/8.

Greg

[denny harvey]

thanks again for your input guys,the master cyl is a manual 67-74 vette with a 1 inch bore,wilwood said this would work..when i start bleeding the brakes, i bleed the pass side rear first.i get a little pedal,but by the time i get to the other side its gone,its like starting over at each wheel???? when we pump up the brakes and open the bleeder ,the fluid has little pressure behind it.....bleeders are higher then the lines..have a good holiday guys,im done working on the car till after x-mas,maybe santa can help...denny

[SPS]

Denny:
GP is correct about the master cylinder size being important. We usually use the Chrysler style master cylinder available from Wilwood for these systems. Also, Wilwood also has an in-house manufactured master made for manual disc/cisc systems that is very good but more expensive.
The geometry issues brought up are also correct.
Finally, either vacuum or low pressure bleeding the system will save a lot of aggrivation. You didn't mention, but location of the master cylinder (firewall or floor mounted) will make bleeding more or less difficult.
Barring that, you could just have a defective master cylinder.
FJ

[ron mattson]

i had a very similar problem on my friends firebird with the same brake setup as you have and it was a defective master cyl it seemed to be getting air bound on the return pedal travel. you could actually hear hissing coming from the master..new master solved all the trouble ..

[Jim Blankenship]

the push rod isn't hitting till 3" from floor ?
should hit with just 1/2 " down any closer it won't let mc piston to fully return

also take the prop valve out till you have brakes blead.
i put one on johns car when went aftermarket 4 wheel disk had LOTS of prob's, it in box in trailer now
car stops good no wheel lock up
it had a soft pedel with the prop valve on it
hope this helps
jim

[gmonde]

sounds like a master cylinder problem,try this ,plug all four lines at the calipers(you can do this with plugs for #4 line ,this dead heads the master,(i asume that you have braided lines)if the master is bad you wont be able to get a pedal no matter how much you bleed at the lines,if the pedal is hard,hook up one line at a time to the calipers could be a caliper piston lip seal not holding the piston out to the pad

gmonde

[Mike Hedger]

First off the corvette master cyl. was designed for a car with 4 piston 4 wheel disk brakes so it moves enough fluid for the willwood callipers but it is not a quick take up like the Chrysler unit so it needs all of its stroke to move the amount of fluid you will need to stop the car. Second you said the pushrod is not hitting the MC piston untill it is about 3" from the floor? If this correct that is your problem, make or buy a longer pushrod. I like to give the MC about 1/4" of freeplay so you don't cover up the compensating or return ports otherwise you will have pressure on the system at all times. Hope this helps and have a merry Christmas, Mike

[Dave Goob Cook]

Gotta have full stroke.
Full bottom and full return first and foremost, with positive retention of the pushrod in the M/C please!!!!!

No need for the valving, but it won't kill ya either.....

Any factory valves have been removed, correct?

M/C is higher than the calipers?
Lines need to not run "up" at any point out of the M/C. (Line-Lock or pressure gauge plumbing?)

Bench bleed, install M/C keeping the outlets turned "up" as much as possible, while you finger in the lines, mount it, leave the lines cracked just a touch while an assistant strokes the pedal all the way down and holds it, while you snug the lines. Then gravity bleed it at all 4, shut off as fluid flows to each one, then start a "normal" bleed process.

Sometimes if the lines have been flushed or dry, you should open all bleeders, stroke the pedal full down and hold, close bleeders, let pedal up, repeat as needed, to get as much air out initially as possible.

I've had to do brakes alone for years, found some tricks. I've replaced many M/C's without the need for any bleeding, only flushing out of the old fluid....
Speaking of that, the lines were clear and dry, no kinks or dents, no excess moisture around when the system was open?
Any possibility of fluid contamination?

Remember that some braided steel lines (non hard Teflon liner) will give you a spongy pedal, and the brake pedal never feels "hard" enough until the new pads/shoes are bedded in properly.

IF you are using a Silicone fluid, there are more details to follow.
Been there, done that, nothing wrong with it at all, you just have to treat it differently.

I like Valvoline Synpower brake fluid.