Bad Master Cylinder???

[frankr]

Help, what is wrong here??
I installed a new frame rail mounted brake pedal kit, comes with with a new Corvette master cylinder and booster.
Can't get a good brake pedal, it goes to the floor but will build up a little bit of pedal pressure if I pump it very very fast!
The car has 4 wheel discs, installed all new lines, flex lines, rotors, pads and calipers. Also installed two Wilwood 2lbs residual valves because the master sits lower than the calipers.
Double checked that the inlet/outet are correctly installed on the residual valves.
The calipers are installed with the bleeder facing upwards.
Bled the system until an entire galon of brake oil had gone empty, no air bubbles coming out and no leaks anywhere but still no pedal!
Is the new master cylinder bad or is something not installed correctly??
Help!!!!
Frankr
1934 Dodge 392 Hemi

 

[RPM]

If the pads and rotors are new to each other, the pads have not seated to the rotors. Drive the car in a safe place and ride the brakes. The pads have little high and low spots on them and this will knock off the high spots.

 

[pacrat]

remove the cap from the mastercylinder have someone slowly apply preasure to the pedal observe the reservoir, if you see bubbles in the chambers the master cylinder is bypassing and is bad.

 

[burnin#2]

it may be nesissary to use a pressure or vacume bleeder if you havnt already, since the master is the lowest point.
and be sure you used the correct steel brake tubing and flex hoses, if you didnt, the tube, if its too thin or if the flex hoses dont have enough braided layers may cause the spongy pedal.[S[S

 

[sgtpontiac]

Pacrat is correct.....

remove the cap from the mastercylinder have someone slowly apply preasure to the pedal observe the reservoir, if you see bubbles in the chambers the master cylinder is bypassing and is bad.

no pedal..... air in lines or bad master..
spongy pedal.....air in lines.... really the easiest way to think about it....

pads not seated might cause firm pedal and little or no braking.... braided lines don't nomally cause No pedal and are usually good for a harder pedal as they don't flex or expand.... if it's no pedal... air or M/cylinder.....JMHO

 

[TiredIronGRB]

Make sure the piston in the MC completely releases and you have a little slack between the plunger and piston.

 

[42chevy]

Did you bench bleed the master first?

 

[frankr]

Good idea, I'll check for the pedal slack.
How do you bench test as master?
Putting plugs in the outlets and bleeding them?[S

Frankr
!934 Dodge 392 Hemi

 

[42chevy]

When I had first put my '42 Chevy I replaced the master and it came with 2 plastic screw in plugs with a nipple for hoses. They ran into thier respective reservoirs. They need to to be clipped in there below the level of fluid, then you actuate the master until no more bubbles come out. I think this is your problem if you haven't done it.

 

[Sniper]

You didn't happen to use 'through the frame rail brake fittings'? The style with the small passageway are generally ok, it's the ones that look like a machined bolt with a large passageway that can cause this problem. Because of the trapped air bubble, it makes a spongy pedal. You can't get enough fluid flow, bleeding a system manually to carry the air bubble out of the system. It can be fixed easy enough, install a steel sleeve inside the 'body' of the fitting, the hole for the brake fluid only needs to be as big as the hole in the brakeline. All your doing, is taking up the air bubble space with a steel sleeve, that can't be compressed like trapped air can. You didn't mention them, so it's just a shot in the dark. I included a couple of pictures of the style so you can see what I'm referring to.

 

[rainman]

I didn't read this entire thread so if this was mentioned I appoligize!!

Have you installed residual valves? If you are running the M/C below or close to the height of the wheel cylinders, you will need to use them!!

 

[Paul_J]

I have worked on several cars where the master cylinder was mounted very low. Air in the system was always the #1 culprit. I also agree with what was mentioned about the push rod not letting the piston return all the way back. We had a truck that a previous owner started and the rod was too long. When we got it up and running it prevented the fluid from fully returning and the brakes locked up as soon as the fluid in the calipers got hot. My old boss ground of the rod by scraping it on bare concrete on the side of the road to get it back to the shop.

 

[Crossfire]

brake problems

As 42 Chevy said bench bleed the master before installing or you are just wasting your time and money in fluid.Even brand new master cylinders can be bad. If you just install the master without bleeding it can be partially working but you can fight it forever and still not get any pedal and that seems to be what you have going on.Most dealers kits come with a direction sheet with them.

 

[frankr]

I checked the pedal/rod and it has about a quarter inch of slack, I also made sure that the little rod coming out of the booster that pushes the master does have a bit of slack also. I tried the brakes again and forgot to sit the cover back on the master and noticed that when I press the pedal, the back reservoir shoots a little bit of fluid upwards but the front reservoir shoots fluid up about 2 inches, clear out of the master! Is this normal?[S

Frankr
1934 Dodge 392 Hemi

 

[rainman]

If you M/C is mounted at, or below the same level as your wheel cylinders, you will need to use residual valves!! Otherwise you will continually be fighting air in the system!!!

But in answer to you're question, yes, thats normal. If I am understanding your question.

 

[RPM]

I checked the pedal/rod and it has about a quarter inch of slack, I also made sure that the little rod coming out of the booster that pushes the master does have a bit of slack also. I tried the brakes again and forgot to sit the cover back on the master and noticed that when I press the pedal, the back reservoir shoots a little bit of fluid upwards but the front reservoir shoots fluid up about 2 inches, clear out of the master! Is this normal?[S

Frankr
1934 Dodge 392 Hemi

That could be the problem right there. 1/4" of slack and then you have a pedal ratio of 7:1 would be 1 3/4" pedal travel before the rod even touches the masters piston. Then you have another rod that has some slack in it? That ads even more travel to the pedal. I would like to see about .005"-010" slack in these rods.

 

[Jimmy Wallbanger]

I saw some one mention the through frame adapters. I was thinking of these after the first few posts. if you have them find a tubing that will barely fit in them and have a fairly small I.D. we did my buddys with a piece of rubber hose steel would be best though if anyone has this problem

 

[Roadent]

Had the exact same issue and struggled with it over and over. M/c mounted lower than the brake cylinders, brand new system, thru frame fittings on the front. Here's what finally worked for me.

(1) pre-bleed the m/c to make sure all the air is out
(2) install residual valves spec'd for discs
(3) install "Speed Bleeders" instead of the stock bleeders
(4) Use a good quality pressure bleeder (not the pistol grip/pump type as they do not have the volume necessary). The one I used was from "Motive Products" power bleeder which worked extremely well.

Start at the farthest brake from the m/c (usually the right rear).

VERY VERY IMPORTANT....Remove each caliper from it's mount and make sure the bleeder is point straight up when bleeding. Apply pressure to the system via the power bleeder. Sometimes it is good to lightly tap on the cylinder to break any bubbles loose when bleeding.

Make sure you do not run all the fluid out of the M/c.

Work your way around the car. Do this procedure multiple times.