Technical Soft brake pedal, is it the correct master cylinder?

I recently purchased a 32 Ford roadster project. The car came with new Wilwood disc brakes up front and a Winters quick change with new 11" Ford Torino drum brakes. The Wilwood calipers have a marking "120-6818" on them. The rear brakes have new NAPA 1" wheel cylinders installed and the master cylinder appears to be a Corvette style that appears to have a 1" piston. The problem is that no matter how long we bleed the brakes we are still only getting a soft pedal that is about 1/4 off the floor. Any thoughts?

 

Did you set the shoe drag on the rear drums?

 

Yes the pedal is activating the front rotors and read drums.

 

Soft isn't normally the wrong sized master, air in lines, or poorly mounted are more apt give soft. Close to the floor I agree could be a sizing problem, but unless touching the floor, it should get hard at some point.

 

We have bled utilizing the vacuum pump and the old fashion pumping of the pedal way. We have had some minor leaks and have corrected them. If what you say is true than I guess we need to continue bleeding.

 

Over the years because of the numerous system design changes by the auto manufacturers, there is really no longer a "rule of thumb", but I always like to start from the corner that is farthest away from the master cylinder. Also, (as I'm sure you know) orient all caliper and wheel cylinders so the bleeder screws are on top.

 

I bled the hell out of mine, still not a hard pedal. after I drove it a few miles it was better. still do not know why driving it helped. are the front(disc) brakes hooked to the correct piston on the master??

 

It is possible to get a tube shaped in such a way that an air bubble in a tube won't push out with the flow and volume that a master cylinder can produce. This is where the pressure bleeders work great.

 

Yes

 

Up - over - down is an air trap

 

That master cylinder needs to be bench bled a whole bunch. Seen this happen before.

 

That is not what I asked.

You need to use the star wheel to adjust the rear shoes, until they lightly drag, with the brakes off.

 

pedal ratio, you need a faster acting pedal

 

Did you use any of those through the frame bulk head fittings? Some are made wrong and trap air. The only way to get the air out is jack up the side of the car you are bleeding.

 

Did you bench bleed the M/C or similar as all you might be doing is compressing an air lock, you can compress a gas but not a fluid? If vacuum bled and the M/C is being topped up there might be a bit more to this saga? More often than not there is a simple solution. My brakes have always worked but felt soft despite having a booster and 4WD.

 

Yes I adjusted the rear brakes until there was a slight drag.

 

Are the front pads pushed out against the rotors? If not that can account for sponginess. Try adjusting the rears a couple of clicks tighter for another round of bleeding and back them off later.

 

if its the 4 port master ( ports on both sides ) you have to crack the unused port caps and bleed the trapped air out behind them ( there is always some air behind them unless this is done ) , its a major problem not adressed in the instructions when you bench bled them . also do not vacuum bleed them as many times the vacuum bleeders will pull air from behind the cups on the rears as they are not mechanically supported like the old ones which had a metal cap in there , pressure bleed from the master back . and if you foot bleed remember to make it long slow strokes ( 3-5 seconds ) so it will not stir up the fluid/air in the lines , many people do it fast and will never get a good bleed .

 

Is peddle under floor? do you have residual valves installed? Are there through frame fittings on front brake lines ? 2 lb disc valve and 10 lb rear brakes?

 

The peddle is under floor. I do have residual valves installed, There are through frame fittings on front brake lines and I do have 2 lb disc residual valve for the front and 10 lb for the rear brakes

 

I had a similar problem and the through the frame fittings were the problem. The chamber of the fitting is larger than
your brake line and traps air. I hope I have described the problem correctly so you understand what I mean.

 

Statement of the blindingly obvious (but included just in case) the Wilwood calipers have bleed nipples on both sides of the disc - you've bled both sides of each caliper, right?

Interesting point on the double sided outlet masters - not heard that one before - must commit to memory.

I have Wilwood front calipers and an 8" rear (not sure of slave sizes) and a 13/16" master and the brakes are phenomenal, and with no excessive travel - dunno the pedal ratio but it's a tci item. All things being equal a 1" should give less travel (but also less pressure so less braking force).

Chris

 

Minor leaks corrected.
Finding one minor leak and correcting it means starting the bleeding process all over again.
Bleed Baby Bleed.

 

Thanks

 

i've had times where i thought i'd never bleed all the air out

 

This is a great post. Please post the fix when you find it.

 

Did you bench bleed the MC. I start by clamping off all the brake hoses and see if the pedal is ok. If it is then start removing I clamp at a time till it goes soft. You will find out which wheel is your problem. If it is soft with the hoses pinched off, bench bleed MC(not with the little hose kits). In stall threaded plugs into the MC and push with a punch. Keep pumping until you get 1/8" or less travel. One of these should solve or find your problem.