Hot Rods No Brakes

58 GMC 1/2t truck; front disc drum rear, Wilwood residual valves,mc mounted under the cab
Can't get a firm pedal with the master cylinder.Bench bled& installed several times. I want to try a different mc.How to tell what I have OR recommend a master cylinder.
Thanks

 

When you say bench bled, which doesn't necessarily have to be performed on the bench but that's another matter, did you have the master orientated such that no air could be trapped in the cylinder? Typically this means having the input to the cylinder slightly elevated ( air can escape into the resevoir). This can possibly be achieved on the vehicle by raising or lowering either end to suit. I've had to remove rear wheels and set the rear down almost on the brake drums as well as raising the front slightly. Seems like a lot of effort but was much easier than removing the master. Taught me a lesson to keep a stricter eye on the fluid level when bleeding!!

Chris

 

Ran into the same thing recently. Pulled the master out to re-bench bleed. During this I noticed one of the circuits was not flowing like the other. Replicated the bench bleed on another m/c and both circuits flowed the same. Put that m/c back in the 39 and got pedal again. As far as I can tell the original m/c was byp***ing one circuit. Damn thing was only a year old...
Try watching the flow during bench bleed and see if the m/c is junk.

 

I just finished up my disc/drum brakes on my 41 PU. used this MC after of course knowing the Pedal radio, caliper area calculations. MC is mounted on firewall. Brakes are as good as on my new F150.

 

I had the same issue on my A roadster, turned out that one of the Wilwood residual pressure valves was bad. And I think some others have had problems with those valves...

 

Thanks I ordered one of those MC.

 

Having spent a few years as a frontend and brake mechanic back years ago I'm going to say that half the problems with brakes not bleeding all the air out are due to errors by those who worked on the brakes or who are actually bleeding the brakes.

1. rear drum brakes have to be adjusted correctly.
2. and just as important, all connections on the brake lines have to seal and even though you may not see a dribble of fluid some suspect flares can leak air back into the system.

As far actually bleeding the brakes I have seen more lame ***ed methods that won't work suggested on here and on FB than I can count. Some no doubt coming from someone who read it or who's buddy or uncle said that was how to do it but never tried it themselves.

A pressure bleeder works best if you are working alone. They aren't spendy to make or you can buy some similar to what you make with a small weed spray setup complete with adapters pretty inexpensive now but the one with the plate and hold downs for dual master cylinders seems to cost a bit more. Like the kit in the image here.

The worst problems bleeding brakes I have had is ******** helpers who cannot follow directons. One who pumps the pedal too fast acting like they are in a panic stop or the ones who let off the pedal to pump it again before you tell them to. They have to pump the pedal slowly and they have to hold it until you have the bleeder tight again.

 

First time with this combo or did it work before?. If it worked before I would say maybe a bum master. If it's a new combo then you might need to bleed the whole system, getting trapped air out in the new lines can sometimes be fun. I've used a cheap vacuum bleeder from Harbor Freight when I've replaced hard lines on multiple vehicles. If it's a new system (disc and master) make sure the master is sized right for your application. I've had (and heard stories) of Wilwood res valves leaking, I always use SSBC res valves with no problems. Also check the master to for res valves installed inside, you might not need them as the master is under the floor.