Technical Drum/disc combo = soft pedal?

Since converting to a disc/ drum setup and after carefully bleeding the brakes the pedal seems softer than what I had with just drums; is this to be expected with disc/drum combination.? I have a proportioning valve going to the rear drums and a check valve going to the front discs. I have checked for leaks and can't find any. The car stops okay but am wondering if I'm getting everything I should from this setup. The car is a '36 tudor, probably around 3000 lbs.

 

Set you rear shoe drag.

If you still have problems after that, post a full write-up of all the components that are in the system.

 

need a 2# RPV to the fronts & a 10# RPV to the rears.

 

Like Gimpy says, make sure the rear shoes are well adjusted, makes a big difference at the pedal. Adjust and give the system a quick bleed, just a shot at each wheel to ward off evil spirits.

I like to run all my brake plumbing through a proportioning valve, which is a handy spot to add residuals if needed.

 

Had the same problem , needed to bleed the master cyl. better.

 

Make sure therwe is clearence between the M/C pushrod & the M/C , especially if you're bleeding them by pumping the pedal. If the M/C cannot return completely , you'll never get all the air out ..
dave

 

Is your master cylinder under the floor or up on the firewall? If its under the floor, as mentioned above, you need a 10 pound residual valve on the rears in addition to the proportioning valve.

 

Assuming you have bled and adjusted the brakes . I take it your master cylinder is under the floor?, since you mentioned a check valve did you mean residual valve?. If that is the case you should have residual valves front and rear 10psi rear and 2 psi front. does the prop valve contain a residual valve ?

 

I****ume you have an under floor master. I've learned from experience most duel masters sold for underfloor use have a 1" bore and on a 35/40 Ford the pedal travel isn't enough, they stop but the pedal goes uncomfortably close to the floor and all the bleeding and adjusting doesn't help. I always use a bigger bore master. Could be the disc take more fluid to operate and that's what your experiencing compared to the drum setup.
I've had several customers complain about soft brakes and I've swapped their master for a 1 1/8" bore, they can't believe how much better they stop. The additional pedal pressure isn't much and if you have a booster it doesn't matter.
Also, curious what you mean by a check valve to the disc? Like 41fordor said you need a 2lb residual valve to the disc and a 10lb to the rear. I normally try the brakes without a proportioning valve first, I've found most the time it's really not needed. If after a test drive I'll add an adjustable valve if the balance isn't exceptable. I never use one of those factory set valves unless it's going on the car it was made for, I figure one of them was set for a specific car and the balance might not be the same for another.

 

If you're using a hydraulic brake light switch, it needs to be installed below horizontal or it will hold air and give you a spongy pedal.

 

All drums use a residual valve under the floor masters for disk need a 2 lb residual.

 

Thanks for replying guys, will digest all of this and retry and let you know the results. Master cylinder is under the floor & do have a 2 lb. residual valve going to the front; not a "check valve" as described in original post, 10 lb. proportioning valve going to the rear.

 

I'm going to be in Vegas in a couple weeks for the B-J auction, if you don't sort it out by then and would like an extra set of eyes on it I'd be willing to hook up and take a look. I've set up many brake systems on 35/40 Fords.

 

Soft pedal is often a bleeding issue.

Long travel is usually an adjustment or m/c bore diameter issue.

jack vines

 

A residual valve is a check valve. I think you mean 10# residual to the rears, correct?

 

I mean I have an adjustable proportioning valve (part# AU-0065) going to rear brakes and 2 lb. residual valve (part# AU-0057) to front as supplied by Chassis Engineering .

 

All drum master cylinders have a 10 pound valve built into them?

 

Just looked in my CE catalog and see I may have a 10 lb. residual for the front instead of 2 lb! Just looked under the car & see that I have a 2 lb. residual going to the front; looked in my "extras bin" and see the 10 lb. valve in there; must have caught my mistake and forgot I did so. Also, pedal is at 4 1/2" from the floor with brake pedal depressed. Master cylinder out of a '78 Cougar with a 7/8" bore. Am using DOT 3 fluid.

 

Not necessarily.

All drum brake systems must have a 10lb. residual valve in the circuit feeding the drums.

This does not guarantee that it is in the master cylinder.

 

what calipers are you using?, 7/8" master may be too small if your using a large piston or multi-piston calipers. its easy enough to check if your system is holding residual pressure , by cracking the bleeder after pumping the brakes and opening a bleeder with your foot off the pedal, should get a little squirt of fluid .

 

Using single piston midsize GMC calipers & Mopar rotors as offered by CE.

 

think the midsize gm calipers are 2.38 making your master cylinder pretty close to the right size by the 12 to 14% rule, athough the rules don't always apply with custom builds . if your pedal ratio is better than 5 to 1 you could move up to a 15/16" or a 1" master cylinder and get a much firmer pedal.