34 Dodge disk brake problems

Erick · July 16, 2007, 01:26:47 PM

Setting up the brakes for a 34 Dodge. Manual brakes with Front disk brakes/drum rear. Master cylinder is from a 71 Dodge Dart, bore is 1 1/32", and is for manual brakes disk front/drum rear. Proportioning valve from a 76 Aspen that's for manual brakes disk front/drum rear. Calipers are 76-77 Camaro. Rear brakes are 76 Granada and wheel cylinder bore is 15/16". I don't have a residual valve anywhere. The M/C is mounted on the firewall.

The problem is that when first pushing down on the pedal it goes almost to the floor and really has no pressure. If I pump the pedal, pressure then builds up, pedal is then higher and have a firmer pedal. Then after it sits the pressure falls back down again. M/C is a reman, prop. valve is used, calipers are reman., and all other parts are new. Have bled the brakes several times but it makes no difference. Have checked all the fittings and all leaks have been fixed.

I removed the lines from the M/C and plugged the ports. The pedal was nice and firm. I looked at Speedway and they offer two different residual valves, a 2 psi and a 10 psi. From doing some searching the internet it sounds like the problem is I didn't use the residual valves. Would I use both the residual valves or just the 10 psi for the rear?

Just checking to see if anybody might have some other suggestions as what to look at for possible problems. Thanks for the help. Erick

Charlie Chops 1940 · July 16, 2007, 03:03:36 PM

Generally speaking if you are using a m/c set for disc/drums on disc/drums and the m/c is firewall mounted you shouldn't need any further residual valve type devices. Are you sure that the correct ports for the correct end of the car are in use? Confident that all air has been bled? Could be a bum reman m/c.

Charlie

UGLY OLDS · July 16, 2007, 05:24:25 PM

Crazy as it sounds...Verify your rear brake adjustment & shoe contact....It almost sounds like the rear brakes are out of adjustment....

Just a thought....

enjenjo · July 16, 2007, 07:46:25 PM

If you have rubber hoses to the front and rear axle, clamp the hose shut, and see if the pedal is good. If it is, then residual valves will help. 2 psi with discs, and 10 psi with drums. Also as mentioned, check the rear brake adjustment.

Erick · July 16, 2007, 08:10:40 PM

We checked the rear brake adjustment and all checked out fine. Checked over all the connections and everything is connected to where it should be from the ports on the proportioning valve. I've bled the system a couple times with a brake bleeder. Have also manually bled the brakes a few times and have tried gravity bleeding the breaks. Haven't seen any more air bubble come out. Pedal stayed the same.

We did try a few different things with hooking up one line at a time. Plugged off the front brake port and left the rear brake line hooked up. It had good a good firm pedal and didn't go to the floor.

But when switching it so the front line was hooked up and the rear was plugged, we ended up with the same problem again. The pedal wouldn't get firm and would go almost to the floor. The pedal would get firm when we pumped the brakes, but let it sit for just a couple seconds and it would lose the pressure again. This is also how it acts when both lines are hooked up to the M/C.

We installed a Fatman Stage III front clip. The calipers came with the kit and were told they are 76-77 Camaro metric calipers. Found some info on this link. http://www.mpbrakes.com/technical-support/troubleshooting-drum-07.cfm
It has some info in the last section about GM calipers and what M/C needed to be used. Explaines that without the right M/C being used with the calipers we have the pedal will always be spongy. We're kind of at a loss. Have tried many times to talk with Fatman about the brakes and various other things but we don't get much help. It's always different answers each time we call. One tech from there explained to us that the setup we went with should have no problems.

After doing all the messing around with the lines it feels like we only lose pressure in the front brakes and not the rear. We hope that we are going about this the right way? Thanks again for the help.

enjenjo · July 16, 2007, 09:35:43 PM

One more thing to try. Clamp both calipers to the rotor so the brake is applied. That means clamping the cack side of the caliper, and the pad on the outside. Pump up the brakes, and let it set. If they are ok after you do this, you will need a 2psi valve in the front.

2buck · July 17, 2007, 09:15:33 PM

I was told that for manual brakes the master cylinder bore should be 7/8 or 15/16. If a power booster is incorporated then a 1" & larger sizes can be used.
I had a situation where I could not get a firm brake pedal after hours of bleeding the system. My brake pedal had a second hole which allowed a little additional movement for the pushrod. I moved the pushrod to this hole and presto I got a good pedal with a few more bleeding opereations.
Apparently, I wasn't getting sufficient stroke to get the air all the way to the wheel cylinders.

Erick · August 04, 2007, 12:38:47 PM

Thanks for the help. We did get a 2 psi residual valve for the front and just finished getting it installed. It did help the pedal so it doesn't feel as spongy. It also doesn't go down almost to the floor like it had previously. The brakes do still feel kind of spongy. Have bled the brakes several times with no difference. We did get the 10 psi residual valve for the rear drums, so we think we'll get that put in too and see if it makes a difference. Thanks again. Erick