Brake drag after residual valve install?

[7T2]

On my 57 GMC, I installed a new modern master cylinder kit to replace the old, single reservoir setup. The truck has discs in front and drums in rear. The kit came with a combination valve for a disc/drum setup, so it should have the 10lb residual valve going to the rear.

After it was installed I discovered I also needed a 2lb residual valve for the front discs, because the MC assembly is mounted below the cab/calipers. Today I got around to installing it.

What I notice now is that I have a very hard time turning the rotors by hand now. That doesn't seem right, but is that normal for a system with a residual valve installed? I don't think it did it before, but to be honest I can't remember.

Should there be any kind of drag in a system like this? I know it's hard to describe the resistance over the internet, but, with the engine off, it is very hard to turn just the rotors by hand. I can do it, but it's tough. If I mount a wheel and tire it is easier to turn, but it still doesn't turn freely (i.e. I can't just grab the wheel and give it a spin, but I can turn it to where I want it to be. If I stop, it stops.)

Is this normal, or do I need to do some more troubleshooting?

[lolife99]

Is there any adjustment on the brake pedal arm?
Could you possibly be "pre-loading" the master cylinder?

Maybe some of the board Vendors can chime in.

[7T2]

Update: I looked at the truck on the way out the door last night, and while the master cylinder is mounted below the cab and not up on the firewall, it does appear to be slightly higher than the calipers. I'm wondering if I really need the residual valve or not?

[lolife99]

I would take it out,... a see how the brakes are without it.

[Richard H.]

Originally Posted by 7T2

Update: I looked at the truck on the way out the door last night, and while the master cylinder is mounted below the cab and not up on the firewall, it does appear to be slightly higher than the calipers. I'm wondering if I really need the residual valve or not?

I'm gonna say yes you do. The residual and proportion valve need to be below the MC. On my 71 , mine is from ECI under the dash ,remote filled. They sent me a residual valve for the rear drums and said to install it as close and below the MC as possible. Also a P. V. to mount between the front disc on the cross member.
My 55 is messed up like yours only mine does it after 30 minutes of driving. I need to get on that...

[7T2]

Well, I ran into a guy from Inline Tube at a swap meet today and told him what I was dealing with, and he said I didn't need it, since the MC was 8 inches above the calipers, even accounting for suspension travel. So when I got home I took it out, and it seems to have cleared up the binding problem, but I'm back to a squishy brake pedal. I'm hoping that's just because I haven't bled the system from swapping out the valve yet.

I have another question though...with no pressure on the brake pedal, should the disc brake pads be lightly touching the rotors, or should they have space in between them? In researching this residual valve issue I came across information suggesting there are 2 (or more) rotor thicknesses? I have no idea what the truck is supposed to take, since the previous owner put a modern subframe in the front, so I have been replacing parts with new parts that seem to match up, but now it has me wondering? Last year I had some issues with one of the front calipers dragging/binding up, usually in very hot ambient temperature conditions. I thought maybe I had a bad caliper so I replaced it, but I really won't know if that is the issue until I get the truck out later this year. I'm just trying to get some suggestions as to what to look for while I have it up on the lift.

Should there be any drag at all on the front discs (like there is on the rear drums) with no pressure on the brake pedal? Right now the discs and drums all seem to have the same amount of drag on them when you try to spin them by hand.

[7T2]

OK, took a little break (no pun intended) from working on the truck, but I'm getting back into it.

I snapped a few pics today of the pads and rotor. Do these look normal? With no pressure on the brake pedal, the pads touch the rotors on both sides. I can turn the rotor freely, but you can hear the pad is in contact with it. Should there be more space than that? Both the pads and the rotors are nearly new.

The reason I ask is because I have read on here that there are different thicknesses of rotors. I have no idea what the previous owner used, so I ordered parts that seemed to match up until I got something that seemed to work.

[lolife99]

Those pics look fine to me.
The pads should be in contact with the rotor.

What front end is under your truck?
Mustang II?
Camaro subframe?
Stock with aftermarket disc brake kit?

[7T2]

I should have asked more questions when I bought it, but from what I have been able to determine it has the front clip from a 73-87 GM 1/2 ton truck. It used to be a one ton, but the previous owner converted it to a more modern drive train, probably for the disc brakes and 5 lug wheels.

[lolife99]

There are two different rotor thickness available in the 73-87 trucks.
But the parts are not interchangeable.
Measure your rotor width.
Should be either 1" wide (light duty) or 1.25" wide (heavy duty) rotors.

I would make sure the brakes have all of the air bled out of them,... and drive it.