Brake questions

Hi all, I picked up a disc brake set up with spindles calipers brackets and rotors off a 71 satelite wagon. These are the pin type caliper with 11in rotors. Question is will this bolt up to my 68 R/R with 11 in drums without issues?? Thanks.

yes it should be fine.

Thanks for the quick reply Andrew. I will tear it down and mock it up then get new calipers( rebuilt) I am sure and rotors. Cant wait to get rid of the drums. I will also add an adjustable prop vale and residual pressure valve F&R.

Agree they should fit and you will like them a lot better than the front drums.

A word on the residual valves. A residual valve should not be used with discs. It will cause them to drag and heat up.

The valve is optional with drums. New drum wheel cylinders do not need the residual pressure... though it may help keep "slack" out of the system. Often, not always, drum master cylinders will incorporate the valve. If you run a new universal "disc or drum" master it will not have the valve. If you run a replacement master for a front disc/rear drum car it may already have the valve.

A prop valve on the rear is a good idea.

Thanks for the tip on the RPV in the front. I did a conversion on my 67 malibu and just added the prop valve and a RPV in the rear and it works well. If you look at the Speedway catalogue it says to use one in the front ckt but I am not convinced. IIRC its 10 psi rear and 5 psi front. They are easy to install so if needed I can put one in at a later date. Thanks again...

residual valves are supposed to be used only if the master cylinder is lower than the caliper or wheel cylinder. think of a hot rod with the master cylinder below the floor boards. this is to prevent drainback into the master cylinder. that is why speedway says to use the 2# for the front and the 10# for the rear. some have said they have used these in systems with the master cylinder on the fire wall, but i believe there may have been other issues with their systems and these valves have just been a band-aid fix.

You Sir are under a gross misunderstanding of the use and reasons to use residual valeves, they are intended to keep a certian residual pressure on the wheel cylinders so the springs don't force the shoes in all the way and make the pistons in the cylinders have to travel a lot more before applying pressure on the brake shoes to the drums
You may be correct on the original designs back in the 1920 and 1930 when all the master cylindes where usually under the floor boards on those early cars though, the drain back is a concern

as i understand the use of these valves, you must take the system used into consideration. i stand by my original response when the master is mounted below the height of the caliper and wheel cylinder to prevent drain back. however, there are certainly instances when these valves must be used. if you remember many, many posts here, when converting to disc brakes on the rear, the typical response has been to "remove the RPV from the front port in your firewall mounted master cylinder". the way to check this is to use a small drill bit to see if there is a "springy" valve behind the seat where the rear lines attach. to remove this valve, you screw in a small sheet metal screw and use either a pry bar or a slide hammer to remove the seat. then you remove the spring and [usually] rubber cup. you then re-install the seat. no need to have the RPV on the calipers because the o-rings limit push back of the piston[s]. how many times have we heard about problems encountered with drag on disc brakes because the pressure doesn't fully release for what ever reason ? no need to compound this problem with a RPV in the line. now drum brakes [may] need a 10# valve to keep a little pressure behind the cups to prevent air ingestion when the brakes are released. nothing more, nothing less. in a typical drum brake cylinder, the seal is known as a "chevron" seal, and only seals against the bore when there is pressure behind it. rapid release of the brake pedal creates a vacuum in the system, which causes the seal to pull away from the cylinder wall, allowing air to enter the cylinder in attempt to relieve the vacuum condition. the 10#[or so] of residual pressure the valve maintains at all times, the valve being either in the master cylinder seat area or an add on valve in the rear line, prevents this from happening. some, if not all, newer replacement wheel cylinders have what is called a "cup expander" behind the seal. it's purpose is to keep the seal against the bore, thus negating the need for a RPV. the total system needs to be looked at to determine if you need these valves or not. if your master is below the floor, such as a hot rod or a race car would use, you need these valves to prevent drain back as i previously stated, and i stand behind that statement. that is also stated in the speedway motors catalog. use a 2# valve for discs [front and/or rear] and a 10# valve for drums. in a firewall mounted master cylinder system, no valves should be required for discs, but if using drums with no "cup expanders" in the wheel cylinders, a RPV must be used. if you are having problems with your brake system, a thorough inspection must be preformed for your safety as well as the safety of others.

one other thing to remember about drum brakes. it usually takes about 50-75# of pressure to overcome the return springs, so the brake shoes always retract to their fullest position unless there are other problems present, such as "wear slots" in the backing plates, or broken or incorrectly installed springs.
cab, sorry if i gave the impression to others that there was no use for RPVs. that was not my intent. total system analysis should be preformed to decide if you need to install these aftermarket valves or not.