The Stovebolt Site Forums The Shop Area General Truck Talk brake residual valves

I have read several posts on this but they do not all agree. My 51 3100 has a new dual master with no built in valves. It sits under the floor but a couple inches ABOVE the drum cylinder bleed holes. In places my brake line is slightly above the master. Do I need the residual valves or not. Thanks

Hy cassie, If you have drum brakes then residual pressure valves are needed (10 p.s.i.), all drum brake master cylinders have residual pressure valves built into them. A lot of the kits sold to convert to dual master cylinder from a single system master use master cylinders from a Corvette which had disc brakes all around, so no built in residual pressure valves. If the master cylinder being installed is from a disc/disc car then each circuit of drum brakes will require a 10 p.s.i. residual pressure valve to function as the drum brake circuit was designed to function. If the master cylinder is installed below the level of disc brake calipers then a 2 p.s.i. residual pressure valve should be installed in that circuit to prevent drainback to the master from the caliper, hope that helps

The MC from Napa is for a late 60's chevy truck or car but I can insert a paper clip past the center line. I thought that meant there is no valve? Is there another way to check? (My truck has all drums) Thanks

Hy cassie, could you give us the Napa p/n or the exact application, that way we should be able to tell you what you have. I wouldn't stick anything in the ports of a master cylinder or combination valve, you may damage the seals.

Napa part number is M1880. For 67-70 C10 and full size. I don't
see anything on the Napa site to indicate valves or not. I can order external valves from Summit or Jegs if needed but obviously I don't want to double up.
Thanks, Howard

Hy cassie, that Napa number interchanges with Raybestos p/n MC36239, that is a drum/drum master cylinder which should have residual pressure valves built in, so no additional residual valves should be required, hope that helps.

Thanks for all your help. Before your last post I finally ran down the phone number for the tech people at Cardone (the manufacturer for Napa). They said this model MC does not have residual valves built in. I will install them inline.
Howard

Hy cassie, after I read your last post, I thought I'll just say nothing, but the tech persons response is wrong! That master cylinder is for a drum/drum application and it would be built with residual pressure valves in it. I have read on many forums about incorrect answers given out on Tech lines, and this worries me especially a Tech line about something as important as vehicle braking.

Hi,

Google brought me to this topic. I've bought a new master cylinder for my 68 4 drum chevrolet. On the box it sais: Replaces M64885 Bendix 11329 | Raybestos MC36239 | Wagner F64885. But when i feel inside the port i dont feel any residual valves. How can i be sure this master cylinder has residual valves inside?
My brakingsystem has full 100% brakepower on the front and back because it has no combination valve. Just a block with a switch for the light on the dash.

The box
https://farm3.staticflickr.com/2945/15359623635_4818ed33db_c.jpg

master cylinder
https://farm3.staticflickr.com/2949/15336605866_37783079cb_c.jpg

Greetings Michael from the Netherlands

I am installing a dual chamber mc from CPP recommended for my 49 3100 with disc conversion on the front leaving drums on back. Mounting in original location. CPP advises residual valves on front (2psi) and back (10psi). Pretty inexpensive addition.