The Stovebolt Site Forums The Shop Area Driveline Dual master cylinder conversion '58 1/2 ton short stepside

I'm getting to the point where I need to get the brake lines run. I have searched the older posts and the tech tips, but still have questions I hope someone can help me with. First, I don't have any lines, fittings, flexible hose, or anything off the original brakes to work with. I ordered the dual master cylinder months ago from The Truck shop and have it dry fitted in the original location using the conversion bracket.

The first thing I need to deal with is the size of the lines themselves: the front port in the MC is larger than the rear. I'm guessing that means two different line sizes. A piece of fuel line which is 1/4" with a 1/2" fitting fits the smaller rear MC port. Is the front port then 3/8 line with a 5/8 fitting? I put new wheel cylinders on all around and those ports are smaller yet.

So, can some one give me some info about the line and fitting sizes, and also whether the larger line should run to the front or back? Thanks for your help.

Well, surely there is a brake expert who can help?

This response is just general information.

The lines to rear cylinder is/are usually smaller diameter than the lines to from front cylinders.

A good "gauge" for line diameters would be the size of fittings/lines that would fit the wheel cylinders. Did you use original size wheel cylinders?

Maybe someone has a diagram of the routing of original lines?

Are you going with original brake system; ie drum/drum? Do you have proportioning valve?

Maybe someone will know if this diagram is correct for 1958?

Also, maybe someone will comment on routing the non-original dual master cylinder?

Hy TimBryant, this is a really BIG project to explain! First we need some more information from you, what line size are the ports on your wheel cylinders. There are adapters available for the master cylinder ports that will bring the ports back to a standard tube size, without those you would have to find compatible tube nuts at a wrecking yard. To give you adapter part numbers we will have to know the diameter and thread pitch of your master cylinder ports. No matter what, your brake lines will not be larger than 1/4" in diameter, either 3/16" or 1/4". You will probably need an original tee for the rear axle. My catalog shows the same part number for all three flexible brake lines in a 1958 Chev. half ton, Raybestos p/n BH13841. Those brake hoses have 3/8" X 24 t.p.i. brake line connection ends on them, that is the size for 3/16" brake line, hope this helps some.

Thanks for the replies. I'm using the stock drum/drum system with the original size wheel cylinders. I bought some fittings to try to figure out the port sizes, but that was not conclusive, maybe due to thread pitch differences. Any way the smaller MC port was a fit using a 1/4 fuel line that had a 1/2 fitting by my measurement.

If I understand it correctly you are going directly from the master to the wheel cylinders? So I guess you would have no warning light when one system fails.

Not to hijack this, but trucker nix, this is what I was planning on doing too. Dual MC to 10# residual valves, to wheel cylinders.
How would one implement a warning light system?

Here is a write-up on converting my '56 to dual cylinder. It includes tubing sizes and lengths. It should be close enough to the '58 to give you some idea.

That is a nice writeup. I haven't read it all but I assumed that the suppliers offered a sensing valve setup that would tell you when one system has failed, just like they have been providing for many years in our cars. Is this not the case?

Yes, mine was installed in the proportioning valve block. I did not hook it up on mine but I'm assuming it is a switch to ground to close a relay for the light.

Cletis,
thanks, now I understand.

Thanks, Cletis. That helps.