VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1933-1936 1936 PU tandem MC project done

If any of you guys are interested my tandem MC project is successfully completed and described in a pdf on the 1936 Chevy Owners forum:

file:///C:/Users/ray/Downloads/Rays%20Tandem%20Mater%20Cyl%20project.pdf

Ray W

Oops, I put in the wrong link. Sorry. This one should work:

I'm computer illiterate and put in the wrong link. I think this is correct:

https://groups.yahoo.com/neo/groups/1936ChevyOwners/files/_Member%27s%20Informational%20Posts/Rays%20Tandem%20Mater%20Cyl%20project.pdf

Sorry for the mistake.

Ray W

I tried the 2nd link and it came up with "error loading content" but like you I am almost computer illiterate.
Tony

"I tried the 2nd link and it came up with "error loading content" but like you I am almost computer illiterate."

Hi Tony.

If I knew how I would send you the information directly. I wouldn't be surprised if the same approach would work on your '38.

Because I couldn't find any information on doing this conversion I had to figure out each little detail as I went along and if I had it to do over the job would be much easier. I did find a 1" bore tandem MC that even had a port in it that accommodated the OEM '36 brake light switch that the OEM wire harness reached no sweat. Pretty cool, huh?

Ray W

This should get you to a link to Ray's .pdf file. Once there, by clicking on the .pdf link you can download the 2.6MB file and view with Adobe Reader.

Dual Master Cylinder Project

Ray
The link that "Leagal" posted took me to the front page of "1936 users" and stated "closed group" and wouldnt let me go any further.

I have an idea on what would need to be done to convert mine but not being to that stage yet havent given any in depth thought but I am open to suggestions. If you have the pics handy it maybe easier to email them to me direct truck38chev@yahoo.com.au.

Tony

Good morning Tony. At least it's morning on the west coast of North America. I emailed you the '36 PU tandem MC story with photos. I think you will find it an interesting read and it may apply directly to your '38 PU. By the way, I have a NOS GM ring gear and pinion that will fit your '38 if you can use it.

It's ironic but the administrators of this site require that one be a paying VCCA member to contribute information like this. In other words one has to pay for the privilege of giving away knowledge. Oh well.

That's why I quit paying dues after a 40 year membership and moved on to the 1936 Chevy Owners forum.

Ray W

Ray
I read and replied to your email, interesting procedure. As I explained in the email there are a few differences in vehicle design that make your cylinder choice difficult but the basic idea is what I had in mind.

As for the ring gear and pinion I was looking for complete internals until 4 years ago and acquired a almost complete donor truck. I have since replaced the bearings and fitted under my truck so the urgency has now gone. The shipping to Aus alone would cost more than the need as spare parts would be worth now but thank you for the offer.
Tony

"As I explained in the email there are a few differences in vehicle design that make your cylinder choice difficult but the basic idea is what I had in mind."

Good morning Tony.

Just like my '36 PU 4.11 to 3.55 rear gear conversion this tandem MC conversion was an interesting learning experience. One of the questions that came up was would residual pressure valves be required? Researching the subject found loud arguments on both sides of that subject.

Authoritative information explained that a RPV is required where the wheel cylinders and/or calipers are above the level of the MC to prevent drain-back of fluid and introduction of air by the created vacuum in the calipers/wheel cylinders. On a '36 PU the wheel cylinders are below the MC. I didn't know whom to believe. So I rigged up a pressure gauge on the pressure side of the MC and found that the OEM MC has a 15 pound RPV built in. I found that a very interesting discovery and the answer to the question. The tandem MC conversion incorporates a Wilwood 10 pound RPV in both lines, since nobody seems to make a 15 pound RPV. It works properly that way.

I really appreciate your observation that each piston in the tandem MC only has to move 1/2 as much fluid as the OEM single MC. It's very convenient that the OEM brake light switch could be could be screwed directly into the tandem MC and could be connected without any change to the wire harness.

Ray W

The rear ratio has been discussed here on chatter and by what I remember it went along the same lines you found on the other forum.

The RPV is needed for drum brakes but not disc so if you use a tandem disc MC you would need to add RPV for use on your 36. Drum brakes use the residual pressure to keep the wheel cylinder seals in firm contact with the cylinder wall but disc brakes the seal is what retracts the piston on brake release and the RPV will hold the piston in the lightly applied position.

With the single MC 1 piston moves enough fluid for 4 WC where the tandem each piston moves for 2 WC. While the same amount of fluid is moved each piston is only doing half the work.

With the switch where you have it I think you will find it wont work if 1 section of the MC runs dry. I think it was Ford down here had similar setup, 2 outlets for front brakes and only 1 for the rear so I would not be surprised if your MC is the same setup.

Tony