The Stovebolt Site Forums The Shop Area Driveline 1946 1/2 Ton Master Cyl to Brake Line Connection

Ready to start connecting up the various components of the brake system on my project and I think I am missing a part.

I had assumed that the brake line connected directly to the outlet of the master cylinder but the thread size on the brake line fitting is too small. (The brake lines were all replaced by a previous owner 30 years ago and not ever connected to a master cylinder.)

Looking at a diagram in the 1929-1950 MPC that I have, it shows an "outlet nut" that might be what I am missing. I am using a master cylinder with the casting #5450256 which shows up in the MPC in Group 4.650 as being for '38-'46 ALL 1/2 TON COMM.

In Group 4.652, it shows an outlet nut of part number 5450607 is being for '38-'50 ALL 1/2 TON COMM (and a gasket for the same).

I have attached a photo of the illustration in the MPC that has me thinking that it shows the part I am missing. I have also attached a few photos of what I am dealing with on my truck.

Please let me know if I am on the correct path or not. Also, if I am heading the correct direction, where might I find the part(s)? I have done a quick search using the part number from the MPC and came up empty handed.

Nick - You have the Group 4.652 outlet nut and copper seal washer already on your master cylinder (see marked up pic of yours from your post).

See the next screenshot snagged from a 1929-57 MPC that has a better picture with the parts you're missing labeled. Your '50 MPC diagram has them present, but not identified with their parts group info, making it difficult to find them in the listings.

You should be able to locate the part numbers for those Group#'s, but should know that the bolt and connector aren't easily found. Usually those pieces will need to be scrounged from a donor truck or master cylinder where they still might be installed.

PS - It looks like your previous owner didn't run the brake line going to the master cylinder properly. Maybe Utah John can chime in and offer pictures of his master cylinder and brake line connections.

EDIT NOTE: See my next reply below for corrected info related to the mis-marked master cylinder diagram.

Thanks Dan!

I see that I was confused by what I thought I was looking at.

Now, I may be in need of more information. Under Group 4.661 in my 1929-1950 MPC and in a '29-'54 MPC I found online, I don't see any listing for the Group 4.661 bolt that covers the 1946 1/2 Ton pickup.

I wonder if one could put together other brake system parts that would allow for the connection of the brake line and the brake light switch.

Nick - Don't shoot me brother, but I'm going to have to back pedal on my above post.

First - The diagram I posted does show a later plumbing connection setup from the the brake line to the master cylinder with what is known as a "banjo bolt" (4.661) and brass connector block (4.686). I dug out a combined 1942-47 Car/1942-46 Chevy Truck Shop manual and that setup is not evident on the master cylinder pictured.

Second - My indicating that your truck would use a "pressure style" brake light switch (added notes in the screenshot drawing) was incorrect as the shop manual indicates that a firewall mounted pedal operated switch was used in your truck. Eliminating the pressure operated switch removes the need for the banjo bolt and brass connector block, which were both used in later trucks (but not associated with a pressure brake light switch in trucks).

The line port on your master cylinder "outlet nut" should be 7/16" - 24 int. thread. You haven't indicated what line nut is currently on the line pointing towards the master cylinder, but did say it's "too small". Perhaps the PO used a 3/8" - 24 int. thread nut when line fabricating?

You can get a brass adapter fitting to connect the 3/8" nut with the 7/16" port like this from inlinetube, although I don't think the length of the adapter may be enough to fill the distance from the master cylinder to the line nut.

Alternatively, I think you should be able to easily remake the main master cylinder line with the correct length and fittings to get things connected and brakes one step closer to operating.

Sorry again for pointing you in the wrong direction and hope this gets you back on track.

PS - I've added an edit note to my post above to line out the bad poop indicated.

Dan,

No stress!

Examining the images and thinking about this has me thinking that it shouldn't be too difficult to go from the fitting that is currently in the master cylinder to a part (or two) that will let me connect both a "pressure style" brake light switch and the brake line.

There are a couple folks at the local NAPA store who seem interested and creative enough to give this situation some thought. (If I went into the other local FLAPS, the folks there would just blink and look at me as though I was from Mars.)

Perhaps I should ask this question in it own thread, but is there a recommended method of making sure a metal brake line is debris free before hooking everything up?

The lines on my project are new...but have been sitting in some barn for thirty-odd years. I have already blown some compressed air through them. The line that would connect to the output of the master cylinder and head to the first brass connector block has been open to the air as the master cylinder was not present.

After blowing compressed air through, should I just go ahead and complete all the connections to the point closest to the wheel cylinders; then, one at a time, starting with the one closest to the master cylinder and plugging the others, pump some brake fluid into a clear glass container until I am convinced that most anything that might be in the line has been flushed out? Then, connect that line to its wheel cylinder and bleed it. Then move on to the line to the next closest wheel cylinder, etc. I would be assuming that with the other lines blocked at the ends, the fluid would be forced through only one branch of the tubing at a time.

Many of the lines are already connected to each other through the brass connector blocks. I am assuming that unless I see there is significant debris in a line, that it would probably be best not to open any of the connections that I don't need to.

Although the above description has too many words, I hope that it is understandable. I would rather waste some brake fluid than have something unpleasant happen when trying to stop in traffic!

Nick, My brake master cylinder has the same casting number as yours. My brake light switch is mounted to the floor board under the brake pedal bracket in the engine compartment. That little adapter that Dan pointed out might work for your situation. Also, I believe my brake line fittings are 7/16 x 24.

Thanks John, I was not aware of that type of brake light switch. Thanks for the photos!

I don't believe that I have those parts in the pile of stuff that came with the truck.

I wonder whether I should go with an original-style mechanical switch or if a switch that is activated by pressure in the brake line might be better considering my truck is a bit of a Frankentruck anyway.

Nick
My ‘37 has the hydraulic switch, as others discussed earlier in your thread. My ‘46 has the mechanical switch shown in John’s photos. My 2 cent opinion is the mechanical switch is better in terms of installation and hassle relief. As others indicated finding the correct banjo fitting for mounting the switch directly on the master cylinder is a hassle. Added to that, it offers just one more potential brake fluid leak to deal with.

I just rebuilt the entire brake system on the Galaxie two weeks ago.

Blow compressed air through all the lines from the master cylinder to the wheel cylinders (disconnect the wheel cylinders if already installed).

Then install the wheel cylinders.

Install brake shoes and hardware.

Adjust brake shoes according to the manual.

Fill with fluid and bleed in the usual manner. Right rear, left rear, right front, left front.

Then do it a second time.

Recheck shoe adjustment.

Thanks for your input, Lee (46 Sparky)!

I figured out a part of my confusion re mechanical switch vs hydraulic pressure switch! My toe board is for a 1940 KC (1/2 ton), and my chassis is 1946!

Frankentruck! I looked for the mounting holes in the toe board that came with my project and there were no holes there for mounting of the mechanical switch.

I spent the afternoon at NAPA and have come up with a kluge, that MAY work. (I have attached a photo of the parts mocked up on the workbench.)

Otto, thanks for your suggestion re the order for bleeding the brakes. The reason I was thinking about doing it in the order I mentioned in my post (above) was to move any contaminants as short a distance as possible before they were forced out of the system. I would then go back and bleed the wheel cylinders in your suggested order to get all the air out. Does this seem like a good plan?

(When I was a younger fellow, it seemed to me that all cars had brake light switches like the one shown in the attached photo. When I showed it to the gray-haired guy behind the counter at NAPA this afternoon, he had never seen one before! Maybe I'm older than I want to believe!)

I was hoping to pick up a couple of banjo bolts for the rear wheel cylinders (the ones I have would work, but they look awful) and the soft copper washers that are needed there and a few other places - NAPA didn't have them! Where do folks get new ones? Sources? Part numbers?

That switch looks identical to the Ford! Ya, pretty much all of my cars have switches that look like that.

If you're legitimately worried about solid stuff contaminating the lines, I would blow out each one individually and have somebody at the end to observe if anything and what comes out. Maybe blow into a bucket or something. Disconnecting them all from junction blocks will avoid any "cross-contamination" and the order they're cleaned won't matter.

Did the guy have tape or rubber plugs on the ends of any of the lines?

I'd be more worried about internal rust than anything else. If any solid particles that look like rust come out, buy new pre-bent lines.

Otto,

Unfortunately, no tape or plugs on the ends of the line. The only line that was actually open to the elements was the one that would have attached to the output of the master cylinder. Perhaps I should start with disconnecting that one at the first junction block and blowing it out into a container of some sort. If I don't see anything worrisome then I could move ahead with my plan as stated above.

I agree. Detach it and blow toward the mc. Anything in there is likely to be close to the end that was open. Mud Daubers love little holes like that.

This is how I usually bleed brakes, but on my '46 the farthest brake cylinder is my rear left, then front left, then rear right and finally front right. There are not multiple lines from the master cylinder. One line goes from the MC to the right frame rail and splits front to rear. The second longest line goes from that point through a split block by the front right wheel and continues past the front of the engine then back to the left front wheel.

My project is plumbed the same as UtahYork's.

Since the plumbing on the '46 1/2 tons had only one line heading to the rear and one line heading to the front, as John says, I think it would make sense to do the left rear first, then the right rear, followed by the left front and the right front last.

Ok. If the brake lines on your truck are routed in such a manner that results in the driver side wheels having longer brake lines than the passenger side wheels, then do it in the order you mention.

Nick - Just a suggestion on your positioning of the pressure brake light switch. I'd veer towards having the switch mounted straight up or at least horizontally. Up or either side is better than pointing straight down.

Pointing down like they are leaves wires potentially hanging low to get snagged by the odd bit of trash/debris your truck might drive over on the roads. An errant plastic bag or cardboard box under the truck could snag on the wires, pulling them off and/or damaging the wiring so you brake lights stop functioning.

Which of course could lead to other less than happy circumstances, like getting rear-ended by some speedy knucklehead - ARGH!!! Just thinking safety here.

Dan, thanks for your suggestion re the positioning of the brake light switch. The photo of the setup on the workbench is just a mockup with things finger tight to ensure that they all will work together.

I had not thought much about the final orientation, but certainly, it makes sense to keep the wires out of harm's way! Now that I am thinking about it, it might be best (if there is room) to have the switch pointing directly up so that any trapped air is easily purged.

I hope to install those items later today.