All of the model truck kits I have had experience with (mostly 1/24 and 1/25 scale) offer some form of brake chamber detail, and some have brake valves that mount on the frame, but none have had axle mounted quick release valves represented. Many of the 1:1 scale trucks I have seen over the years had these types of valves so I decided to add them to the Transtar 4300, using reference photos, information from the "Bendix Air Brake Handbook" and a 1:1 scale Bendix QRN-2 valve as guides. Styrene strip and sheet is the raw material of choice, since many items like air brake valves can be distilled down to a collection of geometric shapes joined together.

0:48 Real valve is 2-1/2" wide...

1:04...which works out to .100" wide when divided by 25 for "scale math". I did use .060" thick x .100" wide styrene strip instead of .040 (which would be an exact match for the real valve's 1" thickness) for practicality since I would be drilling .032" through the narrow dimension for air hoses.

1:22 Small pieces such as these quick release valves are easier to make when the main piece of material, in this case .100" x .060" strip, is left full length to serve as a handle during assembly. File end of the strip round...

1:39...and glue an .015" thick disk to one side to represent exhaust port. The Micro-Mark punch set I use has metric diameters in half millimeter increments, 2.5 mm = .098" which is a close enough match to .100".

1:54 .020" disks that are 1.5 mm diameter (.059") are glued on either side where hoses that go to the brake chambers will be attached.

2:08 These are drilled out for the hoses, I use wire approx. .025" diameter for brake hoses (salvaged from a scrapped i-phone cord or similar) so holes are .032" for clearance. Drill from one side partway through, then finish drilling from other side. This way any misalignment of the drilled holes is inside the part and not visible.

2:46 Another 1.5 mm disk, this time punched from .030" styrene, goes on top of the valve and is equipped with an air hose fitting made from .040" x .040" styrene strip, drilled partway through with an .025" diameter drill and cut approx. .075" long.

3:08 A rib made from .030" x .030" styrene strip is cut .070" long and glued to top of valve body, one end butted against the .030" thick disk.

3:18 Mounting flange is .020" x .040" styrene strip glued on edge across top of valve and tight against the small rib.

3:30 Finished valve can now be cut free using fine tooth razor saw. Four valves are required for a tandem axle truck, two per axle.

3:41 Majority of the trucks I have seen, like the example pictured, have quick released valves attached to a bent metal bracket that is either bolted or welded to axle housing.

3:55 Strength of materials combined with small size makes metal an ideal choice for this mounting bracket, I used K&S .016" sheet aluminum. Tapered piece is trimmed to width of valve at top (.100"), wider at bottom.

4:12 I like to drill and pin parts where possible, rather than relying solely on glue joints, and aluminum is easy to drill for .020" brass wire pin.

4:39 Something I hadn't though about initially was attaching bracket to axle, I chose to make a slot in axle housing so bracket could be securely fastened - again, better than relying on a small glue joint. This would be easier to do before axles are assembled to suspension but this job actually wasn't that bad to do on-board. Small holes (approx. 018") were drilled where slot would be cut...

4:52...then slot was finished with #11 hobby knife blade.

5:14 Bracket filed to width...

5:22...and glued in place to complete installation.

5:30 Hoses were then installed, one valve for the spring brake chambers, the other for service brake chambers, on each axle.

Next installment will be on the rest of valves and plumbing to connect rear axle brakes with rest of truck's air brake system.

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