Geoff Weeks

No idea what it is worth, but love the spokes. Those 15" trailer tires were known for problems. The tube stem is right against the 12" brake drum. Most switched to 17.5 and never looked back. Not surprised it popped a few.

Yes, I know it is wrong, and I very rarely did it, but needs must when the devil drives, a little starting fluid will pop the bead on. Did it once on a trailer for a guy. He had hit a chunk of concrete and bent the steel rim on those real low profile 22.5 tires they run on a step-deck. Took my bottle jack and a 4x4 with the damage part up, jacked it back mostly round, and soaped up the bead with hand cleaner, then popped the tire back with starting fluid. He was in Ontario and they take a very dim view of wheel end problems, he had no Canadian cash or a credit card, I got him back across the boarder, with that trick.

When you are your own carrier, it all comes out of your pocket, the more you keep the better off you are. When I can do it faster and cheaper, I am both money and time ahead!

Disks or spokes, take the same to mount/dismount. Tubeless vs tube type can vary. The rim portion of a disk and spoke are the same (ok, except for Firestone RH 5 deg) so mount time is the same.

One Jamoke saw me patching a tube on one of my trailer tires (I had picked up a nail in a jobsite) before I went into dinner. He commented how "he wasn't paid enough to do that kind of work". I asked him what he did when he got a flat? Oh I call road service. Ok what does that cost? I don't know, company pays Ok how much drive time did you loose? Only an hour or so Well I can patch this tube, re install in the tire and inflate in about 30-40 min, Given road service calls prices I am paying myself between $125- $200/ hr, how much are you paid? silence. I always had a mounted spare and tools to change them. Gotta love spokes, inner or outer, done in 20 mins with hand tools.

Well that sucks!

Please post any casting numbers on the master cylinder casting.

Looks like you threaded a bolt into the piston, this is NOT the way to get it apart. The push rod has to ride in the concave space. If you ever have to do it again, make up a fitting and grease nipple and pump grease into the outlet of master forcing out the piston (after removing the lock ring). Measure the bore, if it 1 3/4" then the rebuild kit I referenced should work. The real question is what shape the bore is in?

I don't think that is the site I remember, it had all kinds of nuts and cones for small engines all the way up to big marine engines. But still, it is a good resource.

There used to be a North American supplier that had all the ends, nuts and tube, I just can't find a link for it, may be putting the wrong search terms in Google. In an emergency I have made a repair to a Leyland 680 (very similar to Mack) by taking the line off, cleaning and wrapping iron baling wire tight over the defect extending out from each end, then carefully brazing over the wire wrap. Far from a perfect repair but enough to get by until a new line could be flown in.

The frame mounted booster allowed for more boost an worked better with bigger trucks, larger M/C, and more overall flexibility in the whole brake system. They were used up and until air brakes took over the medium truck market. You can replace the hydrovac with an "airpac" that is the same booster but boosted with air pressure instead of vacuum, then you have a brake controlled pressure signal that can be used to operate a trailer with air brakes. It was a popular conversion after the war when there were plenty of hydraulic braked surplus trucks and not enough air braked tractors around for towing semi's. throw an air compressor on, exchange the hydrovac for an air pack, a few air tanks and valves and you were set.

genuwine Maine native, out numbered but not out smaaated!

This brings us to the little air cleaner on the hydrovac, it filters all air that gets drawn into the hydrovac to keep from gumming up and damaging the hydrovac, but just as important, any air entering the hydrovac eventually enters the engine as well. Repair the air cleaner and hose to prevent damage.

It wasn't until I re-read what you wrote, that I saw a few misconceptions on your brake system. The brakes are hydraulic with vacuum assist (boost). The thing in blue is the master cylinder, just like a car has. It is bigger and only has a single line. Dual masters didn't come out until much later. The master is connected to the foot pedal by a push rod. It make pressure in the hydraulic line which goes to the wheel cylinders in each brake. Along the way it passes through the frame mounted "Hydrovac booster". If the engine is off and no vacuum, the pressure passes right through the unit and on to the brakes, un boosted. IF the engine is running and there is vacuum in the booster, the control valve closes off vacuum to one side (rear) of the big can and modulates how much atmospheric pressure is allowed to the back side, which moves the piston in the hydraulic portion, boosting the amount of foot pressure from the master. In this way it multiplies the pressure generated by the drivers foot but is always controlled by the drivers foot pressure. So it is not true "vacuum brakes" which work like air brakes in reverse, but vacuum assisted hydraulic.

RD 450 and smaller are lined (dry liners) the 501 is not lined. If it is stuck, dry liners might make the repair easier.

Closest thing I can come up with is a Wagner F2981. It would have a casting number of 1099FE and takes a F8450 rebiuld kit. It has a 1 3/4" bore and not RCV. This is going just off pictures, You MUST verify that it is the same bore. Nothing else I found used the three bolt side mount and didn't have an RCV and was for brake fluid. https://www.brakeproducts.com/Products/Wagner/

Try and get a casting number off the master cyl, I used to have a book that would cross casting number and bore size to MC number. I don't know if I can still find it.

I know the master cyl for my K-7 was still available new from Rock Auto a few years ago. Most of those single line big masters are still available new as they were often used well into the 70's on trucks and long after that on fork trucks. You need to be careful though. Most hydrovac's had the RPV in the outlet of the hydrovac and can't have one in the outlet of the master. You can remove them if all you can find is a master with one. I also got a master rebuild kit at the same time, but haven't used it yet. Hyd brake cyl can be sleeved if badly pitted and new are not available. Masters can also but it is a much more difficult process to make the small drilled holes though the reservoir opening, requiring long twist drills that are easy to break.

Glenn, had a place in the US but I can't find it anymore?

If all else fails: https://cohpro.com/product-category/metal-tube-fittings/diesel-fuel-injection/

RD's top out at 501 CID. Engine number will be stamped into the block (not head) between #1 and #2 cyl, behind the air compressor. Should start with "RD" followed by the displacement and then the serial number of the block.

On other makes with single reduction rears, the tooth count is most often stamped in the head of the pinion (rear-rear on a set of bogies) eliminates guess work, like "was that 3.7 times or 3.9 time around the shaft?" Because the gear set is "mated" at the time of mfg, it will be correct. For Eaton 2spds it will be the "high ratio". Don't know how Mack does it with their double reduction. esp if someone changes the gear-set and doesn't re-stamp the ratio on the housing.

The "can" thing on the frame rail is a Bendix Hydrovac brake booster. It has a little air cleaner (small vertical can) and a large vacuum line to the engine intake. There needs to be a check valve between the engine and the hydrovac, so no pressure from a back-fire in the engine. The Hydrovac are very reliable and it wouldn't surprise me in the least that is works just fine. I have 3 of them and haven't had to go inside on any of them.

Many times they are made up with re-useable fittings, so just buy enough -20 hose and go to town. If at all possible, I run plastic air brake hose, one piece, from the tank side of the relay to the button, this is the only hose that has pressure at all times and a leak is a problem, the rest only have pressure when cranking so a small amount of leakage is no big deal. Making it one piece with as few fitting as possible. Mine would go 4-5 weeks and still have enough in the tank to crank.

Those look to take a "ball seat" nut. I can't blow the picture up enough to look for any casting numbers on them. Getting any numbers off the old ones would be the best way to make sure you are getting what you need.