Geoff Weeks

Mack wasn't the only one to use seals and greased bearings. There are a number of ways it was done.

Checked to see what I have. I have a 777 ratio box and a plain 90 deg but it has 5/8" threads and those look to be 7/8's

Another thing about "swaps" is they are never simple, yes the cut-off may not be that expensive, but then there is all the little stuff that adds up like driveshaft changes, frame splicing if not trying to bolt in. Getting replacement drums made may be the most expensive brake job you ever do, but as long as the shoes can be re-lined (shoe table not damaged) and the wheel cyl castings are not damaged, it still may work out cheaper in the long run. You are then left with something that is factory and not butchered, not only is it correct, but down the road it will make other repairs more straight forward. Take time to assess what you have now, and if drums are the only hurdle on the rear of the truck, I would advise getting them made. You may be able to "hook up" with other looking for those drums to make a "group buy" to bring the cost/unit down.

Just looking though Webb's catalog, I find 3 numbers that match the pilot, mounting hole and brake spec's but not surprising all are being discontinued. I found a few "hits" on those numbers, but unless you find one sitting in someones warehouse that they want to get rid of, it looks like Durabrake, is your best bet in this country. If you are having one made, then they should be able to make an exact fit. Problem with changing rear axles, is IIRC this truck is on juice brakes, so that would preclude swapping a more common and likely air braked axle. I would be looking for a minimum of 2 no matter the other one you have is still in one piece. Other than the above spec's the most important will be the hub mount to brake shoe measurement, that has to be close or be able to be machined to that spec.

The next video you post will be another shop putting the Cummins block back together!

https://www.durabrake.com/brake-drums/ In there "About us" section seam to say they make drums to order and prototypes

Give us the two measurements I asked for and see what can be found. we already know it is 15x 5 brake. needed are the bolt hole circle and the pilot diameter.

Paul, the dual gear starts on pg 62 https://www.rhsheppard.com/wp-content/uploads/2019/02/92-Series-Sheppard-Power-Steering-Service-Manual.pdf

I'm getting old, that is 4k more than I paid for my last cabover (drove it home) and 3k less than I paid for my other two, which didn't need anything to go to work. Everything is more expensive today, but is why I always kept my "cores" and rebuilt when time permitted.

Yes, the tie-rod just keeps the tires in "sync" with eachother and the forces are supplied by the dual boxes. Sheppard made a "box" that looks identical to the "392" but it has no input shaft, the oil is controlled and supplied by the master box (Left in the US). Some others have used a double acting hyd cylinder, much cheaper, but when pressure is on the rod side of the cyl the forces will not be equal like they are with the whole slave gear. (Rod side has less area than the non-rod side).

Glad I could be of help.

Make sure the line between the double check and trolley valve is not "crimped" anywhere along its run.

Yeap, that is the double check, the outlet is the pipe connection that looks like it connects to a tractor protection valve. The reason it fixed it is because without all the air line connected the flow out the exhaust was higher and that was enough to get the shuttle to move. It sound like it was "sticky". It may work for a long time or it may fail shortly, but at least you know where it is and how to fix it. Doesn't look like fun getting it out of there, however.

Output from the trolley. It goes to a T valve where the higher of the two inputs goes to the output (double check). Right now it is not sealing so air can come from the foot brake, back feed up the line to the trolley and since in its normal position that is open to exhaust, the air flows out the exhaust. Another way to test it is to build full air pressure, fully apply the trolley, then step of the foot pedal. It shouldn't leak until you release the trolley valve. Input to the trolley should have system air, output should be 0 psi with the valve in the normal position, and of course the line you already traced just dumps to under the hood. With the air built up, if the line you crack loose at the trolley has pressure, that is not the one you want, if you crack it loose and it doesn't have pressure, then remove it and plug it, then test the foot brake to confirm the problem has gone away. then trace that line to a valve with three lines on it.

There should be 3 lines to the Trolley, (2 on earlier systems where they just exhausted the air into the cab) One should be supply pressure and one should be output that will go to the double check. 3rd is the exhaust you traced. Where it would be located is up to the mfg and I have no idea on that model, where they put it. It could be located anywhere between the trolley, foot valve, and the tractor protection valve. Some are in the cab, some are down on the frame. If you are in a pinch and need to move the truck, remove and plug the output line from the trolley valve (plug the line, not the port on the trolley valve) and the leak should go away if the shuttle (double) check is the problem. You should still put the time in to fix it right.

My 1st guess would be the shuttle check that separates the Johnny Bar from the foot brake feed to the tractor protection/trailer feed.

Ok, we were both writing at the same time, but that is helpful. That should rule out the Tractor protection valve, as it should see application pressure when either the foot or hand valve is used.

wow, I stopped working on trucks commercially in the very early 2000's and it was very rare to see a truck without a 'Johnny bar" even if it was a straight truck (dump truck etc). So, because there are two complete systems that are supposed to be isolated from each other, to prevent a failure on one system from effecting the other, you should start looking where the two come together to feed the trailer brakes. This would include the double check for the tractor protection valve, the double check for the Johnny bar if equipped, and the tractor protection valve it self if it is one of the newer type that has the double check inside the tractor protection itself, unlike the old TP-3 Note, the tractor protection valve is NOT the red and yellow buttons, that some call the tractor protection valve.

Does it leak when the "Johnny bar" (Trolley valve) is applied?

Trace the "Little yellow line"back to what it is connected to. You know where the air is exiting the system, so work back up until you find the problem. Does it drain both primary and secondary tanks? That would be a clue it is a problem in the trailer portion (trailer brakes can be fed by either primary or secondary so a failure in one does stop the trailer from braking). There are portions of that system that are "live" even if no trailer is attached or the "red button" is pushed.

The stamped steel mounts inside the drum, and is held in place by the same bolts that hold the drum to the hub. It seams to be left off newer set-ups, My guess the improvement in seal tech made them obsolete.

Gunite's offerings https://www.accuridecorp.com/sites/default/files/resources/2023-08/WE1.011 Rev. 4 Gunite Brake Drum Product Catalog 8-7-23.pdf

here is Webb's offerings, you can look up by brake diameter, you need inboard with 6 or 5/6 mounting holes, and with the pilot measured from your old drum. https://www.webbwheel.com/webbipad/pdf_files/SD 090 - 2019 Catalog.pdf

15x5 sounds small for a B85? IIRC that size may be used by wedge brakes. I have some that have a stamped steel piece that is like your concave bowl. I don't have a lot of Mack axle experience. I would 1st try and get some numbers 2nd I would grab a catalog and start looking for drums that match those measurements.

1st measure the ID of the drum, along with how wide the shoes are Next measure the pilot diameter (red) and the bolt circle diameter (blue) and start looking for a match Ideally you'll have a Mack # or a casting # to try and cross.