1wonton

I could sure use one of those napkins.............. The return spring and the resistance of the neoprene would have some effect, I think. Now I want to figure out how to actually measure the pull.

My text didn't come through, so I'll do it again. After searching the internet, making numerous unsuccessful phone calls and reading all the advice I decided I had no other option but to try and do it myself. I spent twenty bucks and got a sheet of 1/8 neoprene off Amazon. Then I made a wooden ring and clamped the rubber onto the back of the pod. I centered a small coffee can and a five-pound shotput in the middle and slowly (took about ten minutes) heated the neoprene, allowing the weight to gradually deform the diaphragm, I didn't really think this was going to work but when everything cooled the neoprene held most of its shape. The membrane was a little stiffer than the original, but I thought I'd give it a try. I bolted the whole thing together and using my vacuum pump applied vacuum to the booster. Much to my surprise it retracted 3 inches and worked perfectly and is so powerful I could not hold the shaft back with both hands! I'm going to do a little more experimenting with 1/16 neoprene and 1/16 silicone but now that I've got the plan together, I think I've solved the problem. If I was a rich man, I suppose I could have spent a few hundred dollars shipping these off to some high-end rebuilder/restorer but the fun of successfully doing this myself was priceless.

10/4 Bear. Good idea about cutting and gluing, never thought of that, certainly worth a try, might just work. The system has a manual override in case vacuum fails, so I would always have brakes.

Thanks Woodie, I'm not worried about it, I wasn't going to carry insurance anyway.

Thanks Bear, very interesting research. This gives an idea of about how old the booster is. Obviously not factory. I could go back to the original manual brake system but kind of like the way the brakes are set up now. The truck was owned by the Riverside Water company until 1961 so maybe they added this improvement in the forties.

Yes, I thought of that. I've read where someone in the past has used heavy inner tube rubber with good success. Problem is the outside diameter is 11", and the circle would have to be somewhat larger to accommodate the diaphragm in the retracted position.

All I need is the diaphragm, I don't need the spring or anything else. Vacuum is quite powerful, and I think it will pull the heavy rubber. Top speed on this truck is 18 mph, so I have no concern about "experimenting".

Thanks Terry; I called White Post and they said they do not sell parts, only restorations.

Here are a few pictures of the brake pod. I called Harmon but they said they don't have anything like this. The can says, " part no. 2192548" and the diaphragm "1810 Roadmaster". I see a company named Roadmaster still in business, but no one answered the phone. Surely there's a suitable diaphragm out there somewhere with an 11" diameter.

Thanks for all the fun comments. The vacuum brake pods are on a 1922 Mack truck. These were applied after the truck left the factory (Mack did not install booster brake mechanisms). It was no secret, just something that would mean nothing to a parts supplier or any of you highly qualified experts. No Chinese parts, just good old American equipment of a hundred years ago. Now that everybody commenting knows what I'm discussing I know the correct answer to my question will be instantly forwarded.

I called Harmon and spoke to a (not very helpful) lady, and the first thing she asked me is "What year, make and model". I sure miss the old days when you could go into a parts store and talk to someone who could do more than ask you what year, make and model. Looks like everything they service are sealed units. I couldn't find any listing for just the diaphragm itself. This is an after-market add-on vacuum brake booster, not specific to any particular model vehicle. It's not complicated, I don't need a "rebuilder". Just take the small bolts out around the perimeter, replace the diaphragm and bolt it back together. I just need an 11" rubber diaphragm.

Thank you. I'll give them a call but in case they can't help me I was wondering if anyone has tried making their own diaphragm.

The vacuum brake diaphragm on my old vacuum brake booster is shot and can't find a replacement. Has anyone knowledge about making a replacement diaphragm? The original is a shaped "hat" shape but wondering if I could make a flat disc out of neoprene sheet.