modern dual circuit air over hydraulic brakes

[fleetmech]

I'm interested in one of these myself. Mainly I just need to have a recommendation of what MC we could use. Because that's really nothing more than a brake can with the push rod cut down and a mounting plate made between it and the MC.

I would love to hear from anyone who has done any sort of three axle dual circuit conversion as to what non AF master they used. I'm a bit hung up on the issue of residual pressure valves, as im not 100% sure if they're needed, and some masters had 2, some had 1, and others none. I believe it was mentioned in one of the other brake threads that once the master was mounted high enough, the weight of fluid in the lines would be sufficient, but again, I'm not sure if thats true. If it is true, than thats great, since this system could be mounted well up under the hood witht he bonus of being easy to check and clear of off road obstacles.

I feel like i had a note somewhere of what I thought the correct master to be (ive been through a lot of manufacturer data...) but I might have misplaced it. I'll look and then see if we all agree.

 

[patracy]

Two axles or Three axles, they would use a two circuit MC. Front axle would be on one, the rear tandems on the rear.

The air brake can/MC setup would allow you to easily mount it on the firewall. You'd gain some elevation doing that as well. My only concern with the setup is long term "storage". Since it's a air brake, once air leaks down it would apply the hydraulics all the time. I could see that having a negative effect maybe. But a simple solution to that would be to cage the MC for long term parking. And while it would work for driving as well, I wouldn't want it caged since air loss would mean brake loss. Uncaged and it will apply the brakes if there's a loss of air.

 

[davidb56]

a 150$ master cylinder and a 100$ brake can along with a piece of 3/8" plate is a lot cheaper than 700$ for one set up that we'd have to modify to fit.

 

[patracy]

So the deuce brake system runs at 1800 psi. I know the stock single circuit MC is a 1.75" bore. I found a spec sheet that listed the length as 9.625 and 8.188 compressed. So I assume that'd be the piston travel. So that works out to be 3.46 cubic in. So .58 cubic in for each wheel?

 

[patracy]

I sent Wilwood an email asking if they had any options that would suit the pressure/volume. We'll see what they say.

I like the air brake can idea better because we keep the air system for all the air brake trailers. Hydroboost is a possibility, but I'm not sure how you'd make that also actuate the air brakes for the trailer.

 

[rustystud]

So the deuce brake system runs at 1800 psi. I know the stock single circuit MC is a 1.75" bore. I found a spec sheet that listed the length as 9.625 and 8.188 compressed. So I assume that'd be the piston travel. So that works out to be 3.46 cubic in. So .58 cubic in for each wheel?

I have a pressure gauge on my Deuce and the top brake pressure I ever had was 850 PSI. That was standing on the pedal. The average pressure was 800 PSI.

 

[fleetmech]

Just stopping by, Ive been incredibly busy so I havent found my notes yet. I believe the master I had found was for an 86ish chevy c60 or something similar.

The brake pressure number is good to have. I suppose the threaded pushrod on a standard can would allow a bit of travel adjustment and therefore a measure of force/ pressure control. installing a brake pressure gauge would allow you to tune the system on install.

As for storage, air leakdown would be an issue, one that I think would be best solved with a cage bolt. It might be a great application for a 'remove before flight' tag...

 

[patracy]

I sent Wilwood an email asking if they had any options that would suit the pressure/volume. We'll see what they say.

I like the air brake can idea better because we keep the air system for all the air brake trailers. Hydroboost is a possibility, but I'm not sure how you'd make that also actuate the air brakes for the trailer.

Wilwood emailed me back, they don't make a cylinder large enough for our trucks. So that's out. But I wonder if the three separate MC one would work.... Splitting all three axles. But that'd be a lot of plumbing to make that work.

Anyhow, after speaking with Peashooter. He recommends dorman M630985 for the MC. So now a question for this is how to implement that MC. Maybe a firewall mount setup since it'd be a pain to deal with filling the MC under the floor. I want to keep the air brakes for trailers. I was thinking the brake can setup would make things easier since there wouldn't be an linkages really to deal with. But caging that can for long parking sessions would get old. But maybe a "key" could be made? Or would it be easier to just buy a second air pack and go that path?

Ok, now thinking out loud, the air brake can would be cheaper. Because a airpack is $400+ now. And surely the deuce air compressor would be up to operating the single brake can and trailer brakes. I'd imagine the CFM requirements would be about the same as a USAF deuce with a trailer.

 

[banditt1979]

Searching for Dorman MC630985 I come up with out of stock everywhere. However, Raybestos MC39577 appears to have the same specs. I found a closeout on rock auto for $46. Should be in my hands Friday.

 

[patracy]

That appears to be one without the check valve. Centric 130.79025 is another part number you can use.

 

[banditt1979]

That appears to be one without the check valve. Centric 130.79025 is another part number you can use.

Check valve as in the residual valves in the ports?

emailed dorman to try and get specs on 3 different part numbers but they said they cant help me due to liability issues. Wont even give me spec sheets

 

[patracy]

Yes, Dorman sent me a terrible drawing of the MC I mentioned. I was trying to figure out stroke length.

 

[patracy]

Uploaded the drawing. I think this means there's about 54.5mm of travel. Or about 2" of travel. I'm getting it's from the 20 and 34.5mm measurements where things are measured for the front and rear pistons. Now to figure out brake can setup or just a simple firewall mount and a second airpack. I just don't know....

 

[banditt1979]

I will be going the dual air pack system since I picked up a spare a few months ago and verified it works, plus my original rebuilt air pack works as well.

The MC39577 I ordered is now saying next Tuesday. When I get it I'll check the stroke and report back.

 

[banditt1979]

Searching the web I'm coming up with nada on the remote mount plate for the dual mc. Anyone else have anything to go on?

 

[patracy]

Are you talking about the remote reservoir or are you talking about a mounting plate for the MC? Mount for it will have to be one off made.

 

[banditt1979]

Are you talking about the remote reservoir or are you talking about a mounting plate for the MC? Mount for it will have to be one off made.

The plate that attaches to the top of the master cylinder main body. Guess thats the unobtainium part. Eastern Surplus has a "call for price" for their mc with plate, same as the remote reservoir.

 

[patracy]

Oh. I'm going to either mount mine to the firewall and make a "modern" pedal setup. Or mount a can to it and put it out there on the firewall. I think it'd be easier that way. And if I do, I can mount the second air pack down where the old MC went.

 

[banditt1979]

The plate that attaches to the top of the master cylinder main body. Guess thats the unobtainium part. Eastern Surplus has a "call for price" for their mc with plate, same as the remote reservoir.

As I understand it this plate is needed to do a remote reservoir and in doing so, eliminate the need for residual valves plus better fording capabilities. But I also think that lines could be attached to the reservoir mounted on the mc, and add the remote reservoir. That could be the workaround to the plate.

 

[banditt1979]

Oh. I'm going to either mount mine to the firewall and make a "modern" pedal setup. Or mount a can to it and put it out there on the firewall. I think it'd be easier that way. And if I do, I can mount the second air pack down where the old MC went.

My plan is to either modify the existing mc mount or fab a new one with steel angles and tubing for the clutch linkage.