Disc Brake Engineering Thread

[mudguppy]

With regard to the question of whether or not the OE deuce MC can be used to run disc calipers - even if it can and has the capacity and pressure capability, if I was to do it again, I would still swap in a modern two-chamber MC. The added cost is not in the MC, but in the brake booster. However, I personally believe that most people who will be looking at swapping to discs already have or are considering a power steering swap - perfect source for adding a hydro-boost.

So, all in all, I would do the braking mods post or in conjunction with steering improvements and do it the same way. I know I love how my truck steers and love how it stops (thanks again, Steve!).

$0.02

 

[steve6x6x6]

Thanks, when you first asked me about disc brakes and i said i could make larger disc brakes for your bobbed truck and the 6X6 trucks. And we talked about the the stock master cylinder and you used the hydro boost system from the dodge truck witch is a great setup. The basic is - the 1949, M35A1 single circuit booster and std. master cyl. then the diesel 1966, M35A2 with the same but 1985 or so the dual circuit but the same master cyl. the 1993 M35A3 with dual circuit BUT a larger master cyl. with a massive remote resevoir, great for disc brakes. I installed the disc brake front in my M35A3 and will get to the rear.

 

[peashooter]

M35A2 with the same but 1985 or so the dual circuit but the same master cyl. the 1993 M35A3 with dual circuit BUT a larger master cyl. with a massive remote resevoir, great for disc brakes. I installed the disc brake front in my M35A3 and will get to the rear.

The 87-89 M35a2 and the 93+ M35A3 trucks use a nearly identical master cylinder. Reservoir capacity is the same (although one is remote mounted), bore and stroke are the same, just a difference in volume split betweeen the two and residual pressure valves in one.

 

[rustystud]

I was wrong. I was remembering that the rearmost chamber actually went to the front circuit on most disc/drum setups - I was mis-remembering that the front chamber was the smaller, thus feeding the rear.

Thanks for taking the time to point out that I was wrong. Made your day I'm sure - happy to help.

The point I was making earlier is what SP5 did a better job explaining - discs 'use' much less fluid than drum cylinders during braking, so volume / flow is a negligible factor.

Mudguppy, I'm not trying to "dis you" in any way. I'm trying to get factual information out to the general membership. Steves6X6X6 system is great, and If I had a lot of money and time to devout to it I would go with something like his system. I just think using the stock components which we can get (to convert to a dual brake system) would be one less step we would have to take in our conversion, that being not to have to fabricate up a new master cylinder mount and all the linkage and brackets needed. Then all we have to modify is the caliper mounts.

 

[Section8]

Love all the debating on pressures and the best system in which to go with. As far as the debate on reservoir capacities from front to rear, drum to disc, is very interesting. Did you all forget, cuz I don't 'recall reading it, apologize if it was discussed.
The front reservoir and pressure application is larger because a vehicles braking ability is usually broken down into 60 percent front and 40 percent rear. Probably closer to 70/30.
My real question for the thread is this though.
I am planning to go discs on my 1956 M135 and. Ant for the life of me figure out how the rotors will be kept in place. Translation. How are the rotors mounted. The threads go on about caliper mounts and case hardening other parts.
Also how do you seal the spindle. If I recall in muddguppy's thread you needed to remove the spindle sleeve to mount the setup.
Pics. And explanations please.

 

[m-35tom]

The front reservoir and pressure application is larger because a vehicles braking ability is usually broken down into 60 percent front and 40 percent rear. Probably closer to 70/30.

You are missing the design reason for larger res for the front. It used to be that front was disk and rear was drum, so as the front pads wore, fluid was displaced from the res to the front calipers. Not so much the case today and if you were to use disk on all 6 wheels, you would need twice the size res on the REAR assuming equal wear which I doubt you would have but only experimentation will tell. If only 4 wheels then both res should be the same size.

I would also like to point out that there is nothing wrong with the drum system as it came with some simple mods. I can easily lock up all 6 wheels with only finger pressure on the pedal at any speed and 14.5R20 radials. Full air over hyd conversion and dual system. How can you get any better? Granted there may be some extreme instance where fade may be some issue, but I have never been there.

 

[steve6x6x6]

Love all the debating on pressures and the best system in which to go with. As far as the debate on reservoir capacities from front to rear, drum to disc, is very interesting. Did you all forget, cuz I don't 'recall reading it, apologize if it was discussed.
The front reservoir and pressure application is larger because a vehicles braking ability is usually broken down into 60 percent front and 40 percent rear. Probably closer to 70/30.
My real question for the thread is this though.
I am planning to go discs on my 1956 M135 and. Ant for the life of me figure out how the rotors will be kept in place. Translation. How are the rotors mounted. The threads go on about caliper mounts and case hardening other parts.
Also how do you seal the spindle. If I recall in muddguppy's thread you needed to remove the spindle sleeve to mount the setup.
Pics. And explanations please.

Disc brakes on the M135 will be a big challenge. Rotors on the hubs will be easy, it is the rest of it. I have no proportion valve in my truck.

 

[rustystud]

You are missing the design reason for larger res for the front. It used to be that front was disk and rear was drum, so as the front pads wore, fluid was displaced from the res to the front calipers. Not so much the case today and if you were to use disk on all 6 wheels, you would need twice the size res on the REAR assuming equal wear which I doubt you would have but only experimentation will tell. If only 4 wheels then both res should be the same size.

I would also like to point out that there is nothing wrong with the drum system as it came with some simple mods. I can easily lock up all 6 wheels with only finger pressure on the pedal at any speed and 14.5R20 radials. Full air over hyd conversion and dual system. How can you get any better? Granted there may be some extreme instance where fade may be some issue, but I have never been there.

The longer I have looked at this, the more I'm inclined to just stay with my stock dual brake system. Maybe go with the 1.5" front wheel cylinders, but not disc. If I had a "Cummins" putting out 400HP, then yes lets look at upgrading the brake system, but with the Multifuel engine I see no advantages.
I have found out that "Dorman" makes a 1.5" wheel cylinder that fits our deuce. Part #W37317. I bought them recently. The only thing is their made in China. I will replace the seals with ones made in USA. Hopefully NAPA carries them.

 

[rustystud]

Love all the debating on pressures and the best system in which to go with. As far as the debate on reservoir capacities from front to rear, drum to disc, is very interesting. Did you all forget, cuz I don't 'recall reading it, apologize if it was discussed.
The front reservoir and pressure application is larger because a vehicles braking ability is usually broken down into 60 percent front and 40 percent rear. Probably closer to 70/30.
My real question for the thread is this though.
I am planning to go discs on my 1956 M135 and. Ant for the life of me figure out how the rotors will be kept in place. Translation. How are the rotors mounted. The threads go on about caliper mounts and case hardening other parts.
Also how do you seal the spindle. If I recall in muddguppy's thread you needed to remove the spindle sleeve to mount the setup.
Pics. And explanations please.

The pressures coming out of a dual master cylinder are the same. The pressure is reduced for rear drums by metering valves. Sometimes the valves are in the output ports of the master cylinders themselves.
Summit Racing used to carry a "Adjustable Proportioning Valve" which would allow adjustable front to rear biasing.

 

[peashooter]

Love all the debating on pressures and the best system in which to go with. As far as the debate on reservoir capacities from front to rear, drum to disc, is very interesting. Did you all forget, cuz I don't 'recall reading it, apologize if it was discussed.
The front reservoir and pressure application is larger because a vehicles braking ability is usually broken down into 60 percent front and 40 percent rear. Probably closer to 70/30.

I probably wasn't too clear on this sorry. The dual circuit A2 and A3 trucks have a master cylinder with different output volume ratios. The reservoirs aren't really split, they do have an internal baffle that goes up halfway but that is just incase one circuit fails so the other circuit will have a "reserve" in the reservoir to supply fluid to the functioning circuit.

Anyway the M/C piston is a 2 stage unit, both pistons have the same diameter so they put out the same pressure. The Dual circuit A2 trucks are a 60/40 so when you step on the brake pedal, it applies about 20% fluid to the REAR circuit before the secondary piston starts to activate the FRONT circuit. This is backwards of a "normal car" but that is simply because there are 4 wheel cylinders on the rear circuit and only 2 on the front circuit. I'm sure the thinking is that with the 60/40 split you would end up having the front and rear shoes make contact with the drums at the same time.

The A3 trucks have a 50/50 split system so when you step on the brake pedal it will start putting fluid to both primary and secondary ports and the same time. The A3 trucks have slightly larger wheel cylinders in the front but a 6x6 truck the rear wheels will start braking before the front ones do, a bobbed a3 would have the front start braking before the rear (again this is just on the '93+ A3 trucks).
So both dual circuit M/C versions put out the same pressures to each port.

 

[Section8]

Thanks for the cool Intel! I didn't realize there was that much of a difference between systems from model to model. I was also basing most of my input off of my limited knowledge of brake systems in cars and trucks. I wonder how my system varies from M35 and newer models.
Mind you I am still trying to figure out the logistics of going disc brakes on my rig. GM Corp axles not Rockwell.

 

[Joaquin Suave]

A question for you guys that have swapped your drum brakes for disc brakes... Are the REALLY any better than drum brakes???

I am advancing quickly on my hybrid rear axle and have to decide whether I am going to bail on my 15" x 8" dual circuit drum brakes for 15" dual circuit disc brakes.

Thanks for your advice in advance!

 

[rustystud]

I'll just say this, in the transit industry they played around with using disc brakes for a few years. Now they all are using drum brakes again. There is a reason for this, on a large rig like a bus which makes frequent stops the heat generated by the discs would cause the wheel bearings to fry since all the grease would melt out. We had busses that we would test after running their route. Some would reach over 600 degrees at the spindle ! The grease was literally squirting out the breather holes ! With brakes as large as yours (15"X8" ) I would not even bother.

 

[mudguppy]

A question for you guys that have swapped your drum brakes for disc brakes... Are the REALLY any better than drum brakes???

I am advancing quickly on my hybrid rear axle and have to decide whether I am going to bail on my 15" x 8" dual circuit drum brakes for 15" dual circuit disc brakes.

Thanks for your advice in advance!

It depends on the drum setup you are comparing. I just know that my disc setup put the OE setup to shame - my truck stops like my 2011 F350, maybe better.

Are there other drums that perform as well and are cheaper/easier? Probably.

 

[m-35tom]

stay with drum

 

[JasonS]

The longer I have looked at this, the more I'm inclined to just stay with my stock dual brake system. Maybe go with the 1.5" front wheel cylinders, but not disc. If I had a "Cummins" putting out 400HP, then yes lets look at upgrading the brake system, but with the Multifuel engine I see no advantages.
I have found out that "Dorman" makes a 1.5" wheel cylinder that fits our deuce. Part #W37317. I bought them recently. The only thing is their made in China. I will replace the seals with ones made in USA. Hopefully NAPA carries them.

FWIW, I put the 1.5" cylinders at all four corners in my bobbed deuce and it made a noticeable difference.

 

[rustystud]

FWIW, I put the 1.5" cylinders at all four corners in my bobbed deuce and it made a noticeable difference.

I bought 6 of the 1.5" wheel cylinders. The others where for spares. Now I'm thinking "what if I put these on all the wheels ? " The only thing stopping me is the air-pac. (get it the only thing stopping me ! ) I know bad joke ! Seriously though, I'm not sure the short style air-pac has enough fluid capacity to apply pressure to "4" 1.5" wheel cylinders. Hey Aaron (peashooter) do you know if this is possible ? If it is, I'm going to do it. I have an extra short style air-pac, so maybe I can use two air-pacs for the rear wheel cylinders. One air-pac for each side. But then your running two air-pacs from one side of the master cylinder, and how much fluid can it supply ? So many questions, so few answers.
I just thought of something else. I have a long style air-pac. Maybe using that for the rears and the short style for the fronts will work ? Any of you math guys out there know the answer to this ?
I'm sure if you know the volume of the air-pac and the volume of the wheel cylinders and the amount of fluid put out by the master cylinder you could figure this out. I think this weekend I'm going to start measuring those wheel cylinders and spare air-pacs I have.
Sorry guys for my rambling along here, it seems to help me put things into perspective when it's written down.

 

[gringeltaube]

Please, let's not forget that this thread is about Deuce disc brakes...!


G.

 

[peashooter]

I bought 6 of the 1.5" wheel cylinders. The others where for spares. Now I'm thinking "what if I put these on all the wheels ? " The only thing stopping me is the air-pac. (get it the only thing stopping me ! ) I know bad joke ! Seriously though, I'm not sure the short style air-pac has enough fluid capacity to apply pressure to "4" 1.5" wheel cylinders. Hey Aaron (peashooter) do you know if this is possible ? If it is, I'm going to do it. I have an extra short style air-pac, so maybe I can use two air-pacs for the rear wheel cylinders. One air-pac for each side. But then your running two air-pacs from one side of the master cylinder, and how much fluid can it supply ? So many questions, so few answers.
I just thought of something else. I have a long style air-pac. Maybe using that for the rears and the short style for the fronts will work ? Any of you math guys out there know the answer to this ?
I'm sure if you know the volume of the air-pac and the volume of the wheel cylinders and the amount of fluid put out by the master cylinder you could figure this out. I think this weekend I'm going to start measuring those wheel cylinders and spare air-pacs I have.
Sorry guys for my rambling along here, it seems to help me put things into perspective when it's written down.

I'll try to just add some info that could be helpful to both Disc engineering and those of us with stock drums. I'm not an expert on the Air Packs by any means, but I am under the impression that they only start assisting once the line pressure hits a certain point (probably right after the shoes/pads all contact the drums/discs?). So I think it would be most important to make sure that the master cylinder has enough fluid capacity. Does that sound right?

Anyway, here is what I can add as it relates to the dual circuit trucks:
Master Cylinder Fluid Displacement at full stroke (cu-in)
-1993+ (M35a3 trucks).
Primary Port = 2.56
Secondary Port = 2.56
total displacement = 5.12 cubic inches

-87-89 (M35a2 "air force" trucks).
Primary port(rear axles) = 3.08
Secondary Port (front axle) = 2.04
Total displacement = 5.12 cubic inches

(Primary port is the one closest to the mounting flange/pedal linkage. Secondary port is the furthest away and will be a smaller fitting than the primary).

 

[rustystud]

Please, let's not forget that this thread is about Deuce disc brakes...!


G.

Sorry gringeltaube, I actually did forget that this was about disc brakes ! I usually just go to the end of a thread and read what's new. After awhile you tend to forget what started it all !