Re: Restoring Rusty
 

Yeah, with the '74 C-10, he could have the JB1, JB3 or JB5, but it's probably the JB5, listed as "Optionally Available HD Power Brakes".

The correct GM part number master cylinder for JB5 in 1974 is #18000996. NOTE THAT YOU DO NOT WANT AN NOS PART. It will be junk, due to age-hardening of the rubber seals and cup.

That part number cross-references to a bunch of stuff:
http://www.yoyopart.com/oem/11454860/gm-18000996.html

Large reservoir in front on the Bendix cross-reference, no longer available:
http://www.summitracing.com/parts/ben-11944

Summit has an equivalent:
http://www.summitracing.com/parts/su...del/c10-pickup

Re: Restoring Rusty
 

Wow Rich you so went the extra mile for me on this one, THANK YOU SO MUCH. So I just went out there in the dark with a flash light to look at my brake master cylinder and follow the lines. Ok here are the findings.

My front smaller reservoir has the bigger brake line going to it and is for the rear drum brakes

My rear larger reservoir has the thinner brake line going to it and is for the front disc brakes

this don't seem right, I tell ya mine looks like a manual master cylinder instead of power, like this one (Part # 10-1581) from O'Reillys

Re: Restoring Rusty
 

gvwr 5300

gawr frt 2946 rear 2946

will this Service Parts Identification sticker help? What's a J55 code?

Re: Restoring Rusty
 

You should have a prop valve on the front cross member where the brake lines go to.

Re: Restoring Rusty
 

Yeah, that's wrong. Drums require more fluid movement. Disks are all about pressure, not fluid flow. Bigger reservoir should be front on the MC, going to the rears.

Re: Restoring Rusty
 

That's either JB3, or optional HD power brakes JB5.

The JB5 MC (18000996) would handle either.

Re: Restoring Rusty
 

Seems perfectly correct to me.
The larger reservoir is for the disc brake side of a disc/drum setup always.
the caliper pistons displace more volume than drum wheel cylinders.

Re: Restoring Rusty
 

Oh o, you two are gonna have to arm wrestle for this one! I also found this which sides with Titomars

"A dual master cylinder designed to work with a disc/drum setup will feature two different reservoir sizes. As disc pads wear, the caliper pistons will move further outward toward the rotor, causing the reservoir fluid level to drop more than it would for a drum brake reservoir. As a result, a disc/drum master cylinder needs a larger reservoir for the disc brake circuit to keep more fluid in reserve."

Master Cylinder Selection

Re: Restoring Rusty
 

One difference between JB3 and JB5 (I think) is that JB3 is 2" drum and shoes in the back and JB5 is 2.75" drum and shoes in the back.

enaberif is right, all 1973-78 (years of my parts book) had proportioning valves to control the rear brake pressure.

Re: Restoring Rusty
 

yes that is correct, your point being?

Re: Restoring Rusty
 

Nope not happening. I'll pass on my 45 years of auto mechanics and auto dealer experience. you guys can do what you want with it, but I am not here to get into a pissing match with anyone. I am here to help if needed or wanted and to enjoy the shared love for our machines.

Re: Restoring Rusty
 

And we appreciate that, I did go on to say "I also found this which sides with Titomars" as in you are right sir.

Re: Restoring Rusty
 

I checked a couple other sources. I stand corrected. The larger reservoir is for the discs, because they use a lot more fluid as they wear and the pistons move out. The higher flow *in operation* is to the drums. So master cylinders on some makes apparently have bigger lines from the smaller reservoirs to the drums. The (original?) hard lines on mine are the same size. I haven't followed the plumbing all the way over, under, and around, to see what goes where, but they all go to the proportioning valve originally.

BTW, that's probably why your smaller front reservoir is empty. Wanna bet it's plumbed to the front brakes, and as they wore they sucked it all up?

Re: Restoring Rusty
 

All truck or car brake systems with a dual reservoir has a proportioning valve.
JB3 = 1 inch thick rotors and 11x2 shoes
JB5 = 1.25 inch rotors and 11.15 X 2.75 inch shoes
Both use the same master cylinder bendix to bendix or moraine to moraine and both use the same prop valve

Re: Restoring Rusty
 

Now going back and looking at your pics, you have different sized lines, but they are off the front of the master cylinder, which I think now should be to the fronts.

I'm confused.

Discs as they wear use a lot of fluid. Got that. The actual flow to and from the rears as you apply and release the brakes is higher, because the disc pistons hardly move in and out at all, whereas the rear pistons do. Got that. Larger reservoir is for the fronts, so as they wear and the pistons move out and the calipers have to fill up with fluid, they don't suck the reservoir dry. Got that.

But your setup looks confused. Or is it just me? Does your proportioning valve have a colored stripe on it? That is a GM identifier for which one it is. I think you should also track down which lines go where. Getting this right is important.

Re: Restoring Rusty
 

I'm not going to argue with you now! ;)

I'm still trying to figure out what's going on with his existing master cylinder, because small reservoir in the front looks wrong. Unless the lines are reversed as well....

Re: Restoring Rusty
 

The large bowl of the MC is the primary braking system, front..

Re: Restoring Rusty
 

Looking at this replacement proportioning valve, the larger fittings are for the rears.

http://www.carolinaclassictrucks.com...rtioning-valve

I think the lines may have been reversed on gregskis to match the reversed reservoirs. Or maybe it doesn't matter which reservoir is where, as long as the lines are hooked up correctly, and since they're different sixes, that's hard to bugger up.

Re: Restoring Rusty
 

Line size is not that important to us. It is one trick factory engineers used back when these were built to balance the brake system. Nut size is. The different nut size is so someone does not hook the lines up wrong. This next part is assumed the brakes are adjusted per spec. and working as designed.
Actually a caliper piston requires less pressure to provide the same clamping force of a wheel cylinder. So with the same pressure as drums it equals more clamping force. But it does actually travel about the same as a wheel cylinder. caliper pistons on a floating caliper are required to back off (zero pressure) the caliper needs room to float. So there is actually a slight air gap between pad and rotor. A wheel cylinder by design are required to be tight against the shoe or too much fluid is required via pedal travel to get them in an applied state. this is accomplished via a residual valve usually in the master cylinder.
it keeps the drum line charged with a 2 to 4 lb residual line pressure to keep those wheel cylinders charged so when applied they don't move as much as you may think. drum brakes in good order will use about the same fluid volume as discs in good order.

Re: Restoring Rusty
 

I just went out and looked at mine, and the larger line is definitely on the smaller reservoir.

GREGSKI: I think that Autozone unit will work fine, as long as you understand that the lines are going to switch front/back on the MC, so the larger line will now go on the back, in order to keep the larger line on the smaller reservoir. No biggie: they will only attach one way.

Re: Restoring Rusty
 

OK, there I don't agree with you. Leading-shoe drum brakes grab like anything with less pressure than disks. Back in the day, you had Hemi Cudas with four-wheel drum brakes, with double-leading-shoe brakes in the front, and they were manual brakes. They grabbed like anything. But disk brakes are always power, because they take a lot more hydraulic pressure. The leading shoe design uses the cars own motion to pull the shoe into harder contact as they are applied.

BTW, I do think you are right that the line sizes are just to make it easy to get them hooked up right. Like using different electrical connectors. I think either size line is sufficient for either set, it's just to keep them straight.

Re: Restoring Rusty
 

the difference is between manufacturers
Delco Moraine is one way
Bendix is the other way
The lines would be reversed to match the cylinder.
Both of these were used. I would assume this was a supply thing on the assembly line.
Mine the small reservoir is in the rear next to the booster.
With a 454 I definitely have JB5

Re: Restoring Rusty
 

Very cool work. Have I followed from the beginning. Move on

Re: Restoring Rusty
 

OK, that makes sense. And that's why the parts book lists two part numbers: one for JB3/JB5 (Moraine) and one for JB3/JB5 (Bendix).

I have a 350 but I'm JB5 too, but that's because of the higher GVWR on the K trucks.

Re: Restoring Rusty
 

So GREGSKI, the bottom line is that:

1) that Autozone part will work fine.

2) the brake lines are going to reverse to fit the other-way-around layout of the master cylinder.

3) you have a brake fluid leak in your rear brakes somewhere, leading to the empty reservoir. Note my previous comments about rubber age-hardening and shrinking. I would replace the rear brake cylinders on general principles.

Re: Restoring Rusty
 

I didn't see the last line first time through. Off the bottom of the screen I think.

Looks from the parts book like J55 was an equivalent to JB5. Not sure why they used both for the same thing.

Re: Restoring Rusty
 

Yup. The goal is to get the right answers, so gregski can get his truck fixed up. I'm doing the best I can to figure some of this out as well. Some things I know more about than others, but I'm usually smart enough to keep my mouth shut when I'm not sure of what I'm talking about. Usually.

Re: Restoring Rusty
 

really ? drum brakes do not out perform disc brakes never will. The secret with that cuda was probably huge drum brakes or large diameter wheel cylinders in front to stop that elephant. I am not a Mopar fan but had many friends with them. I don't recall seeing drum drum on any of the 70's High performance E-Bodies. But I will take your word on anything Mopar. Disc brakes do require more effort I did not say they didn't we were not talking about pedal effort we were talking fluid volume and I was comparing line pressures not pedal effort. ... at least I thought that. The same pressure against a 3 inch dia piston will always result in more force than a 7/8 piston. Discs require more effort at the pedal because leading shoe technology is a sort of assist from the very design. Where as discs are pure simple clamping force. Disc brakes do not require power assist and there are many examples of non-power assist disc brake cars. I have owned more than a few and they all stopped just fine without power assist. The power assist is advantageous when you have a heavy weight vehicle like a 4 to 5k car or truck. Actually I have an 81 Jeep CJ7 that has Delco disc brakes no power assist and weighs damn near 4k and it stops on a dime. Sorry Bro I am not trying to argue with you, really I'm not. I think we were not on the same page with line pressure and pedal effort.

Re: Restoring Rusty
 

I hear that I am the same way. ;)

Re: Restoring Rusty
 

Yeah, so I don't think we're really much in disagreement any more. Now that I did some reading and got some misconceptions on my end straightened out. I never said drum brakes outperformed disks. Fade resistance alone due to better cooling is a big deal in favor of disk brakes. ABS is nice. So is traction control on a FWD car. Front disks with rear drums is very popular with manufacturers, because drums are cheaper due to not requiring a separate parking brake mechanism. And I should have said factory-supplied disk brakes are ALMOST always power.

Here's where we may differ a bit. I agree with this: "Discs require more effort at the pedal because leading shoe technology is a sort of assist from the very design. Where as discs are pure simple clamping force." But I think drums also require less line pressure under heavy braking. One of the jobs of the combination valve is to hold back the brake pressure to the rears to keep them from locking up once line pressure gets high enough for the leading shoes to start to pull themselves in, while continuing to give full pressure to the front disks. So we may still disagree a bit there. Doesn't matter. Neither of us designs brake systems for a living.

Anyway, I think we have things figured out for gregski to proceed, which is the goal! And I was on the wrong track, so I thank you for stepping in there before I stepped in it any further.

Oh, here's one of those Mopar hemi cars with factory four-corner manual drums. Yikes. Just don't try to stop it a second time for several minutes....
http://www.rkmotorscharlotte.com/sal...Cuda/133019#!/

Re: Restoring Rusty
 

OK, gresgski, we now return you to your regularly scheduled programming. :D

Re: Restoring Rusty
 

Good Lord. That was intense.

Re: Restoring Rusty
 

Wow, I'm way late to this brake discussion, but I'll also back Titomars and say this is correct. Large reservoirs are for discs. The smaller diameter line goes to the front brakes.

Re: Restoring Rusty
 

Damn, that's one insanely expensive car. For that kind of cash I'd rather have an exotic like a Ferrari or even a Pantera with change! ;) But that's me I was never a Mopar fan.

Re: Restoring Rusty
 

No doubt, great discussion though! Lots of Passion, hee hee

Re: Restoring Rusty
 

Just think I've got manual brakes on my '76.....

Re: Restoring Rusty
 

Loving the thread Gregski! I have done many of the tasks you are doing thru the years but its always good to see them again. Your attention to detail, pictures, and wit are very entertaining and helpful to many I am sure.

Re: Restoring Rusty
 

SOLD ~ Well there you have it the story of my life, hour late and $249,899 short

Re: Restoring Rusty
 

Yeah you would think I said "Ford makes the best trucks!" or something, just kidding people, just joking

Re: Restoring Rusty
 

Geez, a nice car to be sure, but 250 grand? No car is worth that to me.