Restoring Rusty

[rich weyand]

I feel bad about that, since I recommended it. I have never had that kind of delay from that supplier.

[Gregski]

Originally Posted by rich weyand

I feel bad about that, since I recommended it. I have never had that kind of delay from that supplier.

No worries bro, you have helped me so much, this time frame is a first for me too.

[rich weyand]

Looking deeper, I can nail it down exactly if you tell me the GVWR on the door sticker. Add the front and rear axle ratings, I just need the total.

[Gregski]

Originally Posted by rich weyand

looking deeper, i can nail it down exactly if you tell me the gvwr on the door sticker. Add the front and rear axle ratings, i just need the total.

gvwr 5300

gawr frt 2946 rear 2946

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

[rich weyand]

Originally Posted by Gregski

gvwr 5300

gawr frt 2946 rear 2946

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

The JB5 MC (18000996) would handle either.

[rich weyand]

Originally Posted by Gregski

gvwr 5300

gawr frt 2946 rear 2946

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

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.

[enaberif]

Here is a writeup I found elsewhere that really brakes down a lot of the common brake setups.

http://goo.gl/m0Zh1I

[rich weyand]

Originally Posted by enaberif

Here is a writeup I found elsewhere that really brakes down a lot of the common brake setups.

http://goo.gl/m0Zh1I

Oh, and note that both of those pictured have the big reservoir in the front.

[rich weyand]

Yeah, my truck should have a JB5 setup, but when the garage replaced the original master cylinder because the cup was age-hardened and passing fluid (pedal would slowly sink to the floor as you held it), they put the big, honkin' JB7 master cylinder on it, which is fine. Going to a LESSER duty part would NOT be good.

[rich weyand]

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

[Gregski]

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

[enaberif]

Originally Posted by Gregski

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

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

[Gregski]

Originally Posted by enaberif

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

yes that is correct, your point being?

[rich weyand]

Originally Posted by Gregski

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

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.

[Titomars]

Originally Posted by Gregski

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

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.

[Gregski]

Originally Posted by rich weyand

Drum brakes take a lot more fluid movement than disks, which hardly move at all. So if the front reservoir is for the rear brakes, I would expect the front one to be larger on a disk/drum setup.

Originally Posted by Titomars

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.

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

[Titomars]

Originally Posted by Gregski

Oh o, you two are gonna have to arm wrestle for this one!

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.

[Gregski]

Originally Posted by Titomars

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.

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

[rich weyand]

Originally Posted by Titomars

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.

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.

[rich weyand]

Originally Posted by Gregski

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

"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

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?

[greg64]

Originally Posted by Titomars

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.

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.

[rich weyand]

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.

[Titomars]

Originally Posted by rich weyand

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.

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

[rich weyand]

Originally Posted by Titomars

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

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....

[craig113]

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