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 |
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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 |
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gawr frt 2946 rear 2946 will this Service Parts Identification sticker help? What's a J55 code? |
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That's either JB3, or optional HD power brakes JB5. The JB5 MC (18000996) would handle either. |
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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. |
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"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. |
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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? |
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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 |
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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. |
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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.... |
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The large bowl of the MC is the primary braking system, front..
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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. |
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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. |
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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. |
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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. |
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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 |
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Very cool work. Have I followed from the beginning. Move on
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I have a 350 but I'm JB5 too, but that's because of the higher GVWR on the K trucks. |
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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. |
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Looks from the parts book like J55 was an equivalent to JB5. Not sure why they used both for the same thing. |
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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#!/ |
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OK, gresgski, we now return you to your regularly scheduled programming. :D
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Good Lord. That was intense.
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Just think I've got manual brakes on my '76.....
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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.
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