Manual Disc master cylinder

[Andy4639]

I'm going through this now on the ramp truck. The master cylinder I bought was for a 72 C 10 with disc brakes & drums. It was said it was for any Chevy truck for that year. Manual are power, c-10, c-20, c-30.

I'm not home right now but the guy doing the swap says it has a bigger opening than the booster. I will be going home tomorrow and Friday will be taking the parts back and see if we can figure them out, I may look at the 1975 master and see if it looks right.

I can say this though, when I bought the ramp truck it had manual drums all around no power. I bought a power booster for a 71 factory disc to drum truck and installed it with the drum to drum master I had. It works fine, But I did have to swap the push rod out for a shorter one.

[54blackhornet]

Boy this is confusing ?

[jocko]

Originally Posted by Andy4639

The master cylinder I bought was for a 72 C 10 with disc brakes & drums. It was said it was for any Chevy truck for that year. Manual are power, c-10, c-20, c-30.

Whoever told you that was wrong twice. Manual and Power are different MCs as has been discussed above, but an equally important difference exists between C10 vs C20/30. In other words, a 71-72 C10 mc is not the same as a 71-72 C20/30 mc. They are biased and plumbed differently. Front reservoir on a C10 mc is for the front disks, whereas the front reservoir of a C20/30 mc is for the rear drums (note the smaller 3/16" lines are always for disks and larger 1/4" lines are always for drums). 1st pic is C10, 2nd pic is C20 (same as C30). The distribution block is the same - i.e. front is front, rear is rear. To go from a 68 C30 drum system to a 72 C20/30 disk/drum arrangement, you'd technically need a 71-72 C20/30 mc (manual or power, your choice - but note that by 72, power brakes became mandatory on C20 and above), a C10-30 distrib block, and would need to replumb lines appropriately from the mc to the block (front res to rear of block/rear res to front of block) and then replace the remainder of the existing front drum system's 1/4" lines with 3/16" lines for the 71-72 disks. Not everyone does a line reduction in the front, and the system still works of course - but if you want it to stop exactly like a 71-72 C20/30, the front lines should technically be 3/16".

[Andy4639]

I'm beginning to think nobody knows what they are selling anymore. I can't say much right now because I'm not at the house to look at stuff and know. I will figure it out though that's for sure. I'm putting a 86 whole front end in it to make things even worse!

[54blackhornet]

I had a heated discussion with the owner of my local NAPA store about this. He didn’t even believe me about 71 model year trucks having disc brakes up front. As far as his books showing only one # for both power and manual, he’s stands firm. He did ask me for the number cast into the master I have presently installed. I looked but can’t find a #. Can anyone provide a number off theirs ?

[54blackhornet]

Anyone have the # ?

[Andy4639]

I went by and looked at my Ramp truck setup. The master cylinder looks to be for a disc brake system even though it's been on a 4 wheel drum truck. The first 3 pictures are of the booster and master that is on the truck and the push rod.
The last 2 pictures are the O-Reilly part for a C-10,20 and 30 truck for 71-72 disc/Drum master cylinder.
The one in the link is what I ordered today for it. It looks like what is on the truck now. It's a 76 master cylinder for Disc/Drum.
As far as which way the bowls are for the disc/drums it don't mater as long as you hook the lines up to the correct one.
Hope to know later today if it's the right one. It's suppose to be at the store by 2pm.




https://www.oreillyauto.com/detail/b...cylinder&pos=3

[jocko]

Thanks for sharing the pics Andy. Pic 2 looks like a non-power mc to me and Pic 5 looks like a power mc to me (or maybe Pic 2 just "looks" that way in the pic - question, is it the exact same indent as the piston in pic 5 or is it deeper (which is how it appears to me?)). Reservoir size difference is not necessarily the full reason for how you hook up the lines between the mc and the distib block (but they can be "a" reason since some mcs have uneven bowl sizes, just not necessarily in these trucks) - internal biasing is also a reason. Recall the distrib block is not an adjustable prop valve, so the order and amount of juice applied front/back is managed inside the mc and is not adjustable. If you hook up a C20 mc front bowl to the front brakes, you will be providing the opposite of factory biasing in the mc from what GM designed. In other words, a C20/30 mc uncovers/opens the brake fluid passages differently when the piston is depressed than a C10 mc does.

Or maybe a better question would be - if GM hooked up the C20 mc as depicted above in pic #2 of post 29, why NOT replicate it? Why say it doesn't matter when clearly GM hooked up the lines on a C10 and C20 differently - it wasn't a simple matter of choice for the guy working the assembly line that day? Again, I'm just talking about trying to replicate a stock system. If talking 4-wheel disks and so on, then different story. But believe you are trying to replicate a 72 C30-equivalent system(?)

As for the link to the mc you ordered, I only see C/K-5/10 in the applicability chart, no C20/30 anywhere.

[sammywells]

Lots of info and i'm still following along, Thanks for all the replies.

[Andy4639]

Originally Posted by jocko

Thanks for sharing the pics Andy. Pic 2 looks like a non-power mc to me and Pic 5 looks like a power mc to me (or maybe Pic 2 just "looks" that way in the pic - question, is it the exact same indent as the piston in pic 5 or is it deeper (which is how it appears to me?)). Reservoir size difference is not necessarily the full reason for how you hook up the lines between the mc and the distib block (but they can be "a" reason since some mcs have uneven bowl sizes, just not necessarily in these trucks) - internal biasing is also a reason. Recall the distrib block is not an adjustable prop valve, so the order and amount of juice applied front/back is managed inside the mc and is not adjustable. If you hook up a C20 mc front bowl to the front brakes, you will be providing the opposite of factory biasing in the mc from what GM designed. In other words, a C20/30 mc uncovers/opens the brake fluid passages differently when the piston is depressed than a C10 mc does.

Or maybe a better question would be - if GM hooked up the C20 mc as depicted above in pic #2 of post 29, why NOT replicate it? Why say it doesn't matter when clearly GM hooked up the lines on a C10 and C20 differently - it wasn't a simple matter of choice for the guy working the assembly line that day? Again, I'm just talking about trying to replicate a stock system. If talking 4-wheel disks and so on, then different story. But believe you are trying to replicate a 72 C30-equivalent system(?)

As for the link to the mc you ordered, I only see C/K-5/10 in the applicability chart, no C20/30 anywhere.

Picture 2 has the booster hooked to it now. The one I sent the link to is for about any vehicle GM built and as far as I know everything past 72 had power brakes for the masses. You had to special order a vehicle after 72 without power brakes.
The computer said it fits all them at the store. They don't show separate part numbers for them.

Oh the master they got this afternoon wasn't right either. It was a shallow one. Maybe the one in the morning will be right.
Just for info I don't care what year it is are what part it is for as long as it works and will stop the truck. As far as the bowls they don't matter if they are front are back. When you push the brakes they both react it only when one side has a problem but they both react the same. I'm not using a normal proportioning valve I bought adjustable one.

[54blackhornet]

My local Napa owner crossed referenced 29881 to a current Napa # for a non power disc 71/72 cylinder. He ordered one for me. Will get back with the new #.. Jack

[54blackhornet]

You are incorrect stating that one master will work properly for both manual and power ! I have confirmed this by my local Chevrolet parts manager. He still remembers this issue from the days these where still available from GM.

[Andy4639]

Went to O-Reillys this morning and here is the master cylinder they finally got me. Part # 11364 looks to be for a long push stud and booster like what I need. Fitment is for a 74 thru 86 with disc brakes and drum. It looks to be just right.

[dmjlambert]

"long push stud and booster like what I need"
Well I thought the long push rod was for when you were not using a booster. So is that for power brakes or non-power brakes? What is the bore size?

[sammywells]

I've reached the conclusion after 40 post on this that there is not a master cylinder for manual disc brakes for a 71-72 c10. I"ve checked all the parts houses NAPA, Advance, Auto zone, Oreillys and looked all over the internet including cardone, wagner, raybesto. The only factory stock master cylinder that seems to be available is the one with 1 1/8 bore for both power and manual brakes. Looks like i need to make a decision on that one or aftermarket.

[jocko]

Originally Posted by dmjlambert

"long push stud and booster like what I need"
Well I thought the long push rod was for when you were not using a booster. So is that for power brakes or non-power brakes? What is the bore size?

You are correct. A master cylinder with a deep hole in the piston is for non-power applications. A master cylinder with a shallow hole in the back of the master cylinder piston is for power brake applications with a booster.

Originally Posted by sammywells

I've reached the conclusion after 40 post on this that there is not a master cylinder for manual disc brakes for a 71-72 c10. I"ve checked all the parts houses NAPA, Advance, Auto zone, Oreillys and looked all over the internet including cardone, wagner, raybesto. The only factory stock master cylinder that seems to be available is the one with 1 1/8 bore for both power and manual brakes. Looks like i need to make a decision on that one or aftermarket.

Sammy, I am not just not tracking... Again, the correct non-power master cylinder part # for a 71-72 C10 is at the bottom of post #7. It is available at LMC.

[sammywells]

I did call lmc but was caller 20. I"ll try back on monday. Thanks

[54blackhornet]

THERE Is A Master For Power Disc Brakes AND One For NON POWER Disc ! You can’t go off what some young kid says behind the counter ! Nor can you trust the computer they use ! Go to Rock Auto or ask your NAPA guy to go get his old books. It’s clearly shown in the old paper catalogs. GM didn’t take any short cuts concerning proper engineering on brake components.

[sammywells]

Just called Lmc trucks and got through this time. They have 2 master cylinders. One for power one for manual. They sent me a pic of both. The one for power looks like the corvette style both tanks the same size with a 1 1/8 bore. The one for manual looks like a regular master cylinder with one tank larger than the other with a 1 1/8 bore. Could it be that the factory bore is the same on both.

[sammywells]

will wait on your part number. My napa guy looked into it last week for me but no luck.

[Andy4639]

Originally Posted by dmjlambert

"long push stud and booster like what I need"
Well I thought the long push rod was for when you were not using a booster. So is that for power brakes or non-power brakes? What is the bore size?

74 to 86 C-30
Bore Size (in): 1.32 Inch
Port 1 Thread Type (Forward): Inverted Flare, Port 1 Thread Size (Forward) (in): 9/16-18 Inch
Port 2 Thread Type: Inverted Flare,Port 2 Thread Size (in): 1/2-20 Inch
The booster has a fixed rod in it. The picture shows it. The master should be for either power are manual.

https://www.oreillyauto.com/detail/b...?q=11364&pos=0

[dmjlambert]

I think this topic needs more evidence. It will be nice to hear:
1. what 54blackhornet gets from NAPA, and what the push rod hole looks like and what the bore size is, and
2. if anybody has used the 84 c10 manual brakes master cylinder with 1 inch bore KQQL IT mentioned, and if it has the deeper push rod hole, and works on a 67-72 C-10
3. if there is anybody left in the world with manual disc brakes on a 71-72 C-10 that work well to measure the bore size and show casting number.

[54blackhornet]

ANDY we aren’t interested in a part number for later vehicles. We are interested in the proper cylinder for a 71/72 truck with non power disc brakes l Appreciate your project converting from drums to disc but totally different topic. As confirmed by the above information, there are two different cylinders per GM’s engineering

[Steeveedee]

and

4. How far the push rod mounts on the brake swing arm from the pivot point for both power and manual brakes. I always remembered that the manual master cylinder had a smaller bore for more hydraulic force. I've also seen here that the push rod mounts in a different place. If we can get some measurements, maybe we can establish some ground truth.

[54blackhornet]

It is amazing that something so vital to folks safety is so confusing ? The one part that fits all mentally don’t work in this situation.