Master cylinder ID?

[chevy72blu]

Getting the truck back on the road after sitting for 6 years, its probably a good idea to go through my brakes. I'm noticing a bit of sponginess and "pedal sink" while sitting at stop lights, so I've narrowed it down to the MC and fluid flush (I put new pads and shoes on with only a few thousand miles on them before it sat, so I see no reason to replace them unless there is a problem).

I am 99% sure I have a 1 ton booster, but I am not sure what MC to buy as a replacement. Any ideas? I'm thinking 73-87 3/4 ton

[ole dollor]

not sure of the year model you have, but it may have a # on it, or if you can take it off and take it with you to the parts store, and maybe they can match it up.

[SS Tim]

Couple of things.

First I'd take a look at the three brake hoses and probably replace them. Pull the drums and inspect everything particularly the wheel cylinders for leakage. Might sand the drums if they are rusty and adjust the brakes up close. Then see what the master cylinder feels like.

What I don't understand is why you are not thinking about a 71-72 master cylinder as a replacement?

[FirstOwner69]

Looks like a Moraine master as used on 71 & 72 3/4 and 1 tons. AC Delco closeouts at Rock Auto for $25.79.

[chevy72blu]

Thank you all for the responses!

Originally Posted by SS Tim

Couple of things.

First I'd take a look at the three brake hoses and probably replace them. Pull the drums and inspect everything particularly the wheel cylinders for leakage. Might sand the drums if they are rusty and adjust the brakes up close. Then see what the master cylinder feels like.

What I don't understand is why you are not thinking about a 71-72 master cylinder as a replacement?

Do you mean the rubber hoses? I should take a look at that also. Thank you for the tip on the drums - I'll go through my factory service manual (I dont have much experience with drum brakes).

I am just trying to find out what I have so it is a direct replacement. When your truck is a frankenstien of parts from various years it makes things a bit more difficult than they should be

[SS Tim]

Do you have both the service and overhaul manuals?
http://67-72chevytrucks.com/vboard/s...d.php?t=558016

Hoses are often neglected but important components.
A fluid flush is always a good idea on a vehicle that has been sitting.
If you are buying local take the old master cylinder with you (loose) once you have confirmed they have a repalcement in stock. Or at least take a hard look against your pictures before buying it.

[Daaaanz67]

I just replaced my master on my 69c 10 it was sort of a Frankenstein also. I went to oriley and asked for a master for a 71/72 and when they looked it up for my application they said we have one that covers 67/72. I said how can that be when disc didn't come out till 71. Anyways the master I got was identical to yours. I measured the bore and they were both approximately 1 1/8 dia. Also measured the depth of the hole for the rod and both the same. I can try to find the part # if you like.
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[Daaaanz67]

Oh yeah forgot to mention the truck has 71 discs.
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[chevy72blu]

Thank you all for your time!!

I have the factory assembly manual (which has been less than helpful with no part numbers) and a factory service manual which has proven to come in handy. I found the rubber hose going to the drum in the rear which seems to be leaking slightly. That could be the issue right there. I could look it up myself, but do you have the part numbers for the rubber hoses (and the other two locations)?

Thank you Daaaanz67, that is exactly what I wanted to know! My truck was shipped with manual brakes so I have never really known where the power came from. The 72 is also serving DD duties for a while so its important to know that I have the right parts before puling it apart

[SS Tim]

While I can pull up the factory part numbers it would be real helpful to know what you have. There seems to be conflict when I read you have a 72 with "added" disc brakes, no booster and a front rebuild parts list for a 72 C20.
Fact is a 71-72 would have had disc brakes. Only C10s came through without a booster (it was optional factory or dealer).

The three hoses are of course the frame to rear axle, left front frame to caliper and right front frame to caliper.