How to get the right Master Cylinder?

[msg]

Ive got a master cylinder that I pulled from my 66 during the rebuild in 2015. I went to pull it out of the box and saw that its gotten pretty rusty and might need replacing. Since the brakes were converted to disc Im not sure what year to put into the auto parts stores websites for replacements and Id like to get a new one. Whats the best way to match this thing up with a new one?

[Steeveedee]

There isn't a casting number on it? You should be able to match it if you take it to the parts store. You know the brake rotor and drum diameters? That info and what size- 1/2T or 3/4T should be enough to get you a comparable master. You'll have the master piston diameter available to compare as well.

[jayoldschool]

Front discs only or four wheel?

[msg]

Ill take a look for the casting number tomorrow. Its a 1/2 ton with a front disc conversion and rear drums.

[jocko]

a new 71-72 mc (and make sure to specify as 1/2 ton and also power or manual when buying) should work just fine.

[msg]

I couldnt find any casting numbers. I took it by the shop that did the disc brake conversion for me many years back and was told its likely a mid 70s corvette MC. It came in a kit and he didnt know for sure. He said he would just clean it up and reuse it.

[jayoldschool]

Bad advice. The Vette is four wheel disc brakes. Jocko has the right advice, get a truck front disc master from a local source.

[msg]

Ill check local sources for the 1972 which are the usual, NAPA, Advance Auto, Etc but a search on their sites show brands like Carquest Wearever $54, NAPA Ultra Premium $70, and the Rockauto site has an AC Delco for $44 and it looks like what I have now

https://www.rockauto.com/en/moreinfo...sn=594&jsn=594

Is there a brand you guys like better?

[jayoldschool]

I got my truck dual local from my Delco supplier, but when I did my 65 Impala dual conversion last summer, I was out of school so I just ordered one off Amazon. Also Delco.

[Steeveedee]

The thing about a Corvette master cylinder that makes it probably the wrong choice, whether it had disc/disc or disc/drum, is that our trucks don't have a close to 50/50 weight distribution on the axles like a Corvette does. Maybe not a big deal under normal braking conditions, but in the wrong situation, it can be bad news.

[msg]

Thanks guys, I just ordered the AC Delco from Amazon

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Its the same part number that came up in Rockauto for a 71-72 C10


I also ordered this nickel copper 1/4 inch line to run since that was the size that the lines that came down to the from discs, then it reduced down to 3/16 to the drums. Is that ok to do again, or should I go 1/4 all the way? Never done brakes before.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[jayoldschool]

They went to 1/4 on the rear line in 66 I believe. I kept the smaller line on my 65 even though I ran new line. It's fine, brakes are great (dual master, drum/drum, non power).

[jocko]

Disk lines are 3/16” and drum lines are 1/4” from the factory. An all drum truck would have all 1/4” lines. If you convert to front disks, as has been done on your truck, you can leave the 1/4” all the way around or change only the fronts to 3/16” (to build it the same way the factory did). However, 3/16” to the rear and 1/4” to the front, as you mentioned you have, is incorrect - recommend double-checking that.

[msg]

As long as its ok to do and doesnt make something have the wrong pressure I was hoping to go 1/4 all the way round for all. From what youre saying Jocko its ok to do that right? Pretty sure thats what you were saying, just double checking.

Also, for fluid is the DOT3 what I should use or DOT4? Is there a brand that is better than others?

I heard that DOT 5.1 is great cause it doesnt get contaminated by moisture but I dont know if that AC Delco MC can use it.