[beck]

There was a lot of information in the archives but I still have questions.
There have been several posts with master cylinder sizing and part numbers. None of those posts has information stating what MC is used with what wheel cylinder sizing. My project uses a 80s GM ½ ton chassis. That is disc front and drum rear. I have read of guys using from1” to 1 5/16” bore MC. I think the quality of the brakes can be fine with either if they are matched to the right caliper and wheel cylinder.
Does anyone have a suggestion on what MC to use in combination with my brakes?

I have the stock P30, and the stock GM truck master cylinder. From what I read, the GM unit probably won’t bolt to the hydroboost system. The bolt pattern looks right, but the snout of the MC won’t go into the hydroboost. Right? I have not taken the 2 units apart to check.

What fluid is everyone using? Power steering fluid or ATF?
Is a cooler necessary? There wasn’t one on my P30.

 

[Machman]

Unless you're doing something intentionally other, keep it "factory stock" as much as possible from one end to another.

If you want hydroboost, then choose a hydroboost system and copy it: calipers, master, booster, wheel cylinders, line sizing, and proportioning / splitter valve. The factory puts a fair amount of engineering into brake systems to make them balanced and controllable. Nothing is quite as much fun as having brakes that don't have anything to offer until you're at the floor, except maybe those that go into full lockup with less than 1/2" pedal travel.

Now, I'm not saying that combos other than factory won't work, in some cases the result from mixing things up a bit can be superior to original, but unless you've got hard information supporting changing things around, or want to spend a lot of time and money experimenting, leave it stock.

Oh, and you're right that a vacuum boost MC won't fit a hydro booster.. IIRC someone here was turning the snout down on vacuum boosters to fit hydros for some application, but if there's a hydro MC available and appropriate for your application, I'd say go with it instead of the modification.

Except for those vehicles that have a specific requirement for power steering fluid, I've always used ATF. I do a flush and fill on it when I do the transmission. I don't know if I'd consider a PS cooler a critical item, but wouldn't be a bad idea, especially if you're doing a lot of off-road or in-town driving. But, if you're using a hydraulic winch, such as the Mile-Marker units, then I'd say that a cooler would be required.