what steel to use?

[Crazy Ed]

What steel would you recommend for a high pressure app such as brake master cylinders and what wall thickness? This would be for a 2 ton truck that is needs new cylinder, and the orginal had poor design as it was easy to go to the floor IF the slightest wear wasn't adjusted out of the shoes. My friend wants to make slightly longer cylinder for more volume than the stock one that came with it. I think he has 'swapped' out the front and rear end and the factory unit just doesn't 'haul the mail to red rock' anymore. The truck is old..about 1962 and been sitting since '72 or 3 I think. I have casually looked at it and there are a bunch of things that need changed as a result of 'modifications' he has done previously to the 'undercarriage' of this old truck.

Would 4130 rod bored out work? or what metal??

[CCWKen]

They only build up between 1800 and 2200psi. A few go higher. The new stuff is aluminum. The old stuff was cast iron with aluminum pistons. I think SS would be fine. Looks cool too. The wall thickness on the aluminum MC's are only about .160". That's what makes them hard to "save" with a sleeve. Besides, they're cheap enough to buy new (rebuilt).

You might go to a truck salvage yard and get one to rebuild (or modify). If you go with a stock ID, it will be easier to get repair kits. Get one that's in the 70's or 80's for 10k GVRW.

Also: Sounds like you (he) has air in the lines, the flex lines are ballooning or the MC is leaking by the piston seals.

[Crazy Ed]

I have known Wes long enough to know that there was no air in the lines. And he said that before it was parked, when the problem was there, he had changed out a lot of the braking system and that the smallish master cylinder just couldn't produce enough volume. At that time he had exhausted changing out for different ones as the ones that fit volume wise wouldn't fit in the restricted space due to the way they were built. This master cylinder has a 'remote' tank, that is unlike most, it has a tube from a 'firewall/bulkhead' mounted tank to the actual cylinder. Weird setup. I haven't been in the 'backyard' for awhile and don't remember what make/model/etc it is, but it is a strange machine.

Thanks, I thought it didn't need that much strength. I was thinking that using some thick wall (.120-.188) cromo dom tubing (4130) and honing smooth if needed. Or if needed boring slightly to 'fit' the piston/seals. It shouldn't be rocket science to make it and mount it. A small turn on the outside to make the 'clamp' hold it, say .050 or less should hold the cylinder against the pedal pressure, or just mount it in a bore in a block of steel that is a press fit on the other side of the pushrod.

Wes hates aluminum..weird guy that way.

Thanks again, and you're right, it shouldn't have 'extreme' pressures..otherwise the failure rate would be very high. Not to say that 2k isn't low pressure, but not extreme pressure.

[barts]

I'd use either bronze or cast iron. The odd
thing about brake fluid is that it absorbs
water rather well... use a material that doesn't corrode and you'll get longer service
life.

- Bart