Brake master cylinder

[Jim Gaspard]

I am replacing my B3B brake master cylinder this weekend with a new one. I pulled out the piston rod from my old one and it's pittted here and there. There doesn't appear to be a lot of discussion on this subject on the truck side.Where is the line drawn between "you can use it" vs "you need to replace it"? Can this part be found in the local auto store as replacement stock for old trucks, or do I need to start searching for a better condition used replacement? Thanks for advice....and a part number if handy.

[Young Ed]

Jim is this the piece you mean? Well this along with the piece that threads onto it.

[HanksB3B]

I got mine from Gary Roberts. No fitment issues and the price at $129 was $50 less than Napa wanted. The only funny thing was (and I brought this to Gary's attention) that the square plate at the top needed to be reversed so that the filler plug was more forward for easier access (see pic). There were only six bolts, the gasket is not cemented and the position of the filler plug has nothing to do with anything other than filling the rectangular reservoir. I know you said "this weekend" so I am probably writing in vain. Good luck and let us know what you find and how it goes. Not sure about the pushrod though.

Hank

[Jim Gaspard]

Yes, my new replacement master looks exactly like the one posted below by Hanks3B3, had it for some while and can't remember where I bought it. The piston rod attaches to the right piece posted by Young Ed. The piston rod is the part that fits into the boot and its pitted, more at the boot fitting than the male end. Everyone agrees, shouldn't cut corners with brakes. Where can I find a good NOS or NORS piston rod?

Jim

[HanksB3B]

the cover plate 180deg. It's just easier before the install. Check our truck manual and you'll se what I mean. The picture of the pushrod doesn't really show how badly the pitting condition is. If it's not a structural concern wouldn't just sandblasting or wire brushing do the trick? There is no hydraulic interface between the pushrod and metal socket of the MC. The rubber boot just shields the dirt.

Hank

Edited March 13, 2010 by HanksB3B

[Jim Gaspard]

I dug one out of my parts bin in less corroded condition. But I am intrigued by the "turn the plate 180 degrees". I need to investigate that.

[grey beard]

Jim,

They're talking about the top cover. They're just asseemled backasswards from the way a Pilothouse should be. I went to the trouble of adding a remote m.s. reservoir on my firewall, so I would never have to service the thing in its impossible original position, but I also have the type Roberts sells with the six bolts holding the top olate in place, and it is not made for a head pressure from above. Result, is my MS leaked until I took the remote reservoir off. Now it works just fine. I use DOT 5, and like it.

Good Luck

[pflaming]

I went to the trouble of adding a remote m.s. reservoir on my firewall, so I would never have to service the thing in its impossible original position, but I also have the type Roberts sells with the six bolts holding the top olate in place, and it is not made for a head pressure from above. Result, is my MS leaked until I took the remote reservoir off

I have the same 6 bolt lid MC. I want to add a remote reservoir. If the lid does not hold that down pressure, then I am out of luck? Will a gasket work?

[wallytoo]

while i don't exactly have a remote reservoir, i've added a permanent filler pipe to the MC so that the fill location is about even with the top of the fenders. when i fill this, my MC doesn't leak at the cover. alas, my MC is the original, and not a newer one, so perhaps it has slightly better construction, or more gunk in it to prevent leaks.

wally

[HanksB3B]

Why all this re-engineering? I filled my MC two years ago and I'd be hard pressed to get more than a 1/2 oz. in there. Excuse me for being opinionated but this has to do with stopping a vehicle you've probably spent the better part of two years working on. You can jump all over me on this one but I say if you are feeling a need for a brake reservoir then either 1. You are very lazy or 2. There is something wrong with your leaky master or slave cylinders that really justify the proper attention.

I apologize for the rant, but them's the brakes!

Hank

Edited May 31, 2012 by HanksB3B

[Dave72dt]

Without an external leak, you should never have to add fluid. It's a closed system. The level goes down as the shoes wear and should come backup when you readjust. Lid won't leak unless the MC has a poor sealing suface or the lid is warped and they don 't need to be filled to the brim. 1/4inch down is fine.

[Jerry Roberts]

Actually , a little bit down from the brim is BEST . If your master cylinder is filled to the very top , it will leak out of the tiny vent hole in the master cylinder cap .

[pflaming]

I installed my MC today. Before I put the 6 bolt plate on, I stretched some electrial tape where the gasket would go. It revealed all sorts of debri so I redid my surfaces. Then I put clean electrical tape back on as a gasket. Was that a mistake?

[ggdad1951]

Actually , a little bit down from the brim is BEST . If your master cylinder is filled to the very top , it will leak out of the tiny vent hole in the master cylinder cap .

and depending on the type of fluid, eat the heck out of your paint

[HanksB3B]

I installed my MC today. Before I put the 6 bolt plate on, I stretched some electrial tape where the gasket would go. It revealed all sorts of debri so I redid my surfaces. Then I put clean electrical tape back on as a gasket. Was that a mistake?

you'll find out.

Most of my gaskets are a combined effort of a pencil rubbing (I call it tombstone etching, but Ive never done that) which is made by taping paper to the part and using a blunt pencil or better yet a carpenters pencil. I then make a print of this onto clean paper, tape it to gasket material, punch the holes with that $6 hole punch set from Harbor Freight and then use an Xacto No 11 blade and a combination of free hand curves and a straight edge will make almost any gasket look and fit like factory made.

Hank

[TheMoose]

I installed my MC today. Before I put the 6 bolt plate on, I stretched some electrial tape where the gasket would go. It revealed all sorts of debri so I redid my surfaces. Then I put clean electrical tape back on as a gasket. Was that a mistake?

I'm guessing the brake fluid will eat electrical tape, if you have any overlap into the fluid area you may end up with electric tape goo in the brake fluid.

I'd get it out ASAP if it was me.

[HanksB3B]

I'm guessing the brake fluid will eat electrical tape, if you have any overlap into the fluid area you may end up with electric tape goo in the brake fluid.I'd get it out ASAP if it was me.

I agree with the Moose.

Hank

[John-T-53]

A remote reservoir is on my to-do list too. It'll make bleeding a lot easier (for the refilling part). I'm always taking something apart that requires bleeding, and this will make things easier. Also, every couple years, its a good idea to replace the fluid in the entire system to keep your cylinders from rusting and fouling the piston cups.If there's leaks at the cover gasket, I'm sure some Permatex or RTV would be the solution to help the gasket do its work.

[Merle Coggins]

If you really want to seal up your cover, get some Loctite 515 Gasket Eliminator. Clean the surfaces very well, apply a thin bead around the top surface of the MC and install the cover. Wait a few hours before adding fluid to allow the sealant to set up. It will form a hard plastic type seal between the two metal pieces. We use it all the time between two metal flanges. It works great. You just have to give it some time to set.

Napa sells a similar product in Permatex brand as Anaerobic Gasket Maker