Stock 230 master cylinder

[militarypotts]

While over the last 8 years, I've tried to do all of my own work on the truck, I need to ask the better mechanics than me out there about the stock master cylinder.
I've developed a leak in the cab of the truck near the brake pedal linkage.
I pretty much figure it's a seal on the M/C piston rod.
I've never attempted a rebuild of the master cylinder and was hoping someone on the zone could walk me through it, start to finish.
I've seen the rebuild kit online and also new master cylinders. In your opinion is it better to just get a new M/C, or the rebuild kit?
Not sure what's involved with removing the old one and putting new parts in it. I know this would be the time to upgrade, but only driving about 350 miles a year, I'd like to keep the old one.
One other question, why do the newer stock master cylinders I see not have a vent tube on top going to the air cleaner mushroom?
Hope you guys bear with me on this one, as I want to do it myself, but need all your knowledge to do it. Thanks guys.

[MrNeutron]

I think this is what I used to rebuild the stock mater cylinder in my truck:

http://www.napaonline.com/Catalog/Ca...236_0380049626

It was pretty easy to do. The only reason you should ever need to replace the whole master cylinder is if the bore where the piston has to seals against is all rusted out.

[Barrman]

Rebuilding a stock master cylinder is very easy. A bench mounted vise makes it even easier. You will need a snap ring plier to get the piston out. Otherwise it is just a matter of making everything clean. Then clean it some more and then some more.

A cylinder hone will help if bad rust has built up. New seals should be considered, but you can get by with the old ones as long as they are not torn. I would suggest new ones no matter what unless you are stuck out in the middle of nowhere and have to get home.

Have fun doing it and make sure to watch your feet as you carry it around. They leak all over the place.

[militarypotts]

Thanks guys. After putting in the new piston and seals, is it just remounted on the firewall, or do you need to bench bleed it? It would seem to me that it could be bled after reinstalling it and before the brake line gets put back.
Is all of the work done from the engine compartment side, or does something need to be done up under the dash on the pedal linkage?
Sorry for all the questions, but this is all new to this old man.

[Don Cavey]

Thanks guys. After putting in the new piston and seals, is it just remounted on the firewall, or do you need to bench bleed it? It would seem to me that it could be bled after reinstalling it and before the brake line gets put back.
Is all of the work done from the engine compartment side, or does something need to be done up under the dash on the pedal linkage?
Sorry for all the questions, but this is all new to this old man.

This may be "Backyard Mechanic Stuff" but you should be able to put the master cylinder back on the truck, crack the line loose a little (two man job). and "bleed" it similarly to how you do the wheel cylinders. Get all of the air out until you have good fluid flow, then go to each wheel, most farther first, and bleed each wheel cylinder. That should get you a firm pedal.

You may also want to get a NOS master cylinder from one of the vendors. I got mind from Saturn Surplus (drove there) and took it apart, cleaned everything with alcohol, lubricated it with new, clean brake fluid and reassembled it. I then installed it and... it just worked and worked well.

I think cleaning it before using it is important because any contamination that might be there will be noticed and removed. Also, you will know exactly what you have.

You may want to get another NOS spare. (I have one) because they are really not that expensive. I will say that the new ones have the outlet 90 degrees from the original. But it was easy just to make a new piece of tubing and do the bend.

[Barrman]

Bench bleeding can be done several ways. A hose in the line port that goes up to the resevoir and stays under the fluid while you push the piston with a screw driver or something until all the bubbles are gone. Another way is to just plug the line port and push slowly until no more bubbles come up from the cylinder. I like that way better. I really like doing it on the truck with my foot doing the pushing on the pedal. Less chance to spill brake fluid everywhere in my opinion.

Yes, everything can be done firewall side only.

If you have fluid leaking out, there is a good chance you have run dry and the entire system needs to be bled of air. The best thing about the military master cylinders is the screw on cap. That allows a power bleeder which is so amazing compared to any other style of bleeding.

Here is a thread by Warthog talking you through one way of doing it:
http://m715zone.com/vb/showthread.ph...+brake+bleeder

Kenny, 4x4Recovery, on SS has a super informative thread on SS about it from years ago. He also used a garden sprayer for the tank.

[Don Cavey]

I bled my master cylinder by clamping in in the vice on the bench and doing as described (several times!) above. I used a screwdriver and pushed the piston in whilst holding my finger over the outlet hole. Took one minute. Then, I bled the rest of the system.