I noticed its leaking into the cab when the brake peddle is depressed. I'm wondering if anyone has an idea of repairing the thing. I know I can buy a new one and there is no repair kit but I have acess to all sorts of material and tools. Is it just a rubber seal or ? I'm planning on taking it apart soon. Rosco
I suspect that it is the brake master cylinder, not the brake booster, that is leaking if brake fluid is coming into the cab. Rebuilding master cylinders is not something that many experienced technicians can do, much less a do-it-yourselfer. I recommend replacing the master cylinder rather than attempting a re-build.
Like Ray O said, and whether you rebuild or replace with a rebuilt, make sure you bleed it on the bench before installation. It will save a lot of time and hassle.
Do not bench bleed the brake master cylinder. You can ruin it by doing this. Install the cylinder on the vehicle in the original position and do not hook up the brake lines. Put in clean fluid. You will need a plastic (or brass if you prefer) fitting for each of the outlets with a rubber hose that's long enough to route the clean brake fluid back into the master cylinder. Make sure the ends of the tubes stay submerged in the fluid. Pump the brake pedal slowly until you stop seeing bubbles in the fluid. Remove the fittings and install the brake lines.
Doing it this way makes sure you do not screw up the new master cylinder.
A lot of new master cylinders come with these bleeder fittings in the box. Check at the store and if they are not in there, ask about them. They are very handy.
And please just explain how bench bleeding damages it?
you could push the rod too far or too hard when not using the brake pedal to do it.
That is total nonsense. Bench bleeding not only eliminates a probable mess in the engine compartment and floor, but a possible paint repair issue (splashing fluid) as well. Bleeding off the vehicle will remove the air more efficiently for one of the exact reasons you mentioned in your reply, you usually can get a longer stroke. Even when pressure bleeding from a reservoir it's really hard to remove all the air from a new master when it's bolted up. You can do it either way, and most DIYers bleed bolted up, but bench bleeding is preferred for all the reasons I mentioned and is normally recommended.
well in the circles i've run in my short life, i have discovered you can indeed ruin a master by pushing the piston too far on the bench. Not to mention it seems a lot less shadetree to use the brake pedal to bleed the master instead of something that fits in the hole in a vise. Not saying *you* would mar the mounting flange on the master in a vise or even mess up the new master, but many first timers might. Yodas are pretty bullet-proof, but there's no sense running the thing in any further than it would be run with the pedal under even the toughest braking.
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