brake master cylinder rebuild

[faiyaz]

hello, im planning on rebuilding the brake master on my sfa hilux, does any have any tips or tricks , anything i should look out for , or basically a method . I managed to get new seals for the pistons as one of the seals had collapsed. thanks!!

[Mars]

I have had good success with master and slave cylinder rebuilds in the past. The most important factor that will determine the outcome is the condition of the cylinder bore. If it is too badly pitted or rusted it means that you will need to take out too much metal to get a nicely honed surface which would ensure a good seal. The the existing piston and seals end up being fractionally too small and the seals cannot deal with the additional stress for very long.

So if the cylinder bore is bad then it is better to get another one or to have it re-sleeved which would cost almost as much as a new master cylinder in any event. Re-sleeving is a good option for scarce master and slave cylinders though.

If the cylinder bore is not badly damaged or worn then one can hone it out with one of those small honing tools. Wet the stones with brake fluid and hone until the surface is smooth (obviously with honing marks). The less metal you remove the better.

Ensure that the seals and cylinder is not contaminated with any petroleum based solvents, oil or greases. Wash out the cylinder with methylated spirits when done and blow completely dry before assembly.

Make sure that you install the seals in the same locations and facing in the same direction as the existing seals and be careful not to damage the seals as it can be quite a hassle to get the seals over the rings and into the grooves. I use a very thin flat tipped screwdriver to pry the seals over. An old one without sharp edges to the tip. Try to get the shaft of the screwdriver between the seal and the piston and then stretch and pull the seal into position using the smooth shaft of the screwdriver. You can lubricate the seals and cylinder with brake fluid when assembling but silicone paste/grease actually works best.

Cleanliness is of the utmost importance as any residue inside the cylinder can interfere with the integrity of the seal formed between the cylinder and the bearing surface of the seals.

[Borntofish]

Also buy the replacements kit from Toyota. I found that pirate parts do not last that long. Mine leaked again after a year with the pirate parts.

[faiyaz]

alright great!! ive gotten the honning tool, already fitted the seals on the pistons just waiting for the rubber grease then will hone and assemble, hopefully no leaks will get back to you if anything, thanks alot for the info !!!

[faiyaz]

problem! the master cylinder wasent activating for some reason it didnt throw brake fluid when i tried to do a bench bleed, you can feel the pressure when you push in the pistons, what could be the problem, theres slight pitting but its very shallow and is at the beginning of the master cylinder

[Mars]

There is a very small hole/holes where the brake fluid feeds in from the reservoir into the cylinder. make sure that hole is open. It is extremely small and can get clogged with debris when you hone the cylinder. It will not work if it cannot build up pressure with fluid inside the cylinder as it is not good at "sucking" in the fluid but good at "pumping" it once it is inside the cylinder. Be sure not to damage or enlarge the hole.

Hope this helps

[faiyaz]

ok Ill have a look thanks !