Leak from where Master Cylinder goes to Brake Booster
 

Alright So I was working on the TII and then I notice that the Brake Booster is really wet. Check it out looks like theres a small leak coming from where the mater cylinder goes into the Brake Booster. I assume it's only when I step on the Brake.

So I just top the fluid off so no air gets in and am going to buy a re manufactured master cylinder from the parts store sometime next week. So I get home from school today. I go to check the TII and I notice the reservoir is only a 3/4 full. So its leaking even when Im not driving.

So its leaking out from where the master cylinder goes into the Brake Booster. So am I going to need the replace the Brake Booster also. or Am I okay with just doing the master cylinder?

Yes, you'll probably need a new booster. The fluid eventually gets inside the booster if the MC is leaking badly and causes major problems.

You can get a good rebuilt booster for fairly cheap. New boosters are $$$. Also, I wouldn't recommend buying used brake components for the MC side of the system on a car this old. Too risky.

These are re-manufactured ones the ones you would get from like the auto supply store like kragen or autozne.

If it is leaking right at the connection of the MC and the booster, it more than likely is the MC. They tend to leak more when it is cold than when warm. Yes you can drive for awhile, but not a good idea. Yes it still could be the booster, but highly unlikely. I haven't heard of the booster failing in modern cars much. The MC is the first to go. So price a reman(all most are) or if you are feeling frisky you can get the rebuild kit and do it your self. Just depends on your budget.

Yea my TII is only driven as a weekend warrior. I drive my N/A daily so its not a problem.

Something like that. You'll know if the booster is full of fluid by shaking it around. If it's been leaking for a long time, I'd check it while you have everything apart.

BTW, napa has rebuilt MCs on the cheap.

Boosters don't have any fluid in them, just a vacuum operated diaphram that helps you push the MC. Its the MC, no doubt. If it has been leaking for a long time the fluid could have eaten through the diaphram in the booster though. Take the booster and MC off, replace the MC and clean out the booster.

I always thought brake fluid helps lubricate rubber.

I usually just change the mc. If the booster is failing, then i would change that. it wont b much more work to change the booster later

yea just a couple bolts. I'll take a look at it. when i get everything apart.

what are the symptoms of a car that has a fully functional master cylinder but failed brake booster? Is this possible?

there is a test for just that in the FSM, not hard to do... does anyone know if our brake boosters could possibly be replaced with say, one from a 929, or a 626, or other mazda car of the era?

do not buy parts store reman hydraulics......they cause more trouble than they do good.....

there is a 929 Master Cylinder Swap..somewhere in the forum.,.it has been done.

only works on TII's.

My Turbo II is doing the exact same thing. How would I use the master cylinder from a 929?

If the brake booster fails, the brakes get ROCK HARD, and you gotta stomp on it to make the car stop.

If you really want to test this, you can disconnect the vacuum hose and plug up the engine side with a bolt.
DANGER: THE CAR WILL NEED A LOT MORE ROAD TO GET IT TO STOP SO DON'T DRIVE TOO FAST!


-Ted

Where do you get these avatars man! LOL, jk. No, serious. Stop busting our balls and get an avatar of AaronCake. No offense Aaron

i used to go to junkyards all the time and try to find other cars' parts that fit. For brake parts, its not really worth it. A used brake part that has been sitting out for a while has old brake fluid in it. Exposed brake fluid absorbs moisture in the air and screws up the seals. You mightas well rebuild the part you have with new seals or just get a good replacement

So, does anyone have a s4 MC for sale? =]

You be better off going to a junkyard and pulling one off a junked car, and quickly installing it onto your car. As long as the junked car has the master cyl cap on. I rather do that than buy someone's good used MC. It was probably good before, but now the seals have gone to shit

oh just stop the cheapness and possible failure down the road with the same problems and buy a OEM MC.