cobra_280z Posted January 30, 2008 Share Posted January 30, 2008 hey guys, for the last 3 weeks i have been losing brake fluid pretty quickly. My car is an 81 280zx, so i have the dual brake master cylinder. Each time, the rear cylinder (closest to the cabin) is nearly empty, with just a little bit of fluid in the bottom. I can put brake fluid in it,(about a pint) and the brakes feel great, no mushy feeling at all. I just finished checking all of the brake lines, calipers, and bleeder valves, but everything was bone dry. now, about 4 months ago, i rebuilt my front calipers (after which the brakes were greatly improved) , but like i said i could find no leaks. I am thinking that the master cylinder may be going, and leaking internally... Thanks for help in advance Quote Link to comment Share on other sites More sharing options...
S30TRBO Posted January 30, 2008 Share Posted January 30, 2008 Do you have fluid inside the cabin? I would check the pedal set for leaks and a trail running to the floor from the firewall. Quote Link to comment Share on other sites More sharing options...
cobra_280z Posted January 30, 2008 Author Share Posted January 30, 2008 haven't checked that, though i took my mats out last week and didn't see anything. what would that indicate? Quote Link to comment Share on other sites More sharing options...
cobra_280z Posted February 1, 2008 Author Share Posted February 1, 2008 no, i didn't find any fluid in the cabin. any other suggestions/ideas? whatever it is, i've lost about 3-4 pints of fluid out of the back cylinder in the last month or so. Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted February 1, 2008 Share Posted February 1, 2008 That is not a small leak. Maybe try having someone stand on the brake pedal nice and hard and then have a look. It's a pretty simple system, MC, lines, slave cylinders (ie pistons if disc's, slaves if drum brakes), and it's supposed to be a closed system so if your loosing fluid, you definately have a leak. Sometimes drum brakes are hard to spot a leak in for awhile. Quote Link to comment Share on other sites More sharing options...
ezzzzzzz Posted February 1, 2008 Share Posted February 1, 2008 Pull the hose for the vacuum booster to the intake manifold. If it's wet inside (brake fluid) then your MC is leaking at the rear and fliud is being pulled into the booster. It ultimately ends up in the intake through the hose. I'd bet good money that's where your problem is. Replacement of the MC is the fix. Quote Link to comment Share on other sites More sharing options...
cobra_280z Posted February 2, 2008 Author Share Posted February 2, 2008 thanks guys; i had a feeling the master cylinder was the problem too, as it is a pretty serious leak indeed. couple questions- as i mentioned earlier, my brakes feel great as long as fluid is in the cylinder; however, i have heard of brakes going completely out, due to MC failure. reason i ask is im at school, where its harder to do work. also, how difficult is it to change the MC? thanks guys Quote Link to comment Share on other sites More sharing options...
mom'sZ Posted February 3, 2008 Share Posted February 3, 2008 my brakes feel great as long as fluid is in the cylinder; however, i have heard of brakes going completely out, due to MC failure. reason i ask is im at school, where its harder to do work. also, how difficult is it to change the MC? thanks guys It's not to tough to change out, shouldn't even need to jack up the car so this is something you could do in the parking lot at school if you had to. Point is though.... brakes are not something to dink around with!!!! you could hurt yourself or someone else. If the master goes dry, you will have no brakes, instantly! Even if you have to pay a shop to do it, don't drive the car until it is done. That fluid is going somewhere. Here is a simple test. Pump the brakes up with three or four quick pumps, then stand on the pedal... hard as you can. Keeping pressure on the pedal, if there is a leak, you will feel the pedal slowly going down. It could be the back wheel cylinders or the master. I suspect if it was the wheel cylinders you would see it drolling down the back side of the tires by now. Quote Link to comment Share on other sites More sharing options...
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