Guest BadKarmaCreepin Posted October 14, 2002 Share Posted October 14, 2002 so here's the deal, when i hit the brakes, there's a huge amount of play. but when it gets to the end of travel, the brakes work. if i stand on the pedal, it stops very quickly. so the brakes are working, the pedal is just not responsive in the beginning. the guy i bought the car from said it was the "master back" that needed to be fixed or replaced. what is this and how difficult is it to do? thanks. Quote Link to comment Share on other sites More sharing options...
gene_w Posted October 15, 2002 Share Posted October 15, 2002 Originally posted by BadKarmaCreepin:the guy i bought the car from said it was the "master back" that needed to be fixed or replaced. what is this and how difficult is it to do? thanks. You almost got it. It's called a "Master Vac". I believe this was short for master cylinder vacuum servo, or something like that. It's more commonly known as a "power brake booster". These can be found at auto parts stores like Autozone. I bought one from them and it costed me like $90 or so. To replace it, you contort yourself under the driver's dash and undo like 4 bolts (nuts?) and pull the pin from the top of the brake pedal arm. Then you go to the engine compartment and unbolt the master cylinder and, being very careful of the brake lines, pull the master cylinder away from the booster. Then disconnect the big vacuum line going to the booster. Now you should be able to yank that sucker off of the firewall and replace it. As for diagnosing if it's the problem or not, I'm not real sure how. I replaced mine because when I hit the brake pedal, I heard a hissing under the dash and the engine would speed up. Turns out my "master vac" was leaking. Gene Quote Link to comment Share on other sites More sharing options...
Miles Posted October 15, 2002 Share Posted October 15, 2002 Dan My 72 240Z brakes act just like yours. So I checked the brake power booster with a Mityvac vacume gauge. I pumped up a good vacume and it held with no leak down. I still suspect that there is air getting into the lines somewhere in my brake system. The only parts I have not replaced is the switch (distribution block) under the MC and the power brake booster. I still can not get a firm pedal. Let us know how you get this resolved. Also, is your check valve between the carb and the power booster in place and working? Mine is missing and I wonder if that could contribute to brake pedal problem. Good Luck Miles Quote Link to comment Share on other sites More sharing options...
quicker240 Posted October 15, 2002 Share Posted October 15, 2002 I'm suprised you have any power assist at all with no check valve.Long loose pedal could be air or master cylinder bad,booster bad and you hear hissing like he said or pedal very hard to push.bleed the system at the master cylinder and the wheels and make sure your rear brakes are adjusted properly first,brake fluid and labor is cheap.Always check the cheap and simple stuff first,thats almost always what the problem is.... unless your lucks like mine.... Quote Link to comment Share on other sites More sharing options...
Guest BadKarmaCreepin Posted October 16, 2002 Share Posted October 16, 2002 there's no hissing that i can notice, and all this stuff is in the books about datsun's right? i mean, the brakes are completely managable now, but i just don't want them going out on me. how much would a brake place charge for an estimate? should be free right? Quote Link to comment Share on other sites More sharing options...
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