Recently I bought an 86 chevy truck which didn't have power brakes. So I got a new vacuum booster and a new master cylinder and put them on. The brakes work and the truck stops fine, but the pedal doesn't seem to have enough pressure, it goes to the floor with hardly any effort. Then it takes a few seconds to come back up. I bled the brakes so I don't think there's air in the lines. What could be the problem? Did I get a bad booster or something?

 

never heard of disk brakes without power, except for some of the very first ones. are you getting good preasure when you bleed them? if not maybe a restriction, or internal leaking in the MC, or maybe a bad power booster as you said.

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ICON Motorsports

1st & 3rd

 

if the pedal goes to the floor then the booster isnt the problem lol!!
either the master is wrong(diff between non-power and power),or bad,theres still air in the system(did you bench bleed the master bafore installing it?),or the rear brakes are way out of adjustment causing a low pedal.it could be also that theres a different perportioning valve for the non-power brakes,than the power brakes

do you mean that the truck had power brakes but they didnt work,or are you saying it didnt come with power brakes and you added them?
well figure it out
mike

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86 camaro:was a v6 car,now its going to be a v-8 5.7l!!
350:cylinders bored .040 over.a little over 9:1 compression(getting a blower some day when im rich lol)line bored.deck is milled a little(was pitted)
trw forged pistons with summit stage 2 polished rods with arp bolts.
194? intake valves(not 2.02( ),pocket ported,gasket matched,and polished ports,old vette intake with new zinc 650 holley

ase certified for a few years,learned alot though

working on freakin NEONS ,cirruses,tauruses,cobras(well` at least they look nice lol)and intrepids all day makes me drink too much
good job security though

im always on the lookout for cheapv-8 t-5,s
and t-56 setups.they must be cheap.i dont care of they need rebuild,as long as they arent totally blown

 

The truck is a mutant. It's got parts from every year truck/suburban you can think of. It didn't have power brakes when I bought it, there was no vacuum booster. So I got a new booster, and a new master cylinder to match. I bench bled the MC and put the booster on. Then, just to be sure I bled the heck out of all the brakelines. The pedal works fine when the engine is off. But when it's running and the booster has vacuum, the pedal just sorta sucks itself down if you even tap it. And it makes a hissing noise too. Then it comes back up real slow. The weird thing is that the truck stops just fine. In fact, I 'bout put myself through the windshield every time I touch the pedal. The truck is supposed to be an 86 (according to VIN) and manual brakes werent even an option that year. The old MC that came off was the newer style, like 86, but the one I put on was older style, like 78. I had to use the older one to match the booster, and had to use the older booster to match the cab. So I suppose it's possible that I do have the wrong proportioning valve. Like I said, the truck is a mutant hodge-podge of parts. As for the back shoes, I can't check them because I can't get the wheels off. The kid I bought the truck from put locking lugnuts on, and lost the key. I suppose I'll take it to a tire shop tomorrow and have them bust the suckers off. Whew! Sorry this is so long, but I thought the nit-picky details might help.