7'' brake booster problems HELP!

I GOT NO BRAKES!ok I got a MBM chrome 7'' dual diaphram brake booster and master cylinder and I have no brakes! Master cylinder has been bled twice, proportioning valve has been bled twice and the brakes them selves have been bled twice. There is no air in the system at all, getting all fluid from the bleeders.I cannot get shit for pressure on the pedal, pumping the hell out of it does nothing, the pedal just drops to the floor.Does the truck need to be ran to build pressure in the booster or something? Thats about all I can think of, the new 350 hasnt been fired up yet.If anyone has dealt with these booster/master cylinders and has an idea let me know.OPEN TO ALL ADVICE!!Thanks!

booster just makes pressure to pump them aster clinlder harder, sounds like a bad MC to me.

so you have the booster on a new motor that has'nt been run yet? The only thing that i could think of is it's a vacuum booster, since the motor has'nt been run, it's not been able to build up the necessary pressure. Run the motor a little and see if that helps.

The Master may need to be bench bled if it was dry.

im starting to wonder if it is the proportioning valve. It is the stock one, which may not be compatable?

Originally posted by Master Fabber



The Master may need to be bench bled if it was dry.

what does this mean to bench blead the master cylinder?

You bleed the master before putting it in the truck to get out any air bubbles.

i didnt think it woul dbe that easy of an explanation.kinda self explanitory. but it seems to me you can do that with it on the truck... same as bleeding brakes in general right? i mean once you have no air bubbles then u have no air bubbles whether you do it or off the truck.. or am i missing something and am way off? by the way seth.. like that color you choose for you truck

Edited: 8/21/2006 9:53:50 AM by bagged85

if booster isnt getting vacuum, the peddle will stiffen up just like manual brakes. if youve bled it that much, then sounds the MC is bypassing its self internally. get some line clamps and clamp them off 1 by 1, pushing the pedal inbetween each clamp to make sure you aint got a leak internally on a calpier or wheel cylinder. once u get all the lines clamped off, if it still goes to the floor, you need a new MC plain and simple. the booster has nothing to do w/ it not getting pedal.

edit: your factory PV should work just fine, all it does is divide the pressure up.

Edited: 8/21/2006 3:32:57 PM by suckafree

Ok problem solved! The MBM master cylinder isnt worth a crap. The ports were too damn small to let any resonable amount of pressure to run through to stop the truck. I found this out by getting a stock (for the truck) master cylinder and noticed the differance in them.So if anyone plans on buying one of these boosters DO NOT get the master cylinder. Get a MC from a 80 fullsize chevy, it fits right on the booster and has ports big enough to allow enough psi to stop you.

Also I called MBM directly....they have no technical support. The shop I bought it through "Fat Rodder" really had no help, he is sending me another MC but its worthless. He was the one telling me the truck needs to be ran which I had never heard of before, so I kinda figured that was the problem.

Thanks for all the info!