Weak brakes, need help

[jweb]

I have a 51 pickup with mustang2 front 11" rotors and 72 nova rear. It feels like I have to stand on the pedal to stop, what would cause this or is it normal?
Also have 20" wheels and firewall mounted MC & booster.
The brakes will not lock up no matter how hard you push

[OrrieG]

I would start with bleeding sounds like air in the system somewhere.. I assume it has a proportioning valve? Firewall MC rarely need check valves. Are the lines ran to avoid and places where air could get trapped? Some wheel calipers can be mounted upside down so the air cannot be bleed out too. More detail/photos would help.

[whitedog76]

First guess would be air in the system.

Second guess would be bad booster.

Third guess would be too small of master cyl.

[oldman3]

Originally Posted by jweb

I have a 51 pickup with mustang2 front 11" rotors and 72 nova rear. It feels like I have to stand on the pedal to stop, what would cause this or is it normal?
Also have 20" wheels and firewall mounted MC & booster.
The brakes will not lock up no matter how hard you push

jweb, NO this is not normal. I have a 50 MII with 11" rotors and 74 Nova rear drum. I can put you thru the windshield. Like guys posted above, check for air in system, etc...Jim

[jweb]

It has a 7" dual booster and 1" bore MC and the combo valve is under the cab
Is it normal for the booster to make a loud air noise when letting off the pedal?

I will try bleeding tonight and can take some pictures if that helps

[mr48chev]

Well according to my research the 1 inch bore mc is right on the money as that is what a 75 Nova runs and the brake setup on your truck is basically 75 Nova.

Are the master cylinder and booster a matched set or are they mix and match? If you mixed and matched them the push rod between the master cylinder and the booster may not be the right length and may not be giving you a full push on the master cylinder.

When you sit with the engine running and pump the brakes do they build up or does the pedal stay at the same height and feel solid? If the pedal stays the same and feels solid you don't have air in the system while being able to pump the pedal up and have a higher pedal it indicates that there is still air in the system.

Are the rear brakes adjusted up correctly. or have you checked the adjustment on them?

And finally does the engine pull enough vacuum to operate the booster? I've seen more than one cammed up engine that didn't pull enough vacuum to work the booster correctly.

[dwcsr]

Originally Posted by jweb

It has a 7" dual booster and 1" bore MC and the combo valve is under the cab
Is it normal for the booster to make a loud air noise when letting off the pedal?

I will try bleeding tonight and can take some pictures if that helps

No its not normal to hear that. If the pedal is firm and you don't have to pump it. I think you have a bad booster. I see a lot of the aftermarket boosters bad right out of the box, even the USA made boosters.

[jweb]

It's was an eBay MC/ booster and the MC has already gone bad. Replaced with a Napa MC

Doesn't seem to have air in the system so it sounds like the booster

Should I replace the booster and MC to have a matching set?
If so can you recommend any?

[dwcsr]

Originally Posted by jweb

It's was an eBay MC/ booster and the MC has already gone bad. Replaced with a Napa MC

Doesn't seem to have air in the system so it sounds like the booster

Should I replace the booster and MC to have a matching set?
If so can you recommend any?

Try to find one that is made by MBM or if you can find a rebuilt that fits the bracket. I saw a stock booster that fit but can't remember what it was off of.
I think it may have been a 76-77 Ford Bronco bendix type 8"
A-1 CARDONE Part # 5473220

[mr48chev]

That would be best. As you know the application or Napa parts number for the master cylinder I'd think about getting one from Napa that matched it.

I've got some of those Great deal no name parts off Ebay too and some of them will end up in the swap meet stack pretty soon.

[yossarian19]

Hard pedal + whoosh noise = bad booster
I'd look for an OEM application that will fit what you need. In my experience, parts from a NAPA store or other quality supplier *made for a standard replacement* are FAR better than most of the hot rod junk suppliers.

[jweb]

I would like to use OE parts but without a part# it's hard to know what to get from a parts store. They just want to know year/make/model.

Do you know of a car/truck that uses a similar booster/mc ?
Again I would like to use a matched set.

[mr48chev]

Originally Posted by jweb

I would like to use OE parts but without a part# it's hard to know what to get from a parts store. They just want to know year/make/model.

Do you know of a car/truck that uses a similar booster/mc ?
Again I would like to use a matched set.

Your best bet is to pull the booster off and take it to the parts house where you got the master cylinder and see it they can match it. If you still have the parts number for the master cylinder that should give a clue as to what it came on originally. I'd check Mustang II or Pinto/bobcat as they have small diameter boosters.

[yossarian19]

I used a blank hydro boost mounting plate & drilled it to match the pedal's bolt pattern (I've got the same pedal box), but I think the bolt pattern on it is pretty standard for Chevy vacuum boosters. Bring yours to a parts house & start pulling them off the shelf...