my car has rear drums and ever since i bought it the rear brakes didnt work so about 6 months ago i replaced the shoes,wheel cylenders, rear lines and cleaned it all up and adjusted them and they still dont work. Im stuck I can do about anything mechanical but i cant figure out this problem, im really tired of only having front brakes!!!

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91 Z-28 Coupe
L-98, 700-r4
Borla cat back
Performance Resource chip
Centerline wheels
K&N, Gutted air boxes
Gutted cats
Best Pass = 13.710 @100
Best 60' = 1.842
on M/T Sportsman Pros

Race Car:
S/P 91 Camaro Z/28
454 LS7 crate motor
Crane Roler cam
Dart intake
1000cfm TRC Carb
Powerglide
9" Ford rear
Goodyear 14"-32"-15"
Weld prostars
All steal except for hood and rear deck
Best ET: 9.64 @ 145
3000# with driver

 

Will they bleed??

If you are getting a good shot of fluid back there than they are getting pressure, pressure means they should work.

If not a good shot, check the output on the master for the rear lines, maybe a proportioning valve. (usually the pedal will feel funky/low)

Check all the hard lines along the floorpan, I had a car once that the guy before me crushed a line with a floorjack...

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ASE Mechanic/Machinist/Smog Tech

1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R
and 2 POS commuters...

R.I.P. #3
"He can see air"

 

my guess was the proportioning valave but i wasnt sure. I cant find a new one any where hould i trust a junkyard one or will it end up being just like mine. the pedal does feel soft.

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91 Z-28 Coupe
L-98, 700-r4
Borla cat back
Performance Resource chip
Centerline wheels
K&N, Gutted air boxes
Gutted cats
Best Pass = 13.710 @100
Best 60' = 1.842
on M/T Sportsman Pros

Race Car:
S/P 91 Camaro Z/28
454 LS7 crate motor
Crane Roler cam
Dart intake
1000cfm TRC Carb
Powerglide
9" Ford rear
Goodyear 14"-32"-15"
Weld prostars
All steal except for hood and rear deck
Best ET: 9.64 @ 145
3000# with driver

 

You can get a prop valve from your local chevrolet dealer for around $50.I wouldnt even mess with a junk yard piece for this part,there is no way to test it out before you buy it.I recently upgraded the rear disks on my Z to 89+up style and had to change the prop valve and i payed $48 thru my local chevy dealer.A soft pedal could also be a sign of a bad master cylinder or a leak somewhere causing air to get into the system.Check for leaks first (everywhere) and then go after the master.Good luck

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1982 Z28:355,4 Speed,Lots of bolt ons

 

No moving parts in a proportioning valve to go bad, go ahead and use a salvage yard part.
Just make sure you get one for the correct year for the system you are using,

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1987 Black Camaro IROC-Z (original owner) Replaced LB9 @ 86100 miles.
New 350 Crate engine
Balanced & blueprinted
World Prod SR 67cc Heads 9.6:1 C.R.
Cam: 454lift,216dur@50,110ls
TPI Induction(from 305)
22# Fuel Injectors,AFPR&Gage
SLP Intake runners
New GM 1988 chip
K&N filters & Air Foil
Hothkis STB
SLP 1 3/4 Headers
CATCO 3" Catalytic conv.
SLP 3" Cat Back Exhaust
700R4 Auto
SLP Torque Converter (2400 stall)
B-W 9 bolt rear 2:77 Possi. Four wheel disc brakes,245/45/ZR-17 Tires
17x8.5 ATI 5 Razze Wheels
Dyno results: 211 RWHP & 282 RWTQ.
264 HP & 352#/ft at flywheel with all emission controls installed. New Toy!

 

if there is no moving parts in a prop. valve to go bad then why would that be the cause of my brakes not working. it must be something else.

 

Proportioning valves have a piston that "centers" itself in the valve too equally distribute the fluid.

That would be a moving part last time I checked.

They do stick, trust me.

------------------
ASE Mechanic/Machinist/Smog Tech

1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R
and 2 POS commuters...

R.I.P. #3
"He can see air"