I would make sure your rear brake shoes are adjusted properly.
You could try changing the brake fluid, but if neither of the
above help....yes, a master cylinder change may be in order.
This year of GM truck was notorious for lousy feeling
brakes. GM even came up with a brake pedal rubber
pad that was quite a bit thicker then the original as part
of their "solution" to the soft brake pedal and "low" brake
pedal problem. In most cases, adjusting the rear brakes
properly, and making sure that the front rotors have an
excellent surface finish (if the brakes have been done
recently, a poor machining job on the front rotors can
cause problems) will make the brakes perform as good
as they can. In some cases, I've found that replacing
the master cylinder has done wonders. But again, this
year of GM truck (and many other years) simply sucked
when it came to brake performance.
Tell me about it. I just did brake repairs on 2 C-2500 6 lug (7200
GRVW) pick ups. Both are Ex-Fleet vehicles with over 200,000 on them.
Both have Extreamly soft brake pedels. They get hard when bleeding the
system with the engine off. Turn the engine on and pump the brakes they
feel like mush. One of the trucks has new rear shoes and wheel cylinder.
The other has no front pads and calipers. Both have all new lines
running to the rear end flex hose.
The one with new front brakes will hold the truck still untill the rear
tires overcome the brakes and spin/burn rubber on concreate. Yet take
the truck down the driveway, and you don't want to even go 20 MPH.
Other then master cylinders on these, and rear brake adjustments, any
Something to ponder...
Since I've owned my truck (1999) it's had less than ideal pedal feel.
Replaced 1 wheel cylinder, several sets of pads over the 135,000+ miles
I've owned it, master cylinder, had it professionally bled, still had
crappy pedal feel.
I had to replace my brake booster on this 95 K1500 5.7L about 3 months
ago due to it pissing air in the cab. This helped the power assist but I
still had a weak pedal.
7 days ago this rebuilt booster started pissing air so I had to replace
it also. Nice Murray's products! This time however, I left the master
cylinder attached to the brake lines & let it just stay in this
suspended position while changing out the booster (I did support it
As it normally sits in the truck, the master cylinder tilts back towards
the driver. The suspended way it sat while I did the swap job caused the
master to tilt quite a bit forward. I did no bleeding after this fix.
The brakes have been in operation a week now & the pedal travels much
less and is unbelievably quick to get VERY hard. Operation is FAR better
I'm thinking that maybe some air sat in the end of the master cylinder &
would not bleed out no matter how many times it was bled. Tilting the
master forwards for awhile might have moved some air enough so that
normal operation self bled the master. No matter what, I'm extremely
Similar thing happened to an Austin Marina I once had. The brake lines
came off the master in an upward spiral & then down to the proportional
valve. Stupid design to in my eyes. I could not get those things bled
until I cut the lines at their highest point & installed some petcock
bleeders - instant fix.
Sometimes on a motorcycle you have to crack open the top banjo bolt in
the brake & clutch systems to make them bleed all air too.
Last summer my neighbor had a 1 ton ford and couldn't get a brake on it. He
had replaced every pad/shoe, master and booster still no brake. I was over
doing a little inspecting and had a set of wheels off one side on the rear.
Just happened to be looking when he pressed the pedal and the drum was
actually stretching out when he was braking. Pulled a drum and it was wore
out. A local shop had actually turned the drum a few months back and even
though they were well out of spec the shop either didn't bother to measure
them or didn't care. Even though the front brakes do a larger amount of the
braking not having rear brakes really makes a diffrence. Also your front
rotors will heat up and allow brake fade much quicker if they are too thin.
A master cylinder usually tests easy. The most common problem is bypassing.
Test this by holding constant pressure on your pedal with the engine off and
make sure that the pedal does not slowly go down. If you don't want to
simply throw away $ rebuild your own master cyl. They are extremely simple
to rebuild. You can buy the rubber seals for less than 10 bucks and you
probably already have a small hone in your garage. Also a hydraulic guage is
a inexpensive tool to have in your brake toolbox. Make sure your
proportioning valve is working. Check each wheel end for proper pressure. I
would have to guess that 95% of vehicle owners do not change brake fluid.
Even though brake fluid doesnt wear it will absorb water. Brake fluid is
good at what it does because it allows virtually no compression but add
water and it will compress. Fluid in a hydraulic brake system that is water
contaminated will put you in a situation where your master cyl is displacing
all it can but due to the fluid compressing will not apply ample force at
the other end of the line. Also water and steel brake lines don't mix. You
get a little condition called rust. Rust in brake system equals plugged
orfices, wear on seals and in worst case scenario a line that ruptures when
you stand on the pedal in a emergency. CRASH. Also it will cost you some
cash but look at DOT5 brake fluid. It compresses even less than DOT3 and
won't absorb water. But there is a pretty good price diffrence and you must
make sure that all of you old fluid is out of the system as DOT3 and DOT5
are not compatable. You will probaly have to have a shop clean your system
before you switch. If you are doing a complete system overhaul such as on a
restore where you are replacing all components you need your head cracked if
you fill with DOT3.
Pads and shoes are made of diffrent materials. They have a rating system on
how aggressive they are. Some materials will last a hell of a long time but
don't have the bite when it comes to stopping. Your softer compounds
generally grab better but youll be changing them every 20K. Then you have
some of your high end brakes, ceramic and carbon composites that offer both
wear and hold. My wife drives a 04 Pontiac minivan. The original pads lasted
about 25K and I replaced them with a ceramic pad. They were inspected a week
ago with about 20K on them and looked like they were worth at least that
much more. And theyll put you through the dash.
Brake fluid is
Fluid in a hydraulic brake system that is water
Wrong again. Water is no more compressible than most brake fluids. Water has
a low boiling point and in a panic stop can boil and become a gas, which is
Also water and steel brake lines don't mix. You
Also it will cost you some
Wrong... Dot 5 is silicone based and it's molecules are farther apart than
Dot3-4 which makes it somewhat more compressible.
Correct, but that isn't necessarily a good thing. Moisture gets into all
brake systems, no way to stop it. Since Dot 5 won't absorb it, the water
will pool in the bottom of the lines and other low points and corrosion
becomes more of a problem than with the glycol based fluids. Also, pooled
water becomes a serious problem in freezing weather.
But there is a pretty good price diffrence and you must
You will probaly have to have a shop clean your system
Dot 5 can damage seals and other soft parts if put into a system not
designed for it.
Unless he is planning to run his truck at the local circle track, he should
stick with Dot 3( if he is, he could go to Dot 4 which has a higher boiling
point and IS compatible with his system).
On cars and trucks that have sat with broken brake lines. First step in
bleeding is Gravity Bleeding. This means you take the cap off the master
cylinder. Open the bleeder screws to the point that fluid starts to flow
freely. Sometimes you have to remove the bleeder screw for a few
minutes. I use a catch pan and let each wheel gravity bleed for 5 to 10
mimutes. Keeping the master cylinder from going dry by topping off, this
get the old brake fluid out of the lines, removes air from new wheel
cylinders, calipers and the master cylinder. Then I bleed them from there.
You can bleed lines by first cracking them lose. Then having some one
pump up the brakes and slowly opening them and closing them.
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