1965 Chevy C60 brake problem

Installed new master cylinder, new Hydro-vac booster. 6 new wheel cylinders, replaced various brake lines as needed. All bleed points bled as peer normal starting with farthest from the master cylinder 1st. After 6 applications of the brake pedal the pedal becomes very hard an holds pressure while being held down. Upon releasing the pedal, waiting 1 minute, the pedal has lost all pressure and goes to the floor. Bleeding process shows no evidence of air in the system. Entire system shows no signs of leakage. Any help/suggestions would be greatly appreciated!

same truck i have. wonder if its not a faulty brake booster , or the master cyl. is bypassing. is the master cyl bleed.? does your truck have
the hyd. clutch?

Check the adjustment of the brake linings to the drums. Sounds to me that pumping the brakes will
push the shoes out against the drums and they hold. Released, the springs pull them back far
enough you can't make it all up with one push of the pedal.

Hello wremele welcome to YT! How do you have the
brakes adjusted? The brakes need adjusted out until
the wheel stops turning and the adjuster cranks the
shoe tight against the drum. Then they are loosened
until you can turn it about a half turn freely but then
the next half turn has some drag but free enough that
you can readily turn it through by hand to the part of
rotation with minimal drag. And I am talking about both
adjusters on the rear. While you had it apart if you did
not disassemble the adjusters free them up and
assemble with anti-seize it could be a bad deal for you. Secondly, it has been a while but I am pretty certain
those have two wheel cylinders on the rear. Getting
those second cylinders where the line runs down them
to bleed out properly without a power bleeder and only
pedal pumping is nearly impossible. Likely you will
have to take it somewhere where they can do this or
bite the bullet and purchase one. Sometimes by
starting the engine and using the extra pressure of the
Hydro-Vac the foot pump method can prove
successful, but you can easily go through a quart of
two of fluid doing this.

In my opinion if you can get a hard pedal by pumping it is likely the adjustment that is your problem. A faulty MC or HV would give you inconsistent brake application or pedal bleed down once you have achieved the pumped up hard pedal. Not bench bleeding the MC can give you a lot more difficulties on the initial system bleed out, but to me it sounds like you are past that. Not saying that the MC or HV cannot have a problem I am just suggesting it is very unlikely by how you are describing the current system response.

Them old trucks I thought pump six times
and pray was standard equipment. And it
teaches you to be a better driver.

I did adjust all of the wheels to where the shoes are dragging a bit. From your description I think I will go back and adjust til the wheel won't turn and back off a bit as you say. I did have the brakes down to the backing plate and lubed the adjusters front and rear.

No doubt. I'm too old for that kind of excitement!

I agree with the shoe to drum adjustment first then see how they are. IF still a problem I would look to the master cylinder for leak by.

Agree. The backing plate and drums need to be whacked with a mallet (Wood is good, or dead blow) to center the shoes. They just are not going to center themselves. Jim

Did you bench bleed the MC.

i have had the best lock force bleeding them form wheels to the master they are a b----

We had two of those trucks on our fire department some years ago. Both of them had the same kind of problems. What
we had happening was the brake fluid was getting out into the vacuum lines and disappearing. The master cylinder
was always low, we would fill it up and in a week or so it was low again and no visible leakage.

Our solution was simple, we sold the trucks...

I know 60's and some 70's had dual wheel cylinder front and back. The rears were no problem to bleed but the front were. Its one of the rare ones I used a pump up sprayer and back blend the front brakes.

You can soft pinch the rubber brake lines to eliminate issues up stream of the wheels. If you now have a firm pedal release one line at a time till you find the wheel that has the issue. are make some block off plugs, plug the brake lines off going to the wheels at the Booster to eliminate from the booster to the master.

Not familiar with this vehicle but bad flexible hose at front wheels can
cause strange problems. If it has those flexible rubber type lines I
would replacd them.
Dave

That can be caused by several problems.

Air still trapped somewhere is the most common. A good test, pump up the
brakes until there is good pedal, take the cap off the master cylinder, look
in when the pedal is released. a small, short fountain of fluid is normal, but
if fluid keeps returning to the master cylinder, there is still air somewhere.
I have reverse blead them, use a new or thoroughly cleaned pump type oil can,
connect it to an open bleeder screw, and pump fluid back toward the master
cylinder.

Out of adjustment shoes. Tighten the adjuster until the wheel is locked, then
back off until the wheel turns, and the shoes still just drag. If new shoes
were installed, they may not fit the drums exactly. They can be arc ground or
will have to fit themselves with use.

Wrong components. Trucks use a variety of brake options. The master cylinder,
wheel cylinders, and booster must all be the correct bore. They may look the
same from the outside but be different internally. The original and new
booster will have a tag, the numbers must match for it to work.

I remember years ago fighting one of those for several days. Ended up being a
defective rebuilt booster.

i will stick to my saying u have air in the system. pump them up 6 times and it hold,...them release and it goes to the floor next time is
air in system. my truck did the same thing when i bled the brakes. it took a very long time to get the air out. pumping the brakes is air
related. brakes out of adjustment would cause a low pedal. and what i did right off the bat is leave the bleeds open. bled the master cyl.
first when i changed it out. once i saw fluid leaking out from gravity then i closed all the bleeders and proceeded to bleed each wheel. plus
had to keep adding fluid as that tiny compartment drops fast. you let it drop down to suck air and you are starting from scratch again.

I agree, there is a bleeder on the master cylinder on some of those trucks.

We replaced the master cylinder 1
time on our 65 GMC 4000 which should
be the same as what you have. The
only way we could fully bleed it
after bleeding wheel cylinders, was
to leave the reservoir cap loose and
check / add fluid to it regularly
for about a week just letting it
sit. It finally self bled itself.
They can be a pita.

I agree with the majority here,adjust the brakes. If all else
fails unhook the lines at the MC and plug them. You can use short
steel lines and braze them solid to make plugs. Then you know
that the MC is good or bad.

Tighten all brakes. Tighten all brakes all
the way. Back off 6 clicks. Probably can't
turn. Back brakes. But will be ok. You are
running the brake booster to the end of
its stroke. Pumping master does nothing.

Clutch is manual. I do need to find a new boot?cover for the clutch arm where it passes thru the bell housing.

Several years ago when these trucks were popular, we worked on a lot of Hydraulic brakes, now I never see one . Only air brakes. I found
out really quick to have any success you needed a pressure bleeder. I bought one from Snap-on and I still have it. Pour a gallon of
brake fluid in it. Put 40 Psi of air in it. Put an adapter plate on top of the master cylinder and open the bleeders one at a time
starting with the booster. Don't rule out getting a bad booster or a bad master cylinder. Most of those old boosters have been rebuilt
a half a dozen times.

I did not bench bleed the MC. Relied on bleeding after mounting on the firewall.

(quoted from post at 10:09:11 03/12/22) I did not bench bleed the MC. Relied on bleeding after mounting on the firewall.

Click to expand...

Why???????

Always bench bleed a master cylinder before installation.

Always.


Yes, adjustment at the wheels is essential too.

Gravity bleed the entire system in the proper sequence before attempting to bleed by using the brake pedal.

Also, in my experience, "pumping" the brake pedal is not the best way to bleed. I've found that having your helper simply push the pedal slowly down one stroke and hold it, then you open the bleeder until flow stops, close bleeder and have helper release the brake pedal then repeat the same procedure until no air is evident, repeat at each bleeder in the correct order.

In my opinion, pumping the pedal rapidly agitates the fluid and causes the air to mix into the fluid in smaller bubbles making it harder to get completely out of the system.

I've had excellent success bleeding systems that others have failed at by simply using the one stroke method.

STEP 1: Adjust brakes at all wheels ensuring brakes are centered as someone mentioned earlier.

STEP 2: Bench bleed MC before installation. ALWAYS!!

STEP 3: Bench bleed MC before installation. ALWAYS!

No, that isn't a misprint, it's important and can't be said enough.

Bench bleed MC before installation. ALWAYS!

Step 4:Bleed as described above.





This post was edited by Carlmac 369 on 03/12/2022 at 05:49 am.

Good advice here about properly bleeding brakes and checking brake adjustment. One more thing to check out is if you're brake drums
are worn to where they need turning or replacement. What kind of shape are your brake shoes in?

Drums have been chkd for being round. Brake shoes are in very good shape with a lot of lining left.

Ah yes juice big truck brakes. Such a pain . What you have here is that you do not have the brakes adjusted correctly . More then likely you have two adjusters per wheel . Getting them adjusted correctly is becoming a lost art . So here is what ya do . Tighten each adjuster up till it locks that wheel up TIGHT , then back off a couple clicks till it turns with vary slight drag then do the same with the other adjuster . You should be able to hear and feel a slight drag of the shoe to the drum . 90% of brake problems stem from brake shoes out of adjustment and the first thing people do is start replacing master Cylinders and Hydro vac and the problem is not solved after replacement when all along it was just brakes out of adjustment . The other problem is that these old trucks spend more time setting then being used and the adjusters freeze up and will not turn and someone will take a hammer and punch to the star wheel and shear the tabs off . NOW you will not get nothing done but cause more work . Next problem with Juice brakes on trucks are the brake hoses as they go bad on the inside and will and can lock the brakes up then RUST eating the lines . Power bleeding is the best way to bleed them but sometimes you can let gravity do the job sometimes not. Myself even though i have worked on many and can make them work i have always hated them , one small failure anywhere in that system you have no brakes no back up to fall back on . I had one customer that had a water well hole poking company that would bring his two I H two tons down for me to work on . Te one with the drilling rig was a pretty new Cab and Chassis with a DT 466 and JUICE brakes , he was on his way to drill a well for a new home and running along at around fifty MPH going down a long grade and at the bottom of the grade was a cross roads with a traffic light , yup you guessed i the light went red he stepped on the WHOA pedal and it went to the floor , Luckily for him he went between two cars and no kerrrr boom . Bill was quiet shaken over this the brake hose going from the frame to the rear axle had let go at the crimp . Soooo do a better job on your brake adjustment and you will have brakes . When you PUMP the brake pedal what you are doing is putting more fluid into the wheel cylinders forcing them way out to make up for excess shoe travel . Like i said this is a lost art to get then set correctly

The day you have to PUMP the brake pedal to get it to WHOA tells me your five days past a brake adjustment .

My '57 5700 has a bleed screw on the Hydrovac. That needs to be bled first; otherwise, you will have air in the lines no matter how much you bleed the wheel cylinders.

(quoted from post at 10:22:12 03/12/22) My '57 5700 has a bleed screw on the Hydrovac. That needs to be bled first; otherwise, you will have air in the lines no matter how much you bleed the wheel cylinders.

Click to expand...

X2, Jerry.

Some Hydrovacs have TWO bleeder screws.

You got a lot of advice. If the master to hydro vac has any
air in the system the brakes will act odd. I have seen the
brakes go from no brake to full brakes and then fail to
release immediately. I helped a neighbor work on an IH
truck that he was having trouble with bleeding the
brakes. It turned out it had two hydro vacs for a duel
braking system. One visible behind the seat and one
tucked underneath the cab.