C10 Rear Drum brakes lock-up...

[MarkIV396]

I did a search on the site to see if someone has had a similar problem. My 1970 C-10 (Heavy 1/2) Manual brakes fine 1 or 2 times then both rear wheels grab & cannot get truck to move at a stop. Brakes worked fine up until we got some heavy rains here in KC last week. Also I get a really hard pedal when this happens...
I know it's both back -as touching the wheels, they are hot! Rebuilt Master cylinder installed about 8 mo.s ago & whole system bled. I've had the truck 10 yrs. & the brakes have never been really good.
I know air will expand & cause this to happen if you don't get it out of the system. I would go for wheel cylinder, If it was just 1 wheel doing it - but, it's both.

Any Ideas? I don't have alot of $$$ to throw at this.

Thanks.

[MarkIV396]

I'm kinda wondering if it may be the perportioning valve. Since it's manual brakes, no one seems to have these (except Sumitt racing) I'm thinking of taking it off & soaking in brake cleaner, hit with PB Blaster & blow it out with compressed air...

[SCOTI]

Disc/drum or drum/drum? Drum/drum should have a distribution block which is different vs a prop valve.

[MarkIV396]

Scott,
It's Drum/Drum manual, No booster. New Master Cylinder was put on few months ago. Bench Bled 3-4 times, installed & Bled RR the LR, then RF & LF.

Thanks.

[SCOTI]

From what I've read on the two different units (prop vs. distribution), they seem to work fairly similarly... I'm just not sure they're the exact same.

I've had people suggest 're-setting' the prop valves but never heard of it for distribution blocks. My buddy is going through a brake issue on his boys 70 Camino which is why I've been investigating. Not sure if this info will help....
http://inlinetube.com/Prop%20Valves/pro_valves.htm

[MarkIV396]

Scoti,
Thanks for the Inlinetube.com info. This is wonderful source! I will check that out. I did come across this link (below) concerning Brake Master Cylinders. Since this was an O'reilly re-build, I might start with that first! Thanks for the replies Scoti !

Here's interesting link I found:
http://www.freeasestudyguides.com/br...hing-port.html

-Mark.

[MarkIV396]

Last night I bled off all 4 wheel cylinders & did get some air out of them. This AM - I went to drive to work, then would lock at a stop & I would put Trans in Neutral & you could feel brake pressure let off & truck would roll free... Weird!

[Square_78]

Make sure you don't overfill your master cylinder. I've had cars where the brakes become grabby and really drag to the point of slowing the vehicle down when in neutral. The first thing I check is the fluid level. I've had motorcycles that do the same thing. Taking some fluid out to make sure it's right on the full mark. Always works.
Posted via Mobile Device

[Jokerz]

Originally Posted by MarkIV396

Brakes worked fine up until we got some heavy rains here in KC last week.
Thanks.

Parking brake cable maybe?

[MarkIV396]

I got a new cable installed & Mechanism isn't rusty or binding...

[N2TRUX]

Since you feel its both rear wheels and they are hotter than usual I would be suspect of the prop valve/block. It sounds as if its sticking closed allowing pressure in but not releasing.

[MarkIV396]

Yeah, I've wondered about the metering block - as well as the hose connecting the hardlines over the axel. Kinda wonder if that hose is swelled up inside. Letting Fluid pressure in -- but not allowing it to return.

On the Master cylinder - I took out more fluid, so it's about 1" from the top also... That was an O'reilly rebuild & I wonder about it too!

I appreciate all the help & ideas you all have given me. This is my primary mode of transportation right now. Having a rough time $$$ wise in this economy - like 26 million other people !! I've been told to sell off some of my hot rods & I know I would kick myself later...

-Mark.

[SCOTI]

Originally Posted by MarkIV396

Yeah, I've wondered about the metering block - as well as the hose connecting the hardlines over the axel. Kinda wonder if that hose is swelled up inside. Letting Fluid pressure in -- but not allowing it to return. On the Master cylinder - I took out more fluid, so it's about 1" from the top also... That was an O'reilly rebuild & I wonder about it too!

I appreciate all the help & ideas you all have given me. This is my primary mode of transportation right now. Having a rough time $$$ wise in this economy - like 26 million other people !! I've been told to sell off some of my hot rods & I know I would kick myself later...

-Mark.

Easy swap & will help eliminate it from the list of possibilities. Worst case, get a mechanic (pref one that's a brake specialist) to look it over as well. It might be a good investment....

[MarkIV396]

Right Scoti. Brakes are something that need to be done right. I've been lucky & not had to have ASE cert. Mechanic work on my stuff for 22 years. Never had an issue like this come up before ! Threw me 4 a loop! I'm more a Motor guy!

[SCOTI]

Originally Posted by MarkIV396

Right Scoti. Brakes are something that need to be done right. I've been lucky & not had to have ASE cert. Mechanic work on my stuff for 22 years. Never had an issue like this come up before ! Threw me 4 a loop! I'm more a Motor guy!

Sometimes help is all we need (help = a fresh set of eyes on a problem). A brake mechanic might offer more/different options as well.

[Jokerz]

At 8 months, you're still under warranty on the MC. That's the cheapest $$$ to try first. I don't think you'll get an argument from O'Reilly's on it.

[wraprail]

So is this still single circut or does the master have 2 outlets? (front & rear)
If it's single then I doubt the master is causing it.
If it's double check that the pushrod is allowing the pistion to fully retract in the master cylinder bore.
Then replace the master.
Its not cuz the master is overfull. That may happen on motorcycles but not automobiles.

[MarkIV396]

It's a Dual Master Cylinder & I went back to O'reilly & got another rebuild. Put that on & new rear wheel cylinders Sat. Got a new spring/hardware kit for the shoes, lubricated the self adjusters (star Wheel.) It's better than it was, but it's still dragging...

[circuit_doc]

How old are your flexible brake lines? They may look good on the outside but the inside of those can swell up and be restrictive. They will pass the brake fluid one direction because it's under hydraulic pressure but when the peddle is released the pressure can't flow backwards. This will cause the shoes to remain "engaged". A symptom may be the shoes slowly release over time or possibly when you open a bleeder valve there is pressure there and fluid squirts out for no reason.


A second item I saw first hand was just after installing a new master cylinder booster. It was sent with the pin that installs on the back side of the booster that compensates for peddle travel that was to long and wouldn’t let the pressure release. It took about 10-15 uses of the brakes before it would lock up ALL FOUR wheels.

Good luck.