72 C10 brake problem, need help please
 

I bought this 72 truck about 6 weeks ago, want to keep it more like a daily driver. When I bought it, I noticed a problem with the brake system, it does not work very well, only slows down the truck to a stop.

So the first thing I did after I got the truck home was to drain and bleed the system completely. All the parts are in very good condition, booster/master/valve all look like new. After that was done, it didn't help with the brake at all.

I decided to take it to a local shop where several older gentlemen works on older cars. It maybe more like a hobby for them now, but I don't doubt they have the knowledge to do the work. I have had other things done there in the past, and I was happy with their work.

After 4 weeks, they replaced the following parts:
- Master cylinder from Right Stuff
- 11" booster from CPP, they said the existing one was too small
- Proportioning valve
- SS line for part of the system they feel needs replaced
- Cleaned the front caliper to make sure it's working
- Adjusted the 454 to get more vacuum, they say it's getting about 16" of vacuum now.

The total cost is about $700.

I picked up the truck yesterday, but it's only marginally better. They admit it's not where it should be, but they are stumped why it's not locking up the tires like it should. I think they give up on it, they don't know what to do next.

Does anyone have any ideas or suggestions? I can post pictures or more info to help with the diagnosis.

Thanks.

Re: 72 C10 brake problem, need help please
 

What size bore is the master cylinder?
Smaller is better.
And a smaller but better dual diaphragm booster might help.
And sometimes changing the pedal ratio helps. You want 4.5 to 1 for power.

Re: 72 C10 brake problem, need help please
 

How does the pedal feel when pushed? Is it hard right off the bat when you push it down? It is possible that the master cylinder is still incorrect, like geezer asked. Maybe you can loosen the nuts enough to get at it and see what the piston diameter is. Seems like they threw some parts at it instead of digging to find the root cause.

Re: 72 C10 brake problem, need help please
 

Since you bled system right off the bat I am assuming all bleeders where working..I would get a second person to give you a hand with the following..open both rear bleeders(I use rubber hose that fits over end of bleeder and run into a jar so not to make a mess) start truck or not and depress pedal..it should work nice and easy going to the floor.If it goes down smoothly and fluid dumped into the jars I would say problem could be with the wheel cylinders ..if pedal is hard to push doing this and minimal fluid comes out you know your problem is further front.would do this first at the rear as you stated front calipers where checked out.Also make sure your parking brake is functioning on/off correctly with rear tires off the ground.Another test witch can me messy(get plenty of rags)...pull the cover off master cylinder and gently!!! push down on pedal it should go down nice and smooth,,do not push to hard or fluid will push out and make a mess..with hood open you should be able to watch through the gap to see fluid push up..if this works and pedal feels like it drops with no resistance you have ruled this out as problemREMEMBER GENTLEY PUSH or have a buddy hold a rag over open master cylinder.3 checks you can do without spending $$ Rob.........

Re: 72 C10 brake problem, need help please
 

Another thing to check is pushrod being set correctly between booster and master.
And take a pic of your booster etc for us.

Re: 72 C10 brake problem, need help please
 

Here are some additional info:
- The paddle is not to hard to push down now, it was when I first got it. So whatever they replaced made it softer to push down.
- I have asked the guys who replace these parts to tell me the sizes of the new master and booster. I didn't get back the old parts, which I will be getting tomorrow. All these parts were like new, so I want them back anyways. I believe they put in a larger diameter master, something like a 1-1/8 instead of 1", but i will ask again to confirm. I should get the parts list of what they installed, it should tell me on the invoice.
- I checked the emergency brake, it seems to work fine. The wheels can't turn when it's engaged. I also tested it on a slope, it holds the truck in place just fine.
- I will be testing the other things suggested tomorrow, need to get my daughter to volunteer.

I will be posting more pictures shortly, can't figure out how to do this on the Mac, WTF with these POS Apple.

Re: 72 C10 brake problem, need help please
 

Here are some pictures of the master, booster and proportioning valve.

Re: 72 C10 brake problem, need help please
 

Here are some pics of the front caliper and rear wheel cylinder.
- can anyone tell if the caliper seems to be the correct size or anything unusual?
- The calipers all seems to be very clean.
- one picture is a close up of the driver side rooter surface, this is after about 30 miles yesterday and 15 miles of driving today. Does this look to be normal or should it be smoother than this after the such distance?
- The driver rear seem to have more dust, you can see one picture there is some black mark next to the drum, that's what came out. This is much more dust than the passenger side, they were both removed just 50 miles ago, so I would guess the driver side is work more than the messenger side. Is that a good assumption?
- Wheel cylinders all looked to be in very good condition.

Re: 72 C10 brake problem, need help please
 

Once you figure out the issue please post the solution for all of us. I am interested to see what the issue was.

Since you had most of the parts replaced I would check:
-Push rod length
-Check the front calipers to make sure they are functional and you don't have stuck caliper pistons (Doubtful but worth the time)
-The only other thing I can think of is that your front brake pads/rotors have glazed over

Re: 72 C10 brake problem, need help please
 

Yeah...The rotor pic indicates that something is up there for sure.

I suggest you take the truck out to a safe road somewhere and do the rotor seasoning and pad bedding procedure. In a nut shell it goes sorta like this.


https://www.zeckhausen.com/catalog/i...Path=6446_6443


From the link...

From 60mph, gently apply the brakes a couple of times to bring them up to operating temperature. This prevents you from thermally shocking the rotors and pads in the next steps.

Make eight to ten near-stops from 60mph to about 20 mph. Do it HARD by pressing the brakes firmly, but do not lock the wheels or engage ABS. At the end of each slowdown, immediately accelerate back to 60mph, then apply the brakes again. DO NOT COME TO A COMPLETE STOP! If you stop completely, with your foot on the brake pedal, pad material will be imprinted onto the hot rotors, which could lead to vibration and uneven braking.

The brakes may begin to fade after the 7th or 8th near-stop. This fade will stabilize, but not completely go away until the brakes have fully cooled. A strong smell from the brakes, and even some smoke, is normal.

After the last near-stop, accelerate back up to speed and cruise for a few minutes, using the brakes as little as possible to allow them to cool down. Try not to become trapped in traffic or come to a complete stop while the brakes are still hot. ( if you do, put it in park and let it rest there with no brakes applied )

Hth,

-klb

Re: 72 C10 brake problem, need help please
 

I had one like that a few years ago. I put new shoes on using a different brand. Try to get some with FF on the edge of the linings. I also used Ceramic pads on the front. They are great. Good feel & stopping power & they don't leave any dust on the wheels.
It you changed from a smaller M.C. to a larger one that will make it worse. The larger cyl. gives a higher pedal but less pressure to the wheels.
I take it the rear wheel cys. have been serviced & the piston are not stuck.
George

Re: 72 C10 brake problem, need help please
 

The rear shoes are reversed.. Shoe with short lining should be in the front position..

Re: 72 C10 brake problem, need help please
 

Rusty is right. I looked right at that & didn't notice.

Re: 72 C10 brake problem, need help please
 

If it is possible to turn the rotors, have them machined to remove the pits, if that's what they are. If they are pits, you have a lot less friction surface than what a smooth rotor would have. If the rotors would then be too thin after turning, buy new ones.

And yes, if the rear shoes are on backwards, there will be less braking performance.

Re: 72 C10 brake problem, need help please
 

While your reversing those shoes, make sure your adjusters work freely and adjust the rear brakes manually while your under there.

I just had an issue where my rear adjusters were frozen and not adjusting.

If you have good flow at the rear bleeders, the booster would still be suspect.

Re: 72 C10 brake problem, need help please
 

Thanks for all the suggestions guys. I haven't got around to some of these, but decided to try install a new set of pads on the front first. Bought the Advanced Auto ceramic pads. Here is what I noticed when I took off the old pads, the outer pad is worn out about 1/3 more than the inner pad on both sides.

You can see the picture below how they compare. Does it tell you anything? Do you think it's sticking on 1 side or maybe not really sliding like it should? It sure looks like it's only using 1 pad to slow down.

I will be switching the rear pads later this week.

Re: 72 C10 brake problem, need help please
 

I meant rear shoes.

Re: 72 C10 brake problem, need help please
 

In all the drum brake jobs I’ve done the longer lining shoe faced the rear of the vehicle and shorter lining shoe faced the front.

Re: 72 C10 brake problem, need help please
 

I now have a good feel for what your issue is. Your brake caliper is stuck on the guide pins and not allowing the caliper move so equal force is placed on both sides of the rotor. Based on your pictures only the piston side of the caliper is engaging the rotor.

To fix it remove the caliper bolts and move the caliper out the way. The push on the bellows where you removed the bolts. If they don't move your need to replace them. Hope this solves your issue.

Re: 72 C10 brake problem, need help please
 

Remove the little sleeves in the calipers, clean them & put a little silicone grease on them. Put some of the grease in the holes that the stems of the bolts go in. There are rubber O-rings in there that allows the caliper to slide. With the ceramic pads & Correct the rear shoes & I think you will have some good brakes.
It seems your "older gentlemen mechanics aren't too sharp.
George

Re: 72 C10 brake problem, need help please
 

I swapped out the front caliper and installed new ceramic pads last night, the paddle feels better and smoother. However, it's not 100% improvement. It does help it to stop faster, but still not locking up the wheels.

I will be changing out the rear wheel cylinder, the heck with it. It's not that hard, I have to reverse the shoes anyways. Will keep posted here.

After that, is there a way to adjust the proportional valve to put more pressure on the front?

Re: 72 C10 brake problem, need help please
 

Only if you have an adjustable proportioning valve. What did you get as a replacement?

Re: 72 C10 brake problem, need help please
 

subdued

Re: 72 C10 brake problem, need help please
 

An adjustable prop valve doesn’t give more pressure, it’s used to reduce pressure. Usually to the rear drums. Prop valves are metered to give 80% braking to he front and 20% to the rear.
To increase the master/prop valve output you need a smaller bore in the master, a properly set pushrod from the booster to the master or sometimes a change in pedal ratio. Most boosters need a 4.5 to 1 pedal ratio.
Another trick to increase braking is plumbing residual check valves into the brake lines. Installed close to the prop valve. A 2# for the front and a 10# for the back.

Re: 72 C10 brake problem, need help please
 

I'm not one for slotted roaders. They stay they work they make more noise than anything. I like a Full on the surface when I apply my Brake pads roaders look glazed. Nascar uses slotted routers But they're going almost 200 mph If the Mainstream has not gone to Slotted Routers why even bother I don't see semi trucks running them. If they were better why doesn't jet Aircraft use them? To me there just a waste of money.