72 C10 brake problem, need help please

[tcarroll1963]

If everything is looking correct with your brakes as far as no leaks, no air in system, master rod length ok and proportioning valve adjusted for front disc and rear drum my question is...Is there a big lumpy cam in your motor? If you need more vacuum you can buy a vacuum canister this will help the booster. I've see a kit for around $40.

[rpmerf]

When you replace the caliper, make sure you take that guide pin out and grease it up really good.

Story time:
About 5 years ago, I put all new front brakes on my suburban - master, lines, flex hoses, calipers, rotors. The other day I'm driving home and the brakes are grinding when I hit them hard. Take a look and the inner pad on both sides are worn to metal, and the outters still have half a pad. I put less than 10K on this truck since everything was new, and now I'm buying another set of pads and rotors. Moral of the story: even if the calipers are new, take the pins out and grease them up really good.

[tcarroll1963]

On the GM style caliper there is a small metal bushing that needs to be greased that sits in the caliper where the bolt goes through as well as the hold down pin.

[nelson-ohio]

Ok, I have been doing some work on the truck. Reverse the passenger side rear shoes so the longer one is facing forward and the short one facing the back. The driver side was already done this way.

Didn't replace the wheel cylinder, they looked to be in very good shape. I will see how this goes first.

I did find a small block on the passenger front brake line, there are 2 of these, I have no idea what they are. Please see picture below. What are these for? 1 is about 18" down the line from the proportioning valve, the next 1 is about 18" further down the line.

I was going to drive the truck once I reverse the shoes, to see how it works. but I have noticed a leak in the power steering pump, it's been throwing oil all over my wheel well, I've been driving it like that, just have to wipe it down everytime I get home. Finally got tired of it and took the pump of while I was working on the rear shoes. This is a nice billet machined March Performance pump. It's leaking from the pully shaft, got a quote of $125 to repair the whole thing, but will take 7 days to get it back. how hard is it to work on this? Any ideas?

[RustyPile]

Originally Posted by nelson-ohio

Ok, I have been doing some work on the truck. Reverse the passenger side rear shoes so the longer one is facing forward and the short one facing the back. The driver side was already done this way................<snip>.....................

NOPE, NOPE, and NOPE!!!!! Go back and read my post again.. The short shoe faces the front.... The following will help you remember... When taking a group photograph, the short people always stand in the front....

[Ironangel]

Originally Posted by RustyPile

NOPE, NOPE, and NOPE!!!!! Go back and read my post again.. The short shoe faces the front.... The following will help you remember... When taking a group photograph, the short people always stand in the front....

Rusty is correct, maybe the misunderstanding is in the terminology? "Faces and facing" can be confusing that's why "Primary and Secondary" shoes and "Rear and Front" are used in the manuals? The primary shoe always goes to the rear! That's the shoe with the long lining. Short lining shoes are secondary and go on the front, regardless of left or right sides. The self adjusting levers are located on the primary shoes as well with the strut engaging the front secondary shoe. Heres a pic with some instruction, https://pbase.com/nufsed/image/49448862 And not to confuse any further, its easy to mismatch those star wheel adjusters and get them put on the wrong side just as you, me, and anybody else that has done countless brake shoe replacement jobs have done. Everything appears good in your pic except the shoes, simply swap positions of the shoes in your pic and your golden...One fix at a time because my RAM (random access memory) has gone from megabytes to minibytes in my sixty somethin years of breathing asbestos and lead...Good luck! ~Ghostrider~

[geezer#99]

Those small blocks are just tubing tees that someone used to join the brake lines. Likely used because they didn’t know how to bend up a complete brake line.
Potential leak points.

[nelson-ohio]

oops, I guess I just got myself an extra 60 minutes of work for today. Sorry guys, should read the post more carefully.


I guess it was just a practice round yesterday.

[volksworld]

on self energizing brakes (where the adjuster floats and isnt attached to the backing plate),as the brakes are applied they grab the drum and try to spin with it...which basically jams the rear shoe against the drum and mechanically applies more braking force than just the pressure from the wheel cylinder...as a result the rear shoe does more of the work and needs more lining surface area

[Ironangel]

Originally Posted by nelson-ohio

oops, I guess I just got myself an extra 60 minutes of work for today. Sorry guys, should read the post more carefully.


I guess it was just a practice round yesterday.

All good, "The road to knowledge is paved with mistakes." Once everything is correct in those drums, adjust the shoes to where they just begin to contact the drums and your done. From there they should pump up with the least amount of effort and fluid giving a more positive feel at the pedal. I noticed the MC has two of what appears to be same size/volume reservoirs. My 72 C/10s have a large reservoir forward and a smaller reservoir aft or closer to the booster. It is my understanding that disc/drum MC's have the large/small reservoirs and the drum/drum MC's used the MC's with equally sized reservoirs?

[volksworld]

i believe the master he has in there is the typical aftermarket conversion master lots of places sell...its based on a corvette disc/disc master so both resevoirs are large....the only thing i'd doublecheck is whether the front and rear lines are hooked to the correct ends of the proportioning valve...but i think if they werent you'd be locking up the rears

[RichardJ]

>>can be confusing that's why "Primary and Secondary" shoes and "Rear and Front" are used in the manuals? The primary shoe always goes to the rear! That's the shoe with the long lining. Short lining shoes are secondary and go on the front,<<

Yes, the longer lining is on the rear, but it is called the Secondary shoe. Mind, this only applies to single wheel cylinders, mounted on the top and both shoes rotate together in the direction with the drum and are self energizing.

Reservoir size has nothing to do with the operation of the brakes. The rear piston in the Master Cylinder is called the Primary Piston. The front piston is the Secondary Piston. Either piston and outlet can be used for front or rear. As volksworld pointed out, the Combination Valve outlets are very important and can't be interchanged. The Proportioning end of the Combo Valve must go to the rear brakes. The other end of the Combo Valve has a Metering Valve and it must be connected to the front brakes.

By the time Disc Brake Pads wear down to nothing, most of the fluid held in reserve in the Reservoir will have been transferred to the back of the Calipers. If the Reservoir is too small, that circuit will run out of fluid before you find out the disc pads are completely worn out. By then you are pushing air into the lines.

Modern brake systems use a single Reservoir that in most cases is probably too small. They use a Fluid Level Sensor in the reservoir to turn on a dash Brake Warning Light. If everything works correctly the light will come on a few thousand miles before the Pad Screech Bars start dragging on the rotors.
I've seen a few aftermarket replacement pads for newer vehicles that didn't have the Screech Bars.

[nelson-ohio]

Thanks guys for all the info. I reworked the passenger side which I reversed yesterday by mistake, it took about 35 minutes, but that's because I spend 10 of that looking for the spring when it came apart and shot across the floor.

The driver side had a different problem, one of the pin holding the spring in is shorter for some reason. I noticed how tight the spring was when I took it apart. Now I need to get a new pin for this side, hope this is something NAPA has in stock. Since I took the power steering pump out to get it rebuilt, I guess I have at least 6-7 days to get this side done anyways before I can drive it.

[RustyPile]

Originally Posted by nelson-ohio

Thanks guys for all the info. I reworked the passenger side which I reversed yesterday by mistake, it took about 35 minutes, but that's because I spend 10 of that looking for the spring when it came apart and shot across the floor.

The driver side had a different problem, one of the pin holding the spring in is shorter for some reason. I noticed how tight the spring was when I took it apart. Now I need to get a new pin for this side, hope this is something NAPA has in stock. Since I took the power steering pump out to get it rebuilt, I guess I have at least 6-7 days to get this side done anyways before I can drive it.

For a few bux you can replace all the brake hardware, including springs, pins and adjusters.... And yes, NAPA should have everything you need..

[nelson-ohio]

Ok, got the driver side rear shoes done as well. Didn't take long, 20 minutes max. Getting good at this now with all the practice. Most importantly, I believe this time I did it correctly.

Tomorrow I will be dropping off the steering pump to get it rebuilt. Hope to get it back in a week and looking forward to driving the truck again.


I'm considering taking the truck to a brake specialist recommended by a few car shops around, if this does not improve things much. I want to get this done sooner instead of spending time to mess with it.


One thing I do like to add is a set of nice comfortable shock. The truck rides to rough. I don't want to change the springs or lowering it. Does anyone have any good recommendation for suspension shock absorbers for comfort?

[nelson-ohio]

Ok, finally this is done. Being away for a while, so this took a lot longer than it should.

After replacing most of the components, the braking didn't really improve, took it to a local shop that specializes in brake systems. They put on a dual diaphragm booster and everything is OK. The first one they installed to test the setup was 1 they had on the shelf for many years, it failed after about a week, just as I was driving the truck back to the shop so they can put on one that's new and get the paddle set right. In the end, they installed a 9-1/2" rebuilt dual unit, and it feels just about right. It's not a chromed unit, unlike most of the parts in the engine bay, but I'm going to leave it like that for a while, I'm done messing with this part for now.

I also installed a vacuum pump kit, with the engine vacuum as a supplement. Just in case the pump fails for some reason. Been driving it for about 3 weeks now, everything seems to be running well. However, the engine wouldn't crank after I drove for a while and tried to start again within 5 minutes, had to wait about 20 minutes then it was cranking OK. Maybe the starter motor? It's always something right.

[Baker72chevy]

Have you change the 3 rubber line on the brake system just checking

[nelson-ohio]

No I didn't replace any rubber line. Is it a problem with the higher pressure or something?

Are there 3? I only remember 2, 1 for each of the front wheels about 12" long.

[Baker72chevy]

There one on the rear to

[nelson-ohio]

Ok, I think I remember that one in the back too. So they have different ones for different pressure?