Brake troubleshooting help needed

[brossow]

Today I replaced both front calipers on the '79 shortbed I acquired yesterday. As I mentioned in my build thread (link below), the front passenger caliper seized up while taking the truck off the trailer. (At least, I'm assuming it seized up. That wheel, and only that wheel, locked up good and tight and nothing was gonna make it move again.) At only $14 each, I replaced both calipers instead of just the one -- would have been crazy not to while I had all the tools out. The pads were still good on both sides, so I just cleaned them up and reused them. Hoses looked to be in good condition as well.

Here's the problem: even with both front bleeders wide open, the brake pedal is rock hard and won't move more than an inch or so. With both front wheels spinning freely now, I have virtually no brakes. As far as I can tell, no fluid is moving through the front lines at all.

Fluid in the reservoir is exactly where it should be. Back wheels seem to turn just fine (moved the truck carefully using a big log in front of a wheel to stop the truck). Any ideas? Could the MC be frozen up? I'm not an expert when it comes to brake systems and could use some advice. I really don't want to spend hundreds of hours on this and was naively expecting to just replace a caliper, bleed the brakes, and be done with it.

Thanks,
Brent

[brossow]

Now I'm wondering about the master cylinder. All of the parts places online (Auto Zone, Advance Auto, etc.) all picture a solid metal MC, but the one in the truck (pictured below) has a plastic reservoir. Has it been replaced with a newer model at some point? If so, should I switch back to whatever the parts stores list for the truck?

UPDATE: Further searching reveals that the MC looks like one that was used from '81-up. Is that a problem? If replacing the MC, which one should I go with? The type it has now or the type it came with from the factory? It probably doesn't make a bit of difference, but I don't want to screw something up when it comes to the brakes.

[brossow]

Okay, I'm starting to feel like I'm talking to myself here.

Anyway I've narrowed it down a bit at least. One at a time, I disconnected the lines at the master cylinder. With the front line disconnected, the pedal traveled a bit and piddled out a bit of fluid. With the back line disconnected, the pedal hit the floor and shot a bunch of fluid into the can my helper (9yo Shaw) was holding. So it's not the MC and I have a problem somewhere in the rear lines. I'll start with the obvious and replace the wheel cylinders. This scares the hell out of me, however, as this is EXACTLY how my '72 shortbed started out and ended up as a frame-off rebuild. LOL!

[brossow]

Umm ... think I may have found the problem. See anything wrong with the picture below? Yes, that is exactly what I found when I pulled the rear passenger drum. D'oh!

Poked around in the cab and found a bag with all the missing parts. I haven't gotten as far as actually replacing the wheel cylinder, but I'm guessing that a previous owner (I think I'm the 4th owner since 2008, according to old title copies I found in the glove box) had the same brake problems I'm having and got as far as pulling the stuff but never got around to putting it back together. I'm now guessing the guy who sold it to me knew about the brake problems but didn't say anything. (I didn't test drive it -- just looked it over and figured for the price I could fix anything that needed fixing.) I should know by now not to be surprised by any crazy thing a previous owner does, but this still wasn't something I expected to find.

So ... the mini-saga continues....

[raycow]

For starts, I would be wondering why the fronts aren't getting any fluid and why you don't have a really bad leak at the rear. The first thing that comes to mind is the shuttle pin in the distribution block or proportioning valve.

Ray

[brossow]

Originally Posted by raycow

For starts, I would be wondering why the fronts aren't getting any fluid and why you don't have a really bad leak at the rear. The first thing that comes to mind is the shuttle pin in the distribution block or proportioning valve.

Ray

I'll be pulling the lines from the distribution block and/or prop valve later today to see if I get fluid through there. I picked up new wheel cylinders and various new hardware last night, and that will all go on regardless of what I find up front.

I'm sure the reason I wasn't getting any fluid up front is because the pedal wouldn't move with the rear line connected. If I can't push the pedal, the fluid can't move.

[lolife99]

Change the rubber front brake lines. They can collapse on the inside which can be undetected on the outside.
I would just go at it like you are rebuilding all the brakes.
Stock '79 master cylinder would be my first choice also.

[texastrendz]

change the rubber line in the back also... mine broke down inside and had no rear brakes.

[brossow]

Status update:

Virtually no pedal movement with all lines connected. Disconnected (read: twisted off) the rear passenger line at the wheel cylinder and with the line open there is once again full pedal travel and fluid squirting out in full force. Obviously a bad wheel cylinder back there, possibly on the other side as well (have not yet tackled that side).

Visually inspected all three rubber lines and they all look to be MUCH newer than the truck and in excellent condition. At this point (particularly because no local parts stores have the front lines in stock) I'm going to leave them alone. I can always replace them later, but my goal right now is to get the truck drivable -- and stoppable -- for as little money as possible.

Replaced so far:

• Both front calipers
• Right rear wheel cylinder
• Right rear hard brake line
• Right rear brake shoes
• All right rear brake hardware except parking brake lever

Yet to do:

• Same as above for left rear
• Bleed the brakes
• Test drive
• ???
• Profit!

Not sure when I'll get time to do the other side and bleed the brakes, but likely not until next weekend. Thanks for all the advice so far!

[brossow]

Anyone know what this piece is? One came with the general brake hardware kit (with the springs, pins, etc.) and another came with the new adjuster kit (leading me to believe it has something to do with the adjuster). Didn't find one with the old parts, which miraculously seemed to all be there in the bag, nor have I ever seen one before. Hate to leave it out if it's a critical component.

[brossow]

Closing out this thread:

Got the brakes wrapped up (more or less) a couple weeks ago. Ended up with new hard lines, hose, wheel cylinders, shoes, and hardware out back -- the only things reused were the drums, which looked to be in good [enough] condition. Up front it was new calipers, hoses, and one hard line (passenger side -- was easier to cut it off and bend a new one than to try to unscrew it from the hose end of things due to the cramped conditions there). I think the majority of the problem was that the left front hose was fubar, although it didn't help that there was literally nothing inside the right rear drum -- no shoes, no hardware, nada except the e-brake lever.

Don't think the booster is working (replacement on the way) but otherwise things seem good. Wheels lock up under hard braking on my gravel driveway and release when they're supposed to, so I think this problem is 90% solved (with the rest of the solution hopefully involving just six nuts and a few minutes to swap out the old booster for the new one).

[raycow]

Did you ever find out what the mystery part was, or where it was supposed to go?

Ray

[brossow]

Originally Posted by raycow

Did you ever find out what the mystery part was, or where it was supposed to go?

Ray

Nope. Despite disassembling virtually the entire brake system, I didn't come across any parts that even vaguely resembled it, nor any place where it even looked like it might fit, so I'm assuming it's not critical. Sure would be nice to know what it's for, but it doesn't keep me up at night.

[john]

I think your mystery part is a clip in plug for the brake adjusting hole. The older trucks had a metal plug and later ones used a rubber plug. Yours possibly had a knockout in the drum.

[brossow]

Originally Posted by john

I think your mystery part is a clip in plug for the brake adjusting hole. The older trucks had a metal plug and later ones used a rubber plug. Yours possibly had a knockout in the drum.

Oh! That makes perfect sense. I've never seen a metal plug before; all my work to date had been on stuff that used rubber plugs, so that never even crossed my mind. Thanks!