Tech help, heat from hubs after rebuild...

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southerncruiser62 said:
Jerry, I couldn't imagine this being the case but if you are creating alot of heat near the master cylinder or even the brake lines, the fluid tends to expand and thus increasing the pressure on the caliper pistons. Another scenerio could be that the lines are slightly kinked and as you press the pedal you are forcing fluid through however as you release the pedal it isn't drawing as much fluid back through thus keeping the piston from fully releasing.
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What if there were a problem with the brake booster, not having enough vacuum to pull fluid back, is that possible?

I'll be going through the rest of the hard lines to make sure they aren't the issue. When I bleed them, they push out fine but I can't tell if its "sucking" back up when the pedal is released.

Oh well, I knew I shouldn't have bragged that all was good...
 
Did you remove the residual valve from the master?
All drum brake based masters have a spring and a little plug just inside the master where each brake line screws in. This is to keep pressure on the wheel cylinders for just a little bit in case you brake hard again. Disks do NOT need the valve and it must be removed.

Remove by unscrewing the giant brass nut on the side of the master. Pull out the spring and the little plunger deal for the line that feeds the disks. Put the giant brass nut back on and bleed it all out.

Another possibility is that the brake pedal free play is not set correctly. There must be enough free play between the pedal and the cylinder piston that it allows itself to move all the way back out. I don't have the manual in front of me, but something like 1/8" to 1/4" is okay.
 
rutbeer said:
Did you remove the residual valve from the master?
All drum brake based masters have a spring and a little plug just inside the master where each brake line screws in. This is to keep pressure on the wheel cylinders for just a little bit in case you brake hard again. Disks do NOT need the valve and it must be removed.

Remove by unscrewing the giant brass nut on the side of the master. Pull out the spring and the little plunger deal for the line that feeds the disks. Put the giant brass nut back on and bleed it all out.

Another possibility is that the brake pedal free play is not set correctly. There must be enough free play between the pedal and the cylinder piston that it allows itself to move all the way back out. I don't have the manual in front of me, but something like 1/8" to 1/4" is okay.
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Thanks, I'll check on both of those. The master was supposed to be for the 75-79 w/front discs. But, its worth checking that out for sure. Thanks, I had no clue about that. I do have the FSM and I'll check the pedal play as well...
 
Disks didn't start until 76 though.....AFAIK. Maybe that is the issue then. I would check that front port to make sure the spring and seat aren't in there.
 
I'm looking at the specter site and they do show a 75 application for a different style master. If your ports are on the side, check for the valve, if they are on top, I doubt they would be in there. There is "something" that goes inside the port, but the picture isn't large enough to see what that thing actually is. Specter Off-Road-Land Cruiser Parts - Page 014-Brake Master Cylinder, Booster & Pedal

You can clearly see what I'm talking about on the earlier one.
 
rutbeer said:
I'm looking at the specter site and they do show a 75 application for a different style master. If your ports are on the side, check for the valve, if they are on top, I doubt they would be in there. There is "something" that goes inside the port, but the picture isn't large enough to see what that thing actually is. Specter Off-Road-Land Cruiser Parts - Page 014-Brake Master Cylinder, Booster & Pedal

You can clearly see what I'm talking about on the earlier one.
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Yup, thats the one I got (well, similar) and they come out the side.

I did remove the nut and found the part in question, removed it with no effect on the "pumping up" of the brake pressure. I tested this by just sitting there, with the engine off (to remove the heat transfer idea Greg had) and with repeated pumping of the brakes, the pedal rose higher and higher until it was pretty much topped out and the brakes were locked up.

I inspected the lines and didn't see anything obvious. First thing I'm going to do is re-install the old master and see what happens there. If it still does the same thing, I'll be taking all the hard lines off and making up new ones. That is, unless someone else has an idea on what would cause the pressure to build up to a point that it locks the brakes up...:confused:
 
Okay, let me see if I have this right.
You have the early master with the ports out the side. You are running front disk only and you opened up the front port of the master and removed both the spring and the little plunger thingy. Is that correct?
You have checked your pedal free play and can confirm that there is some travel from the fully extended (by spring) position to when you hear, as you press the pedal in by hand, or feel the pushrod click against the piston inside the master cylinder. Correct?

If you are still experiencing problems with the front calipers locking (verified by lifting wheel off the ground and can't turn, then it's likely rust in the line or the rubber lines have fully deteriorated inside.

Try this: pull the flex line off the caliper and hard line off the master. Blow some compressed air in there is verify that it's flowing well. Easy test before you pull it all down.

On another topic, I didn't follow your early thread on what was done with the disk. What did you use for a proportioning valve for the rear? Is it plumbed correctly? They are directional.
 
rutbeer said:
Okay, let me see if I have this right.
You have the early master with the ports out the side.
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Yes...

rutbeer said:
You are running front disk only and you opened up the front port of the master and removed both the spring and the little plunger thingy. Is that correct?
Click to expand...

Yes...

rutbeer said:
You have checked your pedal free play and can confirm that there is some travel from the fully extended (by spring) position to when you hear, as you press the pedal in by hand, or feel the pushrod click against the piston inside the master cylinder. Correct?
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No...

rutbeer said:
If you are still experiencing problems with the front calipers locking (verified by lifting wheel off the ground and can't turn, then it's likely rust in the line or the rubber lines have fully deteriorated inside.

Try this: pull the flex line off the caliper and hard line off the master. Blow some compressed air in there is verify that it's flowing well. Easy test before you pull it all down.
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Good idea. Just to note, I bought new flex lines from the axle to the hub but not the other ones. When I bleed the brakes, it appears to flow very well when we depress the brake pedal, that is why I didn't feel it was a brake line issue. But, of course, it is getting more narrow to what it could be...

rutbeer said:
On another topic, I didn't follow your early thread on what was done with the disk. What did you use for a proportioning valve for the rear? Is it plumbed correctly? They are directional.
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Nothing. They don't shudder or appear to be warped when driving short distances and/or before they "lock up". I was advised that I wouldn't need a proportioning valve since I wasn't running discs on the back. When I have performed "brake checks" (aka, slamming them on in an attempt to lock them up), they "seem" pretty balanced. The backs do lock up first but just. I can brake hard enough to get the back to be "chirping" while the front are still rolling. If I had a proportioning valve, that is about how I would set them up anyway, right?

I really appreciate your guidance through this Barry, I'm getting a bit frustrated...
 
Nope, front brakes should always lock first when you can help it. That keeps the truck from swapping ends in emergency braking. Factory disk brake setups came with a prop valve for the drums in the rear, and if you run disks in the rear (GM parts) you WILL really need one.

Check the free play on the pedal man.... Sounds trivial, but you replaced the master, which means it NEEDS to be readjusted to be right.
For conversation purposes, let's say it returns 98% of the way back. That leaves 2% pressure still on the brakes. Every time you pump them, you add in another 2% and so on.
 
rutbeer said:
Nope, front brakes should always lock first when you can help it. That keeps the truck from swapping ends in emergency braking. Factory disk brake setups came with a prop valve for the drums in the rear, and if you run disks in the rear (GM parts) you WILL really need one.

Check the free play on the pedal man.... Sounds trivial, but you replaced the master, which means it NEEDS to be readjusted to be right.
For conversation purposes, let's say it returns 98% of the way back. That leaves 2% pressure still on the brakes. Every time you pump them, you add in another 2% and so on.
Click to expand...

I didn't mean to skip the importance of the play and that makes complete sense to me, follows what is happening. I'll get on it when I get home tonight and get it adjusted. I just got to start working on it when I had to get to work. It was an easy check for the master cylinder parts.

Thanks for reinforcing the reasoning behind it...
 
i'm not very knowledgeable about 40 parts, but off-the-cuff i would tend to agree with rutbeer in directing your focus on the MS.
 
Sorry I haven't followed up with this...I did get into the MS adjustment as well as the brake pedal adjustment. It "appears" to have made a difference though I can't say for 100% certainty until I get it bled again. All of my assistants have been unavailable (the wife and girls have been busy with stuff in the evenings) but I'll get it bled in the morning then take it for a test drive.

But, initial pumping of the brake pedal doesn't seem to cause the same pressure build as before and I can roll it around in the garage, which is a very good sign.

I'll follow up with final test results tomorrow. Thanks again Barry for thinking this through and getting me in the right direction...
 
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