Prop valve or Dist block?

[ubtripn]

I have been researching a ton and have thoroughly confused myself. I have a 68 with 4 wheel Power drum. From what I read it distributes the same pressure to all four tires.

My question is - Do I need to do anything with it when bleeding? Is there a cylinder in it that needs centering? If it is just there for warning me with a light then I am good to ignore it right?

[cleszkie]

If you have a warning light system, then you have a cylinder that needs to be held in the centered position. The warning light switch is triggered when the cylinder moves and the spring loaded pin on the switch is allowed to move into a deeper groove in the cylinder. Otherwise, you will continually trip the low pressure safety system when you try to bleed your brakes, and kill the flow of brake fluid to the open system that you are trying to bleed. The original proportioning valves have a "button" on the front of the valve that needs to be held in the out position with a special tool. On the newer billet aluminum proportioning valves, you remove the warning light switch by unscrewing it, then you screw in a brake bleeding tool in that hole to hold the cylinder in the centered position. You can find that tool by doing a quick google search.

[cdowns]

you have a distribution block don't listen to the pror clown answer as you don't have a proportion valve and nothing he has to say is relevent

[cleszkie]

Originally Posted by cdowns

you have a distribution block don't listen to the pror clown answer as you don't have a proportion valve and nothing he has to say is relevent

Geez you are an angry SOB aren't you? It was my understanding that he had a warning light system. If he has a warning light, how does it function without somehow monitoring the difference in pressure between the front and rear? Maybe you could educate me on this like a normal contributor to this board instead of just being a jerk.

[davepl]

Originally Posted by cdowns

you have a distribution block don't listen to the pror clown answer as you don't have a proportion valve and nothing he has to say is relevent

Mondays are hard.

[jocko]

The usual tact, I've learned to ignore.

To the question - yes, on 68, all 4 drums - all 1/4" lines - equal pressure, but a braking system that can be isolated on either side of the distrib block (it's not a proportion inf valve - prop'ing is accomplished internally to the mc on these 4 wheel drum systems). If you lose a wheel cylinder or have a leak, pressure will drop on that system overall (i.e. front or rear) and the valve in the block will move to isolate the leak so you don't bleed out all your fluid - it's a safety measure instituted in 67 (for trucks) that leaves you with at least front or rear brakes. If you have the wire hooked up and your light is off (but you know it's functional) then no, there is nothing you need to do with it. If the light is on, the valve is tripped and it may indicate a leak (or a bad distrib block). Bottom line, if the light pops on while driving along, realize you're on a single brake circuit now and get it checked out. You will know which system is bad by checking for the low reservoir in the mc. Keep in mind that across these years and gvwr's of trucks, that the front reservoir is not always the front brakes, etc. Follow the lines to know which system is bad. If the valve has bee tripped to isolate a system and you fix the leak, there is a reset procedure. Several threads herein that outline it and, perhaps more reliably than my directions, it's in the service manual.

[ubtripn]

Here is the deal, the light went on while bleeding cuz I went to the floor with the pedal by mistake but is off now. It is driving like it is on one circuit. I was just about to have it bled professionally again but I don't think they know about this. What is the reset procedure? Thanks all.

Also, can I gravity bleed the front?

I think this is what the inside of the dist block looks like:
http://67-72chevytrucks.com/vboard/a...1&d=1463849047

[jocko]

Hard to quantify "driving like it is on one circuit" after a brake job has been performed, several variables in plan (i.e. several things the mechanic could have hosed up). If the light appears to be working, and is off now, then you are not likely driving on one circuit. What are the levels in the reservoirs? Monitor to see if one is going down and the other is not. A slow leak may not be immediately detected and trigger the light - but, on the other hand, neither would a slow leak suddenly give the impression of driving on one circuit. It is more likely that the brake shoes are not properly adjusted. Yes, you can gravity bleed.

[cleszkie]

Thanks Jocko. I shouldn't let him bother me. But I don't like it when he does it at the expense of spreading misinformation to people who need real answers to their questions.

As I stated above, and Jocko expanded upon, the valve in the distribution block will interpret an open bleeder screw on your caliper as a very bad leak, and will isolate the leaking system (either front or back) to prevent total fluid loss and to maintain integrity of the non-leaking system so you can still stop. in order to prevent this isolation during bleeding, the valve needs to be held in the open position with whatever tool is required for the given distribution block style/type.

[ubtripn]

So, to be clear, with a distribution box like I have (Not a proportioning valve) I need a tool or something to hold open a valve on the distribution block to bleed my brakes?

what I have: http://67-72chevytrucks.com/vboard/a...1&d=1278083868

[cleszkie]

The tool with look like one of the following depending on what type of block you have. Based on your picture, I would say its the one that gets swapped into the hole that the switch is located in.

[ubtripn]

SWEET! Thank you! So I need the valve open while bleeding?

[ubtripn]

If I take the switch out all together does air enter the system?

[ubtripn]

Also, do people bleed without messing with this at all?

[RichardJ]

The tool with the yellow end is used to hold open the Metering Valve while bleeding disc brakes.
You don't have disc brakes, you don't have a Combination Valve and you don't have a metering valve.

If the brake light comes on while bleeding the brakes, all you have to do is go to the opposite end of the vehicle and while someone is pushing on the brake pedal, crack the bleeder valve and close it as soon as your helper tells you the light is out. If you wait too long, the pressure will push the switch piston to the opposite end and the light will come back on. You can literally chase your own tail by going back and forth from front to back, cracking a valve and turning the light off and on again. Think of it as a 3-way light switch and someone is playing a trick on you.
The differential switch is a 2-ended piston that moves to the end with the lowest pressure. The problem is that it will NOT RESET itself after bleeding.

The pin screwed into the switch hole prevents the piston from moving while bleeding. It is simple a time saver for those that don't want to use pedal pressure to reset the switch.

Get the brake line away from the hot headers or you are just wasting your time.

[ubtripn]

sounds good - thank you all!