Brake Pipe Distribution and Switch

[Harmon C.]

I have new calipers,hoses,and M/C. The problem is I have good front brakes but no rear. I have the Motive presure bleeder at 15# and removed the line from the distribution block and get no fluid. The GM manual says replace the unit. The brake light goes on every time I step on the brakes. Is their a way to center the valve? Can this block be the problem? Oh this is the second M/C and it bench bleed OK. I'm working on a 73.

Lyly

[Jeffrey S.]

Re: Brake Pipe Distribution and Switch

Lyle:
Did you try to open the lines at the brass block with the switch on the OPPOSITE side (the front lines) and press hard on the pedal? This might force the switch to the other side. The brake light on my '69 also goes on when I apply the brakes so I have the lead disconnected but I have perfect brakes all around. This trick did not solve my problem but I am told it works many times. The next step wouild be to remove the switch from the block and try to repair it. I don't know if this is possible but there is a hex on the switch which apparently indicates that it is removable. Just some thoughts. BTW- I enjoyed our conversatins at Bloomington. I hope everything worked out well for you there.
Jeff

[Harmon C.]

Re: Brake Pipe Distribution and Switch

Jeff

I have a spare block I am looking at so maybe I will take the switch out and try to learn how it operates. I had a good day at the show Sat. and as allways get to see friends in the hobby.

Lyle

[Harmon C.]

Update

With the pressure at 20# on the Motive bleeder I took the line off the master cylinder and had no flow of fluid. I pressed the pedal and got some flow started. I hooked up the lines while I had flow and blead the rears and the fronts.

Off for a ride and front brakes lock up on a hard stop but rears do very little. This is the second rebuilt M/C I had but I have one more fresh rebuilt in stock I think I will try. I also took back a M/C than when bench blead never stoped blowing bubbles.

I love wqrking on brakes. I think pulling the body off the frame is easier.

Lyle

[Jeffrey S.]

Re: Brake Pipe Distribution and Switch

Lyle:
Please let me know what you see when you take the switch out of the block. I have been putting off this repair for years because I was afraid of damaging the thing beyond repair. Thanks.
Jeff

[Stephen L.]

Re: Update

Had a problem on my M/C. Turned out the rubber cup (and associated hardware)in the bore of the M/C did not travel rearward enough with the pedal out to clear the hole from the reservoir. No fluid would be let into the cylinder chamber. Thus weak/no brakes.
Check it out by looking into the reservoir and watching to see if the rubber passes the hole while someone depresses the pedal. You should be able to stick a small drill bit into the cyl thru the hole when the pedal is fully retracted.
The problem was the rear metal plunger inside the M/C was too long.
In your case, maybe the shaft from the pedal needs adjusting. It may be too long

[Patrick H.]

Re: Update

I had something similar on my 70 Cutlass. I temporarily used an extra washer between the MC and the firewall on each stud to test my theory. When I did this to compensate, all worked well.

I went and purchased a different new MC and problem solved.

Patrick

[Harmon C.]

Re: Brake Pipe Distribution and Switch

Jeff
On the end of the switch was like a rubber seal. Their was a plunger with springs on both sides but I could not make it move with a drill rod in either end. As it turned out I had no flow to the rear side of the switch block so it was not the problem. I started breaking lines a the left rear but next time I will start at the M/C.

Lyle

[Harmon C.]

Re: Update

Steve
I have power brakes and know of no adjustment in the shaft length. I could shim it out as Patrick has said and it is worth a try about 6AM in the morning.

Lyle

[Stephen L.]

Re: Update

I believe there is a rod up under the dash that connects the pedal to the power brake diaphram. (See J50 A2 in the AIM) If you check your AIM there is a note concerning this adjustment on UPC 5 A2 and J50 A3.
The adjustment is made under the dash at the clevis.

[Stephen L.]

Re: Update

Patrick, you compensated for the shaft adjustment by placing washers under the mounts.
In my case the metal plunger inside the M/C was too long and the snap ring that holds the guts together dictated the stop point... not the shaft.
You may have gotten a plunger with a hole for the shaft that was shallow... thus the washer worked.

[Harmon C.]

Re: Update

Steve

I shimed it out to see if this is the problem. I did notice that the plunger was under tension before the bolts were tight so I hope this is the fix I was looking for. I will take a drive later and see how the brakes work.

I will look for the adjustment if the shims help.

Thanks

Lyle

[Stephen L.]

Re: Update

There should be no "tension/compression" when installing the M/C. Adjust your clevis and rod length and you should be home free. You'll probably need to bleed the brakes again after you make this adjustment

[Harmon C.]

Good Brakes at last only took 40 Hours

Steve
The shiming did not help the brakes or I didn't use enough shims. I had one more rebuilt M/C and bench blead it. When I removed the old M/C I noticed their was an adjustment on the rod. I made the rod about 1/4" shorter so the M/C was not under tension. I let the fluid leak out the outlet threads before the final tightening and did not blead the system. I have had the tires off so many times I'm about to wear out the studs. Test drove and now I have good brakes. I now know why I only work on my own junk.

Lyle

[Patrick H.]

Re: Update

Yes, the hole was not drilled deep enough. I still have that MC and have been tempted to drill it, but why?