poor brakes on 71 K20

[Murphy IRE]

OK I've looked through as many threads as I can. There is a lot of good advice and a lot of stuff I need to check. Here is the deal - The pedal is stiff (1/2" free travel, the lights come on at 3/4" & total travel is less than 3"), but I can't get the wheels to lock up on dirt. I do have boost (I will measure to see how much). I stopped the truck with the engine off and it was really tough to stop, so I know I'm getting boost!
Here is what I've done so far:
Replaced the front rotors, calipers, pads and up graded to SS flex lines
Replaced the rear drums, shoes, wheel cylinders and up graded to SS flex lines.
The PO said he replaced the booster with a Delco.
I'm attaching pics of the MC. The brake lines are two different sizes. The large should go to the rear and the smaller to the front. BUT which reservoir should the lines come from? Are they backwards?
A lot of the previous threads have solved the problem with a new MC so that will be my next purchase, but I want the lines to be correct.
Also, the prices on MC range from $18 (local parts store) to $70. Is there a real differnce? As always thanks in advance

[cdowns]

your brake fluid is very low hope your not using like that

[w3lfd]

Your symptoms sound like you haven't "rebalanced" the brake proportioning valve. If you only have a total of 3 inches of travel, that is probably the issue. The proportioning valves will lock the brakes down to one circuit when it senses an imbalance. Then you will get the brake light coming on when it hits the stop at the bottom of travel (at least that is what just happened to me last month).

http://www.classicperform.com/TechBo...t.htm#testprop

Look at the proportioning valve section. Disregard step one. Mine did not constantly trip the circuit but was still a prop valve issue.

What we ended up doing was to crack the line on each output of the prop valve and then press pedal to the floor. You will hear it pop and the pedal will go the whole way down when it recenters the block. Then, since we knew the back circuit was the "bad" one, we concentrated on bleeding it first. I hope this helps.

Also, when bleeding the back, we would get fluid out on the first 'pump and hold' but then no more fluid. The way we got around this was: do a single pump, let the pedal come up. Crack the bleeder. Then have your assistant press down with the bleeder open and hold it down while you tighten the bleeder. Rinse , repeat. We got tons of air out and had the system fixed up within about 10 minutes this way.

Also check out this thread. Lots of good info in regards to the valve: http://67-72chevytrucks.com/vboard/s...d.php?t=241722

[Murphy IRE]

Topped off the reservoir after I opened it. One of the rubber boots is all deformed too! I need to find where it went. I've only put 3 K on since the brake rebuild. I'm sure it's one of the front flex hose connection, you know the impossible location inside the frame.

Good info on the PV. I will attack on the next round!

Thanks guys!

[Murphy IRE]

I picked up a rebuilt MC. I checked the push rod clearance and it's 1/16". Inside the old MC is a sludge on the bottom of the cylinder. In the last couple of days I had some hard pulling to the right. The caliper on the drivers side is toast. So, I'm replacing that. But that's a different issue than the stiff brake pedal and poor stopping performance. It may be a part of the problem.
I've pulled the MC and I will remount it tonight along with the new caliper . The flare nut to the rear system doesn't want to come off, so I'm trying to do that without bending the bracket. I want to bleed the MC in place. I've read that the MC has to be level, but it slopes to the front and I have the Frt wheels already 2" off the ground. As long as I get the air out of the cylinder I should be ok right? Or is really better to bench bleed the MC? Seems to make a bigger mess.

[vectorit]

That power booster looks a lot like a Bendix model, which is popular on 4 wheel drum brakes. Was your truck always a disc brake rig?

[Dieselwrencher]

That's the same booster my 72 Longhorn has and it came factory with disc fronts.

[Murphy IRE]

It's a Delco Moraine and the original delivery ticket says Disc /drum.
I installed the MC and bleed it in place. Hooked the PV back up and started to gravity bleed the lines. The new caliper and the banjo fitting from the flex brake line won't mate up ( it keeps dripping fluid). I took it off and tried again and it's worse. I'll go back to Napa and see if I can get this calpier exchanged. It looks like there's a dip in the machining and that's allowing for the leak (MY luck)

[Lee H]

I check the master cylinder to proportioning valve lines on my 72 VS your pictures and mine are reversed. Not saying mine are right but the breaks work very well. I checked my Chilton's and assembly manuals but that detail is not there. Maybe a few peeps can check and give feed back on line routing.

[jsand6769]

You state the mastercylinder boot is all deformed, you did fill this system with dot 3 brake fluid only right. If you used any petroleum produect at all, you will need to replace the mastercylinder, wheel cylinders, hoses, callipers and flush the system,(petroleum products will swell all of the rubber in the brake syatem)

[71 super]

On a 3/4 ton truck the ports are reversed, so his prop valve is plumbed correctly for his truck if 3/4 ton, 1/2 ton trucks are set up front to front of prop valve, rear to rear. One of the differences in the two model versions of the truck.

[Lee H]

Originally Posted by 71 super

On a 3/4 ton truck the ports are reversed, so his prop valve is plumbed correctly for his truck if 3/4 ton, 1/2 ton trucks are set up front to front of prop valve, rear to rear. One of the differences in the two model versions of the truck.

Thanks for the explaination.

[leddzepp]

Originally Posted by Murphy IRE

It's a Delco Moraine and the original delivery ticket says Disc /drum.
I installed the MC and bleed it in place. Hooked the PV back up and started to gravity bleed the lines. The new caliper and the banjo fitting from the flex brake line won't mate up ( it keeps dripping fluid). I took it off and tried again and it's worse. I'll go back to Napa and see if I can get this calpier exchanged. It looks like there's a dip in the machining and that's allowing for the leak (MY luck)

Did you use copper washers when attaching the banjo fitting to the caliper?

[Murphy IRE]

I can't attest to the PO, but I have only used DOT 3. This is the second flush that I have done. There was some off color (dirty) in the lines, but the main source was the old MC and it's gone.
I used the brass crush washers, but the off-bevel machining was too great to compensate. I returned it to NAPA, only to get another defective caliper. This time the leak is at the bleeder nipple. It leaks at rest and the leak is significant when the engaged. It seems to me that the units aren't being truely inspected and certainly not pressure tested. After the BS from NAPA, I'm done with them. I went and grabbed one off the shelf from O'Reillys and I will install this morning. And YES, I truely inspected this one for defaults. I took off the valve and remove the cap to inspect the threads.

As a side note of frustation, how many millions of these calipers were made back in the day? Once remanufactured, half of them have gone to metric bleeder valves instead of american standard. The last bad Napa caliper used a #8 and the new one has a #10. Now I only need two flare wrenches instead of three!
I'll keep you posted on replacement and hopefully the final repair on my poor brakes!!!

[Murphy IRE]

One more defective caliper, but finally I got a good one. The new MC is in and I bled it in place with a bleeder kit and binder clips to hold the lines in place. Simple and easy. Bleed the lines and the hard pulling to the right is fixed. The old caliper was stuck in the middle.
I have the best stopping power I've ever had, it's almost there.
I checked the vacuum and I have about 14.5 in Park and about 12 in gear. Everything I've read indicates that I need 18 lbs.

Any suggestions??? As always, thanks in advance

[Dieselwrencher]

Has your engine had a cam swap that you know of? Have you checked for any vacuum leaks yet? One thing to consider when purchasing brake components, I always try to purchase new items when i can because you never know how well these parts actually get rebuilt. I mean look at the prices of them, you already know it seems to good to be true and they have a high failure rate from any of the parts stores from what I have seen and heard.

[Murphy IRE]

From all the threads out there, on a lot of different forums, the stiff pedal and low vacuum is a common theme. Again, I only have about 12" Hg in gear. I have to assume that the cams are a major factor. I'll recheck for leaks, but I think I found all of them already. In one of my earlier posts I said lbs instead of inches for the mercury. DUH!!!

I found a more reasonable price on a pump, but I'm going to try the salvage yards on some diesel trucks for a pump and a canister storage tank. One of the other threads indicated that the tank ( with a one way valve) will reduce the run time on the pump. Makes sense to store at 18" to 20" and have the pump rest. With constant use on mountain roads, I don't think that volume ( just a tank) will get the booster to max out on the push rod to the master cylinder. Any opinions???

[swamp rat]

>>> In one of my earlier posts I said lbs instead of inches for the mercury. DUH!!!<<<

I remember reading that but declined to post a comment about it.

[Murphy IRE]

After all the Stuffed I've tried and replaced, it finally came down to $733 plus another $20 for misc stuff and I invested in a hydraulic brake booster.
NOW she finally will stop in an emergency!!! What a difference! I found ABS Power brake in Orange, CA. I still have to replace the fender well. I had to take it off do make everything fit.

[Murphy IRE]

Here's the pic