Push rod adjustment on 71 K20

[Murphy IRE]

My brakes still don't stop the truck like they should. So after all the other things that I've replaced and done, I' ve learned that the adjustment on the push rod is critical. Rememering that the PO said he "Just put a new Master Cylinder in" before I bought it. The pedal is not soft or spongy, it has normal feel. If I stand on the pedal the truck will stop, but I can't do an emergency stop.
So, Do I need to remove the master cylinder to get at the push rod? Also, how much should I adjust it? I've attached a pic (It's a Delco MC). Any and all pointers are greatly appreceiated, Thanks in Advance!

[Longhorn Man]

adjusting this god doesn't do anything but get rid of the free play on the pedal. Do you have more than a 1/2 inch of freeplay at the top end of the travel on the brake pedal? If you aren't sure, lean in and swing the pedal with your hand and you'll fell it no question asked.
If this is OK, then the pushrod is not the problem. Your "I can't panic stop" comment makes me thing you have other issues.

[Stocker]

Almost sounds like your front brakes may not be working, or at least not working well. If the rears are doing the lion's share of the work, your stopping power will be feeble at best.

[cdowns]

whar size are rims and tires? oversize will affect weather brakes will lockup

[cparman]

This is my crude way of checking the clearance between the booster rod and the back of the master cylinder. I will unbolt the master cyl. without disconnecting the lines, and take a small ball of clay 1/4". gently push it into the back of the master cyl. Bolt the master back up, and then unbolt it, without depressing the brake pedal. Look carefully at the clay. See if it got squished? You do not need any more than a 1/16 or so of clearance. IF you have more than that adjust the rod in the booster, if it is adjustable. If not pull it out and weld a small bead of weld on it to make it longer. Done this a bunch of times.

As far as the rest of your braking system, make sure that the rear brakes are adjusted properly, Bleed the system again, make sure that the front brake calipers have the bleeders on the top of the calipers.

[Murphy IRE]

Sorry I didn't put all this in there in the first place, I've replaced the following:
Both calipers, pads and flex lines.
Both Drums, shoes, wheel cylinders and flex lines.
The vacuum line to the booster.
Flushed and bled the lines.
I'm running 285 85r 16 Tires (~32x9) nothing excessive!

When I'm on a steep 4x4 road, you can smell the front pads when I do a lot of braking. The brakes are better today, than when I brought her home. I'm pretty sure that's one of the reason why the PO sold her.
I'll check and post the movement of the pedal, but it doesn't seem to have excessive play. It only travels about 4 inches total and the pedal resistance at the end is about the same as at 2 inches. She hits the end of the movement and that's all she'll give. I'm 6'2" and I can stand on it, but she just comes to a gentle stop.

[Murphy IRE]

Free travel is about 1/2 inch. The brake lights at about 3/4 to 1 inch. Total movement is about 2 3/4 inch

[coloradosean2009]

I guess it would be nice to get some feedback from the "old timers" on the board to let us know how much braking power a '71 K-20 should have. I would expect the truck could lock em up from the factory, but you may be chasing a ghost.

[coloradosean2009]

I compared your connections for the hard lines to my setup to see if the lines may be plumbed wrong. Yours appear to be properly routed (large line to front of MC and back of PV).

[oldblue1968chevy]

Are they sticking (fluid not comming back to MC)

[geezer#99]

A thought. Do you have enough vacuum to run your booster? There's a minimum required. Check it in gear. Might be too low.
You might need a vacuum can!!

[Lee H]

I also looked at my line routing and found it different than yours. Not saying mine is right but by comparison, My 72 2WD, SWB, with PS would lock them up with the stock size tires. Now running sticky 255 70 15s and it will not lock them up but will bring it to a stop very quickly.

On mine, the larger diameter line goes from the rear port of MC to the rear port of the PV and the smaller diameter line goes from the front port of the MC to the front port of the PV. I tried to verify the correct routing in my Chilton's but that detail is not there. Would like to hear from several other folks as to their routing. Guess after 40+ years lot's of things happen. Cheers

[rsavage]

Cparman gave you good advice and a good way of adjusting the booster rod. I would bet that with proper adjustment (providing you have good vacuum) you will stop well. Don't leave the MC just supported by the brake lines while adjusting the booster rods - hang it with a bungee to the hood so you don't kink a line. I have power drums on my 70 SWB 4X4 and was experiencing the same symptons until I adjusted the booster pushrod out. Now it stops well. Same thing occurred when I converted my 2WD Burb to power. Adjusted the booster push rod and now it will put you through the windshield. Of course that one is 2WD

[swamp rat]

I have been reading this thread with great interest, can anybody tell how tight the 90* elbow is suppost to be in the booster? I know mine was a little loose feeling. I heard the way to check was to just hook a hose using ether a vac pump or your mouth ect to it, put a vacume on it to see if it holds.

[coloradosean2009]

Originally Posted by swamp rat

I have been reading this thread with great interest, can anybody tell how tight the 90* elbow is suppost to be in the booster? I know mine was a little loose feeling. I heard the way to check was to just hook a hose using ether a vac pump or your mouth ect to it, put a vacume on it to see if it holds.

It is supposed to be loose. When the vacuum is applied, it pulls tight against the rubber grommet .

[Murphy IRE]

Thanks for all the advice. I have some time off later this week and I will get going on it. I'll let you know how it goes.

[pat 70/71]

maybe try loosening the lines at the master and re bleed it. could be the reason for your poor brake performance. cheers, Pat

[Murphy IRE]

I did the ball of plumbers putty and at best I have 1/16" clearance. In the last two weeks, I noticed a couple of things. It's pulling hard to the right while appling the brakes and it just started pulling left while driving. I put her up this morning and the drivers side caliper is sticking and not fully engaging. So, I'm picking up a new caliper this afternoon. I'll check the vacuum later but the seal was tight when I release the hose from the booster. I have another thread poor brakes on a 71 K20. I'll shift the brake repair to that thread

[1970 CST STEP]

if i were a betting man, i would bet the po did not bench bleed the mc, assuming everything else has been checked!!

[Murphy IRE]

I replaced the MC and bled it in place. Bled all the lines. The brakes are better, but I did check the vacuum and I only have 14.5 in Park and about 12 in gear. I think that explains the really poor stopping while idling down a dirt road in the mountains. Will a vacuum can help or do I need something to build more vacuum. Or both? I didn't see anything in LMC or Brothers. I thought I saw something in the CPP catalog to build vacuum, but it was really expensive. As always any help and/or suggestions is greatly appreciated!