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71 521 stiff brake pedal


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See the rod connected to the brake pedal that goes into the brake master in the photo below.


See how it has a nut and a lock nut.




When you push the brake pedal lightly there should be a little bit of movement in the pedal where the piston in the brake master doesn't move, if it does move then you need to loosen the lock nut on the brake pedal rod then spin the rod counter clockwise till the pedal does move without the piston in the master doesn't move.

Now I realize that my master doesn't have a rubber boot on it and it never will because I have put a dual circuit master into a 320 truck and there isn't room for the boot, but you should be able to feel that slight bit of looseness before the brake master cylinder piston moves.

If you have it adjusted wrong it will not let the piston in the bore return far enough to allow the fluid in the brake lines return into the brake master reservoir, when this happens the brakes start to drag on the drums/rotors depending on what brakes you have, this in turn heats up the brakes which heats up the brake fluid which expands, since the fluid cannot get back into the reservoir and the fluid is expanding from getting hot, the brakes get more and more pressure on them till they catch fire or stop the vehicle, I had this happen on my 1969 Datsun diesel, the engine had the torque to break.shear the drive line bolts between the transmission and transfer case, but this happened to me because I had front disc brakes on that vehicle but still had the stock 521 master for drum brakes all around, so I removed the residual valve from the master and I was good to go.

You need to have a slight bit of play in the brake pedal, if you don't you are going to have issues.

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Mine just has a single nut on it and the arm looks fairly new whereas MC looks old as shit.  No boot on mine either.  PO did the brakes back in 2011 and drove the truck maybe 500 miles from then until I bought it last year. I have since put roughly another 500-600 miles on it.


PO did 'brake shoes all around, drums, wheel cylinders, return springs, and hoses.'

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Ok, still have this problem.   How can you tell if the piston is moving or not when adjusting the push rod??  And seeing that my problem may be the push rod is already making contact with the piston should I just back it out a little bit and see if that helps? 

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I don't think you want the rod to move while adjusting the pedal

on waynos 3rd photo you see there is a space inbetween the end of the threaded rod and the pedal. I notice on Newr master cylinder sold you have to cut this as it could be too long  and causes the rod to be pushed as you mount it on the fire wall.



I always have to cut mine(threaded rod)


just make sure the rod comes out till it natural state(fully extended)  that's pretty much it. then you might have to cut the rod then do a final adjustment with the fork where the pin goes thru to the pedal.


I had adjusted mine and it was still the master was BAD

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All I can say is loosen the lock nut and back it off a couple turns, then either with needle nose pliers or your fingers if you can spin that shaft counter clockwise a few turns, then lightly push the pedal and see if you can feel a little bit of play, if no play keep turning it counter clockwise, go for a quarter to half inch of play at first, once it releases the fluid to go back into the reservoir, then you can go back till you have an eighth inch play.

Now when turning that shaft you may have the issue that Hainz has been talking about, the threaded shaft may start to hit the pedal arm as you spin that shaft and it threads itself closer and closer to the pedal arm, if it get within a sixteenth of an inch of the pedal arm, then you will likely have to remove the master so you can cut some of the shaft off so you will have more adjustment, it would help if you could get a photo like this one below in better focus than mine, then we could all tell how much room you have left before the shaft needs cut, I have lots of room, but this is a photo of my 1963 Datsun L320 with a Datsun 720 truck master installed, and because I didn't have the tool to enlarge the brake master hole and I didn't want to change anything else on the firewall, I used spacers between the firewall and the brake master, so I had to delete the rubber boot on the master, but this works great so I am not going to worry about the boot unless it causes me an issue, I will deal with that later if it becomes an issue.


You may only have to turn that shaft a turn to get it to release the trapped brake fluid, I had it down to a quarter turn on the truck in the photo above, I was fighting that brake system for a week until I finally figured out that I had my disc brake calipers on the wrong sides and they were upside down, it is impossible to bleed out the air in the calipers if they are mounted upside down, but I have a completely new brake system now, as I changed everything trying to figure out the issue I was having, and it was a newbie mistake, the only reason I figured it out was because I decided I had to start over, and I looked at the first thing I put on(the calipers) and seen the bleed screw was at the bottom not the top, but it was pointed up.

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Alright, looks like the push rod is butted up against the brake pedal.  Which means if the push rod isn't fully retracting I would have to cut it to give it more room to retract?  Could this be my problem? 









The pic above the brake pedal is on the right.  

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discconnet the pin an see if the push rod goes out a little bit more.

going by the photo I think you could cut say a  1/2inch



well your going to have to pull the master out to cut unless somebody has a better trick. a spin wheel cut off tool  thn you don't have to bleed the system.  take that fork off find a nut tosrew on there then cut the threads then pull the nut off to clean up the threads as it comes off.


I usually do the fitting before hooking up the brake line on my brake and clutch masters

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Hey so I finally got around to replacing all the flex hoses, wheel cylinders, and master cylinder. Let the car sit for 5 days to find a hard brake pedal. I re adjusted the master cylinder push rod and brake light switch and I have pretty good pedal feel now. I did cut off a very small section of the push rod without removing the master using a cut off wheel. Hope you're able to sort out the issue.

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Got it cut and pedal was somewhat soft after so I went to bleed the rear and it drained the fucking MC so there are no brakes at all.  


Do I have to bench bleed the MC now?  then bleed all 4 corners? 


Fuck nothing ever easy with these trucks.  

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Thanks Wayno, I got the brakes back but there is a lot of travel before they engage.  Would that be push rod adjustement or air in the system? 


Also I have 3 (8mm, 11mm, 12mm) different size bleeder screws (thanks a ton PO) and one of the passenger fronts is completely rounded off.  I bled that one by just loosening the entire cylinder as there was no I was breaking the bleeder screw loose.   Will probably order all new cylinders and speed bleeders to make this shit easier next time.  

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Now it sounds like the rod is too loose, you want just an eighth inch play before the master plunger in the bore starts moving, that is an eighth inch where your foot is on the pedal, maybe you turned it in too far.

It's hard to do this over the internet, first your rods were hitting the pedal and that took a while before that got straightened out because it's likely you didn't even know what you were being told to look for, now you have too much play, is the brake pedal lower than the clutch pedal?

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Nah they are almost even. Maybe brake is a little in front the clutch. Yeah I have never done this, have changed calipers/pads/rotors on new cars but never an MC w/drums and a push rod.  Looking at before and after cutting the push rod it looks like its adjusted further back now but I would think that would mean less travel and not more.  





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Then you need to adjust/thread the rod farther into the master till it feels better, if you go to far it will get stiff and not release the brakes anymore because the fluid cannot get back into the reservoir.

I am starting to wonder if your issue all along was the rod hitting the pedal arm rather than being adjusted to far into the master, this is why it is hard to deal with it over the internet, as we are not there to look at/see everything, we can only guess what the issue might be.

Also you said that one bleeder screw would not open, and you said that you loosened the whole assembly, do you mean you loosened the 9/16ths bolt to bleed it, if so you might have air between that bolt and the bleed screw, normally I would use a pair of vice grips to loosen the bleed screw as there could be air between that bleed screw and the bolt, that would make the pedal spongy, and if you pumped it fast enough the pedal would get to feeling better till you let of, then it would be spongy again.

Try adjusting the rod farther into the back of the master, do one turn at a time and see if things get better.

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I will turn it counter clockwise tomorrow and see if it helps.  


As far as the rounded bleeder I tried vise grips without any luck which is why I just loosened the bolt that holds the bleeder screw in.   This is the one front wheel cylinder on there:  http://www.rockauto.com/en/moreinfo.php?pk=2145718&cc=1212321&jsn=395


I ordered all new cylinders, MC and bleeder screws to get everything on the same page.   Also missing the cotter pin for the clevis, any idea where I can get a replacement?  

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