71 521 stiff brake pedal

[d.p]

Out of nowhere my brake paddle is stiff as hell with little to no travel. Feels like brakes are sticking. What do I need to check?

[wayno]

Pedal rod adjustment.

[d.p]

How do I do that? Out and about and would love to fix this before I head home.

[wayno]

I don't know what you have done to your brakes lately so it's hard to give advise.

Is it the stock master?

You still have the drum brakes?

You can open the bleed valve to release the pressure then close it to get home if it is not very far.

[banzai510(hainz)]

I think I mentioen this before

 

My brake master would pump up and not release.

I had to pop the bleed screw and it would release.  I cooked the brakes when I got home..  I swapped out the brake master.  It was a Doorman brand cast IRON model.

 

 

I noticed the more i pressed the brake the more it got worse.

 

 

when one buys a new master the rod needs to be adjusted where there is no preload(rod being pushed in) when it mounts to the fire wall.   I have to cut a few threads so it dont hit the back side of the brake pedal to get the adjustment correct.

[d.p]

Have not touched the brakes.

 

Still on stock drums an stock master (AFAIK) and everything was working fine until today.  Just got in and drove it around and the brake pedal got super stiff.   In neutral with the ebrake off it doesnt move, so they are locked up tight.  

 

Where is the bleed valve?

[banzai510(hainz)]

All of the sudden?

only thing I cant think of is you left the parking brake ON or there is soemthing jammed up some where.   wheel cylinder not releasing

 

Bleed Valve?  backside of the wheels.  I just picked one. I picked the rear. and released the pressure and brake fluid cam SQUIRTING out. If not under pressure it just oozess out.

[d.p]

Bled the driver side rear, fluid pissed out and now the pedal came back but its spongey as all hell now.  I guess air in the system now.   What causes this?  Should I replace the brake master at this point?

[banzai510(hainz)]

I just hit the bleed real quick and drive it and see what happens. If better then it might pump up again. then I would think its the master but make sure you got it ajusted at the pedal where your rod is fully comming out.

 

Be honest I have ran a master low and just added.

 

if you think there is air at the right rear then blled it real quick.(get your wife to push the padal and hold it and release the bleed. or use a clear hose and keep felling and bledding till its clear..

Its up to you to figure this out . Im just saying what has been my proplem with my 521 over the years.

 

This is why i buy 2 of everything when it come to hydralic parts as most is now mexico china taiwan italy and they dont last on a daily driver. 5 years max.

[d.p]

Bled it again and it feels better know. Will probably move to disc in the front soon.

[rinigado]

Maybe not what you ran into, but I had a problem with the brake light switch. the stopper was too thick (I stuck a bolt in there cuz the original little stopper was missing). It hit the brake light switch before the piston fully retracted, and that made the brake unable to fully bleed back out when I let off brakes. Driving around for a while, and it just kept getting just a little bit stiffer every time I hit the brakes until it was stiff as hell. Make sure the brake piston can get back out (brake pedal should have just a little bit of play when not pressed)

[d.p]

Maybe not what you ran into, but I had a problem with the brake light switch. the stopper was too thick (I stuck a bolt in there cuz the original little stopper was missing). It hit the brake light switch before the piston fully retracted, and that made the brake unable to fully bleed back out when I let off brakes. Driving around for a while, and it just kept getting just a little bit stiffer every time I hit the brakes until it was stiff as hell. Make sure the brake piston can get back out (brake pedal should have just a little bit of play when not pressed)

Dunno because I haven't had any problems since owning the truck (500 miles or so) and haven't touched the brakes. Just assume something is on its way out but not sure what yet. Bleeding the driver rear fixed my problem today and will have to wait to see if it happens again.

[wayno]

If you keep getting air into the brake system every week or so(3/4 days if driven every day), that could be a sign that the brake master is going bad, I had this issue, but my brake pedal would get lower and lower till I had to pump the brakes to get them to work, all I had to do was pump the brake pedal, put a stick between the pedal and seat to hold the pedal under pressure, bleed my right rear brake once and all was good for a few days, I repeated this every other day for a long time, I kept replacing the rear wheel cylinders but the issue kept returning, and the front brakes never had air in them, BTW I have front disc brakes with the 10lb residual valve removed in the stock 521 master brake cylinder, I have been driving it this way for over 10 years, so I don't need to hear about how bad this is the way I have it set up from anyone, it works great for me, and I have electric trailer brakes also, I haul a trailer every day I work with this 521 work truck of mine.

Some day I will put a power brake booster on it with a dual circuit brake master, I just am not there yet.

[d.p]

Yeah thinking that is the way to go.  What did you do for brake lines when using the stock MC?  Metric on one end and SAE on the other?  

[wayno]

Yeah thinking that is the way to go.  What did you do for brake lines when using the stock MC?  Metric on one end and SAE on the other?  

If your talking about the connection from the front hard line to the front disc brake hose, I changed out that fitting to metric as I make my own lines from scratch.

Recently I changed from drum to disc brakes on my 1963 Datsun 320, I was able to use the new caliper banjo bolt on my old 320 hose by reaming the first 1/8th inch of the 320 fitting on the bolt end of the fitting, not the caliper end using my drill press, just the very end needed opened up, and it worked fine.

I make my own brake lines, I make the double flairs and all the bends, cut them to length, I do it all, but I have a good brake line flair kit made decades ago.

[d.p]

If your talking about the connection from the front hard line to the front disc brake hose, I changed out that fitting to metric as I make my own lines from scratch.

 

Yeah that is what I am talking about, the hard line is SAE no?  So is that hose metric on the caliper end and SAE on the hard line side?  

 

Silverminemotors is telling me that 521s came with both metric and SAE brake lines which is news to me. I thought all 521s are SAE on the brake side.  

[wayno]

Yeah that is what I am talking about, the hard line is SAE no?  So is that hose metric on the caliper end and SAE on the hard line side?  

 

Silverminemotors is telling me that 521s came with both metric and SAE brake lines which is news to me. I thought all 521s are SAE on the brake side.  

As Far as I know, all 521s are SAE except for the engine/transmission, all hoses and fittings are SAE.

The thing is that one can use a 620 rear brake cylinder on a 521 as long as it comes with the banjo bolt, as that metric banjo bolt will fit the same hole as the 521 SAE brake line "Y" fitting, so you are still using the 521 SAE front hose or rear hardline while using a metric brake part as long as it comes with the metric banjo bolt.

I can use a Nissan 720 rear brake cylinder on my 1963 Datsun 320, the rear brake adjuster is the same through all them years, lots of stuff interchanges, but you have to have certain parts like the banjo bolts for the rear brake cylinders to make it work, or modify the end of the 320/520/521 front brake hose to fit it to a 1985 Nissan 720 brake caliper.

[d.p]

Ok, can you confirm your front rubber brake hose has an SAE fitting on the hard line and metric fitting on the caliper side?

[wayno]

Ok, can you confirm your front rubber brake hose has an SAE fitting on the hard line and metric fitting on the caliper side?

The 320 did, but I was having issues, I could not get the brakes to work properly, I spent a week trying to get them to work, over that week I changed absolutely everything except the  brake line on the rear end itself, new rear wheel brake cylinders, new rear hose, new rear brake line going from brake master to the rear end hose where I kept it SAE, 2 different dual circuit brake masters, and even all new front brake lines which changed everything to metric fittings so then I went with the metric front hoses, I had started with Mikes disc brake brackets and new rotors and calipers, I changed everything and it still would not work, well I pulled a newbie mistake, I put the new front calipers on the wrong sides, they were upside down, I was stunned when I figured it out.

The 620 was the first truck to have metric brake line fittings, don't know what year it happened though, as I have never owned a 620, so I have never had the need to find out.

My 521 brake hard lines had SAE threads till I changed the front ones to metric when I did a V6 Hardbody front disc brake upgrade, but you need to keep in mind that my 521 work truck is highly modified, I suspect I have more than 50 different vehicle parts in that truck now, there was a thread here about that, but I cannot find it anymore.

[BigLeagueDrew]

A little TL;DR, but I'm having the same problem on mine, also a '71 521. One thing I didn't see mentioned was the old brake lines, the flexible ones, may be causing the issue. What happens when the lines get old is the inside starts falling a part and can make sort of a one way check valve. If the brake pedal feels normal after sitting for an extended period, the pressure is bleeding too slowly, and this may be the cause. I'm in the process of replacing my brake components right now, I'll let you know how it goes in the future.

[d.p]

Yeah I still don't know what caused it on mine.  Pretty sure the PO replaced all those flex brakes lines not too long before I bought it too.  But will keep it in mind if it happens again.  

[DaBlist]

 Make sure the brake piston can get back out (brake pedal should have just a little bit of play when not pressed)

 

Have you addressed this?

 

If the MC piston is not retracting enough inside the MC when it's at rest it will be covering the port to resivoir and you will build up pressure as the brake fluid heats up and have your original problem

[d.p]

Have you addressed this?

 

If the MC piston is not retracting enough inside the MC when it's at rest it will be covering the port to resivoir and you will build up pressure as the brake fluid heats up and have your original problem

 

Not really because I am not sure I understand what he was saying all that well.  

 

Piston at rest allows fluid in the from reservoir, when I push the brake pedal it pushes that piston in which covers that port and pushes fluid out the lines right?  So if it doesn't retract enough at rest to release the pressure than that could be my problem?  I just to need to make sure the piston can move freely inside the MC?   How do I do that?

[banzai510(hainz)]

Is the rod fully extended?  if yes then swap out the MC

[d.p]

No idea, how do I check?