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Another pl521 brake thread!


fisch

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Yup I am having brake issues too in the 521. But I don't know if that is just how they opperate, or if I don't have them adjusted right. I've never had 4 wheel drums before.

 

It stops, but you better plan ahead, and honestly I haven't been driving that much cause if something jumped out in front of me, I don't think I could stop in time.

 

If I am going slow I can get them to lock (like in the driveway), but with any speed you have to really press the shit out of that pedal forcefully to get it to stop in any sort of timely predictable manner. It will slow the vehicle down, but you have no idea if you will make your turn.

 

My wife drove it for the first time with a HEAVY load of dirt in the back, and she was really scared when she hit the brakes and it didn't seem to slow down. She had to use the e-brake when she came down into the driveway.

 

What I've done so far:

 

-rebuilt the brake master (did not bench bleed though)

-Replace the front passenger wheel cylinder

-Replaced front passenger drum.

-Replaced front passenger shoes (driver shoes look fine)

-Replaced both adjusters in the front (rears adjust fine)

-bled the system in order from back Passenger side to front driver side. No bubble in line.

-Used adjusters

 

And this is how I adjusted them:

 

Pumped brakes 5 times, tapped adjuster forward, turned star wheel till it locks, backed it off till wheel rotated with just an occasional little rub. And then I repeated this same procedure at least 3 extra times per wheel.

 

I am not sure what spongy brakes feel like can someone describe the difference? I don't think they are spongy, but I am used to power brakes.

 

AND now that I am remembering that I DID NOT bench bleed that master cylinder when I rebuilt it, could this be the issue???

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Try pumping the pedal a few times and then hold. Do they feel firmer? If so that is what is known as a spongy pedal, it means you have air in the system. Pumping it builds air pressure, creating a firmer pedal.

 

It could be the master if it is new. You can bleed the master on the truck by pumping the pedal, holding and the cracking the lines loose.

 

It migh also mean your shoes are still out of adjustment, but I'm leaning towards air in the system.

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You havent mentioned anything about having to pump the pedal. So i will assume that the pedal is decent/good on the first pump. I also think that the method that you used to adjust the brakes should be fine. I do it a little different, but i think we end up the same. And if your pedal is good on the first pump, then the master cylinder bench bleeding is fine.

 

I think that you have a problem in the wheel cylinders. I think that the wheels cylinder(s) pistons are rusted solid into there housings. This will give you an excellent pedal feel. Even when not adjusted at all. And it will give you zero stopping power from that cylinder.

 

Jack the truck up and apply the brake and see if it will stop the wheel from turning. I am betting on rear cylinder both being rusted solid. You replace one front and if the other front isnt working you would have a crazy brake pull toward the new cylinder.

 

Or remove the drums one at a time, and watch the wheel cylinder piston as somebody else applies the brake slowly.

 

Jason

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Great advise JAson Thanks man!!!

 

How far should the pedal travel before it is firm? Mine feels like it travels 1.5 inches to about a third of the way down before it engages.

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JASON! You are a freaking genius! Sure enough my brake pedal does NOTHING to stop the back wheels turning. NAda! Zip!

 

Man I am so glad I asked!

 

The fronts work, even the old cylinder as you predicted.

 

Man this was a tricky thing. The backs bled fine, they adjusted fine, I thought all was fine back there. I never would have though they weren't working.

 

But based on how near-impossible it was to get that front cylinder off, as it was so corroded, I should have guessed. Hell I had to use a hammer and chisel to get the front cylinder off, and broke the chisel in the process.

 

I am elated that i know what's wrong. Thanks again Jason.

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On the rare chance that you or a previous owner / mechanic have "upgraded" to silicone brake fluid be aware that improved moisture resistance comes at the expense of a compressable brake fluid that give an inherently spongy brake pedal. If you don't know what the previous owner experimented with a full drain. flush. refille and bleed like a champion blood doner is in order.

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Now that we know what the problem is, lets consider something. One front cylinder has already been replaced because it was bad. Now both rear cylinders need replaced cause they are bad. You are working with a 75% failure rate of those old Datsun cylinders. I would consider replacing the fourth cylinder so that i know they are all good. Not maybe good. Your life can depend on your brakes, and its only one more cylinder.

 

Your brake pedal height sounds about right, if anything maybe a little too good. You may find that the pedal gets just a little lower when the rear cylinders are working. When the rear pistons move, the pedal will need to move a little more fluid, creating the pedal drop.

 

Jason

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Your brake pedal height sounds about right, if anything maybe a little too good. You may find that the pedal gets just a little lower when the rear cylinders are working. When the rear pistons move, the pedal will need to move a little more fluid, creating the pedal drop.

 

Jason

 

Ahh, the lack of pedal travel is making even more sense Jason. And I will heed your warning about the third and final cylinder.

 

And thanks for the advise Mikerl411. Sponginess doesn't seem to be an issue, but I will certainly keep that in mind.

 

This beast sat for 10 years before I got it. MAny things have been frozen from white corosion where aluminum meets steel, bolts and t-stat housings broken. I guess it is only natural the same applies to the brakes!

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Heh I am the ass here! Since everything bled and adjusted fine, I just ASS-u-med they were working.

 

Thinking now, it is just common sense that I should have replaced them from the get go, but I thought they worked since the signs told me so. And I heard 521 brakes are not so good even when they are working, so I thought this might just be the way they are... remember this is the first vehicle I have really ever worked on, my inexperience shows through today.

 

But perhaps someone will learn from my inexperience!

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My drum brake 620 stopped reasonably well. It was by no means on par with even 620 disc brakes. But it never scared the shit out of me. I admittedly drove it like it had drum brakes - plenty of distance behind the car in front of me, etc.

 

I drove it daily for two years with stock drums. I replaced the front shoes once and I bled/adjusted them a couple times to keep them working best they could.

 

With all that said, my 521 will have disc brakes front and rear before I ever drive it!

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HOW THE HELL DO I GET THESE DRUMS OFF!

 

Man is there anything as frustrating on a datsun as trying to remove rusty brake parts! (I am sure there even more frustrating things, but can't think of it at the moment!)

 

This is even more aggravating than a corroded t-stat housing. Cause there is more than one to do!

 

I've adjust out the adjusters so there is no rub and PD Blasted and pounded on it w/a hammer. Not a budge yet. Do I need to upgrade to a sledge?

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loosen the star wheel adjusters as loose as they will go. then if you have to use a sledge do it. you'd burn up 50 dremel discs trying to get it off. this is where the phrase use a bigger hammer comes into play.:D

 

also spray loads wd-40 inside from the backside. you can never use too much wd-40.

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if your having trouble removing the rears this has worked for me but others may tell you not to do it. instead of smacking the drum smack the center of the hub. for some mechanical reason it knocks the axle loose from the drum.

 

on all four make sure you leave the lug nuts on so you dont bang up the threads.

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Just bought a 3 lb sledge to try to get er done. Also a propain torch incase the BFH (big F'n HAmmer) fails.

 

I will put cotton in the ears!

 

I have heard propain might not get it hot enough, but I don't have any other torch, and read on line that some have had success w/ it.

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THE B.F.H. DID THE TRICK!!!!

 

I got those bastards off.

 

It is funny, inside, the shoes are barely warn (cause they haven't been functioning!), and the outside of the cylinders is still pretty shiny. The shoes are not rusted to the back plate or anything. You can wiggle them a bit.

 

But even w/the drums off, pushing the brake pedal does nothing back there.

 

I bet those pistons inside the cylinder are frozen. We will see when I get the cylinders out. But I think that job will wait for next weekend. If they are anything like the front was it will be a total PITA!

 

Spinning the hubs doesn't sound that swell. Little grindy, but not massivly grindy. Since I have the drums off I should prolly read up on how to grease those puppies.

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My 620 is doing the same kinda thing. I should check to make sure all my wheel cylinders are working. And yes a BFH works good for getting stuck drummies off. Last time I was in the brakes for my truck I nmade sure to anti seize every piece that could seize. All the rub points on the backing plate, adjusters. And right around the hub openings. That should help with pulling the drums again.

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Fisch, you might just pick up some new rear wheel bearings if they are grindy at all. They are fairly cheap, but you will have to take them to a machine shop to get them pressed on and off. Shouldn't be very spendy for that either.

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My 510 had brake linings separated from the shoe. This caused one side to lock up. I had to beat the living shit out of the drum with a 3# sledge MANY times before it broke loose in the center from the stub axle. Once it was clearly broken loose in the center (it is obvious), I then used the jacking bolt threads to get the drum off. This is how it's made to work and it works very well. As long as the drum is not rusted to the axle. A generous soaking in PB Blaster also helps.

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Fisch, before you reinstall those drums, I would recommend getting a round file of some kind and filing the inside rust ring of the drum where it rides on the axle. then Antiseize the crap out of it, Helps a lot next time you have to take it apart. You could also antiseize the part of the wheel cylinder that goes through the backing plate.

 

Jason

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Drilling and tapping some wholes in the drum wouldn't be a bad idea, it seems some datto's have them and some don't. I like that system much better than the big hammer one :D

 

Steve I had the same thing happen when we took the orange good out on the first test run. I kept wanting to take in on the freeway, Thrillen and Frank didn't want to. Good thing, one of the rear breaks feel apart! An auto L series VS. a fucked up break... The L series did win though, the rear drum put up one hell of a fight!! :D

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  • 3 weeks later...

Just a follow up on this thread y'all.

 

Sure enough I got the rear cylinders replaced, and took JAson's advise and replaced that last front cylinder too. So I now have 4 new cylinders all around!

 

I read a tip on how to remove that stubborn front one. Just thread the nut till it is flush with bolt, then whack it with a hammer. That got it off!

 

I got everything bled including the master. Go the adjusters adjusted, and took it for a spin!

 

In an empty parking lot I got up to 30mph and hit the brakes. It stopped! It even tracked straight through the stop. But I tell ya these aren't antilock brakes that's for sure.

 

Then on the way home a guy pull out in front of me and the brakes got a real world test. They did their job! I don't know that it would have stopped in time before the replacement.

 

Thanks again for all the advice guys!

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