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'72 521 brake rebuild time


ttyR2

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There's a leak in the brake system on my son's 521. I replaced the three hoses and bled the system. It's still weeping somewhere but it hasn't been easy to find. With the age of the truck, I'm going to replace/rebuild the master cylinder/wheel cylinders. Is the Beck/Arnley parts on Rockauto of decent quality? They list Beck/Arnley, ACDelco, Centric, Dynamic Friction, and Raybestos as brands. new-datsun-pars.com has some of the cylinders available as well, but more expensive.

 

Would the '72 521 have 3/4 or 13/16 brake cylinders?

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Yes. Agree with the dual circuit master. With drum brakes, you will need residual valves in both front and rear lines. If you can find an early (not disc brake) 620 master, it will have them installed already.

 

Splitting the two circuits is easy enough. Just make sure you have the front going to the front and the rear going to the rear. You may need a coupler or two to get it done. Summit Racing sells a couple different generic 10x1.0 inverted flare couplers for a couple bucks apiece - https://www.summitracing.com/search/part-type/brake-fittings/universal/yes/fitting-attachment-1/female-inverted-flare/fitting-attachment-2/female-inverted-flare/fitting-size-1/m10-x-1-0

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can you see where the weep is?

 

I was loosing fluid just enought I need to top off every 2 weeks or so.

My wheel cylinder had a little fluid in there but ot enought to what I was loosing

Make long story short, my brake line was rusted by the fuel tank hose on top of the frame. Dirt will cake on the frame and cause it to rot out.

521 use SAE brake threads on the lines I think its 5/16

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On 7/24/2022 at 1:04 PM, mklotz70 said:

If it's the m/c, it's hard to tell.  It runs down the firewall and hides under the floor mat or carpet.  Now would be a good time to upgrade to a dual reservoir m/c.....much safer!!

 

Easy enough to check for wetness under the carpet.

 

On 7/25/2022 at 9:40 AM, Stoffregen Motorsports said:

Yes. Agree with the dual circuit master. With drum brakes, you will need residual valves in both front and rear lines. If you can find an early (not disc brake) 620 master, it will have them installed already.

 

Splitting the two circuits is easy enough. Just make sure you have the front going to the front and the rear going to the rear. You may need a coupler or two to get it done. Summit Racing sells a couple different generic 10x1.0 inverted flare couplers for a couple bucks apiece - https://www.summitracing.com/search/part-type/brake-fittings/universal/yes/fitting-attachment-1/female-inverted-flare/fitting-attachment-2/female-inverted-flare/fitting-size-1/m10-x-1-0

 

Get an adjustable brake line pressure valve so you can dial in the rear bias so they don't lock up before the fronts.

 

 

Wheel cylinders are the most obvious place to look. If bad enough the inside of the tires will have a wet spray pattern or drips on the drums.

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4 hours ago, mainer311 said:

The threads are 3/8-24 everywhere.

 

It’s likely weeping from a slave cylinder inside one of the drums. Popping the drums off should make it immediately evident.

Oh, yeah. 521 is SAE. Even easier to find parts for.

 

I don't know why, but the metric brake bias valve from WIlwood uses 10x1.0 bubble flare. Who the hell uses bubble flare anymore?

Edited by Stoffregen Motorsports
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