'72 521 brake rebuild time

[ttyR2]

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?

[mklotz70]

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!!

 

[Stoffregen Motorsports]

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

[banzai510(hainz)]

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

[mainer311]

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.

[datzenmike]

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.

[Stoffregen Motorsports]

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 July 29, 2022 by Stoffregen Motorsports

[ttyR2]

Truck has been parked for a while. I need to get the brakes taken care of.

 

Which dual-master cylinder do I want to buy? One off of a specific model? And how do I want to split the brake system? Both fronts on one circuit, both rears on another?

[datzenmike]

Most dual brake masters are front disc/rear drum. Your 521 is all drum.

 

The 510 masters were 3/4" so slightly larger than the 521's 11/16". I actually put a '68 510 dual master on my '71 521. IIRC the 521 brake line fitting was the wrong flair for the 510 master but any dual master might be. Also I didn't know about the residual valve mentioned below...

 

Because it is a front disc brake master the residual valve isn't compatible with front drums.  You'll need a residual valve from a rear drum master and swap it into the front circuit.

 

 

I added an extra line from the master to the rear brake line to separate them. That's all I remember. Once bled they worked just fine.

[mklotz70]

'77 620 m/c should be a dual circuit and drum/drum.  Keep in mind that the 521 lines are SAE and the 620 m/c will be metric.  You'll need to add a line to connect the rear circuit to the rear brakes.  If you can flare your own lines, then that line will be SAE at the firewall end and metric at the m/c end.  The front line will either need a new metric nut flared on or you can use an adapter BLF-29C which you should be able to find at Autozone.  You'll need a barrel to connect the new rear line to the existing rear line at the block on the firewall.  Disconnect the stock rear line from the block and connect it to the new line with a barrel connector.  Make sure to get a plug to block off the hole you just created in the block.  Not the prettiest or best place, but if you add an adj proportioning valve to the rear circuit, you can use it in place of the barrel connector.

Edited March 20 by mklotz70

[banzai510(hainz)]

On 3/19/2024 at 11:35 PM, mklotz70 said:

Keep in mind that the 521 lines are SAE and the 620 m/c will be metric. 

I had a leak for years in my 521 .come to find out it was the brake line under the fuel filler hose. Mud cakes up there and is always wet and was rotted.

 

Now I replaced the rear section. was under the cab going across. the union was there. I but a new union and the fucker still has a slight leak. Cant win

Edited March 27 by banzai510(hainz)

[datzenmike]

Mike I started that post with an early 620 master then remembered I had done it with 510 master so erased it. YES the 620 would already had all drum masters. They are just a hair larger but have boosters. Should work on a 521, even better if you can keep the booster.

[ttyR2]

One of these guys? Off rockauto.com

https://www.rockauto.com/en/moreinfo.php?pk=8170632&cc=1210138&pt=1836&jsn=859

 

Would this work for a proportioning valve? It's labeled as having two inputs, but I see no outlet...nevermind. You can see "outlet" cast into the body, even though the stickers say inlet.

https://www.summitracing.com/parts/wil-260-8419

Edited March 20 by ttyR2

[datzenmike]

 

https://www.rockauto.com/en/moreinfo.php?pk=8170632&cc=1210138&pt=1836&jsn=859

 

This is a 3/4". The 521 is 5/8", just a little smaller. Would work if this master is for four wheel drum brakes. Try one for a '73-'77 620 truck.

 

You don't need a proportioning valve. The brake bias is built into the system. If (for some unexplained reason) the rear wheels lock before the fronts then yes you could fit one to dial back the line pressure to the back. They should lock together.

[ttyR2]

That link was from a '77 620 on the Rockauto site..sounds like it should work. The 521 is four wheel drums.

[banzai510(hainz)]

remeber 521 is SAEon the trucks  later Datsuns all metric

Edited March 30 by banzai510(hainz)

[mainer311]

On 3/27/2024 at 4:11 PM, banzai510(hainz) said:

remeber 521 is SAE threads(pre 1970) on the trucks  later Datsuns all metric

 

NOT pre-70. My 71 and I’ll bet the 72 is still SAE.

[datzenmike]

Christ I had one in the '70-'80s for 8 years, changed engines and transmissions and don't remember. At the time I would only have had SAE wrenches and would have had to buy metric. 45 years ago and a lot of water under the bridge.

[banzai510(hainz)]

4 hours ago, mainer311 said:

72 is still SAE.

Correct 521 last truck to have SAE.

All Roadsters also SAE