Disc Brake Conversion on 71 521

[Crashtd420]

32 minutes ago, Sapoo said:

Well if anyone has a spare kit from Mike they’d like to sell I’d be very interested 

Try reaching out to mike , hes extremely nice .. maybe he'd be willing to share the specs on the bracket and you could have them made... then just source the remaining components yourself....

[Sapoo]

On 2/20/2023 at 11:43 AM, Crashtd420 said:

Try reaching out to mike , hes extremely nice .. maybe he'd be willing to share the specs on the bracket and you could have them made... then just source the remaining components yourself....

Good idea!!! 

[d.p]

Wouldn’t beebani’s bracket be easier to copy?  

[mainer311]

I think Beebani’s required the use of 15” wheels.

[mklotz70]

On 2/20/2023 at 11:43 AM, Crashtd420 said:

Try reaching out to mike , hes extremely nice .. maybe he'd be willing to share the specs on the bracket and you could have them made... then just source the remaining components yourself....

 

Thanks. :)   I posted the steel bracket CAD on my site a few years ago. http://www.bluehandsinc.com/brake-kit-cad.html  If you guys can find another Datsun machinist to make the aluminum ones for you, I'm not against the idea of sharing the CAD models for those too.  

 

 

On 2/21/2023 at 6:16 PM, mainer311 said:

I think Beebani’s required the use of 15” wheels.

 

Yes, they required 15" rims.  My brake setup, steel or aluminum, was the only one that would allow stock steel 14" rims....or any 14" rim for that matter.  The steel brackets used 720 rotors and require an 1/8" wheel spacer to run stock rims.  The reason is due to the 3/8" plate used.  If the main plate was made from 1/4", then HB rotors could be run.  The ears could be 1/4" too.  I wanted to be sure the plates wouldn't flex.  Bee's brackets were 1/4" armor plate steel.  

Edited February 24, 2023 by mklotz70

[mklotz70]

deleted as I said I would.

Edited February 24, 2023 by mklotz70

[Sapoo]

3 hours ago, mklotz70 said:

I'll try to remember to come back and delete this stuff.

 

I just went through the parts/supplies.....I have one 620 kit available....that's it.  It can't be a 521 kit because I can't add metal back to the inner bearing adapters. lol  The other 4 are already spoken for.  Once the 620 kit is spoken for, I'll delete this post and most of the last and I'll do the rest of the communications via email.  

DM sent and I also sent you a message through your site. More than happy to prepay. Thank you! 

[Biggs]

Hoping the participants of this thread are still involved with the site.

 

I’m a glutton for punishment as I have followed through on modifications to my 72 521 including an L-18 (it was rebuilt and available), Weber carb (planning to go to dual SUs), GM one-wire (wouldn’t repeat) and 4-wheel disc brake conversion.  
 

I did the front brakes first and liked them so decided to move on to the rears.  It was much more of a job than the fronts, but in always up for a challenge.  My issue with this work, though, is I don’t seem to have enough volume of brake fluid in my 7/8” bore 280 Z master cylinder.  I’d hoped the Z’s m/c would do the trick, but it does not. 

 

Any suggestions on what to try for a master cylinder?  I’d like to keep it all Datsun/Nissan, if possible. 

[thisismatt]

Only option would be the 15/16 280ZX master but the correct ones are getting really hard to find. There's a 1" Wildwood that will work. Are you sure everything is bled and you have the correct residual valves in? Does the pedal get hard, just too much travel?

[Biggs]

Brakes have been bled and re-bled.   The fronts will brake.  The rears less so.  I guess I could try different residual valves, but not sure that will help since pedal goes all the way.  I’ve looked at 1” Willwood and thought that seemed a logical next step but wanted to check to see what others have done. 

[Crashtd420]

14 hours ago, Biggs said:

Brakes have been bled and re-bled.   The fronts will brake.  The rears less so.  I guess I could try different residual valves, but not sure that will help since pedal goes all the way.  I’ve looked at 1” Willwood and thought that seemed a logical next step but wanted to check to see what others have done. 

I'm not sure residual valves are the answer to your issue....

They only hold a certain amount of pressure...

2lbs for disk....

10lbs for drums....

 

If you have a disk/drum master and disks all around you should change the rear residual valve.... 

 

With that said I'm pretty sure I'm running a 3/4 bore master from the 620 on my 521 .... haven't experienced any issues.... I have 4 wheel disk using the nissan calipers in the front and Isuzu in the rear.....

 

Also by design the fronts brake more than the rears.... average around a 60/40 ratio..... 

 

How are you determining that the rears are less so?

Also what does pedal goes all the way?

Do you mean to the floor?

 

Is it possible you just need to adjust the free play in the pedal? 

[datzenmike]

The stock 521 master is a single cylinder (my '71 was) that has to provide for all four wheels..  If you have a 7/8 from a Z car then you have a dual circuit so the question is, did you separate front from rears? You  probably know this but the front of the dual master is the rear circuit and the rear of the master is for the fronts. They are marked F and R.

 

Another point is... what calipers are you using? as larger will need more fluid to work than smaller. The master can be guesstimated by what was required to work with them. A 7/8" is basically 14/16" so definitely larger than the stock single 11/16". If not moving enough fluid the brakes will work, but the pedal travel will be excessive and feel mushy. Moving more fluid is fine, but comes at a cost of more effort. Nothing is free and a 7/8" working properly might be extremely stiff to operate. Most dual circuit masters have a vacuum powered brake booster.

 

The 7/8" Z car had drum brakes on the rear so find any Datsun dual MC and pull the front (disc brake) residual valve out and replace the rear residual valve with it. The residual valves are on the output line on the the master body. Pay attention as drum and disc look identical.

 

 

Hold brake on and loosen the output hard lines slowly, one at a time. Have rags handy to catch any fluid expelled. Hold brake while tightening the line so air is not sucked back in. This is to remove any air trapped in the master. See if that firms up the pedal.

[Stoffregen Motorsports]

16 hours ago, Biggs said:

 

Hoping the participants of this thread are still involved with the site.

 

I’m a glutton for punishment as I have followed through on modifications to my 72 521 including an L-18 (it was rebuilt and available), Weber carb (planning to go to dual SUs), GM one-wire (wouldn’t repeat) and 4-wheel disc brake conversion.  
 

I did the front brakes first and liked them so decided to move on to the rears.  It was much more of a job than the fronts, but in always up for a challenge.  My issue with this work, though, is I don’t seem to have enough volume of brake fluid in my 7/8” bore 280 Z master cylinder.  I’d hoped the Z’s m/c would do the trick, but it does not. 

 

Any suggestions on what to try for a master cylinder?  I’d like to keep it all Datsun/Nissan, if possible. 

Wilwood sells a 1" master that's nearly identical to the Datsun master  - https://www.wilwood.com/mastercylinders/MasterCylinderProd?itemno=260-8794

[Stoffregen Motorsports]

I believe the main difference, other than the bore size, is the bolt spacing on the mounting flange. If I recall, it needs to be filed slightly to fit a Datsun.

 

[mainer311]

Obvious question, but have BOTH circuits of the MC been bled? It’s hard to get air out of the MC. You need to start there first.

Edited January 29 by mainer311

[datzenmike]

No Datsun brake system above 3/4" is without a booster and for good reason.

 

A 1" is 30% larger than a 7/8" so effort is also increased by 30%

 

A 7/8 should perform better than what's described. Soft pedal is from air or too small a master.

[mainer311]

There’s no way that there isn’t enough volume to actuate all four brakes. Something else is wrong.

[Stoffregen Motorsports]

Yep, good point. Bleed it again and check all the adjustments.

[datzenmike]

It's assumed that this was converted to dual braking system?

[Biggs]

Wow!  You guys are AWESOME!!  I appreciate the enlightenment and showing me the error of my ways.

 

I hadn't thought enough about it but using a disc/drum dual circuit M/C on a disc/disc dual circuit setup is asking for problems, especially when not done correctly.  It's a no brainer to require the addition of a residual valve on the new back half of the equation.  It worked great when I'd just done the front and still had the drums on the back, so why not go ahead and do the back, too? Sometimes you can't see the forest for the trees.

 

I like the idea that I've over master cylindered the setup, too.  I knew pedal force would need to increase (F=PA) but thought I'd need the extra volume due to the size of the dual piston 300ZX non-turbo front calipers and the Isuzu Tropper single piston rears.  As stated above though, extra volume should not be needed if the correct residual valve is added to the back circuit.

 

There may also be other issues with the setup.  With the truck fully elevated and tested with the wheels on, the fronts spun manually stopped hard when braked but the rears seemed to stop much less abruptly.  I bled the brakes using the pressure pot on the m/c which works great when everything fits correctly and makes an incredible mess when fit is less than perfect.  Good thing paint is planned!  It did find a blockage in the old splitter mounted on the H190 axle.  Given this, it's likely the rear drums never worked as I don't recall having tested them prior to removal.  I'll test again in the coming days with the old vacuum pump and install the needed residual valve.

 

Thanks again!

[Biggs]

9 hours ago, datzenmike said:

The 7/8" Z car had drum brakes on the rear so find any Datsun dual MC and pull the front (disc brake) residual valve out and replace the rear residual valve with it. The residual valves are on the output line on the the master body. Pay attention as drum and disc look identical.

 

Please help me out with this comment.  Why would I want to remove the front circuit's residual valve and move it to the back?

 

BTW, I just see one place for one residual valve on the m/c.

 

Thanks!

[datzenmike]

No. Pull a disc brake residual valve from another Datsun master cylinder. Put it in the rear circuit of your 7/8" master.

 

The residual valve has nothing to do with fluid volume passing through it. The residual valve prevents all the brake pressure from returning to zero when letting off the brake. There's a small spring inside that requires more than about 2 PSI to hold it open. Thus about 2PSI remains in the rear brake lines. (well also in the front lines too) This is just enough to keep the pads gently against the rotors to keep them clean. If you have ever spun a wheel with disc brakes obviously it does not at all drag.

 

Drum brakes have springs and linkages and plenty of slop so 12 PSI is used to remove any slack and have the shoes instantly ready to move when the pressure rises.

 

If disc brakes are used with a drum 12 psi residual valve (5-6 times more) the pad can rub hard enough to drag significantly and heat up the rotor and wear the pads out faster.

[mainer311]

It should be noted that you can also just remove the drum residual valve from the rear circuit, and reinstall the cap with no residual valve, and the whole thing will work just fine.

[demo243]

Does the 521 have a load sensing  valve like the 620?

 

I had a hell of time getting that bled on my 620, but once it was done it make a big difference.

 

That would drastically effect the rears if you have an issue there

[datzenmike]

No. Not all 620 have it either. '77 and on have it