which brake master? and why?

[datson4life]

Need a brake master. Went 4 wheel disks from 4 wheel drums on a 521. In the front are wilwood piston calipers, and in the rear single piston isuzu. Which brale master is recommended and why? Dont care for brake booster, a nissan direct swap would be nice, but im a newb to why they are different sizes or bore

[datson4life]

Nevermind. Found a link

http://community.ratsun.net/topic/66525-521-front-disc-swapmaster-cylinder-proportioning-valve/

[wayno]

That thread doesn't really apply too your situation, you have disk brakes all around, so you need a brake master for disc brakes all around, I believe some of the Z cars had disc brakes all around.

You need to understand that brake masters with drum brakes all around have a 10lb residual valve, brake masters with front disc and rear drums have dual reservoirs with the front disc brake circuit having a 2lb residual valve, and the back circuit has a 10lb residual valve, now with disc brakes all around, you need a brake master that has 2 reservoirs that both circuits have 2lb residual valves, if the rear circuit has a 10lb residual valve on a disc brake, it could get hot and catch fire or maybe it would seize up first.

[datzenmike]

I put a 16/16" zx master in my disc brake front, drum brake rear car. It had the disc brake residual valve in the rear as the zx is disc brake all round, so I simply swapped the 10? pound residual from my stock master into it. Works fine. 

 

Any Nissan master that had front disc brakes is a source for residual valves. Note that the front brakes are at the rear on the master and there is usually an F and an R cast into them. The residual valves all look the same so have a care handling them.

 

The residual valves are just above the brake line fittings on the underside of the master.

 

 

 

The 521 has a single master so unlikely it will move enough fluid to work the larger disc brakes. The pedal will be mushy and travel much farther to the floor than feels comfortable. To move more fluid you will need a larger master and best that you have a dual master, so a failure in any line does not cause a total brake failure. Loss of fronts still leaves the rears working for example. Now...

 

To move more fluid will take more effort. Think of jacking up a heavy and a light car. You can't expect to increase your braking without any extra effort. A larger master will require more foot pressure. Putting a larger master on will make the brake pedal seem stiff with much less travel and seem like there is a brick under it.

 

This is why the brake booster was developed. It allows more braking on larger heavier cars and trucks. Using intake vacuum, it increases your foot pressure about 50% and does some of the braking for you. The 620 and the B-210 brake booster should fit a 521 (see wayno) and a '78-'79 620 has a 13/16" master that should be almost large enough for you but a 3/4" is even better. You will have to split the front brakes from the rear with a dual master.  This give you the added safety from total brake loss in the event of a leak.

[flatcat19]

Get master from later Z car that came with disc/disc.

[Draker]

16/16" or typo? For the future readers.

[flatcat19]

Custom 1 incher, eh?

[wayno]

I don't know about disc brakes all around, but my 521 work truck has the Hardbody(D21) V6 dual piston caliper disc brakes in the front, and has the 1985/86 Dually axle in the rear, I still have my stock 521 master brake cylinder and it works just fine, but I haul a trailer around behind the truck 99 percent of the time, and it has electric brakes that work great(will lock them up), so I just have not been that motivated to figure something out on a brake booster and a dual circuit brake master, as I have dual SUs in the truck, and clearance is a big issue.

I believe I could do it if I re-locate the clutch master so the booster can be mounted right on the firewall without a pedestal, I have an idea on how to do it, but just never got around to it as the brakes work fine as long as the electric trailer brakes work good.

Any brake booster will need a pedestal in the 521 to clear the clutch master, I have found that either the smaller 620 boosters or the Ford Courier booster/master will work in the 521, I have a 620 booster with the ford Courier master in my 520 with dual SUs, but I had too put a 521 pedal assembly in my 520 to clear the dual SUs and use thin/pancake air filters, not a lot of room left.

The Ford Courier brake master on a 620 brake booster

You can see the clutch master clearance.

The remote reservoir on the Ford Courier brake master cylinder

The Ford courier Booster will fit, but the inner fender needs some massaging, you can see I have the stock 521 brake master also, I had to gut the residual valve out of it to make it work, as before I took it out, the brakes seized and I had to open the brake bleeder on the front brakes to tow the truck, as I turned the driveline out of the truck 5 blocks from getting back home, this truck has a diesel, and has a shit load of torque.

 

I have since changed over to a dual circuit/reservoir brake master.

 

[datzenmike]

Thanks draker it of course was meant to be 15/16"

[flatcat19]

Ah, gee. I'm awfully sorry aboot that.

[datson4life]

Thanks fellas for the input. Lots of good info