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master cyllinder change for disk brakes swap?


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I have a 72 4dr 510 with 280zx brakes in front and 240 rear brakes. Will the stock 3/4" master work to power these brakes? It did fine for the front but i just changed the rear to disk. Also do i need a different porpottioning valve or anything? i bought a 15/16 master from a 280zx but then was talking to people and they said i didnt need it. Some people also said theres something in the system that keeps pressure in the line for the rear drums which would cause draging if converted to disk in the rear. Any input is appreciated.

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Coments on Proportioning valves. Proportioning valves unrelated to the master cylinder. If your front & rear brakes are a matched set (e.g. both from a 280ZX) then you won't need a proportioning valve. If they are mix-n-match then you might need a proportioning valve to achieve a correct proportion.

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Will the ... master work to power these brakes? ... i just changed the rear to disk.


Master Cylinders have a Residual Check Valve which preloads the drum brakes with about 10 psi pressure. Only the portion of the M/C for the drums has a residual valve. This is sometimes called RLPV (residual line pressure valve), or RPCV (residual pressure check valve).


Disk brakes must not use a Residual Valve, but only need a weak pressure which naturally results from the M/C being mounted high on the firewall.


So, no, in stock form it won't work correctly -- the brakes will still work OK, but will wear faster than normal if the RV is left in place.


You should do either:

* swap in an all-discs Master Cylinder


* remove the Residual Valve(s) from the master cylinder. Like this:


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i bought a 15/16 master from a 280zx but then was talking to people and they said i didnt need it. Some people also said theres something in the system that keeps pressure in the line for the rear drums which would cause draging if converted to disk in the rear.

Correct me if I'm wrong ...

I think the 15/16" master cylinder from a 280zx is designed for four wheel disc brakes, so there isn't a "Residual Valve" to be concerned with.

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I think that is true. As far as I know all 280ZX had 4-wheel disc brakes.


Yes 4 wheel disc brakes.


ok so i took apart the 510 master and found that there are residual valves on front and rear should i remove both? or should i just use the 280zx master? the 280zx m/c mounting holes are perpendicular to the stock 510 holes. (hortizontal vs vertical stock)



I would remove both, since your M/C is already correct mounting style.


When you refill it, be sure to bleed right at the M/C outlets, before you bleed at the wheels.


I have a 15/16" 280zx master in my 710. They do have residual valves front and rear. As far as I know all disc brake masters do to retain several pounds of pressure in the lines to keep the pads slightly against the rotors to keep them 'clean'. Drum brakes use a stiffer spring to run an increased pressure on the drum shoes to reduce their travel.


Residual valve.



ZX rebuild kit. Both springs are identical. I would imagine a master with rear drums would have a larger or stiffer spring.




I would leave the residual valve in the rear of the master. (for the fronts)


Disc brakes require a lot of pressure to work effectively so a few extra pounds of residual pressure shouldn't hurt anything. But if worried, replace the front one (for the rears) with a proper valve. Pull one from another master cylinder that has disc brakes in the front.









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I have a 15/16" 280zx master in my 710. They do have residual valves front and rear.

This is good to know (great post, important information here) - Thanks!


I have a 15/16" 280zx m/c for my 620. The one I have has mounting ears in the same direction as my stock m/c, I guess that's an easier way to do it.

Since I am in the process of installing 4 wheel discs; I assume I can use the 280zx m/c I picked up, without having to modify these residual valves?

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Traditionally, disc brake masters have no residual valve. It is interesting that the Datsun 280ZX included them, as you say probably with low-pressure springs


In the 280ZX service manual it does show a "check valve" in both front and rear portions. In the older Datsuns this is completely left out for the front disc brake portion of the M/C.


It still holds true though: The drum brake valves are not appropriate for disc brakes. Oh you can still use them, but they say the brakes will wear faster than normal.

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My Nissan parts manuals show a residual valve on the front (disc) but not the rears on the 510. ???


The Tokico 3/4" 620 master only has a residual in the rears, while the Nabco only in the fronts... these are the 4 drum trucks.

The 13/16" Nabco and Tokico have both valves on the front disc brake trucks.


The B210/310/610/710/720/S10/S110/A10 all have residual valves front and back.

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ok well i was looking at wilwood brake stuff and i remeber seeing little inline hex cylinders probably 2 inches long and less than half an inch wide and they all had numbers (in psi) from 2 to 10. I dont think wilwood really sells drum brakes but dont quote me on that so perhaps there is a need or want for residual pressure on disk brakes. I would think that it would reduce the pedal throw and possibly a slightly stiffer pedal.

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Yes, there is a need for residual pressure with disc brakes. The word in kustom circles is that the M/C being mounted high on the firewall, there is a small pressure naturally. But when they put discs on a car with floor-level M/C, they have to add a valve.


Sounds like once again, the Datsun engineers are a bit more sophisticated than average car manufacturers.

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  • 2 years later...

ok so i tried everything for bleeding ,no dice so i drained the entire system to get to the proportioning valve,


opened it up cleaned it out had some crusty rustys in side... seals were all intact and had a smooth bore so put it back together .



i opened up my 13/16 master cyl. also to try to add the zx pressure regulator but found this


so the funny thing is, the one on the right with a hole in the center was on the rear brake line and the closed one on the left was on the front??



soooo i went and grabbed an extra 3/4 stock bmc i had opened it up and the two pressure reg. seals were opposite the one with the hole in the center was on the front and the closed one on the rear line.


im assuming the one with the hole is to allow fluid to flow back?


so what i did was take two of the sealed ones and put them in both front and rear i will test 2maro and report back 

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I don't know what the pin hole is for, if you can see threw it, then my guess would be it is a front residual valve of some sort, rear drum brakes should have a 10lb valve, while the front disc should have a 2lb valve or none at all, if you put a 10lb valve on a disc brake caliper, and take it for a drive, you should have at least 2 things, a wrench to open the front disc brake caliper bleeders to release the pressure that will build up as they get hot and start seizing, and a fire extinguisher to put out the fire if you are able to keep it moving long enough.

I have made the mistake of using a 521 master with residual valve on my 521KC when I first built it, it was a 4X4 briefly, my front disc brakes started seizing because it had a 10lb valve in it, but it was a diesel, I turned the drive line out of it before I made it back home, I drove 10 blocks out, and made it back 6 of them before it sheared the bolts off, I ran home and got a wrench and a tow strap, as my Datsun friend that lives near me towed me home.

Funny thing is that I towed that truck to blue lake that year, the brakes started seizing just towing the truck, I had to just open the bleeder to keep towing it, when the calipers get hot, they build pressure. 

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  • 4 months later...

been searching around and this seems like the right place to ask. what single reservoir master cylinder can I use on my Datsun 510. I have the 280zx front struts and the 200sx rear disk conversion. I'm doing a KA-T and want to keep my brake booster. thanks for any points in the right direction.

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Disc brake calipers are huge compared to the wheel cylinders they replace and will need correspondingly more fluid to move them. (larger master) A single master will (maybe) work but the pedal will have a lot of travel to move that much fluid and will feel mushy. I would imagine that a larger bore single master is needed.



I had a '68 dime with single master back in the mid '70s. I put a dual master in from a 620. I had to separate the front and rear brakes. The flair was wrong but I 'fixed' this and it worked well. The biggest advantage was that if there was any failure in the brake system it would only affect the front OR the back but not everything like a single master would. Single master is very '50s and '60s and all are dual system now. It was common back then to hear of accidents that were caused by 'brake failure', who hears that today? Any leak or failure in a single master system causes a total failure in the braking system.

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True I didn't really think about that. I'll just stick with the dual for now and work the turbo around that. After I posted that though I saw something about a wilwood master that's bolts up. So I checked them out and they have singles with the same bolt up pattern. It'd be a 70 dollar experiment if all else fails. Or a several thousand dollar experiment if it fails hahaha

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