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neRok

Is having too big a brake master cylinder a problem?

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my brake master cylinder is crook, so im going to get a new one. thought i may as well get a big one in preperation for brake upgrades. the stock master is 7/8" (JB1133, $86) and the 280zx (JB1361) is 15/16", a nice upgrade but really overpriced at ~$170. ive found the G60 patrol 1" (JB1419) for ~$150, this is way overkill for the stock brakes but would be better in the future. so, will it be a problem having a 1" master with the stock brakes, im guessing it will just result in a really touchy brake pedal?

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It is overkill, even Arizona zed car say that the 15/16th MC is fine for their 6pot Wilwood system.  I have the 1" MC with Hilux fronts and R31 rears and its a bit overkill even for that..

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thanks. i think i will get the 1" master. those AZC kits look the good, tihnk i might get them! so cheap as well, ive just put a similar setup on the front of my commodore and it was $1300+.

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I've got a JB1419 in my 240 - and it's too big for the Hilux S12 (solid) + R31 combo I was running. the 7/8" OEM MC was too small, and the 280ZX MC is NLA here (from Nissan or PBR).

 

I'm hoping that with the 4Runner S12W (vented) brakes up front (4x large pistons) the pedal will be a little softer (i.e just right!)

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if you fit a 15/16 or 1 inch master cylinder with standard brakes dont expect them to work cause they wont , increasing bore diameter will reduce line pressure and increase the amount of pedal pressure or effort ,in other words you will have a rock hard pedal and no brakes

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if you fit a 15/16 or 1 inch master cylinder with standard brakes dont expect them to work cause they wont , increasing bore diameter will reduce line pressure and increase the amount of pedal pressure or effort ,in other words you will have a rock hard pedal and no brakes

ah, wish you had of chimed in with this earlier. ive bought the big 1" master and put it in lol. i had no brakes prior, i have some brakes now but its not good. i bled it pretty good, so im kinda hoping there is a problem somewhere else. im gonna jack the car up and pull the wheels off, see whats going on under them. it also seems i have 2 bias valves or something in the engine bay, there is tubes going everywhere. im thinking of taking a pic, see if anyone knows whats going on.

 

but thinking about the line pressure, how will this change? doesnt the piston within the master just push fluid down the brake line, and as you push more into the same area, the pressure increases. so with a bigger master, i would think you could push the pedal less as it is moving more fluid as it moves a set distance.

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but thinking about the line pressure, how will this change? doesnt the piston within the master just push fluid down the brake line, and as you push more into the same area, the pressure increases. so with a bigger master, i would think you could push the pedal less as it is moving more fluid as it moves a set distance.

 

I would have thought the same thing.  I would have thought that the most likely problem in these circumstances would be that you would have trouble NOT locking the brakes rather than having no brakes.  that's my understanding of the physics of it anyway.

 

Ie with the same pedal travel you would push more fluid out of the master, thus creating more pressure in the system, thus applying more braking pressure.

 

I suspect that differences in pedal length and/or position on the lever (pedal) where the master cylinder actuating rod is conected, may affect the mechanical advantage of the lever and therefore would require more (or less) leg effort to apply the same pressure to the actuating rod and therefore producing system pressure.

 

I hope I've explained this well.  It's preety late for this old man.

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Yes! the smaller piston gives better multiplication of the force applied by the pedal, however moves less fluid requiring longer pedal travel to take up the slack. By increasing the bore diameter of the master you have reduced the actual pressure that can be applied by the pistons and slave cylinders but reduced the travel of the pedal.  When bled, your pedal will feel rock hard and be very high but not stop as well as you think it should for the force applied. R33, R34, Z32 all have 15/16 master, along with multiple piston callipers. Maybe Nissan are on to something?

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Yes! the smaller piston gives better multiplication of the force applied by the pedal, however moves less fluid requiring longer pedal travel to take up the slack. By increasing the bore diameter of the master you have reduced the actual pressure that can be applied by the pistons and slave cylinders but reduced the travel of the pedal.  When bled, your pedal will feel rock hard and be very high but not stop as well as you think it should for the force applied. R33, R34, Z32 all have 15/16 master, along with multiple piston callipers. Maybe Nissan are on to something?

i think i get you. so your saying if you push the pedal with x force, on the smaller cylinder this means the force is distributed over a smaller piston, so more force per area. this allows it to get the pressure up. the big cylinder with the same force applied has it spread over a larger area, so it cant get the pressure up easily, even though it is moving lots of fluid. to get the pressure up to work the brakes, you need the same force per area as the small cylinder, which means applying a lot more force to the pedal.

 

well, thats not very good  :'( but it should still work, so im going to try fix it first. i can live with a rock hard brake pedal, as long as the car stops. otherwise im going to have to buy another master, and stick the big boy in the corner for another time. i hope the steel pipes like bending that many times.

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Dimitri has R33/R31 combo, anyone know what MC he's running?

 

Dimitri runs 15/16 master. It's the size most people with 4pot fronts and disc rears seem to use. All the track zeds I know of run this size.

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I thought I saw a pic of a JB1419 master on the forum (maybe yours Gareth?) and the bleed nipple was on the outside near the strut towers but the one I just bought has them on the other side?

post-192-144023611267_thumb.jpg

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neRok, are you still with standard brakes all round? What setup are you running...and yes, Gareth is right, I'm using the 15/16 cylinder with zero problems and with excellent brakes!

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neRok, are you still with standard brakes all round? What setup are you running...and yes, Gareth is right, I'm using the 15/16 cylinder with zero problems and with excellent brakes!

yer, still standard.

 

bleed nipples on my JB1419 are on the LH (inside) also.

 

maybe my bleeding method isnt quite right? i read somewhere that when the master has nipples, you just bleed them and wait for gravity to start dripping the fluid out, so i did that. then i just bled like normal and there seemed to be plenty of fluid coming out at the wheels. i didnt notice anything on the bias valve(s), maybe these need something special, ive never worked with them?

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Another way to bleed brakes is:

 

1. Bleed master as per normal

2. Crack all your bleed nipples with clear hoses on the ends to drain fluid without making a mess.

3. Make sure the master has plenty of fluid and wait for gravity to do its job.

 

This can take around 30 to 45 minutes. The fluid will flow through and expel all the air in the system and gives you time for a couple of refreshing beverages. Just keep an eye on the fluid level in the master cylinder.

 

The best way I have found is to use a pressure bleeder bit the above method works well for an initial bleed of the whole braking system.

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lucky you - mine are on the tower side.

 

PS

The 2 brake 'distribution' blocks in the engine bay are bias and front/rear brake fail warning (the handbrake light will illuminate if a circuit has no pressure). Don't expect it to work - it's probably got over 30 years of gunk in it...

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hey ben,

 

on a side note can you tell me the colour of the wire going to the pressure switch??

 

 

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Yellow/green, exiting the harness near the starter solenoid wire (black/yellow).

Note that I don't have this differential pressure switch fitted any more

And I told a lie - the bleed nipples on my JB1419 are on the engine side, not the strut side...

::)

post-11-144023612863_thumb.jpg

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Hi all

I recently fitted the Arizona 6 piston front ,4 piston rear and went with the 1 " master

and took it out on the track yesterday , after a few hairy moments with to much rear

brake bias i would highly recomend the 1 " . Pedal travel and feel is to my satisfaction.

But on standard brakes as others have said may be to hard to push.

 

Regards

Paul

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