13/16" Master Cylinder on 3/4" system?

[MicroMachinery]

Hey, I was recently going through my things, and I found an old box that contains a brand new NABCO Tandem Reservoir Master Cylinder. It has a 13/16" bore, and I was wondering if it would be foolish to install this on a 71' 510 that uses 3/4" Master Cylinder. Granted, it is IDEAL to use a 3/4" M/C with the system it was designed for, but other than a stiffer pedal, what other consequences(if any), am I looking at(Blowing wheel cylinders, seals in my calipers, etc..?)

If it's unsafe and ridiculous to put a 1/16" oversize master cylinder in my Dime, I'd like to know, but I'd also like to know why. Thanks guys.

 

 

Here 'tis. NOS Nissan Pt#46010-M7900

[datzenmike]

Conservation of energy, or energy in = energy out, also known as 'you can't get something for nuttin'. Basically for the same amount of pedal pressure you can have either more volume or more pressure. Since you are going to a larger bore you will move more volume but at less pressure. In order to get the same braking effect as before, you will have to press harder on the pedal. Do you have a booster?

[I'm BLUE]

Since you are going to a larger bore you will move more volume but at less pressure. In order to get the same braking effect as before, you will have to press harder on the pedal. Do you have a booster?

 

 

Can you please re-clarify this , I didn't quite understand the last thanks :D

[DISLEXICDIME]

Can you please re-clarify this , I didn't quite understand the last thanks :D

 

It will feel like dead petal with out a booster hooked up

[I'm BLUE]

It will feel like dead petal with out a booster hooked up

 

your saying it will feel like going to the floor , but hard to stop ( more pressure required from the foot ) with a larger MC bore , but no gain in braking power to the wheels ((( since it moves more volume and reduces braking pressure which is why you have to press harder ? )))

 

Whoops , My Mistake, I need to clarify my question, , I was more curious and wanted to know what datzenmike meant by the comment "Since you are going to a larger bore you will move more volume but at less pressure."

 

Thanks,

 

DTP

[MicroMachinery]

It will feel like dead petal with out a booster hooked up

 

Really? I would think that since you're moving a larger volume of fluid, that the wheel cylinders/calipers would fill more quickly, and the pedal would have a stiffer feel. That's why I was concerned about the possibility of blowing seals, cylinders, etc(higher pressure with less effort). I would think that with a SMALLER bore M/C, the pedal would drop MORE before the cylinders and calipers engaged.

However, in this case, we're dealing with a LARGER bore M/C. 13/16" > 12/16(3/4)"

Are my hydraulic fundamentals a little rusty?

Wouldn't it be the other way around, as in if I replaced the 3/4" wheel cylinders with 13/16" wheel cylinders, then the demand for fluid would increase, and thus cause a "dead pedal" feeling?

[I'm BLUE]

Micro,

 

yeah , I am kind of leaning towards your understanding of this a bit more , and it's always good when everyone chimes in :D

 

No your understanding of Hyd. fundamentals is good , because if it isn't were both in trouble ---- >>>> :lol: :rofl:

 

Let me know how this goes

[sssr20det510]

I don't think its that much bigger that you would notice a big diff

[datzenmike]

Think of a hydraulic jack. It uses a very small piston (pumped by hand) that moves a small amount of fluid that lifts the car a fraction of an inch with each pump. If you were to double the size of this piston you could move twice the volume of fluid which would lift the car twice as high. Obviously you would have to pump twice as hard to do this.

 

The same pressure is needed inside the jack to begin lifting the car no matter which size piston you use. Same with the brakes. A larger master cylinder will require more force to reach the same pressure applied to the brakes.

 

If you have just a master cylinder and increase it's size you can offset the extra effort needed by adding a booster. The booster uses engine vacuum on a diaphragm to reduce pedal effort.

 

 

I don't think its that much bigger that you would notice a big diff

 

Moving from a 3/4 to 13/16 is a 16.8% increase in piston area. Presumably an almost 17% increase in pedal pressure. So if you need 60 lb of force to stop, you now need 70 lbs.

 

Hey math has only become interesting in the last few years for working out these real world problems. I could be wrong so if anyone sees this differently I have no problem with that.:D

[DISLEXICDIME]

do you have a car with power brakes ? If so go out side push in the brakes with the car on then turn it off and push on the brakes with the car off.

 

my car has 15/16 master and it is very stiff

[MicroMachinery]

Oh, yeah, more pedal effort is something I can definitely live with, even welcome.

Honestly, I prefer the feeling of no power brakes vs power brakes. To me, power brakes seem like they take away from the human-machine connection, the same way that power steering or automatic transmissions do.

Extra effort? No problem-o.

.. an no. I have no cars with power anything. That's how I like it ;)

[I'm BLUE]

Think of a hydraulic jack. It uses a very small piston (pumped by hand) that moves a small amount of fluid that lifts the car a fraction of an inch with each pump. If you were to double the size of this piston you could move twice the volume of fluid which would lift the car twice as high. Obviously you would have to pump twice as hard to do this.

 

The same pressure is needed inside the jack to begin lifting the car no matter which size piston you use. Same with the brakes. A larger master cylinder will require more force to reach the same pressure applied to the brakes.

 

If you have just a master cylinder and increase it's size you can offset the extra effort needed by adding a booster. The booster uses engine vacuum on a diaphragm to reduce pedal effort.

 

 

 

 

Moving from a 3/4 to 13/16 is a 16.8% increase in piston area. Presumably an almost 17% increase in pedal pressure. So if you need 60 lb of force to stop, you now need 70 lbs.

 

Hey math has only become interesting in the last few years for working out these real world problems. I could be wrong so if anyone sees this differently I have no problem with that.:D

 

Good analogy !

 

Hey Thanks for clearing that up datzenmike , wasn't trying to cause ya grief ;) :D I guess I was over-analyzing this :lol:

 

DTP

 

P.S ( Micro , I hear ya I absolutely love the manual-steering old school rack and pinion in my 73-S30 , I let my brother drive it and he hate's the steering :lol: :rofl: I call him a "pussy cat" minus the "cat" :P :lol:

[I'm BLUE]

Oh, yeah, more pedal effort is something I can definitely live with, even welcome.

Honestly, I prefer the feeling of no power brakes vs power brakes. To me, power brakes seem like they take away from the human-machine connection, the same way that power steering or automatic transmissions do.

Extra effort? No problem-o.

.. an no. I have no cars with power anything. That's how I like it ;)

 

c'mon I've seen your prius in your garage , washing it , waxing it , shhhhhhhh I won't tell !!! :lol: :rofl:

 

ya I'm with you on the "power" thing :lol:

 

Here it is Micro , Very Sexy , That's what I like , WOOOOOOWWWWW !!!!!!!!!! hahaha joking ;)

[MicroMachinery]

c'mon I've seen your prius in your garage , washing it , waxing it , shhhhhhhh I won't tell !!! :lol: :rofl:

 

ya I'm with you on the "power" thing :lol:

 

Here it is Micro , Very Sexy , That's what I like , WOOOOOOWWWWW !!!!!!!!!! hahaha joking ;)

 

Hehe, yeah, and I only take it out on the sunniest of sunny days. But you can't forget to put special, high-dollar organic sunscreen on em, otherwise that ^^^ happens. Pansy-ass Vegan car. :lol:

[I'm BLUE]

do you have a car with power brakes ? If so go out side push in the brakes with the car on then turn it off and push on the brakes with the car off.

 

my car has 15/16 master and it is very stiff

 

:lol: Yes I do :D -----> I've replace them many times on FLEET vehicles at the shop I work at , some are so damn shitty they get replaced every 4-8 months on different vehicles ( same brand re-manufactured units that we use to replace ( cheapness ) that are probably cleaned , painted and sent to the next poor bastard ) We had to call a tech in for a second opinion he said " I can't see anything incorrect on installation. " The one he installed failed in the same amount of time :blink: :rolleyes: :angry:

 

Hey, Good to know that it is stiffer with the 15/16 Bore though ! We are talking brake boosters right ? :rofl:

 

Thanks,

 

DTP

[I'm BLUE]

Hehe, yeah, and I only take it out on the sunniest of sunny days. But you can't forget to put special, high-dollar organic sunscreen on em, otherwise that ^^^ happens. Pansy-ass Vegan car. :lol:

 

:lol: organic sunscreen = gas/oil ? :blink: :D :lol: or do they piss on the car "evenly" :lol: :o :P

[banzai510(hainz)]

3/4 = 12/16 remember "common dinominator" in school? I failed spelling myself!

orginal was 13/16 a 16th off isnt much to worry about. New is better than a cheap rebuild. Some of these are getting harder to find.

 

I would just run it

[MicroMachinery]

However, in this case, we're dealing with a LARGER bore M/C. 13/16" > 12/16(3/4)"

 

 

3/4 = 12/16 remember "common dinominator" in school? I failed spelling myself!

orginal was 13/16 a 16th off isnt much to worry about. New is better than a cheap rebuild. Some of these are getting harder to find.

 

I would just run it

 

Yeah, that's what I got too. I went and found a NOS 3/4 M/C at the same place for $20, so I'll use that first. I do have this other one for a backup, however. Thanks everyone.

[banzai510(hainz)]

I went and found a NOS 3/4 M/C at the same place for $20,

 

Buy all of them and bring it to a datsun show and sell for 40-50 and keep a spare.

[MicroMachinery]

I wish I could. It was the last one. The guy said he may have more at his other shop, so we'll see. I'd love to spread the wealth around :)

[JDM510]

i ahve a 15/16 with 280zx brakes non power.. brakes are stiff but if you push them it will throw you threw the windshield.....

 

 

i love them feels way better then the spongy ass stock MC i took off and threw in the trash.....

[racerx]

So the bigger the bore the more sensitive it is....since you already have it, micromachine try it out. If it's too sensitive or spongy then go back to the orig. But let us know if you do.

[john510]

I tried the 13/16 and i had to use a lot of force to stop my car,there was no way i could have stopped quickly if i had to.the only reason i tried it was because i couldnt find a 3/4 .I ended up putting the 35 year old master cylinder back in and it was much better.I ended up buying two new ones on e-bay at 75.00 each.Stick with a 3/4 master cylinder.

[nochrome]

I'm running a Tilton racemaster 13/16" on my 521(direct bolt on). I have to stand on the pedal to get it to stop. I get nervous in heavy traffic and my leg will be sore after any kind of "spirited" driving

[ggzilla]

A larger master cylinder is not more sensitive. It will require more leg pressure, but will require less pedal travel. Even though you press harder on the pedal, the maximum pressure at the wheels is the same.

 

It won't affect front-to-rear brake proportion.

 

A larger master cylinder will generate LESS pressure but the pedal will be STIFFER. Because there is less pressure, you have to push harder on the pedal to make it stop the same. You get more volume (firmer pedal), but less pressure.

 

The reason Datsun chose 3/4" had nothing to do with blowing out seals, but with how much leg pressure is required. That's why vehicles with a brake booster can have larger master cylinders, so that you get a firmer brake pedal, less travel required, but with the booster even a housewive can drive it.