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Better brakes - Master cylinder upgrade
https://ausmini.com/forums/viewtopic.php?f=5&t=9547		 Page 1 of 3
Author:  jill200sx [ Wed Jul 27, 2005 11:25 pm ]
Post subject:  Better brakes - Master cylinder upgrade
I found out today that the master cylinder Im using (came with '78 stock 998cc van) will "never give me a good pedal" so Im upgrading the master cylinder to the plastic one that JAMs just put in.
The catch is Im also told I need to upgrade the top lines as the ones that will be on the car now are apparently metric :roll:

Is replacing these lines difficult? and from where to where will I need to replace? Can the lines be made up or do you have to buy premade?

This is my current master cylinder (old pic before anything was done, dont worry its not like this anymore, but I dont have a current engine bay pic with the master cylinder in it)

Image
Author:  Mini68 [ Thu Jul 28, 2005 8:39 am ]
Post subject: 
You can make up the shape you want for the new lines with some coat hanger wire then take that to a brake place and have them make up the lines to that shape. Make sure the lines are made up in steel and not copper. I was told by a miini specialist when I got mine done that the brake lines need to be steel and not copper as the copper can crack with vibration.
Author:  minstar [ Thu Jul 28, 2005 8:50 am ]
Post subject: 
Jill when I converted to dual master cylinder I had to have mine made up and it was $50 for the lot. Either give them measurements or as Mini68 says bend coat hanger wire to shape and supply that. I bought a smallpipe bender and just ben the straight pipe to the shape I wanted.
Author:  drmini in aust [ Thu Jul 28, 2005 8:30 pm ]
Post subject: 
I believe it's illegal to use copper brake pipes in Australia, for the reason above. But in UK it is common practice, they can buy kits of copper pipes ready made. :?
Author:  justminis [ Thu Jul 28, 2005 9:03 pm ]
Post subject: 
The reason why you don't have a very good pedal is because you have Metro 4 pot calipers don't you? That master cylinder is filling bigger capacity brake calipers than it was with standard set up. Unless the bore size of the new proposed master cylinder is bigger than your current master cylinder, you will continue to have a low pedal. If the bore size is the same, you will still have the same situation you have now.
Metro 4 pot calipers with stock bore size master cylinders = low brake pedal. Fact of life!
Author:  jill200sx [ Thu Jul 28, 2005 11:50 pm ]
Post subject: 
Thanks Steve. I confirmed today that my master cylinder is cactus regardless of if its the wrong one for the Metro 4 pots.
I can get a decent pedal, but can also slowly depress the pedal with constant pressure. M/C buggered. and yes I know I could sleeve it, but Id rather replace.

So the question now is which master cylinder will give me the best brakes with the Metro 4 pots?
I thought Id be happy with a replacement that keeps a decent pedal, but is there a better option better suited to the 4 pots?

Im happy with no booster.

78 van, 4 pot fully rebuilt Metros on the front, good drums, new cylinders on the rear.

PS did some braking this afternoon to test out if any wheel/s were locking up or not locking up. All 4 wheels locked up at exact same point :) I just want a pedal that stays firm now :)
Author:  J_A_M [ Fri Jul 29, 2005 9:24 am ]
Post subject: 
justminis wrote:
Metro 4 pot calipers with stock bore size master cylinders = low brake pedal. Fact of life!


thats quite interesting...... Thanks!

I assume it applied to Honda discs as well (which I have).
Author:  fuzzy-hair-man [ Fri Jul 29, 2005 11:04 am ]
Post subject: 
jill200sx wrote:
So the question now is which master cylinder will give me the best brakes with the Metro 4 pots?
I thought Id be happy with a replacement that keeps a decent pedal, but is there a better option better suited to the 4 pots?

Im happy with no booster.

I just want a pedal that stays firm now :)


I think it goes like:

The larger the master cylinder bore the more fluid you are moving to your brakes with a certain amount of pedal travel.

Also the larger the bore the harder the pedal will feel

As the metro 4 pots take more fluid to actuate it means for the same sized master cylinder you will use more pedal travel but require less pedal pressure(resulting in less feel).

So I think the answer is go to a bigger bore master cylinder. How big? don't know what size did the metros using the 4 pot calipers use?

Please correct me if I'm wrong anyone...

Isn't the Master cylinder Jill has a twin circuit brake setup? doesn't this change the type of master cylinder she is looking for as well?
Author:  jill200sx [ Fri Jul 29, 2005 4:14 pm ]
Post subject: 
yup, it is twin circuit apparently (has a line to the rears and another line to the fronts).

Im happy with the pedal when its firm, so if the plastic M/Cs that JAM has used normally replace this twin M/C then I'll use it. Would JAMS replacement M/C have the same bore size as the M/C shown in the pic above?
Author:  fuzzy-hair-man [ Fri Jul 29, 2005 6:05 pm ]
Post subject: 
I found this:

http://www.ausmini.com/forums/viewtopic.php?t=8708&highlight=metro+master+cylinder

couldn't find anything on what the metros had as thier master cylinder though :(
Author:  9YaTaH [ Fri Jul 29, 2005 8:39 pm ]
Post subject:  Bernie Knows!
fuzzy-hair-man wrote:
jill200sx wrote:
So the question now is which master cylinder will give me the best brakes with the Metro 4 pots?
I thought Id be happy with a replacement that keeps a decent pedal, but is there a better option better suited to the 4 pots?

Im happy with no booster.

I just want a pedal that stays firm now :)


I think it goes like:

The larger the master cylinder bore the more fluid you are moving to your brakes with a certain amount of pedal travel.

Also the larger the bore the harder the pedal will feel

As the metro 4 pots take more fluid to actuate it means for the same sized master cylinder you will use more pedal travel but require less pedal pressure(resulting in less feel).

So I think the answer is go to a bigger bore master cylinder. How big? don't know what size did the metros using the 4 pot calipers use?

Please correct me if I'm wrong anyone...

Isn't the Master cylinder Jill has a twin circuit brake setup? doesn't this change the type of master cylinder she is looking for as well?


Bernoulli's Theorem

How pressure and velocity interact
static pressure + dynamic pressure = total pressure = constant
static pressure + 1/2 x density x velocity2 = total pressure = constant

General Concept:
The Bernoulli effect is simply a result of the conservation of energy. The work done on a fluid (a fluid is a liquid or a gas), the pressure times the volume, is equal to the change in kinetic energy of the fluid.

General Facts:
Where there is slow flow in a fluid, you will find increased pressure.
Where there is increased flow in a fluid, you will find decreased pressure.

In a real flow, friction plays a large role - a lot of times you must have a large pressure drop (decrease in pressure) just to overcome friction. This is the case in your house. Most water pipes have small diameters (large friction), hence the need for "water pressure" - it is the energy from that pressure drop that goes to friction.

Example: the showerhead
A showerhead (if you have a fancy one) has a number of different operation modes. If you go for the "massage" mode, you are moving a little water fast. For the "lite shower," you are moving a lot of water slowly. It takes the same amount of energy to move a little water fast as it does to move a lot of water slowly. This is the amount of energy you have due to your "water pressure."

:D :D :D
Author:  Mini Mad [ Fri Jul 29, 2005 9:13 pm ]
Post subject: 
J_A_M wrote:
justminis wrote:
Metro 4 pot calipers with stock bore size master cylinders = low brake pedal. Fact of life!


thats quite interesting...... Thanks!

I assume it applied to Honda discs as well (which I have).


Can't speak for the metro's..but my honda's grab after about 10mm, maybe less of pedal pressure...at a guess..it's pretty high.
Author:  drmini in aust [ Fri Jul 29, 2005 11:05 pm ]
Post subject: 
I had Honda Civics on Barney, with a Clubby tandem MC- pedal was good. I swapped for S brakes, pedal is still good.
Note the Hondas are only a single piston sliding caliper... but it's a pretty big piston. S brakes take more fluid according to my calcs. :wink:
Author:  jill200sx [ Sun Jul 31, 2005 12:37 am ]
Post subject: 
Does anyone know what bore size my current M/C is? (0.7 or 0.75")
and if I were to go bigger bore Id get softer pedal?
Id prefer a firm, high (I dont care how touchy) pedal.

and apparently some models came with rear brake bias, can I just plumb one of them in if I want to reduce the rear brakes a tad?
Author:  justminis [ Sun Jul 31, 2005 8:17 am ]
Post subject: 
Jill, the size should be .70 of your current m/cylinder. If you go bigger bore then pedal will be harder. Your car should have a brake proportioning valve somewhere, I'm not overly familiar with the later (Clubby) models, there were a couple of different types. For me, the simplist thing would be to buy an adjustable rear proportioning valve, Mini Spares sell them and bin all the other valves. The adjustable valve mounts on the rear subframe (or anywhere else you like) and it is done. If you go the Madza m/cylinder route, then an adjustable rear valve will be a must to set it up properly.
I ran the std tandem m/cylinder, metro 4 pots and adjustable rear valve on my race/sprint mini for a while, got used to the low pedal and it all worked very well. Even ran it with a S booster at one stage, could really stand on them.
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