MIRAFIORI BRAKE SERVICE AND UPGRADES

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   This Thread should be for all mirafiori brake fixes and upgrades from standard to modified cars, 1300 to Bigger, Road, Rally and Race.  

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Drilled and grooved Disc's types.

  Some years ago I was after some replacment but standard size discs for one of the family cars, I put in a call to Brembo Brakes, not the dealer but Brembo them selves, got on to the Tech department, sales only goes so far with information. Any way, So as you would I asked about drilled and grooved sets and what was available, here's the surprise. 

The first upgrade was;

  Group N disc, it's the same as standard but made of a better than Standard material, with this type the disc will stand high temps and operating use than the normally available Fiat types.

  Vented disc's, these were not an option as a standard bolt on swap for 131, but as a discussion point, you can sap over to the Uno Turbo front brakes, but back to the Vents. Vented disc are an improvement due to there ability to get rid of heat, to look at they are like two normal solid discs joined together, normal 131 disc is about 11mm thick from memory, but a vented disc will be up around 20mm thick. Now, with the extra surface area of two discs joined, the air can now flow between the inner surfaces getting rid of all that extra heat. Well so what,     well, as the disc disperses more heat, this reduces heat transfer both into the pads and brake fluid, and still using a standard pad material, I'll get to this in a Mo'.

  Grooved Disc's, these can be ether on a normal solid or vented disc but with a set of ether straight or curved grooves/slots machined into there braking surfaces. The idea of these which many people confuse with the vented types, is too allow the pads the both vent gases (describe in another Mo') and too a leaser effect face up/clean the pad surface.

  Drilled Disc's, lots of holes drilled through each disc solid or vented, but here's the thing, as you would, I said so what about drilled discs, well it seems it's like this, if your using your brakes hard, the problem comes from heat cycling. In a race car the disc's will be changed after every few races or practices, but on a road car they will be used for, well, my sort of fun then driven nicely to the shops, the problem is that with the constant prolonged heat cycles each of those little holes is a starting point for tiny cracks in the surface. Surface cracking means the disc is starting to come apart, bad news for ether a race or road car, may look cool but not the best for long life road use.

  Conclusion, we ended up with a some Group N grooved disc's without holes but with slots cut, and how did this work out, well, after some very spirited use the brakes still faded but this was more a balance / fluid problem, but the point of interest was that the disc's had turned Blue and stayed that way, the suggestion was that the disc's had been up to around 700deg' but had still remained straight and true, the Gp N material.

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Race and Rally Disc's

Fully floating,
  Ok the best information I have here is that the disc or rotor is now separate from the mounting bell that bolts to the hub. We have some of these for Big Toad (330x32mm) but as you know big T is still under construction. My understanding is that the disc will both center itself and allow the heated disc to expand.

J Hook design
  This has many other designs other than the J design, but is a variation on the slotted idea.

My advice which is limited thus far, don't over do the brakes size or they will never get up to temperature,  and glaze the pads, road cars beware. 

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Brake Pad types.

Standard road Pad;
  So what do we have available to us, well we know the pads need to stop the car from speed, but most road cars don't do repeated stops from 100+ again and again.  So our Sta' pads is designed to work up to a temperature that the designer would expect a normal road car to be driven at, yes they will stop you from max speed, but not too many times before they overheat. So lets look at the other end of the heat range, when we jump in our road car we expect the brakes to work straight away from dead cooled on a frosty morning, so what does this tell us?  well when it comes to pads you can't have it at both ends    if you fit an uprated material, what you add at the top of the temp range has to be paid for at cold start, or should that be stopping. The brakes will feel dead for the first few stops in the morning. 

Fast road Pad;
  These are the materials to use if you still need to go shopping but then want to press on a bit sometimes later, there supposed to be a nice mix between cold morning warm up and more high speed running with many high speed stops (Me  ) but still you must remember these still have there limits as well, road racing may still need more top temp tolerance but again there is a draw back?  The problem is as the material gets, shall we say harder it's low temp tolerance falls away, go back to that cold start braking. A competition pad material needs to be warned up before it stats to work, but this temp is now much higher than the sta' pad,  "yes and so what"  all is well and good when your ripping through the county roads, but as soon as you slow for say, traffic,shopping or maybe Motorway driving, these pads cool down below there working temps. "Yes Yes get on with it"  well as the temps go down, the pads will start to become polished or glazed, the glaze does not grip the disc half as well, but it does rip the disc's to pieces, grooves, high ware rates, squeeks, generally there a bad idea for the road.

Track Pads;
  As above, now your starting to understand, these will be much harder, need warming for the first few laps and wear faster along with the disc's as well. There are an intermediate material between the fast road and Race materials.

Race Pad, 
  Hum, Ok this is a simple one, these will most likely not start to work until the temps are up around that where a standard pad is starting to fad, don't go here it's not a cooling thing to fit and your brakes will be poorer for it on a road car.

Last bit, One of the things to understand about pads is when they get very hot, part of, or all of the problem, I don't know which, is that when the pad starts to over heat, the material starts to produce gas for it, this gas if not removed through the machined slots, will effectively lift or lubricate the pad surface off the disc. This will feel like you have a good pedal but no brakes, no mater how hard you push.

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Brake Fluid Types.

Ok where to start, Hm, first thing why do we need to change our brake fluid regularly, the problem is that with the exception of Silicone fluids all the other types are Polyglycol ether based, and are HYGROSCOPIC (This is not a mis spell the word is spelt with a    G  Hygroscopic )  these fluids attract water and water moisture even through the brake hoses. You will see and here Hydroscopic with a D, from many places and people, including College, its wrong, you choose. 

Ok I've down loaded this that seems to cover most of the subject apart from a DOT 3 car can have DOT4 OR higher, but a DOT4 car should not be downgraded to DOT3.


Automotive brake fluid has many responsibilities. Corrosion protection and lubrication of brake system components are only a portion of the role brake fluid must play.
Because brake systems may reach extreme temperatures brake fluid must have the ability to withstand these temperatures and not degrade rapidly.

POLYGLYCOL ETHER BASED FLUIDS
Fluids containing Poly glycol ethers are regarded as DOT 3, 4, and DOT 5.1. These type fluids are hygroscopic meaning they have an ability to mix with water and still perform adequately. However, water will drastically reduce the boiling point of fluid. In a passenger car this is not an issue. In a racecar it is a major issue because as the boiling point decreases the performance ability of the fluid also decreases.
Polyglycol type fluids are 2 times less compressible than silicone type fluids, even when heated. Less compressibility of brake fluid will increase pedal feel. Changing fluid on a regular basis will greatly increase the performance of the brake system.
FLUID SPECIFICATIONS there are three main standards of brake fluid that meet Department of Transportation (DOT) minimal specifications for brake fluid. They are DOT 3, DOT 4, and DOT 5.1 (for fluids based with Polyalkylene Glycol Ether) and DOT 5 (for Silicone based fluids).

SILICONE BASED FLUID
Fluids containing Silicone are generally used in military type vehicles and because Silicone based fluids will not damage painted surfaces they are also somewhat common in show cars.
Silicone-based fluids are regarded as DOT 5 fluids. They are highly compressible and can give the driver a feeling of a spongy pedal. The higher the brake system temperature the more the compressibility of the fluid and this increases the feeling of a spongy pedal.
Silicone based fluids are non-hygroscopic meaning that they will not absorb or mix with water. When water is present in the brake system it will create a water/fluid/water/fluid situation. Because water boils at approximately 212? F, the ability of the brake system to operate correctly decreases, and the steam created from boiling water adds air to the system. It is important to remember that water may be present in any brake system. Therefore silicone brake fluid lacks the ability to deal with moisture and will dramatically decrease a brake systems performance.

MINIMAL boiling points for these specifications are as follows:

    Dry Boiling Point   Wet Boiling Point
DOT 3   401?F     284? F
DOT 4   446? F   311? F
DOT 5   500? F   356? F
DOT 5.1   518? F   375? F

 Racing brake fluids always exceeds the DOT specifications for dry boiling points. Wet boiling points generally remain the same.

WET VS. DRY BOILING POINT
The term boiling point when used regarding brake fluid means the temperatures that brake fluid will begin to boil.

WET BOILING POINT
The minimum temperatures that brake fluids will begin to boil when the brake system contains 3% water by volume of the system.

DRY BOILING POINT
The temperatures that brake fluid will boil with no water present in the system.

MOISTURE IN THE BRAKE SYSTEM
Water/moisture can be found in nearly all brake systems. Moisture enters the brake system in several ways. One of the more common ways is from using old or pre-opened fluid. Keep in mind, that brake fluid draws in moisture from the surrounding air. Tightly sealing brake fluid bottles and not storing them for long periods of time will help keep moisture out. When changing or bleeding brake fluid always replace master cylinder caps as soon as possible to prevent moisture from entering into the master cylinder. Condensation, (small moisture droplets) can form in lines and calipers. As caliper and line temperatures heat up and then cool repeatedly, condensation occurs, leaving behind an increase in moisture/water. Over time the moisture becomes trapped in the internal sections of calipers, lines, master cylinders, etc. When this water reaches 212? F the water turns to steam. Many times air in the brake system is a result of water that has turned to steam. The build up of steam will create air pressure in the system, sometimes to the point that enough pressure is created to push caliper pistons into the brake pad. This will create brake drag as the rotor and pads make contact and can also create more heat in the system. Diffusion is another way in that water/moisture may enter the system.
Diffusion occurs when over time moisture enters through rubber brake hoses. The use of hoses made from EPDM materials (Ethlene-Propylene-Diene-Materials) will reduce the amount of diffusion OR use steel braided brake hose with a non-rubber sleeve (usually Teflon) to greatly reduce the diffusion process.

THINGS TO REMEMBER
Brake fluids dry boiling point is more important then wet boiling point when used in a racing brake system.
Passenger cars very rarely will undergo a brake fluid change making the wet boiling point more important.
Racing brake system fluid is changed often and a system with fresh fluid will most likely not contain water.
Because of this, racers should be concerned with the dry boiling point.
Racing fluid exceeds DOT 3, 4, and 5.1 dry boiling point specifications.
Never use silicone based fluids in racing brake systems.
Using racing brake fluid will increase performance of the braking system.
Never reuse fluid. ? Never mix types or brands of brake fluid.
Use smaller fluid containers that can be used quicker.
If fluid remains in container be sure to tightly seal and do not store for long periods of time.
Purge system (complete drain) and replace fluid often.
Immediately replace master cylinder reservoir cap following any maintenance.
 

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Balance Valve / Load Proportioning Valve.

  These valves are fitted to ether compensate for heavy loads being carried, or adjust the amount of braking pressure being sent to the rear wheels under heavy braking conditions. Ok so what does it mean to any of us here, well when set up and working properly, the idea is that as you brake hard the body will tip forward transferring weight from the rear wheels forward. With this weight loss the rear wheels try to lose traction and lock-up causing the back end to spin round.

  So where are we, well as you drive along, brake the front end drops or dives and the valve senses this and reduces brake pressure to the rear end, brakes come on, but not to the point of locking, so car stops in a straight line, "Ok and so what" well you come along lower the car all around, the front does not drop or dive as it did so the valve does not prevent the rear wheels locking.  If you want to be safe, always re-adjust this valve after playing with the car's suspension rates.

UPGRADE TIME.
  Ho-Hum here's the fun stuff,    so what we need is a way of adjusting this balance for ether wet weather, Tarmac, or just to balance out a brake conversion. The two ways I have experiance of are these, the first and simplest is the brake pressure valve fitted inside the car beside the driver, this can be adjusted with a lever or knob whilst driving along so lets get this something straight, if you fit these and do it badly, or use them badly, you will without doubt crash, how do I know this, well, once racing Toad I had left the brake balance adjusted to the rear to much, at the second bend I did a perfect hand brake tern with the foot brake to go off backwards, lost race because of this. Now this OFF was done with the next type of set up, but it would be just the same with the inside valve fitted.
 
  A twin Master cylinder set-up with inside adjusting knob on the dash,  the normal set up for cars these days is to have a system that is in effect two system joined together. The sta' system has one master cylinder that you push on, but the pressure is separated and split into two circuits, diagonally split accross the car, one front one rear to each circuit. Should one brake circuit get a hole, the other circuit will still have full braking pressure to stop the car safely.
  The Upgrade to this combines two smaller master cylinders, but you have to re-plumb the brakes from digital circuit, to one front one rear.  As you push on the pedal, the rod from the pedal push's on a bar that in tern pushes both of the new cylinders mounted side by side, one goes only to the rear, the other only the front.  
  Now the clever bit for this, if you look at the rod between the two cylinders,  a flexible wire can be attached to the end of this and run to the dash inside the car, by turning this knob the rod can be wound across so that more pedal pressure is put on which ever end of the car the rod is wound towards, so in Toad after I had spun off, I was able to turn and re-adjust the braking as I was regaining the track to continue the race, but now with the correct balance for the track conditions.

First pix Standard type Master cylinder.
Second pix is a internal adjustable balance valve.

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Third pix is the split braking system master cylinder layout.

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Remote adjuster Pix.

Remember, be careful these system's bit if you get them wrong

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Whats left ?

1. Servo's do not stop the car any faster, they only make it easier to push or modulate the pedal,  really it's true.  

2. Braided hoses are not all wonderful you know, yes there better at transferring pressure, but on steer'ed wheels that are turning, the over braid can start to fray and puncture the inner tubing, with this in mind, regular inspections should be carried out when these are fitted to road cars.  

[miro-1980]

DIAGNOSING THE HAND BRAKE

Before making any modification you have to remember that a car is complicated machine consisting  of many interdependent  parts / components /subsystems  designed to work as ONE INTEGRATED SYSTEM. This means that if you change one element you probably have to modify / upgrade several other elements to maintain the integrity of your car as a mechanical system.

This especially applies to all critical systems like brakes.

As our cars are getting to 40 years old and were in many hands before us it is worth making sure that brakes - a critical safety system - operate properly.

In 131 you have two bake circuits the front and the rear.

131 Brake system consists of :

BMC ( one twin section unit for front and rear brakes)

  Rear
- one stiff brake line
- brake force corrector 
- Y connector / line splitter 
- two stiff lines each going to one rear wheel
- each line connected to the wheel by a flexible line
- rear brake cylinders (for drums) or calipers for discs

  Drums:  cylinders , brake shoes and drums
     or   
  Discs: calipers, pads , discs

In addition there is  mechanical hand brake consisting of  a lever, cable with adjuster connected to each drum/caliper in the rear

(NOTE In my car ( sports/racing) there was also a rear brake fluid pressure limiter just near the BMC. I do not know if this was factory installed or someone's modification).   

 Front:
- two stiff lines each going to each front wheel
- flexible line connecting the stiff line to each caliper
- two floating calipers mounted on a bracket
- pads
- discs 

Diagnosing the brakes requires all of these elements being inspected for wear/ damage/rust/ leakage/ adjustment.

Unless all this is done : no diagnosis can be seen as reliable.

131 has a pretty simple and reliable system. It works like magic provided it is assembled properly and maintained properly,  parts are not worn, there are no leaks.

Here is a my to do list for checking the 131 handbrake.   

Inspect for the following elements :
 
1/ no rust in handbrake line linkage  ( cable moves smoothly in both directions, was not bent, burned by the exhaust , etc.)
2/ the hand brake is properly adjusted
3/ the return springs work   
2/ the pistons in the calipers or pistons in the drum cylinders are totally (100% !) free of any rust
3/ all seals are in good shape
4/ the system is bled including the BMC !
5/ the fluid is a DOT 4  (OR dot 5.1 ) and was replaced in the last 12 months and has no water in it. 
6/ the pads are in good shape (not worn, not scorched, not covered with a metallic glaze) If new - make sure you drive at last 100 miles before hard 
braking).
7/ the disc?s surface is flat (no grooves) and have proper thickness
 
If all these are true both foot brake and hand brake must work well.
   

[miro-1980]

RE : Balance Valve / Load Proportioning Valve.

I have used a Tilton proportioning valve and this is my experience :

On a standard system , even with the standard rear brakes adjuster removed this does not really do the trick.

The proportioning valve role / function is to adjust the front/rear balance depending on traction (surface). According to Sandro Munari he used in his Gr 4 131 Abarth the following balance adjustment depending on a road:

(front-to-rear )
tarmac :60/40
gravel : 50/50
mud : 40/60
snow : 30/70    


Interesting is that the more slippery surface the more braking power goes to the rear.  See the way the Tilton works  (picture below).

I do not know this for a fact but strongly suspect that the twin section Fiat BMC does not deliver 50/50 pressure split. But even if it does installing a Tilton on the rear assumes that in max open position the Tilton delivers 70 to rear and when closed it delivers 40.  

Installing a Tilton should be on front brakes, as the objective of bias adjustment is limiting the slippage (loss of traction) on the front , not rear wheels. In fact this is one of the possible applications as shown on the installation sheet you get with a Tilton.

Even if you do not need such a professional wide range of adjustment (60/40 - 30/70) I believe ( totally contrary to the existing practice) that installation of a brake proportioning valve on and standard 131 brake system with servo and single twin section BMC should be done on the front wheels not rear ones.

The only possible sense of rear end installation is when the braking power with valve open is 50/50 , as this gives you adjustment between 60/40 to 50/50 which is the desired range. This however would mean unadjusted braking power of 50/50. In real terms this would mean the same discs and calipers would have to be installed on rear and front. Well I have never seen a 131 with the same front rear calipers and discs though two of ex factory homologated brakes (Lockheed and Girling were of the same diameter , the discs ware different ( see friction surface data below)

Miro    

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Brake size to Tyre Ratio.

There is no point in putting big brakes on a car with small or low grip tyres, apart from the problem of getting the brakes up to temp, if you are using small tyres the brakes will try to lock far to easily for good control.

  It will be found that having an over sensitive or overly hard brake pedal will make good brake modulation very hard, or harder than it needs to be.  So make sure you think before going further than uprated Disc's and Pads.

                      COME ON CHAPS PUT UP YOUR BRAKE CONVERSIONS HERE.

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 Convert to all flexible hose

  I got so fed up with the brake pipes rusting, I changed all of them over to flexables, looked nicer and I think the burst pressure may be high as well, needs checking if any ones bothers. The MOT man is never going to fail on rusty pipes again is he, and if there inside the car as well, because there easier to run, there protected as well.   It also makes it easier if your plumbing in a balance valve as well.

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Road Going Hydraulic handbrake.

  Simples,  Plumb in the handbrake cylinder to the handbrake lever using the normal 131 handle, this keeps the normal 131 cable under the car. Now run the rear pipes through the new cylinder and back to the rear brakes.  Here's where you get clever, leave the cable a little lose, just so that the hydraulics work before the cable pulls tight, this way the brakes work and the car has the legal cale as well, job done