19 replies to this topic

[69Cooper]

Afternoon All,

 

Need some advice/help with the brake system on my MKII Cooper. (1969)

 

It's mainly used as a Track car these days so pure fun, Over the winter I plan on fixing lots of bits on it but at the moment it's the brakes that need attention.

 

Last trackday at Snetterton I had brake failure, 1st of all the brake pedal biting point moved down quite a bit, I checked the brake system out in the paddock but couldn't see anything obvious, so did a couple of brake tests (in the paddock area) and even though the pedal moved quite a bit before anything happened the brakes did still work.

Next session out they gave up on me completely, I ended up go off at the Hairpin and nearly flipping it!!!!!!!

 

Anyway I now want to 1. See why and 2. thinking of changing the braking system.

 

Current setup (even though I know it's wrong for the period of the car, well some of it)

7.5 Cooper S Callipers Front, Ordinary Drums on the rear.

GMC227 Dual Master Cylinder (2 Years old)

Front to back brake bias on bulkhead.

 

I think the master cylinder and brake bias are wrong for the age of car, and to be quite honest the Master cylinder is not the prettiest of things!!

 

I was thinking of going for the KAD twin master cylinder setup, one for brakes the other for clutch, but not sure if that is do'able seeing as the brake master cylinder has only one out put and not 2 like i have at the moment.

 

So Has anyone experienced the same things with brake failure?

and

Has anyone fitting the KAD setup?

or 

What would be the preferred setup for Track Use?

 

 

 

[rww]

   There's nothing wrong with your 'S' 7.5 front discs or rear drums.  Your brake fade/failure will have been caused either by the brake fluid overheating or the brake pads not being suitable for circuit use and probably both.

 

  Minispares do a carbon metallic pad for the Cooper S caliper. We have used these for race use and they are 100% reliable, totally fade free and wear very little. You may not want to use them on the road but changing them is pretty easy and you would want to check all the brakes prior to using it on track. Standard rear linings are fine for track use - the rear brakes do very little and brake balance should be set towards the front. With the brake pedal FULLY applied the rear wheels should JUST turn when gripped with two hands.

 

Minispares can also provide Millers 300 brake fluid. Again, absolutely essential for track work, we overheated a lower temperature brake fluid during a pit stop. Once we had put in the Millers, no more problems.

 

There are other suppliers of spare parts for Mini's, I use these parts from Minispares.   

Edited by rww, 23 December 2020 - 05:15 PM.

[Quinlan minor]

Sounds a lot like you experienced brake fade ( https://en.wikipedia...wiki/Brake_fade ).

 

When did you last change the brake fluid?

Have you fitted apprpriate pads? Mintex M1144 would be a start, or Carbon Metallic. You pays your money,...

 

 

[69Cooper]

Thanks RWW & Quinlan minor,

 

Already running Mintex pads but good shout on the brake fluid, I'll look into the Millers 3000 and will change what I have.

 

If it was brake fade, wouldn't they feel better after everything had cooled down, tried them the other day and the pedal travels a long way!

 

I plan on taking the master cylinder out and stripping it down to see if I can find anything, but initially I'll try bleeding the brakes to see what that does. 

[GraemeC]

First inspect everything - it is very possibly that with the heavy on track use that one of the seals that was previously just hanging on has now given up.

I have had the sudden long pedal you describe when a rear cylinder seized under brake pressure.

[absx2]

Is the brake bias this http://www.minispare...|Back to search

If so they can be a nuisance and cause the problem you describe. The long travel you experienced is due to only one of the two pistons inside your master cylinder working giving you a little slack before moving the brake fluid.

I recently had this problem, the brakes worked fine but the travel was long. I bled the system and the pedal travel returned to normal and the rear brakes worked again ( I didn`t notice they weren't working     )

Anyway although it wasn`t the master cylinder at fault I replaced the master with a brand new http://www.minispare...|Back to search

and fitted a MS72 http://www.minispare...|Back to search on the bulkhead after blanking off one port in place of the other rubbish so I could fine tune the rear brake balance.

As you have a 1969 car that had a single circuit braking system from new and you use it for the occasional track day this would be your best set up in my opinion as the rears tend to lock up under heavy braking and its nice to know where the brake pedal lands every time you need it   

If you go for a KAD or Willwood  ( worth a look ) system using a 5/8" bore master will give your 7.5" discs a bit more bite without noticing extra pedal travel, I have an non servo 7.5" set up with a cooper 5/8" bore master on my 1967 Cooper and it`s great.

Your issue could be caused by slightly leaky rear slave cylinders or the brake limiter valve playing up as it`s unlikely the master will be playing up so soon but it would need checking

I have also experienced this same issue with a dual circuit master that didn`t have the a brake limiter fitted to the bulkhead, the problem was leaky slave cylinders. I personally don`t like the FAM7821 and wouldn`t fit one on anything I own but for insurance purposes they need to be fitted to vehicles manufactured from 1978 on

s the brake bias this http://www.minispare...|Back to search

If they can be a nuisance and cause the problem you describe. The long travel you experienced is due to only one of the two pistons inside your master cylinder working giving you a little slack before moving the brake fluid.

I recently had this problem, the brakes worked fine but the travel was long. I bled the system and the pedal travel returned to normal and the rear brakes worked again ( I didn`t notice they weren't working   )

Anyway although it wasn`t the master cylinder at fault I replaced the master with a brand new http://www.minispare...|Back to search

and fitted a MS72 http://www.minispare...|Back to search on the bulkhead after blanking off one port in place of the other rubbish so I could fine tune the rear brake balance.

As you have a 1969 car that had a single circuit braking system from new and you use it for the occasional track day this would be your best set up in my opinion as the rears tend to lock up under heavy braking and its nice to know where the brake pedal lands every time you need it   

If you go for a KAD or Willwood  ( worth a look ) system using a 5/8" bore master will give your 7.5" discs a bit more bite without noticing extra pedal travel, I have an non servo 7.5" set up with a cooper 5/8" bore master on my 1967 Cooper and it`s great.

Your issue could be caused by slightly leaky rear slave cylinders or the brake limiter valve playing up as it`s unlikely the master will be playing up so soon.

I have also experienced this same issue with a dual circuit master that didn`t have the a brake limiter fitted to the bulkhead, the problem was leaky slave cylinders. I personally don`t like the FAM7821 and wouldn`t fit one on anything I own but for insurance purposes they need to be fitted to vehicles manufactured from 1978 on

Edited by absx2, 24 December 2020 - 09:23 PM.

[nicklouse]

If going for the KAD set up with just the 2 master cylinders for the brake and clutch. You would need to change it back to a single line brake system so you would need to bin a few parts and fit a pressure regulator for the rear.

[Spider]

The first thing that comes to my mind here is the brake fluid maybe a little old and have some moisture in it. When the Front Brakes heat up, the moisture boils in the fluid and so makes gas pockets, effectively giving the same result as if you have Air in your system.

 

All competitions cars I've been involved with, I always made a point of bleeding fresh fluid through the system either the afternoon before the meeting or in the paddock before the car goes out on the track, even if I had done them the week before.

[69Cooper]

Is the brake bias this http://www.minispare...|Back to search
If so they can be a nuisance and cause the problem you describe. The long travel you experienced is due to only one of the two pistons inside your master cylinder working giving you a little slack before moving the brake fluid.
I recently had this problem, the brakes worked fine but the travel was long. I bled the system and the pedal travel returned to normal and the rear brakes worked again ( I didn`t notice they weren't working     )
Anyway although it wasn`t the master cylinder at fault I replaced the master with a brand new http://www.minispare...|Back to search
and fitted a MS72 http://www.minispare...|Back to search on the bulkhead after blanking off one port in place of the other rubbish so I could fine tune the rear brake balance.
As you have a 1969 car that had a single circuit braking system from new and you use it for the occasional track day this would be your best set up in my opinion as the rears tend to lock up under heavy braking and its nice to know where the brake pedal lands every time you need it   
If you go for a KAD or Willwood  ( worth a look ) system using a 5/8" bore master will give your 7.5" discs a bit more bite without noticing extra pedal travel, I have an non servo 7.5" set up with a cooper 5/8" bore master on my 1967 Cooper and it`s great.
Your issue could be caused by slightly leaky rear slave cylinders or the brake limiter valve playing up as it`s unlikely the master will be playing up so soon but it would need checking
I have also experienced this same issue with a dual circuit master that didn`t have the a brake limiter fitted to the bulkhead, the problem was leaky slave cylinders. I personally don`t like the FAM7821 and wouldn`t fit one on anything I own but for insurance purposes they need to be fitted to vehicles manufactured from 1978 on
s the brake bias this http://www.minispare...|Back to search
If they can be a nuisance and cause the problem you describe. The long travel you experienced is due to only one of the two pistons inside your master cylinder working giving you a little slack before moving the brake fluid.
I recently had this problem, the brakes worked fine but the travel was long. I bled the system and the pedal travel returned to normal and the rear brakes worked again ( I didn`t notice they weren't working   )
Anyway although it wasn`t the master cylinder at fault I replaced the master with a brand new http://www.minispare...|Back to search
and fitted a MS72 http://www.minispare...|Back to search on the bulkhead after blanking off one port in place of the other rubbish so I could fine tune the rear brake balance.
As you have a 1969 car that had a single circuit braking system from new and you use it for the occasional track day this would be your best set up in my opinion as the rears tend to lock up under heavy braking and its nice to know where the brake pedal lands every time you need it   
If you go for a KAD or Willwood  ( worth a look ) system using a 5/8" bore master will give your 7.5" discs a bit more bite without noticing extra pedal travel, I have an non servo 7.5" set up with a cooper 5/8" bore master on my 1967 Cooper and it`s great.
Your issue could be caused by slightly leaky rear slave cylinders or the brake limiter valve playing up as it`s unlikely the master will be playing up so soon.
I have also experienced this same issue with a dual circuit master that didn`t have the a brake limiter fitted to the bulkhead, the problem was leaky slave cylinders. I personally don`t like the FAM7821 and wouldn`t fit one on anything I own but for insurance purposes they need to be fitted to vehicles manufactured from 1978 on

Thanks absx2
Yes I’ve got the FAM7821 on the bulkhead.

Ok so it sounds like I’ll have to give the whole system an overhaul and I could change to the KAD type dual master setup with a few changes .

Even though I’ve quoted the KAD setup
https://kentautodeve...er-cylinder-kit
I won’t be getting it from them, I’m going to source the parts individually and make my own support setup.
I’m guessing I just need to change the FAM7821 for a standard 3 way splitter ( Minispares 3H2424) on the bulk head and install a brake regulator pressure valve on the rear subframe (there would appear to be 2 different ones, one for MK3 with 3/4” rear wheel cylinders and one for MK1/MK2 with 5/8” bore wheel cylinders)
So the other question is which rear wheel cylinder to use (I will probably replace both)
Is larger or smaller better for brake systems?

A bit more thought needed I think.

Thank you to others for your input I’ll keep you posted once I get out to the garage

[absx2]

The first thing that comes to my mind here is the brake fluid maybe a little old and have some moisture in it. When the Front Brakes heat up, the moisture boils in the fluid and so makes gas pockets, effectively giving the same result as if you have Air in your system.

 

All competitions cars I've been involved with, I always made a point of bleeding fresh fluid through the system either the afternoon before the meeting or in the paddock before the car goes out on the track, even if I had done them the week before.

That would explain why with a quick bleed through every thing seems to be normal again although it does knock the confidence a bit.

[absx2]

69cooper the MS72 is adjustable so you can control the amount of braking to the rear so wheel cylinder size is not a big deal so I would  stick with 3/4" bore personally.

That 7/8" cylinder from KAD would be very hard to press ??

[69Cooper]

69cooper the MS72 is adjustable so you can control the amount of braking to the rear so wheel cylinder size is not a big deal so I would  stick with 3/4" bore personally.

That 7/8" cylinder from KAD would be very hard to press ??

 

Thanks I had spotted that on the MS72, a good option I suppose but not sure!

 

Might just stick with the standard 5/8" master and rear cylinders.

 

The KAD setup actually uses standard AP Racing master cylinders and you can choose what bore size you want.

 

So looks like I have a little shopping list to put together.

 

1 x AP Racing Master Cylinder 5/8" Brakes. (https://www.rallynut...r-cylinder.html)

1 x AP Racing Master Cylinder 3/4" Clutch.

3 way splitter

Brake Pressure regulator

2 Rear Wheel cylinders 5/8"

Millers 300 brake fluid

 

Hopefully all of the above should sort things out, might need some brake pipe to make up some new pipes.

[nicklouse]

Not a straight fit those MCs.

 

the rod will need cutting down to just about nothing. And the studs on the pedal box will need replacing for longer ones as the standard ones are not quite long enough.

[69Cooper]

Not a straight fit those MCs.

 

the rod will need cutting down to just about nothing. And the studs on the pedal box will need replacing for longer ones as the standard ones are not quite long enough.

 Ah...................I did wonder, the KAD kit comes with spacers for the base plates, is that because of the rod length issue?

The kid ones also have the clevis attachment on them?

 

Just checked the AP website and there are detailed drawings, showing the base plate as 9.5 mm, so that should be OK shouldn't it?

 

Maybe I'll have to revert back to the original style Master Cylinder, 

http://minispares.co...|Back to search

 

But it states you can't use Racing fluids????

 

Just when I thought it might be simple!!!!!

[nicklouse]

But you also need a spacer under the base to lift it away from pedal box due to the position of the piston and shaft.

 

fitted the KAD clutch kit earlier so you can see what I had to do.

 

https://www.theminif...date-it/page-50

 

as to the race fluid comment. It only really means Non glycol fluid. There are many race brake fluids you can use.