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Mini brake modification
https://ausmini.com/forums/viewtopic.php?f=5&t=79109		 Page 1 of 2
Author:  craig goss [ Tue Nov 06, 2012 8:34 pm ]
Post subject:  Mini brake modification
Hi all,

I have been having problems with my brakes for a while now. Im running rebuilt metro front brakes with new cooper s slave cylinders in the rear. I am using a rover master cylinder with a old style bias valve on the rear subframe. The brakes arent spongy but they arent very good. I have had brake specialist look at it and they dont know what it could be. Im just wondering what could it be? did the rovers come out with different master cylinders for the disc and drum front ends or was it the same one? Also is there any other master cylinders that can be used eg from a mazda? I just dont want to use a brake booster.

Cheers
Author:  i got a mini [ Tue Nov 06, 2012 8:43 pm ]
Post subject: 
i have the same issue i got 7.5s disk brakes on the front and they arnt the best still lock up but no were near as my brothers gt brakes
Author:  craig goss [ Tue Nov 06, 2012 8:54 pm ]
Post subject: 
Yea i dnt have a hope in hell of locking them up. It takes about 40m to stop from 60km/h. its just dangerous
Author:  Harley [ Tue Nov 06, 2012 9:05 pm ]
Post subject: 
What are the pads and how old?
Do the brakes improve with use (when they're hot)?
Author:  drmini in aust [ Tue Nov 06, 2012 9:06 pm ]
Post subject: 
What pads are you guys running? Disc brakes are only as good as the pads they are wearing.
I like EBC Greenstuffs... I have run cheapo pads in the past and they were rubbish for stopping power.

Adding a servo helps as you need less pedal pressure, but I am used to running my S brakes without one. And I have no room....
Author:  craig goss [ Tue Nov 06, 2012 11:45 pm ]
Post subject: 
I originally was running standard pads but i thought it was possibly the problems so i went to green stuff pads. The pads are only 3 months old. And the brakes dont really get better they fad very quickly too.
Author:  diecast [ Wed Nov 07, 2012 8:39 am ]
Post subject: 
I doubt it would be the EBC Greenstuff pads fading, i have run greenstuffs at plenty of Wakefield Park track days for 20 minute sessions, brakes still fine at the end of the session. I use 7.5" S discs and calipers.
Author:  MiniVLT [ Wed Nov 07, 2012 10:30 am ]
Post subject: 
I remember my aussie tandem master, 7.5" discs with cooper S rear wheel cylinders having the same issue, ie didn't seem to feel that effective!
One thing I tried was actually blocking of the rear brakes all together by blanking the rear brake line off in the engine bay. The pedal was instant and the discs on their own pulled the car up easily! Which means the rears are the problem area.

So my guess is if the rear brakes are adjusted correctly then the bias valve on the rear subframe may be letting too much pressure to the rear?? Incorrect pressure distribution??
Have you thought about getting an adjustable one??

Cheers Shane
Author:  kiwiinwgtn [ Wed Nov 07, 2012 4:50 pm ]
Post subject: 
what bore size are the rear wheel cylinders, try 1/2 inch ones.

Also check the disks are dry, zi had an issue with grease getting on the rotor

Kiwiinwgtn
Author:  simon k [ Wed Nov 07, 2012 6:08 pm ]
Post subject: 
MiniVLT wrote:
One thing I tried was actually blocking of the rear brakes all together by blanking the rear brake line off in the engine bay. The pedal was instant and the discs on their own pulled the car up easily! Which means the rears are the problem area.


not so much that the rears are a problem, but there's only so much fluid to go around - which is why we put in smaller rear cylinders - less fluid needed at the rear means more available to the front.

Put in a bigger bore MC
Author:  drmini in aust [ Wed Nov 07, 2012 6:29 pm ]
Post subject: 
Simon a bigger bore MC will make it worse, you are reducing the hydraulic pressure advantage.

This is why the 998 Cooper went down to a 5/8 MC, so they would stop without using a hydraulic intensifier like the 997 did.

Trust me, I'm an engineer. (sort of) :wink:

re the rears, S are smaller (5/8") as they lock the rears up with Oz standard size (3/4") ones. Ask me how I know this... :shock: :shock:
Hint: sideways on the F3, braking @ 110kmh in the rain ain't funny.
Author:  MiniVLT [ Wed Nov 07, 2012 9:21 pm ]
Post subject: 
Simon, I agree with you that there is only so much fluid to go around......
However, like the good Dr said, it's all to do with pressure!

If you increase the diameter of the MC you increase the fluid being moved, but you decrease the pressure to both the front and the rear for the same given input. Likewise if you decrease the size of the rear wheel cylinders you decrease the amount of fluid required to move the pistons and you also decrease the pressure to the rear brakes due to surface area.

Just out of interest do you have the outlets of the UK master cylinder going to the right brakes? If I remember correctly it's opposite to the Aussie MC. The top should go to the rear brakes and the bottom goes to the front. If I'm wrong on the connections someone will jump in here!

Cheers Shane
Author:  Bubbacluby [ Thu Nov 08, 2012 11:26 am ]
Post subject: 
There is a difference between rear brake limiting Valves on a cooper S/GT (disc braked cars) to a drum-braked car. So could this be the problem??
Author:  drmini in aust [ Thu Nov 08, 2012 12:12 pm ]
Post subject: 
Bubbacluby wrote:
There is a difference between rear brake limiting Valves on a cooper S/GT (disc braked cars) to a drum-braked car. So could this be the problem??

It's really not much different..

Cooper S or GT, 370 then 340psi
Most others 390psi, except Cooper & 850 450psi

These numbers from 1976 Leyland Black book.
Author:  craig goss [ Fri Nov 09, 2012 10:43 pm ]
Post subject: 
Sorry about the late reply in the desert working at the moment,

The rears im running the cooper s slave cylinders because larger than that the wheels will lock-up and its what the cooper s ran so it should be okay. The rotors are free of dirt, grease, and the pads have been bedded in. The brake bias hasn't been rebuild could this be the problem.

I have plumbed the rear brake pipe in the top of the master cylinder whilst the lower fitting is for the front. The lower piston is a larger size so i suspected that it was for the front.

Cheers
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