12 replies to this topic

[alpder]

Somewhere, on one of the many Mini forums, I read a detailed thread about how there's a particular rear-cylinder piston-dia that will give the best match to each of the many various front disc-brake conversions, without needing a brake balance valve. But ****ed if I can find the thread now.

 

Vehicle is a 1968 van half-way through a nut-and-bolt resto. Unmodified dry suspension, on 10" 145 radials. 1275 A+. It's for daily-driver type road use - not track. MiniSport 7.5" front disc conversion is about to be fitted. Mintex pads at front. Mintex shoes at rear.

 

Could anyone remind me, please, what's the best size rear cylinder to fit? Or direct me to the relevant thread?

 

[Chris1275gt]

My 1975 1275gt has no bias valve or servo with 8.4 disks at the front and 1/2 cylinders at the back. The back wheels don’t lock up and the pedal is fine.

[KTS]

the bottom of this page lists usual brake combinations

 

http://www.minispare...tion~Chart.aspx

[Ethel]

There is no ideal, especially for a van, if you're going to carry anything in it. The diagonal split system, without a valve used 1/2" cylinders, as Chris said. Vans used an inertia valve: the most versatile as it directly senses the same factors that would lock up the rear.

[alpder]

Thanks all. That MS link led me to this link: http://www.minispare...bias-adjustment
which is probably the "forum post" I'd remembered reading before.

 

Roughly summarised it says ''11/16inch rear cylinders will probably be fine paired with 7.5inch front discs even when plumbed direct. Alternatively fit 3/4inch cylinders and an adjustable pressure reg in the rear line.'' And then presumably you fiddle with the reg until the back end ceases to overtake you

 

Does anyone out there have a van/estate/pickup with either of these set-ups?

[Spider]

With 7.5's I've always fitted the 5/8" Rear Wheel Cylinders and a valve of one type or another for the Rear Brakes. The (original) Cooper S and early 1275GTs came that way from the factory.

 

11/16's Cylinders will have a tendency to lock up and 3/4" Cylinder do lock up.

 

If you want to fit them up without a Valve. then 1/2" is the only option there, but they give much less then optimal braking on the rear wheels and for a Van, not ideal.

[SKIDDERWOLF]

With 7.5's I've always fitted the 5/8" Rear Wheel Cylinders and a valve of one type or another for the Rear Brakes. The (original) Cooper S and early 1275GTs came that way from the factory.

 

11/16's Cylinders will have a tendency to lock up and 3/4" Cylinder do lock up.

 

If you want to fit them up without a Valve. then 1/2" is the only option there, but they give much less then optimal braking on the rear wheels and for a Van, not idealf

Followed Spiders advice (Thanks Spider  ) when I recently fitted 7.5" discs to my mini and changed rear cylinders to 5/8". I have since driven around 100 miles or so and I can lock the fronts up fairly easy with a firm push to the pedal. Obviously I tried this on a quiet road but from 50mph or so I can have the fronts on the brink of locking with no issues from the rear.  pretty pleased with the performance. Much more confidence with the car over the previous drums and certainly dont feel as the rear may snap round.

[Quinlan minor]

Followed Spiders advice (Thanks Spider  ) when I recently fitted 7.5" discs to my mini and changed rear cylinders to 5/8". I have since driven around 100 miles or so and I can lock the fronts up fairly easy with a firm push to the pedal. Obviously I tried this on a quiet road but from 50mph or so I can have the fronts on the brink of locking with no issues from the rear.  pretty pleased with the performance. Much more confidence with the car over the previous drums and certainly dont feel as the rear may snap round.

 

In dry or damp conditions?

 

I had mine snap on me, when some toerag pulled out of a junction, in front of me on a cold, wet night, without looking.

It wouldn't have mattered if he had, all his windows were steamed up.

Mounted the pavement backwards, luckily via a driveway, so missing the kerb, stopped between a lamp post and a wall, without touching either.

When I caught the *******, further down the road, I had a sharp word, or two, with him.

I now run 1/2" cylinders on the rear.
 

Edited by Quinlan minor, 23 April 2023 - 06:32 PM.

[SKIDDERWOLF]

A bit of both really, it was earlier today and the road was still dampish from last nights rain although not wet!

 

Sounds like you and your mini had a lucky escape.

 

Any issues with brake efficiency for MOT?

[Quinlan minor]

A bit of both really, it was earlier today and the road was still dampish from last nights rain although not wet!

 

Sounds like you and your mini had a lucky escape.

 

Any issues with brake efficiency for MOT?

It's often been mentioned as lowish, but most Testers are used to the numbers they see from a two ton four by four, not a ten foot long 600kg Mini.

[Spider]

Skiddy, happy for you that you're impressed with your new brakes

 

 

 

Followed Spiders advice (Thanks Spider  ) when I recently fitted 7.5" discs to my mini and changed rear cylinders to 5/8". I have since driven around 100 miles or so and I can lock the fronts up fairly easy with a firm push to the pedal. Obviously I tried this on a quiet road but from 50mph or so I can have the fronts on the brink of locking with no issues from the rear.  pretty pleased with the performance. Much more confidence with the car over the previous drums and certainly dont feel as the rear may snap round.

 

In dry or damp conditions?

 

I had mine snap on me, when some toerag pulled out of a junction, in front of me on a cold, wet night, without looking.

It wouldn't have mattered if he had, all his windows were steamed up.

Mounted the pavement backwards, luckily via a driveway, so missing the kerb, stopped between a lamp post and a wall, without touching either.

When I caught the *******, further down the road, I had a sharp word, or two, with him.

I now run 1/2" cylinders on the rear.
 

 

 

What Master Cylinder are you running and is the Rear Brake Shut Off Valve, what ever type you are running with, working ?

[Quinlan minor]

What Master Cylinder are you running and is the Rear Brake Shut Off Valve, what ever type you are running with, working ?

Stock MPi Master with stock twin line brake PDWA valve but PO had fitted 11/16" rear slaves. At that time it was on 12" wheels, now on 10" with 1/2 inch slaves.

 

[SKIDDERWOLF]

Right just a bit of feedback on this topic I have had the brakes on the car for a while now and have had chance to test how it reacts when braking in damp and wet conditions. 

I have found the car to behave very well, braking is much better and controllable than the drums were and I did not have any concern from the rear potentially or feeling like it was locking up. 

I had the fronts locking and nothing from the rear - make of this what you will. It is my experience in my car - Obviously this was done on a quiet road out of the way and not in my local high street!