Brake master cylinder design and plumbing layout.

[Conor]

Hey guys,

Quick one here. On other forums I'm just getting lots of "do this", "do that" around the brakes setup for my road going track car (Renault Clio MK 2)

Anyway, from a safety aspect what is the best way to plumb the brakes to the master cylinder.

My understanding is tat there are two sections on the master cylinder - front and back. The intention (I have read) is that one front and one rear goes on one end of the MC and the remaining wheels go on the other end. So if one part of the system springs a leak, then you still retain some level of braking ability.

I will be running a proportioning valve in the cabin, and as such can only use one line to the rear (very little bias in this car anyway). So that means one of the outputs on the MC will be blanked.

Now here is a question - some people are suggesting to blank another and just one outlet for the fronts and just tee off that after the MC. This removes any redundancy offered by the MC. It might be fine for a track car, but I don't like that for an MOT'able road going car.

Having just realised I have a second line going to the rear (A).. I think that needs to be removed, and (B) blanked off.

What do people think?

 

[Wighty]

Looks like you should get someone else to test drive it after all that lot buddy

 

[Conor]

Looks like you should get someone else to test drive it after all that lot buddy

No seriously, though.

It will be all proper when done and i'll have somebody else (actual mechanic) do the flaring etc.

I'm just trying to get opinions on design and a general understanding of how these systems are done.

What I have outlined above is the setup defined by Renault for "Clio Cup Racers" .. this is competition though, so I am just wondering where the differences (if any) are with a road going vehicle.

 

[Wighty]

That’s so far out of my experience buddy , I’m sure someone will know .

 

[Uncle Benz]

Careful now, in general the two ports close to the bulkhead serve the front wheels, the two ports nearer the front of the car serve the rear wheels. The two pistons inside are seperated by a spring, so the proportioning favours the front wheels until further effort overcomes the spring and brings the rear wheels in. You need to understand what’s inside and how it works before you make your decisions

 

[Conor]

Careful now, in general the two ports close to the bulkhead serve the front wheels, the two ports nearer the front of the car serve the rear wheels. The two pistons inside are seperated by a spring, so the proportioning favours the front wheels until further effort overcomes the spring and brings the rear wheels in. You need to understand what’s inside and how it works before you make your decisions

Ok, fair enough. So there is an element of checking out how the Renault OEM MC works. I must dive into it a bit more.

Do you reckon it could ever be the other way around, as per the Clio Cup Racer spec above, it's the [closest to front] outlets that serve the front.

I must see if I can find a workshop manual for the 172 Cup variant. The cup is a little different to anything else as it has no ABS and as such verry little bias on the rears. So much so that MOT testers were failing for low rear brake effort, to the point that the DVSA had to issue a bulletin.

 

[Conor]

Ok.. found so found this in the parts catalogue.

It's basically the same as cup racer except one of the rear outputs on the MC is blanked and one single output into the cabin to the bias adjuster.

So I guess i'm going with the cup racer setup.

I'm not sure when I came across the alternating/diagonal config.

Thanks for being my sounding board, guys. Sometimes you need to just talk about this to somebody and as you explain it, it starts to make sense.

But don't worry guys, out of everything in this build the braking system is something I am being very fastidious about. I share some space with another mechanic who helps me out from time to time.. and I jokingly (but seriously!) say that the real test of how well/safe the build is, is whether or not yer man will drive it once it's built.