MK2 16V master cylinder.

I'm fitting a MK2 servo and master cylinder and have noticed the holes in the master cylinder (reservoir feed holes) are massively different in size!
So the common thoughts on plumbing one front wheel and one rear wheel don't seem to make sense to me … any thoughts folks?

Just read this and makes perfect sense to me so no need to do the diagonal thing, in fact it is totally the wrong thing to do!

Master Cylinder – Auto Repair Help

That was writen for older gm/ford type of cars.

VW used a Diagonal system, that is left rear right front and right rear left front.
Why, so that if one side went for some reason you still had a diagonal braking of opposite sides.
Also VW incorporated a proportional valve to vary pressures and fluid to the rears to prevent locking.

On the Golfs/Rabbit/Cabriolet there were 3 styles that I know of.
2 single lines off the MC to a valve on the fender which split off to 4 lines.
There was the one where the proportional/load sensing valve was located on the right rear by axle to vary pressures to the rears.
then the later cabriolet which had 4 lines off the mc with proportional valves on opposite corners.

I have never seen a system on a VW Golf/rabbit/cabriolet that had a mc that was to both fronts, and both rears.
But then I have only been working on Early Westy Rabbits, since 81, and Cabriolets since 2003.

I do know that there were 2 mc;s that I have seen a 20, and 22mm I don't have any first hand knowledge of the rear disk brakes off a Scirocco, or mk2…
as I think it took the larger mc.  I also think that the rear disk had no proportional valves.

Thanks for the info but the bit I'm struggling with is if the plumbing goes diagonal then why the different size holes in the master cylinder?
Surely the circuit with the bigger hole will flow more fluid ie more braking power would go to the front disks and the small hole circuit to the rear drums!

Early ones had the Brake light switches in them and it was a different sized hole as well as a pressure loss switch.

pics? if you mean the holes in the top the reservoir pushes into those are just a gravity feed into the main body, it wont affect braking

Pete M - i am assuming your upgrading the brakes because the current set up is rubbish??

I am on doing the same, i've got rear disc set up with standard brake bar, servo, brake block under master cylinder, inline valves on the nsf chassis leg and the dreaded compensator on the rear.

With my current set up, and despite numerous attempts at bleeding, the brakes are still going to the floor and are spongy.

I'm going to abandon all the valves etc and plumb a diagonal split from master cyl and add some bias valves for the rear  - what's everyones thoughts on this or is there a better solution before i get too deep into this?

Cheers

did you remove the 2 inline residual pressure valves near the bottom of the bulkead on the rear lines?  how does the bias valve feed when you clamp it fully open to bleed? if it feels all floppy its probably siezed

I stripped the compensator down again and it moves ok, i've not removed the inline valve things yet but all these valves etc seem a bit clumsy .. probably a vdub after thought because brakes are poor.
I'm going to order a couple of straight connectors to replace them but i suppose i could just remove the insides.

what I did was put a couple mk2/3 T pieces in and put my brake pressure switches in there, handy as it meant all the lines in the bay could stay stock with my 4 port master

My master cyl has 6 ports, 2 per side, 2 underneath. I have a brake switch in the car so dont need it on there anyway.
I was gonna run the front lines out of say the engine side and the rears out of wing side .. what do you reckon?

ah sorry didnt spot your servo was original! with the mk2 9" and 22mm master theres just the 4 ports, not that it matters to you either way with your pedal switch.

you can route your pipes any way you like, just as long as you have diagonally opposite corners on each circuit. the front 2 ports are 1 circuit, rear 2 are on the other one

Mk1 use all the ports, mk2/3 only use 2 ports with T pieces on the passenger side to split to each corner

I'll give it a go with the block under the master cyl and the valves removed.

Cheers for your help John - you're a legend !

God, i took the 2 inline valve off the N/S chassis leg - i dont know what pressure it takes to lift the valve off its seat but i sure as hell cant blow through them.

cool removing can only help you when bleedign the rears then

I'm running drums on the rear so can't help there I'm afraid. Bled mine in 15 mins with an easybleed.

so after bleeding my brakes numerous times I reckon my master cylinder is allowing fluid to pass the seals. there are no leaks and when you open the bleed valves fluid comes out but as soon as you close them if you pump the pedal and hold it down it'll go to the floor. before I order a replacement has anyone got any advise on an upgrade ??

Have you been pressure bleeding? If not it might be worth a try.
You may have air stuck at the calipers/wheel cylinders or other places where it can sit and let fluid pass but not remove the air, I had this on my motorcycles.
Try cracking the pipe or hose from points like the caliper hose connection.

If you have a leak you will have to keep adding fluid but if you are pumping the air up the fluid will go up and down in the res.

check your rear calipers, if they're later 38mm units and you have the handbrake cable on the top of the beam then they are fitted upside down (which is how it has to be if you fit late calipers with pipework as per early cars)

if so remove the caliper and hang it so the nipple is pointing straight up, then try again. dont pump the pedal obviously