gti rabbit rear disc help

I have just recently converted my 84 GTI too rear disc. The brakes are from
from a 87 Jetta GLI. My question is do I need to get a bigger master to run the 4 disc's? Not yet finished bleeding them and seems still to be spongy!
  Thanx Dwayne

No, not really. If you've not yet finished bleeding them….they'll be spongy. Which technique are you using to bleed them?

I bought the hand pump unit that sucks the brake fluid threw.
Maybe I'm just not using it correctly.
So the stock master is big enough!……

mountaintaz said

I bought the hand pump unit that sucks the brake fluid threw.
Maybe I'm just not using it correctly.
So the stock master is big enough!……

Yeah the stock master cylinder is big enough, but on the scale of things, a rear disc conversion is quite a 'full on' alteration; and an upgrade of the master cylinder and servo is normally done well before, or as part of a package of changes. There's no one set way of doing things, though.

I've used 4 different methods of bleeding brakes but I've not heard of a hand pump vacuum unit. I guess its similar to a (compressor) air operated vacuum pump - these are convenient but not that great, all told. I prefer plain old pumping the pedal and a one way valve on the end of some clear tube.

Do you have a rear pressure regulater (underneath, connected to rear beam with spring) If you do make sure its pressed in (or out cant remember) when bleading or you will never get the rears bled.

I've got rear discs on mine, just word of warning mate, once you get them bled make sure you are very happy with the front / rear brake bias before driving too fast. I did a lot of testing and its really easy to do a 180 in the wet if you have too much rear bias.

Oh yeah, make sure you dont still have the residual pressure regulators still in the rear braklines, these are found under the bonnet on the rear lines and are for drum brakes only.
Sorry if this is all obvious stuff but I found it all out the hard way!

rustyGolf said

Do you have a rear pressure regulater (underneath, connected to rear beam with spring) If you do make sure its pressed in (or out cant remember) when bleading or you will never get the rears bled.

I've got rear discs on mine, just word of warning mate, once you get them bled make sure you are very happy with the front / rear brake bias before driving too fast. I did a lot of testing and its really easy to do a 180 in the wet if you have too much rear bias.

Oh yeah, make sure you dont still have the residual pressure regulators still in the rear braklines, these are found under the bonnet on the rear lines and are for drum brakes only.
Sorry if this is all obvious stuff but I found it all out the hard way!

I thought the things on the bulk head were limiters? I have 2 sets in mine with the rear disc conversion,

also you could do with the larger mc, the mk2s had them for a reason and it will help with the feel of the brakes and make the pedal shorter.

and you will need to look into the bias as I will garantee you end up backwords!! I have 280s up front but mine will still lock the rears first. im looking into a mk2 compenator to help with things.

M7R, I think the in line valves in the mk1 are spring valves to maintain residual brake pressure in the back lines. This is only needed for rear drums. I left these in at first thinking they were pressure regulators too but having them in made my rear brakes lock up.
In the end i left them in place but took the springs + balls out so i didnt have to redo my brakelines.

Now i'm just running the standard load sense rear pressure regulator, but have 22mm 16v master cylinder and 256 front brakes. Dont have any problems at the moment. I think if i ran with the rear interior stripped out i would need to reduce the rear bias further though.

There are a scirocco pressure regulators that are meant for rear discs that screw into the master cylinder outlet, tried to get some from vw but they said these are obselete now.

aahhhh!!! right! this may prove some of my issues…. my bias valve doesnt work i I think, as I can bleed the brakes no probs with the back end off the ground.

I got some what i belive are limiters from a guy on clubgti and fitted these inline with the rear, and they seemed to calm down a little…but not masses.

Well I found out what's gone wrong. Since my old master hasn't had to move a full stroke it is now no good. The stroke needed for the four wheel disc has move the piston into a rough part which wreaked the seals. I have now bought MK2 master and adjustable proprotioning vavle. So now I can dail it it!!!!
       I'll let you know how it works cheers!!!!