BS5620 Posted April 30, 2011 Share Posted April 30, 2011 This may be a silly question but I'm stumped I have changed the brake m/c in my car. The original only had one outlet but the new one has two. Original was the mk1 cortina one and the new one is a Nabco one from a Subaru. Bore size with the new one is 1 1/16 but I'm running AP 4pots and discs on the rear now so need a bigger bore (but is 1 1/16 to big?). I have a vh44 to put in aswell. But what I'm wanting to know is will it matter if I just block one of the outlets on the new M/C so i can plumb it up to existing lines or is this actually a return feed or something???. Cheers Quote Link to comment Share on other sites More sharing options...
Simon Posted April 30, 2011 Share Posted April 30, 2011 It's supposed to be a safety circuit, so if something cuts the rear brake line like flying piece of metal flicked up my the front tyres there is still the front brake circuit which will work. It will probably be all right, make sure you block the port closest to the cabin. Just make sure you check it at a low speed first. Quote Link to comment Share on other sites More sharing options...
cletus Posted April 30, 2011 Share Posted April 30, 2011 the subaru one will have an outlet for the front brakes and one for the rear. the original one would have had just 1 for all 4 wheels. you will need to make new lines to suit the new cylinder. Quote Link to comment Share on other sites More sharing options...
mjrstar Posted April 30, 2011 Share Posted April 30, 2011 Agreed with cletus you will need to use both ports, blocking off 1 port will just allow pressure to build in the blocked off portion of the m/c and you will end up with bugger all/no braking performance from the port which is in use. Also basically for a road car there is no such thing as a master cylinder which is too big. The bigger they are the higher and firmer the pedal will be (which is awesome) Quote Link to comment Share on other sites More sharing options...
KKtrips Posted April 30, 2011 Share Posted April 30, 2011 Also basically for a road car there is no such thing as a master cylinder which is too big. The bigger they are the higher and firmer the pedal will be (which is awesome) The bigger the bore - the firmer the pedal but the less effective the brakes will be.. Its like a seesaw - the further away from the fulcrum you sit the easier it will be to get the other end to travel through its arc of movement, but the length of the arc you will need to travel is a lot greater.. So think about it this way - the larger the bore the closer you stand to the fulcrum.. Quote Link to comment Share on other sites More sharing options...
BS5620 Posted April 30, 2011 Author Share Posted April 30, 2011 So think about it this way - the larger the bore the closer you stand to the fulcrum.. That makes sense, last time I bleed these brakes with normal drums on the rear I had a very hard peddle with no movement, would like some movement in my peddles, so should have a smaller dia bore?? the subaru one will have an outlet for the front brakes and one for the rear. the original one would have had just 1 for all 4 wheels. you will need to make new lines to suit the new cylinder. So from that logic I plumb my back brakes directly to the m/c (i assume the one closest to the firewall as this one is the last one to move fluid in a stroke) and then put the front outlet to the T junction to split to left and right brakes. So to use the vh44 remote brake booster i really need one outlet so all brakes will run through the booster, and not just the front ones??Or could I have it so both outlets plumb into one line then through the booster and back to a junction where it gets split front to back brakes again?? Quote Link to comment Share on other sites More sharing options...
yoeddynz Posted April 30, 2011 Share Posted April 30, 2011 i think with a vh44 remote servo you can only have the one circuit. So its a no go.. I was going to use a remote cv one point but yeah- it won't work with twin circuits. Some cars like old alfa romeo's use twin remote servos. Best you keep the twin circuit too as its a good safe backup. Can you fit a servo in between firewall and master? You'll have to make new lines anyway which is easy and quite satisfying. Btw if your pedal feels hard using new master with drums in the back it'll soften/get more travel a bit when you fit rear discs. This is because most calipers require more fluid to move and your leverage ratio will go up. Quote Link to comment Share on other sites More sharing options...
mjrstar Posted April 30, 2011 Share Posted April 30, 2011 The bigger the bore - the firmer the pedal but the less effective the brakes will be.. Totally Agree Mr KK, I am not suggesting scratch building a 3'' dia master and expecting the best braking performance, but I still believe with any OEM Master Cylinder used under a normal ratio pedal you will not get to the point where braking performance is deminished due to massive displacement Master cylinder. Be it used on drums, opposed piston calipers, or sliding calipers all which have a slightly different appetite for fluid. Well unless you had an amazingly weak leg with no muscles etc.. Also I suspect the brakes will "soften" up slightly if a vacuum booster is used. Quote Link to comment Share on other sites More sharing options...
yoeddynz Posted April 30, 2011 Share Posted April 30, 2011 I looked at your build thread greg and shit- there aint much room for a normal servo is there! Quote Link to comment Share on other sites More sharing options...
Valiant Posted April 30, 2011 Share Posted April 30, 2011 Hi BS5620. Plumb your rear brakes into the front port on the master cylinder. Plumb the rear port on the master cylinder into your VH44 and from there to your front brakes. You can mount your VH 44 under the dash or inner guard if you are short on space. I've built a system like this, it works well. Quote Link to comment Share on other sites More sharing options...
Seedy Al Posted May 1, 2011 Share Posted May 1, 2011 Truth has been spoken^^ Quote Link to comment Share on other sites More sharing options...
yoeddynz Posted May 1, 2011 Share Posted May 1, 2011 good idea! Quote Link to comment Share on other sites More sharing options...
BS5620 Posted May 1, 2011 Author Share Posted May 1, 2011 Yeah I will try this ^^^^ I looked at your build thread greg and shit- there aint much room for a normal servo is there! Yeah not much room at all. Probably try and put it up and under in the dash Cheers for all the help guys Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.