'65 leaking back through master cylinder cap. Rear brakes

[Old guy]

Hi, noticed that my new master cylinder's reservoir for the rear brakes is going down and the master cylinder seems to be leaking out of the cap/lid. What could cause this? Seems to be a large amount of pressure on the pedal and I'm thinking this has to give somewhere so is taking the  easy way out to the area of least resistance...the cap. Kelsey Hayes setup with a duel master cylinder, obviously. Has the adjuster knob thingy for the master cylinder (decrease/increase). Have had that in various spots but no difference to the fluid disappearing issue. Blockage?

I heard somewhere you can give that adjuster the flick by changing the rear wheel cylinders? What would I have in there now and what do you change them to? Read so many conflicting stories. 29/32, 7/8, 3/4, 13/16, etc.

Cheers.

[shaunp]

Hi, noticed that my new master cylinder's reservoir for the rear brakes is going down and the master cylinder seems to be leaking out of the cap/lid. What could cause this? Seems to be a large amount of pressure on the pedal and I'm thinking this has to give somewhere so is taking the  easy way out to the area of least resistance...the cap. Kelsey Hayes setup with a duel master cylinder, obviously. Has the adjuster knob thingy for the master cylinder (decrease/increase). Have had that in various spots but no difference to the fluid disappearing issue. Blockage?

I heard somewhere you can give that adjuster the flick by changing the rear wheel cylinders? What would I have in there now and what do you change them to? Read so many conflicting stories. 29/32, 7/8, 3/4, 13/16, etc.

Cheers.

what model car? 67 on can make do with falcon 13/16, pre 67 need 5/8

[Dwayne]

I have a new pair of 13/16 cylinders here, thought I needed them instead of 5/8 

[Old guy]

65 model. Ive read so many "experts" saying this and that for what size cylinders I need. Looking for a definitive answer which may help others in the future also.

[Old guy]

what model car? 67 on can make do with falcon 13/16, pre 67 need 5/8

So 5/8 will mean I can flick the adjuster unit?

[shaunp]

yep 5/8 if it has disc fronts, these are XY ute and GTHO rear cylinders, but you can't buy them off the shelf any more they are obsolete, you have to get them sleeved to that size. Ray at Knights old school brakes at Wynnum in Brisbane does them often

[Old guy]

OK. So what is on it now? So 5/8 rear wheel cylinders off a GT falcon from 70s model?

Also the leaking master cylinder issue. Any thoughts?

[shaunp]

OK. So what is on it now? So 5/8 rear wheel cylinders off a GT falcon from 70s model?

Also the leaking master cylinder issue. Any thoughts?

Yep originally on Utes so they didn't lock the rears when empty and on Falcon Gt's which had much bigger rear drums from like a Thunder bird. Its its leaking out of the lid its over full or the lids seal is crook, lid not straight or something..  You cant buy the 5/8 cylinders anymore, you have make them.

[Old guy]

yep 5/8 if it has disc fronts, these are XY ute and GTHO rear cylinders, but you can't buy them off the shelf any more they are obsolete, you have to get them sleeved to that size. Ray at Knights old school brakes at Wynnum in Brisbane does them often

Thanks Shaun. Ray quotes $200 plus $20 for postage for future reference for anyone. He can make a little W or V shaped (can't remember which he said. lol) bit of metal to go into the rear brakes reservoir position, to stop the fluid coming out via the cap. Seems he has seen this issue many times before.

[shaunp]

Thanks Shaun. Ray quotes $200 plus $20 for postage for future reference for anyone. He can make a little W or V shaped (can't remember which he said. lol) bit of metal to go into the rear brakes reservoir position, to stop the fluid coming out via the cap. Seems he has seen this issue many times before.

 He makes a lot of custom stuff for Mal Wood transmissions the Tremec dealer, also John Greene , though he is retired now had a mustang business in the next street for 30 years called Probe engineering, who used to do lots of RHD conversions, he used to get Ray to do his brake stuff.

 I think the 5/8 thing is actually John's idea. Not much he doesn't know about sorting out Mustangs, I learnt a lot from him over the years, proper  engineer, was acredited by QLD Transport etc