Hi all,

I am new to the forums, but have been around Monaro's my whole life - my Dad had his Monaro when I was born.
Anyway I'm helping Dad get it roadworthy as it has been in his garage 20 years we decided to get new master and slave cylinders for brakes and clutch. We bought a reconditioned big nut MC as Dad put a PBR MC in about 30 years ago.

We have a slight leak at the front outlet on this reconditioned big nut MC.
Dad reckons that the pipe seat (brass insert) in the reco' unit is the incorrect shape and is the cause of the leak. I am not so sure, as Dad has had some stories with the brakes over the years. So far I can tell you...

* HQ disc brakes installed up front (about 30 yr ago)
* PBR MC installed approx. 30 years ago, but recently replaced with reco'd HT big nut MC
* About 30yr ago auto engineer required a 'balancing valve' be installed between front and rear brakes as rear brakes were working too strongly. It was just there to reduce pressure to rear brakes
* The PBR MC never leaked, also the pipe seats have 'sharper' points and smaller outlet holes
* Dad noted that the big nut pipe seats were more rounded with larger outlet holes and was concerned it may leak

The flare nuts and lines were never changed. We have removed the 'balancer' between front/rear brakes (replaced the whole line from balancer all the way back).

Dad feels that the tube inserts on the reco'd big nut MC are incorrect, and that the inserts should be more like the PBR pipe seats. I have attached a photo of the PBR with pipe seats installed, and one of the pipe insert itself.

I have searched a lot about big nut MCs and read alot here today, I have already learned/noticed Dr Terry probably knows more about them than anyone else on earth, but hoping anyone can help!

Regards,
Steve

Edited by user Tuesday, 6 February 2018 9:38:42 PM(UTC)  | Reason: Not specified

The only 2 causes for the brass olives to leak are where they seat into the m/cyl case or where the tip of the cone seats against the pipe flare. The latter is more likely.

I would see a good brake shop, show him the m/cyl & maybe purchase some replacement olives.

Can I ask why an engineer was involved in the first place. What other mods are done to the car. I fitted plenty of HQ fronts to HK/T/G over the years & have not needed a proportioning valve.

Also AFAIK the early 'Big nut" m/cyl had 2 reservoirs of the same volume, but the PBR alloy type had 2 different sized reservoirs.

Dr Terry

Hi Terry and Dave,

Thank you for your helpful replies, and Terry thank you for pointing us in the right direction after I gave you a call :)

It turns out that the reconditioned Bignut MBC we bought did not have new brass pipe seats installed. They were a bit scratched on the surface/face that seals against the pipe. Terry pointed us to a brake/auto parts store near us that could supply us with new pipe seats. Once we bought new seats and installed them it has not leaked :D

To answer your question Terry about the other modifications that needed the engineer's certificate, Dad actually had a Ford 9" in the back and Phase III rotors and calipers up the front and he said that is the reason why he needed engineering clearance those many years ago. Sorry I didn't make that clear I didn't know he put Ford brakes up front years ago.

We have it all back to standard/original now except for the HQ discs and calipers on the front.
Thank you all once again.

No doubt I will continue loitering and posting on here in the near future as there's still quite a few things I would love to restore/replace on the car as the time comes.

Cheers,
Steve