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HTSteve Offline
#1 Posted : Tuesday, 6 February 2018 9:22:28 PM(UTC)
HTSteve

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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

HTSteve Offline
#2 Posted : Tuesday, 6 February 2018 9:35:51 PM(UTC)
HTSteve

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I wanted to outline the symptoms in my initial post, but after having searched and read a lot on here today about the big nut MCs used in HK/HG/HT etc. I have some queries about Dad's setup.

I'm curious as to why Dad was made to install the brake balancer/limiter for the rear brakes.
I read that the big nut MC has the larger reservoir at the front (for front brakes) but the PBR has the larger res. at the back.

I wonder if when my Dad installed the PBR 30yr ago if he was supposed to swap the front & rear inlet pipes? ie: does the PBR pictured use the rear res. for front brakes, and the front res. for rear brakes?

Is that the reason the balancer was required? Dad reckons the PBR above was all bolt on and no worries but I'm now not sure.
Now that we have the big nut MC back on I thought everything would be fine, but we still have leaks around the outlets :( :( :(

We've worked on many different components over the last year, the brakes have been causing us the most grief. This is the last thing left to solve hopefully!
Thanks in advance.

Steve
Dr Terry Offline
#3 Posted : Wednesday, 7 February 2018 7:10:47 AM(UTC)
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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
If at first you don't succeed, just call it Version 1.0
8D11PCH2 Offline
#4 Posted : Wednesday, 7 February 2018 8:49:37 AM(UTC)
8D11PCH2

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Originally Posted by: HTSteve Go to Quoted Post
I wanted to outline the symptoms in my initial post, but after having searched and read a lot on here today about the big nut MCs used in HK/HG/HT etc. I have some queries about Dad's setup.

I'm curious as to why Dad was made to install the brake balancer/limiter for the rear brakes.
I read that the big nut MC has the larger reservoir at the front (for front brakes) but the PBR has the larger res. at the back.

I wonder if when my Dad installed the PBR 30yr ago if he was supposed to swap the front & rear inlet pipes? ie: does the PBR pictured use the rear res. for front brakes, and the front res. for rear brakes?

Is that the reason the balancer was required? Dad reckons the PBR above was all bolt on and no worries but I'm now not sure.
Now that we have the big nut MC back on I thought everything would be fine, but we still have leaks around the outlets :( :( :(

We've worked on many different components over the last year, the brakes have been causing us the most grief. This is the last thing left to solve hopefully!
Thanks in advance.

Steve


Hi Steve

The current PBR alloy M/cyl castings have the larger reservoir at the rear and the smaller at the front however the divider between them has a cutout so the majority of the fluid in the reservoirs is shared anyway. These M/cyl's are supplied in two configurations, one has the front brake circuit to the smaller reservoir at the front of the casting to suit Holdens built before 1/01/1977 and the other configuration has the front brake circuit to the rear reservoir to suit Holdens (that still used these type M/cyls) built on and from 01/01/1977.

Were the brass flare seats in your reco bignut M/cyl brand new?

Cheers
Dave.
HTSteve Offline
#5 Posted : Tuesday, 27 February 2018 8:17:45 AM(UTC)
HTSteve

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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
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