Master cylinder size

[Glenn]

Anybody know the bore size of master cylinder for :

single piston type

dual piston type

ie early and late model master cylinders.

EDIT I think the bore size is 3/4" or 19mm ?? No doubt the 19mm is more Factory accurate.
Not sure if same on both types?

[Glenn]

any confirmation of bore size ???

[CQGT]

Hi Glenn.
Your correct. Both bores are 3/4". 19.05mm.
The secondary cup on the single master cylinder is the same cup on the secondary piston on the twin.
The secondary piston is the piston at the back of the cylinder and operates the front brakes.
All the other cups are different part numbers. Did notice that the dust boot is the same and the valve
on the front (for the rear brakes) are the same.
PR91W with the remote reservoir is different as well as PA Florian twin. Mabey 7/8". 22.2250mm. Not sure.
PR20 kit K7308X. Primary cup P4344. Secondary cup P4464A. Valve P4346. Valve seat P4599Z. Dust boot P4384.
Hope this will assist you and other owners.

Dave.

[A.J.]

Glen, if you google K7308X you should come up with VCCAtas.org.au listing one for sale on their club website.
A.J.

[Glenn]

Hi Glenn.
Your correct. Both bores are 3/4". 19.05mm.
The secondary cup on the single master cylinder is the same cup on the secondary piston on the twin.
The secondary piston is the piston at the back of the cylinder and operates the front brakes.
All the other cups are different part numbers. Did notice that the dust boot is the same and the valve
on the front (for the rear brakes) are the same.
PR91W with the remote reservoir is different as well as PA Florian twin. Mabey 7/8". 22.2250mm. Not sure.
PR20 kit K7308X. Primary cup P4344. Secondary cup P4464A. Valve P4346. Valve seat P4599Z. Dust boot P4384.
Hope this will assist you and other owners.

Dave.

Thanks for the detailed info Dave. I was lucky when I got the Sport there was a full rebuild kit in the boot for the dual master cylinder (and other things too)
I was wondering if an increase in bore size would 'improve' the brakes. (disk) Was a common upgrade when Peter Brock was doing mods to early commodores.

Something else i saw on YouTube ? or just the web, not sure, was to change the pedal ratio of the brake pedal to get more assistance. The guy moved the hole for the clevis that drives the master cylinder to get a better ratio. It did though mean the firewall for the master cylinder also had to be moved up to align with the new point.
Not sure how practical that is on a Bellett or even if it's advisable.

glenn

[flying]

Hi Glenn
Have you tried different brake pads
Regards
Flying

[peterd]

Glenn,
If you have not already got it fitted, what about adding a power booster?
Cheers
Peter

[Glenn]

Thanks for replies.....

Like all GT's and the Sport I have had, a Bellett does stop but it needs a bit of 'planning' in heavy traffic.

not tried other pads, the ones in there are near new, but unknown compound. I do have a few worn sets that could be re-done. I'm a bit loathe to fit any pads that may wear the disk much as they are the close end of being unusable after another machining.

I have a VH??? booster exact type unknown, but it needs to be overhauled. Quote i had was about $300. There are Chinese copies on ebay too that some have used with success.

I was just mulling around ideas for now.