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-   -   master cylinder question 68 Pontiac (https://forums.maxperformanceinc.com/forums/showthread.php?t=868027)

punisher7 07-18-2023 03:27 PM
master cylinder question 68 Pontiac
 
Can somebody tell me which circuit is the front brakes and which is the rear brakes? I am assuming that the circuit closest to the firewall is the front. Disk front, drum rear power brakes.
Thanks!

Scarebird 07-18-2023 03:39 PM
Bigger reservoir is the front circuit.

punisher7 07-18-2023 03:44 PM
If both reservoirs are the same size was I sold the wrong master?

Scott Thelander 07-18-2023 04:11 PM
Same size is correct
Front is rear
The stay off valve for front disc to delay rear drum
Plums from front reservoir .
Are you running disc r drum??

Scarebird 07-19-2023 02:00 PM
I disagree.

GM usually had larger reservoir for factory disc, certainly with the later designs that had the front circuit in the rear.

Are the fittings different size nuts for the hardlines?

Scott Thelander 07-19-2023 02:20 PM
1 Attachment(s)
Oh man

I guess I should toss my 67-69 delco
Moraine disc master cylinders away

Not …

punisher7 07-19-2023 02:48 PM
Quote:
Originally Posted by Scarebird (Post 6441146)
I disagree.

GM usually had larger reservoir for factory disc, certainly with the later designs that had the front circuit in the rear.

Are the fittings different size nuts for the hardlines?
The ports are the same size. I have it plumbed with the front brakes closest to the firewall, but the brakes aren't doing their job. It isnt in a 68 Bonneville, it's in a 63 with disk brakes up front from scarebird. I am going to try the 74-80 C10 master and see if that works and better.

Scarebird 07-19-2023 03:13 PM
Quote:
Originally Posted by Scott Thelander (Post 6441153)
Oh man

I guess I should toss my 67-69 delco
Moraine disc master cylinders away

Not …

the operative word here is "usually".

60's stuff is different. My guess is that as the circuits use the same amount of pressure, the front pads/shoes wear much quicker and since the piston is MUCH bigger will require more fluid to replace the space as the piston start point is further inward - hence the larger rez so it does not run dry.

The OEM's did not sort this out right away - it took some time.


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