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Old 12-06-2003, 09:16 PM
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Question Confusing master cylinder ports...

Really confused on master cylinder ports...

I converted my vehicle from stock dual circuit all drums to dual circuit discs+drums. (just put discs on front and now replacing the master cylinder)

The original master cylinder had the frontmost port connected to the rear wheels.
The rearmost port of the master cylinder, obviously to front wheels.
Both ports same thread, pipes same size.

The new master cylinder intended for discs+drums has the rearmost thread larger (for larger pipe) and went to the rear drums on the donor vehicle.
Other cars with disc+drums , ports are reversed !

What is the rearmost port intended to be for > Front or rear ?

What is the largest pipe intended for > discs or drums ? I have read conflicting information about this !
Or depends on the design?


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Old 12-07-2003, 11:34 PM
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to be able to correctly answer your question i need to know the type and age/year of your new master cylinder.
as general rule though the larger diameter tube will almost always go to the front calipers as they have larger pistons and require more fluid to move them.
hope this will be of some help.

old rodder 60
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Old 12-08-2003, 08:18 PM
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Hello old rodder60 and thanks for the reply.

The new master cylinder is a DelcoMoraine dual circuit disc+drums from a 1969 Cadillac ElDorado .
That car has the larger pipe to rear drum brakes.
The opposite; disc brakes use less fluid to brake because the travel is minimal. But the reservoir better be larger to fill the larger caliper volume as pads wear out.
The pipe diameter only changes the fluid velocity... and maybe prevents swapping them if have different size threads.
Learning, learning, getting there...
What I still need to find out is WHY some vehicles use the front port for rear brakes and some other vehicles are reversed.

It may well be it is irrelevant.

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