Thread: GM dual master cylinder...which is rear, which is front?

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I just swapped out my old GM single reservoir master cylinder for a dual reservoir master brake cylinder but am confused as to which reservoir is the front and which is the rear? Someone told me that the 1/2" fitting is the rear line and the 9/16" fitting is for the front. Others have told me the front reservoir on the MC is for the front brakes and the rear res for the rear brakes...

Now I am nervous I may be plumbing this wrong...any help?
Thx guys!

The one closest to the booster is for the rear,(usually the smaller resevoir)

If both reservoirs are about the same volume, it won't matter much. If one of them is considerably larger, then you will have to match that reservoir to the end of the car that requires the most VOLUME to operate.

Go to the ECI hot rod brakes website they have a lot of good information there.