GM master cylinder ID

joeskylark

Active Member
I have 2 master cylinders and have 1 rebuild kit. Does anyone know if either of these would have been an original from a 1970 skylark? They are in the same condition. 1 was from my skylark and the other from a wrecked 71 GS. Also, 1 had a silver piston, the other a gold one. I prefer to rebuild the original part. Thanks
 

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A pic of the top side would tell use IF the car was equipped with drum brakes or disc brakes for the '71. Does your car have drum all the way around or disc front/drum rear????
 

joeskylark

Active Member
Thanks. Sorry so late. I didn’t get a notification that you replied. My car is a 1970 custom convertible with front disc and rear drum. Not certain what the donor car had.
 
Cars with disc brakes in front had a 1-1/8" piston dia. on the mstr cyl. Cars with drum brakes in front had a 1" piston. From the picture both appear to be 1-1/8" pistons.

The 1970 shop manual shows the mstr cyl was stamped EA on the front of the cyl at the top. The secondary piston had 6 grooves or rings on it. See attached.

I could not come up with markings for the '71 Buick mstr cylinders. The part number is different for '70 and '71 in the Buick Master Parts Book (5468120 vs. 5471802).

Olds used the same part no as Buick for their '71 A-body cars w/front discs. That '71 Olds mstr cyl was stamped BE, so maybe the Buick was a BE also.
 

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