how do you check master cylinder in junkyard

[oldsmobile joe]

what is the best method of measuring master cylinder bore size in junkyard. i saw what looked like a new m/c in the pick n pull. new style with plastic reservoir in a second gen camaro. is it as easy as measuring the
piston bore area with a veneer caliper?

 

[lilbowtie]

Joe - Do your self a favor and just buy a new - reman master cylinder of your choice. O"reily, Rock Auto are very cheap and you know what your getting.

 

[Texas82GP]

Also, Rock Auto lists the bore size by application.

 

[theoldsone]

Even though it's true he can just go buy a new one. That doesn't answer the question. This question can pop up in another situation. I've never measured the Bore of a master. But I think you have to take it apart to find out...

 

[oldsmobile joe]

Joe - Do your self a favor and just buy a new - reman master cylinder of your choice. O"reily, Rock Auto are very cheap and you know what your getting.

stopped by the picking yard after work, the master cylinder was is in much worse shape than i thought. but i do have an old master cylinder
laying around. i'll bring to work and check the idea there and report back.

 

[oldsmobile joe]

ok, to answer my own question. measuring the inside diameter of the brake booster end of a master cylinder will get you fairly close to the
actual size of the cylinder. i measured three master cylinders that i knew the size. now obviously this may not be an exact science. i started with a stepped bore cylinder from a late '80s camaro, book stated it is 24mm and 32mm. i measured 32.5mm. next up was a straight bore cylinder of 13/16, i measured it at approximately .817. and last was a '70s corvette cylinder of 1-1/8, which measured at just over 1.130. i used a veneer caliper but a machinist rule would work also.
i did not take pics but can do so for clarification if you would like.

 

[manualbrakes.com]

Measuring the ID of the booster will not get you close to what you need to know.

A master cylinder casting can be used for different bore sizes.

Most stock 1978-1981 G-body master cylinders came in two sizes. The manual brake version was 7/8" bore and the power booster version used a larger 24mm bore. Both have the same housing/casting. 1982 and later, there where step bore master cylinders. They came with two bore sizes. They had a larger bore for volume and a smaller bore pressure. For g-body cars, the larger bore measures about 1.25" (if memory serves), but the smaller bore should be 24mm. You cannot measure the smaller bore, because it is inside the master cylinder. The larger bore size is easier to measure.

You will need to unbolt the master from the booster and use the vernier calipers to measure the bore diameter. There is a snap ring that holds the master cylinder piston in place. Set you vernier calipers on top of the snap ring and then measure the bore diameter. Hope that made sense.

 

[oldsmobile joe]

"measuring the inside diameter of the brake booster end of a master cylinder will get you fairly close to the
actual size of the cylinder"
I was afraid this would be misinterpreted. And I was right.
Let me clarify.
Measure the master cylinder end closest to the booster. Not the booster. Please reference pic.

 

[oldsmobile joe]

Measuring the ID of the booster will not get you close to what you need to know.

A master cylinder casting can be used for different bore sizes.

Most stock 1978-1981 G-body master cylinders came in two sizes. The manual brake version was 7/8" bore and the power booster version used a larger 24mm bore. Both have the same housing/casting. 1982 and later, there where step bore master cylinders. They came with two bore sizes. They had a larger bore for volume and a smaller bore pressure. For g-body cars, the larger bore measures about 1.25" (if memory serves), but the smaller bore should be 24mm. You cannot measure the smaller bore, because it is inside the master cylinder. The larger bore size is easier to measure.

You will need to unbolt the master from the booster and use the vernier calipers to measure the bore diameter. There is a snap ring that holds the master cylinder piston in place. Set you vernier calipers on top of the snap ring and then measure the bore diameter. Hope that made sense.

sorry for writing it in a confusing way. i did not intend to imply that the measurement would be of the booster.
you are correct on everything else you posted.

 

[manualbrakes.com]

sorry for writing it in a confusing way. i did not intend to imply that the measurement would be of the booster.
you are correct on everything else you posted.

No issues. But when measuring the bore, make sure you do NOT measure the inside diameter of the snap ring.