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Old 04-27-2009, 07:57 AM
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G-Body Master Cylinder - Bore Size?

I am currently using a master cylinder from a 83 G-body on my 54. It is the aluminum body with plastic reservoir model. The fittings are metric. I want to change this out to one of the cast iron models but do not recall the bore size for the G-body MC. Can someone identify that for me?

Also is there a cast iron MC with the metric threads out there?

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Old 04-27-2009, 06:33 PM
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The bore of the MC is 24mm and 36mm. It is a step-bore (aka quick take-up) MC for use with low drag calipers. The output ports should not be metric. They should be 9/16"-18 & 1/2"-20. Why do you want to swap in a heavy cast iron MC? Are you using G-body front calipers of the same year? If so and you swap masters you will need to get older non-low-drag calipers.
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Old 05-01-2009, 01:39 AM
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82 & later are metric.
Some Info here.> http://tech.oldsgmail.com/sus_bbrake.php
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Old 05-01-2009, 02:18 AM
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Both napa and autozone list the master cylinder for an 85 monte as non-metric outputs. Further the 87 B-body and 87 S10 master cylinders of mine were both non-metric outputs. The bore sizes are metric, the mounting pattern is metric, but the outputs are regular old 45 SAE inverted flare fittings.

Originally Posted by NAPA
Item#: TS 101926

Price: $32.49
Core: $5.60

tax and shipping not included

Disclaimer: The stated price may vary from the in store price and may change at anytime.

Features & Benefits:100% OE Quality New Seals Are Installed On Every Unit. OE Performance And Reliability.
# of Line Ports:2
Brake Cylinder Bore Size:24mm
Finish:Rust-preventative Finish.
Line Thread Size:1/2-20
Originally Posted by AutoZone
Part Number: M1926
Weight: 3.25 lbs
Warranty: LLT
Notes: - installer warning - unit must be bench bled. If you experience any installation problems, call toll free: USA 1-866-787-5132 can 1-800-293-0760
Reservoir: No Reservoir
Bore Size: 36Mm X 24Mm
Cylinder Honing: Never Honed
New Sleeved Bore: Yes
Special Installation Notes Included: Yes
Primary - Hole Size and Location: 1/2"-20 Fender Side
Secondary - Hole Size and Location: 9/16"-18 Fender Side
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