Front Valve (Round), Rear Valve (Rectangular)
Short answer: GM’s own names are inconsistent, which is why this valve has several. The rear valve on the frame rail of V8/AC cars is called both “rear brake pressure proportioning valve” (parts book) and “rear brake pressure regulator” (illustrations catalog); tech textbooks call it the “proportioning” valve.
Practically: the round valve just under the master cylinder is the front metering valve (on all disc-brake cars); the rectangular valve on the frame rail under the driver’s seat is the rear valve (V8 A/C disc cars only). From 1971 a single combination valve replaced all of it. The rear valve’s part number is 3908326 — listed only for the 1967–69 Firebird.
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Content last modified: June 13, 2026 at 10:06 am
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