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I have a '65 with PB w/original master cylinder. I have just finished a frame-off on this and I am working out the bugs. After the car warms up or builds up vacuum, the brakes seem to get tight, it is like the parking brake is on. I removed the master cylinder to see about adjusting the rod from the booster (like the shop manual talks a bout) but the rod coming out of my booster is not adjustable, is this the correct rod? What could be the problem?
That first post of my brake question was wrong, after I thought about it, I went out and jacked up the front end and there is no drag on the front wheels, but there is drag on the rear, I adjusted the parking brake star in the wheels to provide the least amount of tension and the cable from the handle is not tight, but I still have drag on the rear wheels. In '65 there was not a proportioning valve. What could be the problem?
i assume you replaced the rear rubber hoses . if not , do so as that is easier than tearing the rear emergency brakes apart, which is the next diagnostic venture if the rubber hoses are new or replaced..good luck, mike
use the bleeder valve on the rear calipers to release any pressure, then check for drag. Some (light) drag is normal on the rear and is attrituble to the "machinery" hooked to the rear wheels that must be turned to make the wheels rotate. If the release of pressure via the bleeders improves the drag situation, then you need to look for an obstruction in the line, or a problem between the master cyl and booster. BTW the Corvette must have an adjustable pushrod to make sure the piston in the master cyl is fully retracted. This can cause drag.
I agree with Mike and Bill. Also, one other point of clarification: VERY few Corvettes ever had a brake system PROPORTIONING VALVE. The only ones that did were 66-68 with J-56 HD brakes (this was an adustable proportioning valve) and 78-82 (this is a COMBINATION valve which has a fixed proportioning ratio).
Twenty five years ago I rebuilt and replated many Delco Moraine 1963 and 1964-1967 PB Boosters. I would guess well over 250 units. I even purchased the Kent Moore tools to perform the job correctly and disassemble each style down to their finite individual components. I can unequivocally state that I have never seen a 1964-1967 PB booster with an adjustable FRONT push rod. That was a feature found on 1963 only and that 1963 rod is not interchangeable with the 1964-1967 version and visa versa.
Other than a felt filter and a foam seal, I cannot recall another part in common between these two boosters. Totally different inside and outside.
On both 1963 and 1967-1967 models the brake pedal clevis is adjustable via a rear threaded push rod, but only 1963 has the adjustable FRONT push rod. And even there some 1963 even lack that style of adjustable front screw.
The GM Workshop manuals for 1964-1967 are in error. The GM photographs that accompany the text for the PB booster disassembly shown are faithful and authentic in comparison with real life PB boosters. Several show the solid 1964-1967 push rod accurately. However, there is a small illustration that shows a threaded plug in a push rod and how to make a gauge for checking adjustment. That illustration is a carry over from the 1963 GM Workshop manuals and shows exactly what the 1963 rod and adjustment screws look like. That is how this urban legend for 1964-1967 adjustment has been spread. And then it appeared in Chilton books, then Cylmer books, etc.
Unless someone can show photographic proof of a 19674-1967 adjustable FRONT PB push rod, I’ll remain a skeptic.
I had this same problem with a Mazda. The hose from the intake manifold to the PB booster had an internal check valve and if this hose was installed backward you got the "parking brake on" effect! However, I believe the 65 booster's check valve is the white (or brownish) plastic device the vacuum hose connects to on the booster so it may be impossible for this to be installed backward.
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