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Another brake bleeding question



Of course AFTER we replaced the rear calipers & rotors & bled the system, my copy of the 1971 Chassis Service Manual came in. The bleed seemed to go OK, but in reading the manual it states:

"NOTE: On disc brake cars a combination metering, proportioning and failure warning switch is in the hydraulic system and mounted either on the frame rail or under the main cylinder. This valve must be held in the open position while bleeding. This can be accomplished by installing Tool J-23709 with the open slot under the mounting bolt and pushing in on the pin in the end of the valve. Be sure to re-torque the mounting bolt after removing Tool J-23709."

Not only did we not perform this step, but I've never heard anyone else mention it (it isn't in the "other" service manual we have for the car).

Did I do irreperable harm to my baby? If not, then what's the point of doing this step (besides them selling XX number of "Tool J-23709" at a profit)?

Barb :w
brake bleeding

I have bled many brakes and that is the first time I have heard ofthat ,maybe both of us was lucky. On my 78 I put the silicone brake fluid in it about three years ago, I have been very satisfied with it . before I used the slicone fluid I had problems with my brakes.
OK, let me see if I can explain this valve, as I understand it. Keep in mine that I ain't no GM engineer. The porportioning valve on a 69-74 is mounted to the frame right behind the left(driver's) side upper A frame. What this thing does is give equal pressure to the front brakes and the rear brakes. In addition, it will notice a differance in resistance, if there is less resisitance in the back then the front, it will cut the back off as soon as it runs out of fluid. thereby not allowing all the fluid to run out of the back. This is why, you will find that a caliper is leaking,say the right rear, but you still have front brakes. As soon as the valve "bottoms" out it will trigger the brake light on the dash to indicate that there is a problem. When this happens and you run it for a while with no fluid in the front or rear the valve will somtimes stick in one position. This makes it difficult to bleed this part of the system. When this happens, stand on the brake pedal as hard as you can, without breaking it off, and this should reset the valve. As far as the tool.............Ah.er , this is the first I've heard of it, and I have bled a lot of Corvette brakes..........Steve

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