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my 69 manual brake car was missing the brake warning switch assembly. i got 2 in a package deal and noticed that the orifices at the connections from the master cylinder on one are the same size, the other one has a large hole for the rear and a smaller one for the front. is one of these maybe for power brakes? if so, which would is correct for manual brakes? in my assembly manual, it looks like the same one is used for manual or power brakes, only using a different one for heavy duty brakes.
thanks in advance,
mac
For any given year, the brake distribution block and pressure differential sensing switch were the same for all Corvettes. Even J-56 cars used the same block for that given year except that a proportioning valve was also added to the system. The first year for the switches was 1967. Since the proportioning valve was only used for J-56 installations and since it's use ceased after 1968, the only years that have BOTH the switch and the proportioning valve are 1967 and 1968.
While the switch assemblies were the same for any given year, there were a total of FIVE different assemblies used over the 67-82 period. The 67-68 switch used a steel block and can be easily distinguished. Some SERVICE were brass, though. The 1969 switch was a one-year-only item. 70 to 73 were the same as was 74-77. 78-82 was the last switch. That switch was a COMBINATION VALVE. This means that it combined pressure differential warning, brake fluid distribution, and a proportioning function (fixed rate; non-adjustable).
The 69-73 switch assemblies are, basically, all the same. The way they differ is in the size of the tubing nut used for each of the brake line fittings to the block. So, you need to compare the size of the tubing nuts at each of your brake lines to/from the block and determine which one of the switch assemblies that you have matches that. It's not very difficult to do. Unfortunately, the part number is not stamped on these switch assemblies so there's no easy way to ID them.
Another thing: some of the SERVICE switch assemblies, even though of the original part number, are constructed a bit differently than original PRODUCTION and early SERVICE pieces. They're 100% functional, but may appear different. The primary difference is that one of the fittings on the upper side of the block looks like a seperate fitting that has been factory-assembled to the block. Original switches had all of the tubing nut fittings tapped directly into the "monolithic" brass block. So, don't let this difference fool you.
All of the 67-73 switches are GM discontinued, although the 67-68 is reproduced. The 74-77 and 78-82 pieces are still available (at least, they were the last time I checked).
thanks for the information Joe, i think you are right. i'm a little puzzled though, i'm reasonably sure that both of these blocks are the one-year-only 69's. they are identical except one does have a larger tapped connection for the rear brake side. they are both brass and i did find a small stamped # on each of them, 9-142 on one and 0-324 on the other. unfortunately, the original brake lines were missing also so i can't use that to go by. i may have to just pick one and try it. thanks again Joe
You might want to pick up a set of the reproduction lines for your car. They aren't very expensive and if you have incorrect lines why not change them out for the correct ones? For something like a brake system, "correctness" is not just an issue for judging purposes. You want to have a correct brake system for SAFETY purposes. Brakes are important; keep the car as-engineeried as far as configuration of the brake system goes. With the correct lines, you can easily figure out which block is the correct one. And, you can restore the car to correct brake system configuration.
i agree joe, i've got a 68 with brakes that do not work as well as they should and i've replaced everything but the switch assembly, so when i saw these different size ports, it got me wondering if the 68 one is incorrect. i think terry is right about the date codes, it makes sense. as usual, both dates are too late for my march car. thanks for all the help.
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