Heavy Duty Brake Proportioning Valve - J56 and up

[Mike Cobine]

Something I hadn't thought about until today was the proportioning valve used on the J56 brake setup. Since its purpose was to allow the car to be tuned to track conditons and car set up, I had just assumed (yes, I know) that it was part of J56 always. After all, J56 purpose was to have race-ready brakes.

However, checking two '69 L88s today, I noticed either had the large barrel-shaped proportioning valve with the giant threaded adjustment.

Can anyone share some info on this in '69 up through '75?

[Michael H.]

Re: Heavy Duty Brake Proportioning Valve - J56 and

Mike,

The porportioning valve for J56 was last used on 68. Not exactly sure why it was dropped for 69 and later HD brakes.

[Michael H.]

Re: Heavy Duty Brake Proportioning Valve - J56 and

Mike,

The porportioning valve for J56 was last used on 68. Not exactly sure why it was dropped for 69 and later HD brakes.

[Mike Cobine]

Re: Heavy Duty Brake Proportioning Valve - J56 and

Thanks, Mike.

It doesn't make any sense to not have it on the later years. Granted that most set it once and never changed, but then, the purpose and application were in a bit of a conflict. The dash-mounted adjustable proportioning valves of today are much more sense, since you needed to change as fuel went out, not at pit stops under the hood.

[Mike Cobine]

Re: Heavy Duty Brake Proportioning Valve - J56 and

Thanks, Mike.

It doesn't make any sense to not have it on the later years. Granted that most set it once and never changed, but then, the purpose and application were in a bit of a conflict. The dash-mounted adjustable proportioning valves of today are much more sense, since you needed to change as fuel went out, not at pit stops under the hood.

[Joe L.]

Re: Heavy Duty Brake Proportioning Valve - J56 and

Mike-----

The Kelsey-Hayes-manufactured proportioning valve was used only on 1966-1968 Corvettes with J-56. It was the only adjustable proportioning valve ever used on a PRODUCTION Corvette and the only proportioning valve used on any Corvette until the 1978 model year.

Many folks THINK that this valve was used on all J-56-equipped Corvettes, but that's absolutely not the case. J-56 was available right through the 1975 model year, although, after 1969, only as part of the ZR-1, ZR-2, and Z-07 packages. No 1969-75 Corvette with J-56 ever had the valve, though.

Also, a Kelsey-Hayes-manufactured valve very similar to the 66-68 J-56 Corvette valve was used on some late 60s-early 70s Mustangs.

[Joe L.]

Re: Heavy Duty Brake Proportioning Valve - J56 and

Mike-----

The Kelsey-Hayes-manufactured proportioning valve was used only on 1966-1968 Corvettes with J-56. It was the only adjustable proportioning valve ever used on a PRODUCTION Corvette and the only proportioning valve used on any Corvette until the 1978 model year.

Many folks THINK that this valve was used on all J-56-equipped Corvettes, but that's absolutely not the case. J-56 was available right through the 1975 model year, although, after 1969, only as part of the ZR-1, ZR-2, and Z-07 packages. No 1969-75 Corvette with J-56 ever had the valve, though.

Also, a Kelsey-Hayes-manufactured valve very similar to the 66-68 J-56 Corvette valve was used on some late 60s-early 70s Mustangs.

[Mike Cobine]

Re: Heavy Duty Brake Proportioning Valve - J56 and

Thanks, Joe.

I had never really thought about it before, and had just assumed that the J56 HD brakes portion of the later suspension packages had contained all of the pieces. Since the intent of J56 was a race-ready braking system, it was a necessary item.

My comment on the dash-mounted adjustable proportioning valves was a reference to the aftermarket ones that most racers used so they could adjust on the fly. While it was ok to adjust the J56 unit to get the car set up, the change as you went from full tank to empty tank couldn't be made on the unit as you drove. So its real usefullness was limited.

The Mustang units show up on eBay occasionally. Some are a bit different that can be easily seen, but I think the others are nearly identical, but I haven't examined both to see in person, only by photos.

[Mike Cobine]

Re: Heavy Duty Brake Proportioning Valve - J56 and

Thanks, Joe.

I had never really thought about it before, and had just assumed that the J56 HD brakes portion of the later suspension packages had contained all of the pieces. Since the intent of J56 was a race-ready braking system, it was a necessary item.

My comment on the dash-mounted adjustable proportioning valves was a reference to the aftermarket ones that most racers used so they could adjust on the fly. While it was ok to adjust the J56 unit to get the car set up, the change as you went from full tank to empty tank couldn't be made on the unit as you drove. So its real usefullness was limited.

The Mustang units show up on eBay occasionally. Some are a bit different that can be easily seen, but I think the others are nearly identical, but I haven't examined both to see in person, only by photos.