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Metering valve. Used in ... 68-70?? ... disc/drum cars. This was before the common combination valve (it's not *just* a proportioning valve) was designed, so the various functions of the combination valve were performed by different units.
The metering valve slightly delays the application of the front discs. This gives the rear drum shoes time to take up their slack from the springs pulling them back.
The proportioning valve was a separate unit in the line to the rear brakes, and that limits pressure to the rear drums to prevent them locking up before the front discs.
The common combo valve does both of those functions *and* the pressure differential safety warning switch.
Metering valve. Used in ... 68-70?? ... disc/drum cars. This was before the common combination valve (it's not *just* a proportioning valve) was designed, so the various functions of the combination valve were performed by different units.
The metering valve slightly delays the application of the front discs. This gives the rear drum shoes time to take up their slack from the springs pulling them back.
The proportioning valve was a separate unit in the line to the rear brakes, and that limits pressure to the rear drums to prevent them locking up before the front discs.
The common combo valve does both of those functions *and* the pressure differential safety warning switch.
Never seen this before! I wonder if someone eleminated them on my other cars before I bought them.
Never seen this before! I wonder if someone eleminated them on my other cars before I bought them.
Most likely the cars you've seen were incorrectly converted to disc brakes.
To review, the 1967-70 factory disc brake cars used this metering valve (also known as a "hold off valve") to slightly delay ("hold off") the application of the front disc brakes to give the rear drums time to take up the slop in the shoes and associated linkages. This was to prevent the fronts from engaging prematurely, which could cause a control problem under certain severe braking scenarios. This metering valve function is combined into the combination valve (get it?) on 1971-later cars with disc brakes. And contrary to popular belief, the 1967-70 Olds A-body cars with disc brakes did NOT use a proportioning valve, just this metering valve. Do not be confused by the fact that people call the metering valve a proportioning valve, even vendors who should know better (are you listening, Inline Tube???).
Do not be confused by the fact that people call the metering valve a proportioning valve, even vendors who should know better (are you listening, Inline Tube???).
Come on, Joe. One step further to close it off. Don't be confused when people incorrectly call a combination valve a proportioning valve.
EDIT: I was attempting to be funny - operative term = attempting, but it may have appeared peculiar as I stated it. It probably would have made more sense and I should have said "...one step further to go full circle and close the loop..."
I've been known to walk and talk at the same time, honestly.....
Last edited by Vintage Chief; June 22nd, 2021 at 10:40 AM.
Let's start from the beginning. What exactly do you have right now? The device you are thinking about is not a "proportioning valve", it's a combination valve that incorporates the metering valve, the prop valve, and the differential pressure switch. If you've done a disc brake conversion, you need something.
Let's start from the beginning. What exactly do you have right now? The device you are thinking about is not a "proportioning valve", it's a combination valve that incorporates the metering valve, the prop valve, and the differential pressure switch. If you've done a disc brake conversion, you need something.
I am converting to disc brakes from drum Joe. And no I have never did a swap before. I am using factory correct disc system off a 1972 to put on a 1970 Cutlass.
Last edited by wr1970; June 22nd, 2021 at 01:53 PM.
I am converting to disc brakes from drum Joe. And no I have never did a swap before. I am using factory correct disc system off a 1972 to put on a 1970 Cutlass.
OK, then just transfer everything from the 72. The 1967-70 cars that did not use a prop valve instead used smaller rear wheel cylinders on the disc cars to balance the front/back braking force. The 71-up cars used the same wheel cylinders and did that balancing with the proportioning valve part of the combo valve. It doesn't matter if you change the wheel cylinder diameter or the line pressure, the effect is the same.
No prop valve in the 67-70? Huh, that's interesting.
If you want a points-correct install on the 70, then install the metering valve and don't use a combo valve. It's expensive, can be hard to find, and I had one that was bad out of the box.
If you just want a system that works, then use the 71-later style setup. The extremely common "proportioning valve" you see marketed *everywhere* is the same piece. There's a couple of variants (disc/drum, drum/drum or disc/disc) and brass or aluminum (get brass!!), but they're all the same thing. Probably from the same assembly line. Don't pay $100 for the thing. Note you need the mounting bracket that puts the prop valve down on the frame rail - if you want it to look like a Cutlass. The aftermarket uses the Chevy approach and mounts the combo valve right under the master.
Then get/make lines that are correct for whatever setup.
No prop valve in the 67-70? Huh, that's interesting.
All the prop valve does is reduce line pressure to the rear wheel cylinders to reduce the brake force. Olds used smaller diameter wheel cylinders on disc brake cars to accomplish the same thing.
If you want a points-correct install on the 70, then install the metering valve and don't use a combo valve. It's expensive, can be hard to find, and I had one that was bad out of the box.
If you go that route, you also need to swap to the correct disc brake rear wheel cylinders to maintain the correct brake balance.
All the prop valve does is reduce line pressure to the rear wheel cylinders to reduce the brake force. Olds used smaller diameter wheel cylinders on disc brake cars to accomplish the same thing.
If you go that route, you also need to swap to the correct disc brake rear wheel cylinders to maintain the correct brake balance.
Joe it will get a Chevy rear so I don't know about rear wheel cylinder swap. I will need to see what year rear it is but I think 1972 Monty Carlo.
To throw this into the mix.
The Distribution block on the frame under the power booster is the same on disc and drum cars 1969-70
If your interested i have original 1970 rebuilt and core metering valves available.
Thanks
To throw this into the mix.
The Distribution block on the frame under the power booster is the same on disc and drum cars 1969-70
If your interested i have original 1970 rebuilt and core metering valves available.
Thanks
actually it may still be working because there was fluid in the master cylinder. I am positive the other combination valve is still working as all lines were in place and fluid looked okay. I have no numbers matching .
Be aware that the fact that fluid flows doesn't mean that the pistons aren't seized in the body. Be especially skeptical of the original cast iron combo valves.
June 22nd, 2021, 07:50 AM
