Ď68: Brake distribution block Q. - Chevelle Tech
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post #1 of 4 (permalink) Old Sep 22nd, 19, 9:54 AM Thread Starter
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Tom
 
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Ď68: Brake distribution block Q.

My Ď68 SS El Camino came to me with power brakes. Front Ď69+ single piston calipers and rear drums. My warning light switch at the distribution block was grounded full time.

Iím installing a new set of Wilwood rear discs. Iíve called both Wilwood and TRS asking about the compatibility of the stock distribution block with the rear discs. Both told me not to worry about changing it. I was always under the impression that there was some sort or delay valve built into it to hold the front disc pressure off until the rear drums had a chance to overcome their spring pressure and activate.

Yesterday I pulled the stock distribution block off to see what it was doing. I was pleasantly surprised to find no real corrosion inside. I cleaned it out and was able to free the piston so that it now moves freely against forward/rear spring pressure and my warning light terminal now remains ungrounded. But I was also surprised to find no resistance at all on either end. Free fluid travel both ways from rear inlet to outlet and free fluid travel both ways from front inlet to both front outlets. In other words, there doesnít seem to be any delay built in.

Can anyone tell me if this is normal? Perhaps itís no more than a distribution block with provisions for a warning light?? If so, Iím happy. Iíll just run the car and add a proportioning valve to the rear if necessary.

Thank you for any input.
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post #2 of 4 (permalink) Old Sep 22nd, 19, 10:28 AM
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Steve
 
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Re: Ď68: Brake distribution block Q.

Hi. What you are thinking of is a Combination valve, and it sounds like you have the stock distribution block.

To answer your main question first - yes, if you have the stock distribution block on your car, it is just a distribution block with a provision for a brake light indicator in case either the front or rear brakes lose pressure. In your case, it sounds like it was stuck, so most likely only 1/2 of your brakes (either front or rear) were working properly.

Now, back to your first thoughts - a disc/drum Combination valve has 3 parts - a Metering valve, a Distribution block and a Proportioning valve. The Metering valve does exactly what you were thinking - under light braking, it will delay the front brakes slightly so the rear drums have a chance to start kicking in. The Distribution block part does the same function as the stock distribution block and blocks off one or the other if the opposite system (front or rear) loses pressure and grounds the brake light indicator. And the Proportioning valve part biases less pressure to the rear brakes to prevent the from locking up before the fronts do.

Before combination valves came into being, these three parts were carried out by three different components.

Note that on a disc/disc Combination valve, the front Metering valve is eliminated.

1972 Chevelle, 454, 2004r non-lockup, 4.10
1981 Camaro Z28, 355, TH350, 3.73
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post #3 of 4 (permalink) Old Sep 22nd, 19, 11:01 AM Thread Starter
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Tom
 
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Re: Ď68: Brake distribution block Q.

Quote:
Originally Posted by lucifershammer View Post
Hi. What you are thinking of is a Combination valve, and it sounds like you have the stock distribution block.

To answer your main question first - yes, if you have the stock distribution block on your car, it is just a distribution block with a provision for a brake light indicator in case either the front or rear brakes lose pressure. In your case, it sounds like it was stuck, so most likely only 1/2 of your brakes (either front or rear) were working properly.

Now, back to your first thoughts - a disc/drum Combination valve has 3 parts - a Metering valve, a Distribution block and a Proportioning valve. The Metering valve does exactly what you were thinking - under light braking, it will delay the front brakes slightly so the rear drums have a chance to start kicking in. The Distribution block part does the same function as the stock distribution block and blocks off one or the other if the opposite system (front or rear) loses pressure and grounds the brake light indicator. And the Proportioning valve part biases less pressure to the rear brakes to prevent the from locking up before the fronts do.

Before combination valves came into being, these three parts were carried out by three different components.

Note that on a disc/disc Combination valve, the front Metering valve is eliminated.
Thank you for your response. It sounds like Iím in luck. But for the next question:

If/when I do add a rear proportioning valve, my thinking is that I want to add that downstream of the distribution block rather than between the master cylinder and the block due to the working of the pressure differential switch? Or am I wrong?? Iím thinking if I reduce pressure before the block the switch will activate with every press of the pedal because of the reduced input pressure to the rear circuit???

Thank you again,
Tom.
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post #4 of 4 (permalink) Old Sep 22nd, 19, 7:42 PM
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Steve
 
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Re: Ď68: Brake distribution block Q.

Yup, you are thinking about it correctly. Put it after the distribution block.

Quote:
Originally Posted by any4xx View Post
Thank you for your response. It sounds like Iím in luck. But for the next question:

If/when I do add a rear proportioning valve, my thinking is that I want to add that downstream of the distribution block rather than between the master cylinder and the block due to the working of the pressure differential switch? Or am I wrong?? Iím thinking if I reduce pressure before the block the switch will activate with every press of the pedal because of the reduced input pressure to the rear circuit???

Thank you again,
Tom.

1972 Chevelle, 454, 2004r non-lockup, 4.10
1981 Camaro Z28, 355, TH350, 3.73
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