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Old 09-03-2011, 06:42 PM
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11" rear drums lock first.

Driving on the service road, I decided to test my brakes and my 11" rear drums locked before my front disc. My chevelle originally had 9.5" drums in the back. Do you think I need an adjustable pro valve?

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Old 09-03-2011, 08:25 PM
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Yes..........

Sam
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Old 09-06-2011, 06:35 AM
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What kind of adjustable distribution block do I need? The kind that replaces my excisting prop block or the one that goes behind it?
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Old 09-06-2011, 07:10 AM
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Quote:
Originally Posted by ss396si
What kind of adjustable distribution block do I need? The kind that replaces my excisting prop block or the one that goes behind it?
This kind. Left click on the image for a larger view. Available at most aftermarket suppliers. I like Speedway for my source. Use the Wilwood or the Speedway brand.

This unit installs after the master cylinder in the rear line. It can reduce the rear line pressure up to 60%. Turning the adjustable valve all the way clockwise is wide open. (Reverse from what you would think).
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Old 09-06-2011, 07:12 AM
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Quote:
Originally Posted by ss396si
What kind of adjustable distribution block do I need? The kind that replaces my excisting prop block or the one that goes behind it?
It will help immensely if you would give a complete run-down of just what you now have. Drum/drum, disc/drum, original master cylinder or aftermarket or from another vehicle, is it a fast take-up type, what type distribution block do you have, as in does it contain a prop valve (i.e. is it a combo valve), is the m/c above or below the brake cylinders, do you have any residual pressure valving installed?

If it's a combo valve w/a functional prop valve:

If you don't like the front/rear balance, and you were to add an adjustable proportioning valve to the existing combo valve, you would in effect be adding a prop valve to a prop valve. In your case (having too much rear brake), this wouldn't be an issue unless other changes to the brakes or weight distribution, etc. were to be made that required there to be more rear brake pressure than the existing combo prop valve allows.

If you add an adjustable prop to the existing prop, you would not be able to bias the rear brakes to have any more pressure to them than the existing setting of the existing prop valve- all you could do would be to take pressure away from them. But as I said, in your case this isn't so much of an issue.

Should you want to disable the combo valve prop function:

On most GM combo valves, you can disable the combo valve's prop valve by unscrewing the fitting from the combo valve that has the rear brake line coming from it, then remove the (rubber or spring loaded metal) valve inside the body, then reattach the fitting.



So- in your case- I would keep the existing combo/distribution block and simply plumb in an adjustable prop valve aft of the existing block. Should the need ever arise that you needed more rear brake bias than the existing combo prop valve allows, you will need to disable it. I hope I didn't confuse you too much.
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Old 09-06-2011, 01:28 PM
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It's a 69 chevelle, disc/drum setup. The prop valve, Mc is new as well as the 11" booster, all parts not original. The prop valve is one of those big brass types from original parts group.
My problem occurred when I installed 11" rear brake (9.5" drums origanily) I got off a 76 monte carlo.
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Old 09-06-2011, 02:54 PM
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The factory prop valve is calibrated for the original brake setup and works fine on a factory car. when we change the brake setup as you have done then the old calibration does not work and then you need the adjustable prop valve..

Sam
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Old 09-06-2011, 03:15 PM
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Quote:
Originally Posted by OneMoreTime
The factory prop valve is calibrated for the original brake setup and works fine on a factory car. when we change the brake setup as you have done then the old calibration does not work and then you need the adjustable prop valve..

Sam
How close does the adjustable prop valve need to be to the distribution block? I would need to buy extra steel lines for this install as well?
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Old 09-06-2011, 03:20 PM
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Just needs to be where you can access it easily to make your adjustments. Start out on gravel and then proceed to higher speeds until you are satisfied. the goal is to be able to dynamite the brakes at freeway speeds without lockup on one end or another so the car stays straight and controllable in a panic situation..

Sam
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Old 09-08-2011, 11:14 AM
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I was checking out the adj prop valves on summit and jegs. All these valves on the market come with 3/16, Would it be a good idea to change from a 1/4 in to 3/16 line??
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