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shiner 04-15-2003 07:46 AM

disk brakes conversion no pressure to back brakes
I've just installed a set of disk brakes on my '69 Chevelle. Once complete I bled the brakes. I am not getting any pressure to the rear brakes. The front seem to be working fine. I get a trickle out of the rear brakes but not the pressure that it should have. I left the existing proportioning block on and installed a balancing valve between the block and the rear brakes as noted in the instructions. It just doesn't add up. Anyone got an idea.

chevy1 04-15-2003 01:51 PM

Is your brake warning light on? Sounds like you need to center the valve inside the proportioning valve. It slid over and is blocking the fluid flow to that side of the brakes.

6567GTO 04-15-2003 04:56 PM

Did you prime the master cylinder in a bench vise first? Does your kit have the adjustable proportioning valve?

Lou 04-15-2003 06:53 PM

Shiner, A friend of mine had a simlar thing happen. Are your bleeder valves at the top? if the calipers are on the wrong sides the bleeders will be on the bottom pointing down you won't get a good peddle.

PrimeMover 04-15-2003 07:22 PM

Shiner, look closely at your proportioning valve. Some of the early ones had a little button that needed to be manually depressed to center up the valve in the valve body. As previously mentioned, if the pressure differential function of the prop. valve sees zero pressure on one side and pressure on the other it will shift, closing the zero pressure side to stop any inadvertant fluid loss. If this is the case, it will need to be manually centered back up with the button (if you have one.) If possible, have someone depress the button while you bleed the rear brakes. If you dont see one, you will need to crack open the front again to try and center the valve back up.

Once you get them bled, if the brake lite stays on, you'll need to center up the valve by bleading off pressure to either the front or the rear, depending on which side the valve has shifted to. Usually the diff. valve centers itself once all the air has been purged from the system but sometimes not.

Have fun... :)

chevy1 04-16-2003 06:08 AM

Some Proportioning Valves also required a special spring loaded clip to be installed on the little Button to pull it out of the valves groove so the valve could re-center itself. You don't use the spring's not going to center itself and you'll still only have brakes on one circuit. You'll center the valve by bleeding off some fluid to either the front or the rear lines depending on which side the valve slid over and it should be good to go!

shiner 04-16-2003 08:15 AM

Thanks for all the suggestions.
There is no button on the outside of the body. I took the line off the bottom of the proportioner and tried to push a small allen wrench into it to see if this would move the valve. It didn't seem to work. I am thinking of bypassing the proportioner with the rear brakes. The kit I bought included a regulating valve to adjust the pressure to the rear brakes so I am thinking it won't hurt to bypass. Anybody know why this might not work?

PrimeMover 04-16-2003 04:36 PM

On some of the Fords with early disc brakes you had to unscrew the get-up where the wire goes in to "re-arm" or center up the pressure diff. valve, once the light came on. I've had some trouble in the past with them too, but I always seemed to work it out one way or another.. Sometimes with a pressure bleeder you can persuade the valve to go in the right direction and get the job done. If you have someone stepping on the brakes for you, it's touch and go. The Brake peddle guy should have the key on and let up on the brake as soon as the light goes out. The guy with the bleeder wrench should then go to the other end of the vehicle and work with as light a pressure applied to the peddle as possible.

If push comes to shove, Willwood makes a good adjustable proportioning valve. It comes without that pesky pressure differential spool. No brake light feature either.

I think you can make it happen with what you've got. Don't give up yet...

Grogetter 03-08-2005 06:31 AM

Propo valve
Shiner, was the car originally equipped with front discs? If so, you porbably need to ditch the propo valve. The valve in my 82 malibu is set up to apply pressure to the rear drums before pressure is applied to the front discs. They do this because of the greater amount of fluid required to fill the back slave cylinders and apply the shoes. The discs take far less volume to apply pressure to the discs. Either way, check with the kit supplier. They should have the straight scoop.
Let us know what you come up with.
Good luck.

trees 03-08-2005 08:23 PM

If you are using an adjustable proportioning valve, throw the block in the parts bin. If your MC is on the fire wall, you should not need any residual valves, but if you are having to pump a couple of times to get a good high pedal (after bleeding), then put a 10 PSI residual valve on the rear line as close to the Mc as you can get it. If you have two lines coming out of your MC to the rear, plug one fitting in the MC , install the residual valve with line to the Adjustable proportioning valve and T to the rear wheels down stream where it is convienent.


gost-rider 01-24-2011 11:09 AM

i have changed a few cars over like you did and i used the same proportioning valve and it worked just find it dose not need any other block

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