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centering proportioning valve
#1431135 Wed Nov 24 2021 01:16 AM
Joined: Nov 2008
Posts: 253
R
rc356s Offline OP
'Bolter
Hi Guys,

I installed a dual master cylinder with front disc on my 1950 1/2 ton. I have been having trouble bleeding the brakes because the proportioning valve is not centered. I looked and online and some have suggested to stomp on the brakes with the line that does bleed open. I just cannot get it centered so I can install the locking tool. Since it is under the floor board, it makes it difficult to see down into the sensor hole. Anyone else have a similar problem and have done this?

thanks,
skipper

Re: centering proportioning valve
rc356s #1431188 Wed Nov 24 2021 02:52 PM
Joined: Feb 2000
Posts: 4,445
J
'Bolter
The valve blocks the side with the least amount of pressure. Higher pressure forces the slider to the lower pressure side. If both side are low pressure ( air or no fluid ) the valve will not slide either way, it has nothing to move it. You must have fluid in both side, and then you can open the opposite side line and slowly move the slide valve back to center with the brake pedal.

Taking it apart is another option.

Re: centering proportioning valve
rc356s #1431193 Wed Nov 24 2021 03:18 PM
Joined: Apr 2005
Posts: 2,997
C
'Bolter
Many street rods do away with the proportioning valve and use residual pressure inline; 2# disc and 10# drum. It is not an on demand set up but works well.


Evan
Re: centering proportioning valve
rc356s #1431206 Wed Nov 24 2021 05:30 PM
Joined: Apr 2005
Posts: 10,686
Grease Monkey, Moderator General Truck Talk & Greasy Spoon
This may or may not work for you. If you have the proportioning valve with the pressure switch screwed into the center, you can remove the switch and using a small pick move the slider to the center and put the switch back in. It’s been many many years since I had to do that.


Martin
'62 Chevy C-10 Stepside Shortbed (Restomod in progress)
'47 Chevy 3100 5 Window (long term project)
‘65 Chevy Biscayne 4dr 230 I-6 one owner (I’m #2) “Emily”
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Re: centering proportioning valve
rc356s #1431241 Wed Nov 24 2021 09:07 PM
Joined: Apr 2005
Posts: 1,972
R
'Bolter
I have used the procedure that Martin has suggested. Depending on the design, some of them will push the pin out the end, remove the rubber cap and push it back in to reset it.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine
Re: centering proportioning valve
rc356s #1431475 Fri Nov 26 2021 11:14 PM
Joined: Feb 2004
Posts: 24,297
H
Kettle Custodian (pot stirrer)
Once you get the switch centered, either use a pressure bleeder or a MityVac pump on the bleeder screws to avoid displacing it again.
Jerry


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Re: centering proportioning valve
rc356s #1431552 Sat Nov 27 2021 06:23 PM
Joined: Jul 2000
Posts: 1,458
G
Insomniac
Recently, I installed a new master cylinder. After bleeding the brakes in the old fashioned way (2 people; one bleeding, one pushing the pedal) the red light was on. A couple of stomps on the brake pedal and the light went out. ISTM that if the switch slider doesn't centre (light is still on), there is still air in the system.


Gord
----
1954 1/2 ton 235 4 speed
Re: centering proportioning valve
rc356s #1431790 Tue Nov 30 2021 05:49 AM
Joined: Nov 2008
Posts: 253
R
rc356s Offline OP
'Bolter
Hi All,
thanks for the suggestions. I got the valve centered by moving it with a pick. I stuck it in the center hole and moved it. I then checked by installing the light switch and verifying that it is off. I then inserted the locking tool to keep it centered. Got my BIL to help me bleed the brakes and using the pushing the pedal method. We managed to bleed the brakes and get the air out where only fluid was coming out.
Before replacing the front drums with disc, the brake pedal was real high, always felt like my knee was way up to brake. The pedal would go down a couple inches of travel. Now with the disk in front and the new dual MC, the pedal travel is almost to 3 inches from the floor. Something does not seem right, I have a lot of travel before the braking begins to engage. I think I have to shorten the MC push rod so the pedal will sit lower down. How much travel does the push rod need to move into the MC to get full pressure of the MC? The pedal feels way different the the single MC with drums all around. we bled the brakes a couple times, made sure there was always fluid in the MC. The pedal still feels soft until it almost reaches the bottom?

Re: centering proportioning valve
rc356s #1431822 Tue Nov 30 2021 02:48 PM
Joined: Feb 2000
Posts: 4,445
J
'Bolter
Be sure the drums are adjusted correctly. Adjust till tight to the drum, then back just enough to rotate with a slight drag. Be sure to tighten the drum to the axle with the wheel or washers and lug nuts.

Re: centering proportioning valve
rc356s #1431925 Wed Dec 01 2021 05:36 AM
Joined: Nov 2008
Posts: 253
R
rc356s Offline OP
'Bolter
good point, I will check the drum adjustment

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