Power Disc conversion/ proportioning valve question

bahamabecomb · Sunday at 5:42 PM

Previous owner completed a power front disc/ rear drum conversion from manual 4 wheel drum. The car seems to brake much harder in the front than the rear and when the brake pedal is pushed firmly the brake light comes on. Does this sound like the proportioning valve needs to be reset? Anything else I should test first? Rear distribution block, front proportioning valve and brake booster photos attached. Thanks

67Dart273 · Sunday at 5:45 PM

I would start by making sure the valve seems to reset. There used to be centering tools (for bleeding) that you could by, to hold them centered.

How hi/ lo is the emergency brake pedal when set? Maybe the rear shoes are out of adjustment.

I would also do a "check bleed" AKA just dribble a little from each (at least the rear) corners to see if you strike "air."

While you are at it make certain it is plumbed correctly. The rear end of the master (large section) goes to front brakes. Likewise, the prop valve is front/ rear sensitive.

See post 7 if yours looks like this one

Diagram and Plumbing the Proportioning Valve

hello everyone, what i need is detailed pictures of where to mount/postion the proportioning valve(PV) pictured here and how to run/where the brake lines go into the PV on a 68 barracuda with the 73-76 disc brake upgrade. as always thanks in advance. bruce

www.forabodiesonly.com

bahamabecomb · Sunday at 6:12 PM

Thanks. I'll start going through those items that tomorrow afternoon.

Professor Fate · Sunday at 6:45 PM

67Dart273 said:
While you are at it make certain it is plumbed correctly. The rear end of the master (large section) goes to front brakes. Likewise, the prop valve is front/ rear sensitive.

Yes, this ^^^
Plus, keep in mind that contrary to popular belief, the front brakes do more than 70% of the braking. Too much rear bias, and YOU. WILL. SPIN.
As far as the brake light coming on, it sounds like you're either low on fluid or there's still air in the sysem. Most likely the latter.

4mulas · Monday at 10:42 AM

Is that an aftermarket proportioning valve? (It looks to be). I’m starting to think they aren’t very good. I have brake bias the opposite way on one of my cars

Cuda Al · Monday at 1:08 PM

Make sure that on the lines on the distribution block are correct, placement can make a difference in how the switch works. The switch works on a differential of pressure, this might be your brake light problem.

Alan

bahamabecomb · Monday at 1:30 PM

4mulas said:
Is that an aftermarket proportioning valve? (It looks to be). I’m starting to think they aren’t very good. I have brake bias the opposite way on one of my cars

Yes it's aftermarket, but only a couple of years old. I'll keep that in mind

bahamabecomb · Monday at 6:00 PM

Thanks for the proportioning valve diagram, looks like everything is connected properly, master cylinder has both sides full. Emergency brake is a hand pull type and is tight with about 4" extended. Will get some help tomorrow to bleed the rear brakes and see if there is any air bubbles.

bahamabecomb · Tuesday at 6:28 PM

Bled the brakes at all four corners and was able to get it out on dry pavement today for some hard braking and everything feels as it should, no loss of pressure in the brake pedal and car stops in a straight line even when locked up. Only issue is the brake light still comes on under hard pressure. May swap the proportioning valve out next or possibly try a new electrical wire at the valve, old one is bent up inside but not sure if that really matters?

4mulas · Wednesday at 1:34 AM

bahamabecomb said:
Bled the brakes at all four corners and was able to get it out on dry pavement today for some hard braking and everything feels as it should, no loss of pressure in the brake pedal and car stops in a straight line even when locked up. Only issue is the brake light still comes on under hard pressure. May swap the proportioning valve out next or possibly try a new electrical wire at the valve, old one is bent up inside but not sure if that really

Do this:

Not running or driving. Sit in the car and kinda turn your foot sideways and then jab/stomp on the brake pedal as hard your can. (Once or twice) This can reset a proportioning valve back to the neutral position and stop your brake light issue.

70SwingerGuy · Wednesday at 2:03 PM

I was going to post a separate thread but I think my question is related, so not trying to hijack, but is the proportioning valve the same regardless of power or manual brakes? My car is also rear drum front disc.

bahamabecomb · Wednesday at 2:03 PM

I tried that yesterday and again this morning but the brake light still comes in under pressure. I read that you can have someone hold the brake on while you open a bleeder valve until the light goes off and that will reset it. I'll try that next.

bahamabecomb · 2025-01-02T10:11:54-0600

The one I have is a BLK250 from Inline Tube and was installed by previous owner.. Not sure what the original 4 wheel manual drum proportioning valve is

jbc426 · 2025-01-02T10:17:37-0600

bahamabecomb said:
The one I have is a BLK250 from Inline Tube and was installed by previous owner.. Not sure what the original 4 wheel manual drum proportioning valve is

4 wheel drum systems use a distribution block, not a proportioning valve.

4mulas · 2025-01-02T10:56:54-0600

bahamabecomb said:
I tried that yesterday and again this morning but the brake light still comes in under pressure. I read that you can have someone hold the brake on while you open a bleeder valve until the light goes off and that will reset it. I'll try that next.

Maybe. I have never heard that. How would you know which one to bleed? Ie: you’d have to know ahead of time which side or way it is unbalanced, otherwise you’ll just be creating more pressure imbalance scenario’s hence re-triggering the piston or valve to make a ground connection and trigger the light again? Not sure on this one though.

I would think that If your light is not on all the time and only happens under application you systems still has air in it, a small leak, is weak, or maybe the master isn’t holding pressure on one of the legs and fluid pushes back.

Or; the pro valve is **** like the one I have. I’m going to install an oem one and see if my issue on that car goes away.

And btw, the Oem 4 wheel drum is just a distribution block. No valve.

4mulas · 2025-01-02T11:00:03-0600

bahamabecomb said:
The one I have is a BLK250 from Inline Tube and was installed by previous owner.. Not sure what the original 4 wheel manual drum proportioning valve is

I would bet money that all the individual sellers of these all buy them from the same place. Ie: they are all made in the same factory off shore somewhere.

bahamabecomb · 2025-01-02T11:23:33-0600

Do you think if the master cylinder was not bench bled initially that it could be causing the problem? The entire system is new and only has a couple hundred miles on it.

bahamabecomb · 2025-01-02T11:34:33-0600

Not sure if bench bleed applies to this type of Master Cylinder.

Inertia · 2025-01-02T13:03:48-0600

When you say the light comes on with hard braking, does the light come on as you are increasing pressure, or come on after "max" pedal is achieved, - pause, lite comes on ?

The imbalance switch on the Mopars I can remember are self centering, no reset, or tool required, but other breeds do, iirc.

The 2 pix (one with proportioning valve) show the shuttle switch with spring each side, to center it.
That's why the imbalance lite goes off when you release the line-lock, lol.

Inertia · 2025-01-02T13:22:31-0600

Here my thoughts.
If the lite comes on as you are applying increasing pressure, then one side of the pump isn't keeping up with the pressure of the other side, so pump/Master cylinder is suspect/likely.

If the pedal goes down to hard, and it takes a second for the lite to come on, - then equal pressure in both systems was achieved, then one side lost pressure to trigger the lite. (that still could be M/C)
Do you have reservoir fluid loss ?
Does the pedal "diss-appear" while stopped ? (Slowly sinks to floor)
You gotta leak somewhere.
Take all wheels off, check under wheel cyl dust cups for seepage, look for dampness somewhere,
That's the way I'd approach it.
Good luck.

bahamabecomb · 2025-01-02T15:33:57-0600

I appreciate all the additional info.

The brake light comes on right before full pressure is achieved at the pedal and turns off when pressure is backed off a little bit. I'm not seeing a leak anywhere and the fluid seems to be staying full. I'll get get the wheels of tomorrow and do some more searching, possibly a leak or air in the system somewhere.

Inertia · 2025-01-02T15:41:23-0600

Adjust the rear brakes while there, for high pedal .
Next time, set the emergency, then pump peddle a coupla times, then try to get lite to come on, be aware of disappearing pedal, hold it a while.

jbc426 · 2025-01-02T17:02:08-0600

bahamabecomb said:
Not sure if bench bleed applies to this type of Master Cylinder.

It absolutely does. Also, make sure that your bleeder petcocks are at the highest point of whichever item you're bleeding. I have to unbolt my calipers to rotate the bleeder to the top to get the last bit of air out of them.

Don't forget that Mopar drum brakes are self adjusting, too. All you have to do is get the car rolling backwards about 10 to 15 MPH and firmly press the brakes a couple times. Depending on how far out the adjusters are, you may have to do this multiple times. That is, if they are assembled correctly.

4mulas · 2025-01-02T17:10:08-0600

jbc426 said:
It absolutely does. Also, make sure that your bleeder petcocks are at the highest point of whichever item you're bleeding. I have to unbolt my calipers to rotate the bleeder to the top to get the last bit of air out of them.

Yah this

for sure! When some people do conversions they use the wrong calipers for their orientation (front or rear mounted), if the bleeder is pointing down it’s very harder to bleed the brakes. @bahamabecomb post a picture of the front brakes on your car so we can see the calipers clearly.

bahamabecomb · 2025-01-03T16:00:42-0600

Thought I would post the pictures before I get started, @jbc426 and @4mulas. Let me know if you think the calipers should come off to bleed. Also sent a couple rear brake pictures incase something looks off. I followed all of the lines and did not find any leaks. Also if you get your proportioning valve replaced with an OEM one I'd like to hear if that fixed the problem on your car. I am going over to my daughters for dinner so it's probably going to be tomorrow morning before I can get going on this again.