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Disc brake swap now light coming on (still having issues)

formercruiserhead

formercruiserhead

1/2 ton status
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89' k5 swapped in a 14bff and dana 44 front. Did a disc brake swap on the rear and also installed a PV4 proportioning valve (disc/disc). Bled the brakes a couple of times and read that the valve has to be centered to properly bleed. Did that for the second try, also installed the "tool" that goes in the spot of the switch on the proportioning valve. Got alot more fluid through the rear discs the second time. Reinstalled the switch.

The problem is that when it is running the brake light will come on when the pedal pushes to the floor. When released the light goes out. Why is this?
I have no ebrake and the pedal assembly for the ebrake is not installed either. Also fluid is topped off in the reservoir.
 
the biggest problem i have seen over the years is the stock 1/2 ton master is not setup for the flow amount needed for the disc brake swap in the rear . lots of people get away with it but they also say there pedal is over 1/2 to 3/4 down yet hard . so you get no reserve then like this .

i run k30 hydroboost and master for disc/drum and 1/2 ton calipers in the rear and no factory prop valve . just a tee in the front and willwood adjustable in the rear . few road tests and its dialed in no problems .

also a guy here years ago goofed up and had his calipers on the wrong sides so the bleaders were NOT the high point in his rear system and he had trapped air . so check this also as some braket kits let you clock them on the axle and then this problem can happen .
 
My calipers are mounted correctly. What is the benefit of swapping to hydro boost? I have a stock engine so vacuum isn't an issue. I read in a fourwheeler article they did the disk swap and added a corvette master cylinder in addition to the PV4 valve. I would guess it has a larger bore? So maybe the corvette part may help?
 
formercruiserhead said:
My calipers are mounted correctly. What is the benefit of swapping to hydro boost? I have a stock engine so vacuum isn't an issue. I read in a fourwheeler article they did the disk swap and added a corvette master cylinder in addition to the PV4 valve. I would guess it has a larger bore? So maybe the corvette part may help?
Click to expand...

Swapped generic parts store parts for 1ton booster and master and it works fine. I don’t think you need corvette parts. You might try making sure there’s no air in the lines by jacking the rear end up as high as you can so the brake lines all run uphill to the rear. Then bleed the rear brakes. That seemed to help get some bubbles out for me that I could never seem to bleed out normally. I also just gravity bled them.
 
My bet is there is still air in the system. I had the same issue.
 
The light turns on when the pressure on one side of combination valve is higher than the other.
Usually it shifts to lower pressure side and stays there.
Air could cause a spring effect allowing the spool to ground but not shift completely.
 
Ok so here is what I have so far. Swapped in a PV4 proportioning valve, and now a 1980 corvette master cylinder still have same problem, although the light comes on maybe at a little different time? It still comes on after pushing down on the pedal all the way. As far as I know I have the same calipers front and rear.
 
When I bleed mine I take the calipers off and I have metal pieces to put in the calipers and put the bleeder down.

The other issue that I had on mine, so I was told was the rear drum brakes allowed air to enter the system after the pedal was pushed down because they back off to far so a residual pressure valve was put in the rear and I do have an adjustable proportioning valve in the front. I did a bunch of skid tests and adjustments to get it the best I could. No problems now in 12 years. https://www.jegs.com/i/JEGS/555/631...&utm_term=4579259773812008&utm_content=Brakes

I can look at what brand mine are if you are interested.
 
70jimmy said:
When I bleed mine I take the calipers off and I have metal pieces to put in the calipers and put the bleeder down.

The other issue that I had on mine, so I was told was the rear drum brakes allowed air to enter the system after the pedal was pushed down because they back off to far so a residual pressure valve was put in the rear and I do have an adjustable proportioning valve in the front. I did a bunch of skid tests and adjustments to get it the best I could. No problems now in 12 years. https://www.jegs.com/i/JEGS/555/631030/10002/-1?msclkid=f7f111402e441d4f76264f132780b9de&utm_source=bing&utm_medium=cpc&utm_campaign=BSC - JEGS Brand&utm_term=4579259773812008&utm_content=Brakes

I can look at what brand mine are if you are interested.
Click to expand...

So you have drums in the rear? I just want to make sure that is what you are saying as it is the first time I have heard about using a residual valve on 4 wheel discs.
 
formercruiserhead said:
I will bleed the prop valve. Does anyone use the tool that replaces the brake light switch when bleeding?
Click to expand...

no, you’d get air in there I’d assume when putting the switch back in. You should be able to just crack the lines on the prop valve and fluid should come out. Sometimes you can aim some short lines back into the master reservoir. Then you can see bubbles coming out and just keep bleeding until no more bubbles. Then hook the lines back up.
 
Im unsure what year it started but does your 89 have the rear anti-lock break setup thing? With the black box with wires next to the proportioning valve and the other valve thing that the rear brake lines run through? Mine is a 90 and had this, apparently getting rid of it all helps.
 
rderosier said:
Im unsure what year it started but does your 89 have the rear anti-lock break setup thing? With the black box with wires next to the proportioning valve and the other valve thing that the rear brake lines run through? Mine is a 90 and had this, apparently getting rid of it all helps.
Click to expand...
No mine doesnt have that.
 
Wow what a pain. So we have unequal pressure one side, not much
Just enough that the shuttle starts to move. This could be air, or maybe one side has much more volume of fluid to move, and the other side gets pressure first.
Oh and if your combo valve is in good shape, removing the brake light switch shouldn't introduce air.
 
So tried another thing, removed a rear caliper from the rotor, pushed the brakes till the piston came out and then compressed it to back bleed into the master, same problem. When I changed to the corvette master the brake light comes on when you first touch the brakes, goes out about mid stroke, then back on again toward the end of pedal travel. Is there another way to get air out? I find it hard to believe there is still air in the system. What about an adjustable proportioning valve for the rear circuit? Could dial it in to restrict fluid to the rear just a little? Open to suggestions
 
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