I did a disc swap on my 47 sedan. Calipers cam with pads. After first test, i wanted to put the drums back on. Got the cheapest organic soft pads and the issue was solved. Do not use long like pads…too hard
I suspect this in my case as well. My pads have a lot of material left, but I have no idea how old they are. After a good cleaning of the rotors (per xr7g428’s suggestion) his will be the next thing I try.
That made a big difference on my car too - acetone to clean rotors, and sanded the brake pads. Like yours, my pads were like new, but 20 years old and glazed.
Ford refers to it as the “Pressure Differential Valve”. It actually performs two functions, one being to block off the circuit with the leak, the other being that when the valve moves off center it turns on the light.
You are confused. It only turns on the idiot lamp
According to the Ford Manual, it does block off the circuit that is at fault. From the description of the OP, it appears that the fault was in the front. Once the Differential Valve is offset, the Manual says that the fault must be fixed and then the Valve re-set for proper brake operation.
Perhaps Royce can explain in more detail why it only turns on the idiot lamp and doesn’t affect the braking.
The brand new one i had in my shop was just a light switch. Shuttling the piston made no difference in flow. One needs to turn down the end of a 3/8-24 bolt or allen to replace the switch and hold the piston centered while bleeding the brakes
What the Manual means is that fault must be fixed and the valve reset in order for the warning light to go off. Here is a good explanation (scroll down to Brake Pressure Differential Valve):
Proportioning Valves 101 - FORDification.com
Thanks, Calicat, for that link: Royce was right and I was wrong (once again).
That article was actually for Ford trucks, but I am pretty sure our cars use the same valve. The question I still have is if it is possible for debris to plug the passages in the valve so that it does restrict fluid flow to front or rear brakes?
It’s easy to over think hydraulics. If you’re not sure that fluid is passing through the system to a particular wheel just open the bleed screw and put your for on the pedal, engine not running. If you get good flow it works. If not work your way back to the master cylinder and you will find where the problem is. Throwing parts at it is a waste of time and money.
3 Likes
I doubt it. More likely you have a technique that does not work when bleeding. The valve simply turns on the idiot light (or not). That’s all it does.
1 Like
no body has mentioned if the rotors were cut The must be completely flat no groves. a poor machining job and you will not have brakeing form the front… the distribution block that that you discribe is not what I have on my 70. mine is totally different.
A poorly machined rotor will not cause these concerns. It could cause several other types of concerns but not what is being described here in this thread. Now contamination on the rotor surface or poor pad material could cause this but seems like that’s being checked now
The 70’s originally came from the factory with the same Brake Pressure Differential Valve as described above. But lots of them got changed out over the years.
Update, but still no solution. I decided to work off xr7g428’s advice above. I had previously verified that I had good fluid flow to all four corners, but I didn’t know what pressures I was getting. The local parts stores don’t loan brake pressure gauges, so I bought one of my own. Took forever, but it finally arrived yesterday, and I ran out to the garage to test it.
I checked the front brakes first and found 1500 psig. From what I’ve read, that’s pretty good. So, I checked the rears and found 1500 psig also. I think I need 600-800 psig back there, so evidently my proportioning valve is the problem.
I didn’t have time to test the rear brake pressure at various PV settings, but that’ll be next. However, when I did driving tests (panic stops at ~30 mph), the PV made no difference regardless of setting. So I suspect either both my original PV and the adjustable PV I replaced it with are both bad (seems unlikely), or I’ve plumbed the new one incorrectly.
I installed the APV in the “bypass” loop that the original was in. I’m thinking maybe I need to relocate it to the line out of the distribution block that leads to the rear brakes and plug the two PV ports on the distribution block. I’ve searched the internet fairly extensively, but I haven’t found anything specifically for my situation. There are plenty of disk brake conversion discussions, but those use a different distribution block.
Any thoughts or suggestions are appreciated as always. Thanks in advance.
I installed my adjustable prop valve between the master and the original block. My car was originally a drum brake non power brake car so my original distribution block is a little different but overall function is the same. It just ended up being cleaner that way and I left the factory block alone. Wilwood makes a nice prop valve/combination block that would replace all that stuff and give you a compact setup but that would require reworking all your lines.
Anyway a couple things I’m thinking off. If your seeing equal pressure at all 4 wheel positions you may just have the rear locking up before the front due to the lack of bias. Double check you have the flow correct on the prop valve. And remove the original as well if you have not already. Or replace with an OEM prop valve, with a stock brake setup your really don’t need the adjustable prop valve.
Also I didn’t see where you replaced the front pads only reused them? It may be a good idea to get a new set of pads on there and if your rotors are glazed up get them machined so the pads and rotors will seat up well.
Pressure should not be equal on the front and rear. More pressure on the front as the front does about 60-70% of braking. My 67’ was a four wheel drum non power car that I converted to disc and power. Could not install the aftermarket proportioning valve due to rear brake line sizing. Installed a 70-73 Mustang distribution/proportioning valve combo that bolted directly in and it works great. I can still lock up the rears before the front but only on hard braking. Get a new proportioning valve.