64 Ford falcon brakes issue

[roush2win]

I have a 64 ford falcon 2 door wagon with manual drums all the way around with a 68 mustang duel master cylinder all shoes and drums are replaced but I can't drive it because the front brakes grab so bad they skid by barely touching the brake pedal, I put a proportioning valve on the front brakes and that did not help. any idea's on how to fix this problem.

[Rick_101]

You need the correct proportioning valve for your application. I suspect the one you have is not the right one for your vehicle. If you are can't work it out any other way, some speed shops sell and adjustable P/V which you can play with until you get the proper braking.

[roush2win]

I have a adjustable proportioning valve 10 psi to 100 psi I turn it all the way down to 10 psi and it still skids the front tires

[Rick_101]

Originally Posted by roush2win

I have a adjustable proportioning valve 10 psi to 100 psi I turn it all the way down to 10 psi and it still skids the front tires

Ok. I'm out of ideas. I hope someone else has the cure. Sorry

[yank with ute]

My three cents worth -

Spotted a potential problem: 68 Mustang dual chamber master cylinder.

#1 Did the Mustang it came from have drum or disc brakes on the front? Disc brakes need a higher VOLUME of fluid to activate then drum brakes. You will notice the chamber in the master cylinder for the front brakes has a larger volume then the chamber for the rear.

#2 Did you also install the factory proportion valve from the Mustang (brass block with several "wings")? That block was made with the correct size passages for a disc/drum set up (if the original car had that set up). If uesd on an all drum set up then there is too much fluid going to the front brakes. Installing another proportioning valve inline can really make a mess of things.

I see this as a major problem since the original master cylinder had only one chmaber w/ three lines going out to the brakes: left front, right front, both rear combined. The dual chamber master cylinders required completely different routing at the master cylinder.

#3 Exactally how/where did you splice the new proportioning valve into the car's brake system? I'm thinking you have too much volume going to the front brakes but without knowing how your system has been routed I can't say that is the problem.

#4 I think it was the 2000 Car Craft Magazine article on converting the Falcon to late model brakes that mentions SOME replacement master cylinders come set up for disc brakes on front which needs to have an internial spring (on the plunger) removed to allow less pressure for front drums.

With the internal spring in place too much pressure is routed to the front brake system. But again, you need to provide more info in regards to what you have done to the stock brake system.

However, I had a 62 Comet that locked up the right front wheel (only) and after several hours the shop became frustrated and replaced the wheel cylinder. That worked.

Upon closer inspection it was determined that the factory had install the wrong bore wheel cylinder as it didn't match the one on the left side or what the replacement guide called for.

What you have mentioned suggests to me that there is a gross mis-match somewhere in your brake system. Wrong sized (bore) front cylinders, dual chamber master cylinder with the chamber for the front having too much displacement, etc.

Most people think too much pressure but volume displacement also is a factor.

Of course there are other potential problems like very small tires on front and very large in back (too much braking force on the front), or tires with radically different amounts of grip. I doubt if any of these apply here.