I have a 92 f150 that I converted the rear drums to disks using the kit from jeffs bronco graveyard and now it seems like the brakes are slightly hanging up. When I put it in gear it doesn't roll forward and I have to give it some throttle to get it to move. I can feel the truck leaning to the back right when giving it gas then it lets go and jumps forward. When I lifted the rear their was some drag on the brakes not alot. Someone told me I need to remove the internals of the proportioning valve on the master cylinder because it's keep pressure in the line for some time and not allowing the caliber piston to go back in. Is this true? The problem didn't happen until it was converted over and the pedal goes flat to the floor which hasn't happened either and it's been bled 3 times now.

 

for one you needed to install the correct proportioning valve, second sounds like those used calipers needed to be rebuilt.they may be simply hanging up, third do you have a worn out master cylinder which is miss sized for disc brakes

 

which valve do I install? The calibers are new gm calibers they came with the kit. And the master cylinder is new but its a stock replacement. I was told by them that I didn't need to replace the master cylinder nor the booster. Everything is new on this truck as I'm rebuilding it.

 

CALIPERS not calibers , were not talking about guns here, the proportioning valve is up by the master,

 

sorry about that. Stupid spell check keep correcting it to calibers instead of caliper. And i know where the valve is at I wasn't aware that their was more then one valve available. My understanding was nothing has to be changed that I could just slap these on and it would be fine.

 

No. The system is set up for drum brakes so there has a be a residual valve to keep some pressure for the drums. Many years ago I replaced the drum brake 8.8 in the Bronco with a 9” rear with disk brakes. I removed the RABS valve and replaced it with one of those adjustable valves.

 

I'll have to check into it. I thought about remobing the rabs and using a valve as well as removing the pressure valve on the master cylinder and just using a proportioning valve like i did on my camaro. But after doing this swap the truck seems to be getting held back. I have to give it gas to go and it seems like itll jump ahead as if the brakes are being held. But when i lift the front and rear they spin freely. I also did 4.56 gears and 37" tires I'm wondering if it's just a aide effect of that. I never drove anything like that so I'm not use to it. But I don't think it's that.

 

37 is quite a tire, what motor do you have?

 

a 4.9l with some work done to it. Like cam ported head and intake stuff like that. With 4.56 gears

 

Gotcha, I'm gonna stuff some 33s on my 5.0. it isn't out of the question that even a very light brake drag will stop the truck, especially with that heavy a tire.

 

agreed. Im going to look over it tomorrow and see what I can see. Figured I'd come here and see if anyone else had an issue.

 

Yes a drum master has residual valves on the drum side.
So if you are using a new master for disc / drum you have to remove the valve in the master.
I have not done this but you need to remove the flare seat and the valve and spring then comes out.
You put the flare seat back in and you should be good to go*(1)
(1) the master is still a disc / drum master and if you look it over you will see the disc side holds a lot more brake fluid than the drum side.
Also some masters the pistons start moving at different times when you push on the pedal.
You really need a disc / disc master for the truck and not the mix you have.

I would not worry about the combo valve at this time as it may be ok, it was balanced for the truck front / rear.
It dose not know it was a disc / drum and now a disc / disc setup. If you are that worried get one for a disc / disc setup, how can you tell what it is for?

The other part of the valve sets a light off when there is a leak in 1 side of the system. It dose not close off that side as you keep pumping the pedal and it will push out all the fluid so it dose not close it off.
Oh and the 2 systems (front / rear) are not connected in that valve and you still have brakes to stop just a vary low pedal.

Did I read you are running 37 inch tires?
If so I think you would of been better off going with a hydro boost and disc / disc master and the rear disc set up but that me.
Dave -----