brake bias/proportioning valve? HELP

[adamke35]

hey guys got a rn41 hilux drums all round was converted to discs up front on the weekend.
found a sr5 which had discs, hubs, lines, load proprtioning valve, ripped it all out and fit it to the drum hilux.

problem is now the rear wheels are locking up under firm braking, is there a problem with the load proportioning valve?, i never looked at the size, but could the master cylinder be differnet? all the brake lines were the same drum to disc at the master cylinder, and i would assume the load proportioning valve would bias the front and rear? the drum and disc valves were different, the disc valve is in there now. help im stumped and dont want the car causin an accident. cheers

[81hilux09]

did you change the master cylinder?
i have done a simialr thing to you in that my rn41 had drums all round, since then i have converted front and rear to disc's ( std fronts ) had the prop valve resleeved and have installed a MX83 master clyinder. in saying that i haven't got around to bleeding the brakes and actually trying it all as i still haven't finished my engine conversion.

there was talk on some of the threads about this that there was something in the std master cylinder you have to remove if you upgraded the brakes.. can't remember exactly what it was though, try searching for hilux brake upgrade stuff.

curt

[pandaah]

try bleeding the brakes again first bro... even try pressure bleeding them you might have abit of shit in the system, ive had that at work a few times and the proportion valve gets abit of bad fluid in there maybe..

[ra28_miles]

you have the lines to the MC around the wrong way. Pretty much as the pressure rises in the MC the fluid to the rear will brake away from the front, allowing the front pressure to keep rising.

BUT utes don't have this, the load proportioning under the tray controlls this.

And again Brake drums are self energising, meaning they need less brake pressure to work. Where as disc don't and need a lot more pressure to work. Think of a wedge in the door, the more you push on the door the more the wedge forces down and asgainst the door.

Try a MC off a later hilux with front disc and rear disc.

[allencr]

the drum and disc valves were different, the disc valve is in there now.

The old prop./limiting valve for the drums kept the rear from locking without regard to the fronts. Isn't that what you need now?
Leave the MC alone unless you want to change the length of pedal travel vs the amount of push/force on it.
If it is spongy, then bleed it.