brake problems

[rockcrawlerbronco2]

hey guys i just did a disk brake conversion on my 9 inch and i cant seem to get and pressure at the pedal.do I need a porportioning valve or a bigger master cylinder?

[Nobody]

what mastercylinder are you using?

[rockcrawlerbronco2]

stock 1990 master

[Nobody]

What happens if you open a front bleeder? Does it build pressure in the rear? I've had a similar problem, I think fromt the stock distribution block on the frame. I"m not sure if it's also a proportioning valve, but I believe there's a rod in there that will move to one side if there is a pressure differences front to rear....that trips the brake light on the dash.

Anyway, I believe it's possible to get that rod jammed to one side. So by opening a front bleeder, it will create enought pressure to move it back. I think it happened to me when I did my hydroboost. There was a pretty significant pop when it came loose, then I got pressure to the rear again.

You might also try cracking the lines at each junction to see where you what point you loose pressure. Could be blockage.

Lastly, your master cylinder is designed for drum brakes, and may have a residual pressure valve, but I don't think that would cause your problem.

And make sure you bleed from the wheel furthest from the master and work to the closest to the master So RR, LR, RF, LF.

[Bob Myers]

Swap it for a 79 bronco unit, it has a larger piston and will provide enough fluid for the job. A disc needs more volume than drums.

[Nobody]

I agree that it's too small. I think stock is only 15/16" bore. Most the rear disc apps seem to use 1-1/8.

I put a hydroboost and corvette master cylinder on my bronco II. One of the best mods I could have done. Easy too! Pretty much bolts right in.

[ranger5.0]

Chevy parts???

[rockcrawlerbronco2]

So I ended up using a 75 f250 master with the 1 1/4 bore. works sweet and there the best brakes ive ever had! thanks for the input guys.