[mondo]

Hi Guys,

I have done my own rear disc conversion on my SJ80 using galant vr4 calipers, everything appears to work well, brake testing on gravel seems to indicate that the brake bias front to rear is acceptable. I am noticing that after a 60km drive, most of it at 110kmh, that my rear brakes are warmer than my front discs. The car can be pushed without resistance and the rear wheels can be spun by hand but there is a little bit of grabbing.

I had been told that i need to bypass the rear load proportional valve when doing the rear disc conversion as it apparently has a 1 way valve which is apparently required for drum brakes. This is not something I have read in any rear disc conversion for zooks. Does anyone know anything about this?

[TASSIETOYUKI]

Sounds like you need to remove the residual pressure valve. They hold a small pressure in the rear brakes to keep the wheel cylinders "primed" for want of a better word. You don't want that with discs brake calipers.
No idea where it is housed on Sierra's though..

[mondo]

Thank you Tassietoyuki. It turns out the coily's have a different braking system to the leafy's and the RPV is built into the Rear Load Proportioning Valve above the rear diff. I decided to throw that system away and I replaced it all with a Wilwood adjustable proportional valve. After doing this work my brake still got hot!!!!! At which point i put a dial indicator on my axle and measured the flange that my caliper mount bolts too. It was out a significant amount, I shimmed the plate until the dial showed my caliper plate was within 0.1mm and hey presto, brake doesn't cook anymore. Lesson learnt, don't assume factory stuff is square.

[mondo]

Lucky I had a spare master cylinder to do this with