We've had a few discussions on the Aussie forum about Harrison brakes and various ways to maintain correct brake bias when pairing VT-VZ Commodore front brakes (original spec being the smaller VR-VS series) with R33 Skyline rear brakes.
My setup is as above (all new or reco'd), together with XF Falcon ute master cylinder which provides 50/50 pressure to front/rear. The car pulls up well in most situations, but my engineer was not satisfied with the rear brakes under very hard braking. ie, they don't lock up. The car tends to pitch forward a lot even under moderate braking, which suggests the rears aren't quite up to it.
With some handy work from Kenmer Engineering, I now have Holden Camira front calipers on the rear and the improvement is incredible. These are "only" single pot but the much larger brake cylinder and pad surface area have done the trick. The conversion involves machining the rear uprights and sandwiching an adapter plate between the wheel bearing and the hub. This allows the larger calliper to be mounted square on the rotor. I also fitted new braided lines (different ends) and a $21 set of pads. TRW make a race pad for $80.
Previously the car pitched forward as a result of exaggerated weight transfer to the front. Now the whole car hunkers down during hard braking, the fronts lock and then the rears. It's gone from "stops well" to "my eyes hurt" and I'm rapt.
The beauty of this approach is that a taller adapter plate can be machine up to accommodate larger diameter rear discs and/or calipers.
I have a spare set of R33 uprights so if anyone is interested in doing a changeover, shoot me a PM and we can work something out.
And a few photos...
Harrison brake bias - solved!
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