Any reason not to use ABS?

[deezee]

First off you would need compatible hubs and drive shafts for ABS..... so there is 90% of the Sierra donors out the window. Then you'll need to install the ABS controller, which are pretty big. Then you'll need the ABS ECU, which you'll have to get out of the loom from the donor car. Then depending on how advanced the controller is, it will automatically sort out the bias, but not all of them do, so you will still be left with crap bias.

Or just use drums and discs, like from the donor. I've never heard of that combination locking. Of course the super cheap option is just to buy an inline, adjustable restricter and limit the rear breaking until it stops locking.