Date: Fri, 25 Mar 2005 22:37:50 GMT From: Robert <rxobert.bxrownnospampnet.se> Subject: Re: 9-3 brake rotor
doug wrote: > Dave > > What I posted says it all - if one forces brake fluid through any ABS system > in a direction it was not intended to flow, there is always the potential > for damage. The electronically controlled solenoid valves in a hydraulic > control unit are not designed for bi-directional flow. The act of forcing a > piston back into its bore in the caliper can - and occasionally does - > cause damage. Why even risk it if it can be avoided so easily? > > This isn't a Saab issue specifically; rather it's concept that applies to > cars with ABS in general. My advice is based on many years of experience and > common sense. Factory repair manuals are great for providing info on how to > do repairs on proprietary components, or for wiring diagrams or > troubleshooting diagrams. But does one need to refer to Saab documentation > to do decide if it's better to avoid damaging an expensive component by > following my suggestion? I think not. > > doug > I'm now driving an Audi (just couldn't bring myself to buying a GM Saab after many pleasurable years with 99's and 900's) and the recommendation from their workshops is the same - open the bleed screw as the piston is returned, for either front or back brakes. Their argument is that if there are contaminants that have collected inside the pistons (quite likely after a couple years' use), they would travel up to the ABS and contaminate the valves there. I haven't heard the info you'd collected about damage to the solenoid valves due to flow; I kind of doubt that fluid travelling in different directions would harm anything. *Clean* fluid, that is ... We may as well leave it up to the OP what the best course of action is, when pushing the pistons back. Some here find no use for bleeding off the fluid; fine, let them do what they want. I, for one, bleed the fluid because I'm convinced that the fluid upstream of the ABS (i.e. closest to the reservoir) is cleaner than that in my brake pistons. Another possibility may be that it might not be necessary to bleed, as long as the car owner's been a good little boy/girl and had the old fluid flushed every 2 years. YMMV. /Robert
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