Brake Bleeding- Special Concerns With ABS?

[Greg Gore]

I just rebuilt all the calipers on a 96 with 110K miles and am trying to flush the old fluid and am having a difficult time getting fluid to the rears now. A vacuum test on a disconnected rear caliper line indicated obstruction and is the same for both sides. Is the ABS system interfering in some way? Air was allowed to get in the system because I planned on flushing anyway but perhaps I missed something. FWIW the battery ground cable is disconnected.

Thanks, Greg

[froggy47]

I flushed my 96 many times (pressure flush) and never had a problem with abs. How are you trying to flush? Pressure, suction, gravity?

[Greg Gore]

I should have mentioned I have all four brake hoses temporarily disconnected from the calipers with each positioned over catch containers. I cut the banjo ends off and capped the tubing stub on each one. Plan was to remove one cap at a time to flush each leg individually. I am using a Motive Products pressure bleeder but just using it to apply 5 to 10 PSI air pressure to a full master cylinder reservoir. The arrangement seem to work Ok but I noticed quite a bit of resistance in getting fluid to flow from the rear hoses when I uncap them. I wondered if there were valves in the ABS that were working against me for whatever reason. When I get the fluid flushed out I will of course install four new GM brake hoses and bleed the brakes in a conventional fashion. It dawned on me that the ABS could be interfering somehow and might even have old contaminated brake fluid trapped inside that I am unable to flush out. Perhaps a scanner needs to be connected to run the ABS to permit a more thorough flush, I don't know. This is my first experience with a brake system this complex

Thanks, Greg

[froggy47]

5 to 10 psi is not enough to get a good flow to the backs. I use 12 to 16. I have (motiv) the GM adapter that gets a better seal at the m/c than the universal. Never had much luck with the universal. It would always leak at the m/c.

I think you would be ok with the old fashioned 2 man push/hold pedal pump. Don't go all the way to the floor with the brake pedal.

Maybe you have a restriction in the old hoses. Put the new ones on. It won't hurt anything.

I don't think there is any abs problem, but you will not flush the abs without the tech tool.

My way to flush the abs is to engage it (when safe to do so) after I do brake jobs on the street or track.

:)