test for a small air bubble in braking system

Nov 08, 2003 1 Replies

One question regarding brake bleeding... I replaced the ABS pump in my 91 bmw



318i, and then got a motive pressure bleeder system and went at the brake system. I first jumpered the ABS pump relay so the pump ran a bit, then went to bleeding it. I have to wonder if the pedal feels ever so slightly ewither mushier or has slightly more travel now. Is there any real way to tell if you have a small bubble in the system? Why I ask is because I believe I got the sytstem OK, and the more Id use it driving, the better the pedal felt. However, it seemed that after turning off the car and pumping a few times so the pedal was prety hard, there was still a bit more travel than before. With the car on, a small bubble might not be that noticable, because the vacuum boost makes the pedal softer, due to the power assist, but would a small bubble become more noticable with the car off, comapred to with it on? I plan to rebleed at some point after I get the ABS squared away and working completely, but Im just curious, as I dont want any surprises. I know I got the bubbles out, as I bled for a while until the bubbles came (as fluid filled the abs pump) and then came all out and nothing but clear light new ATE SL DOT 4 was coming out with no small bubbles or solid junk. But you never know in a closed system like this, and i dont want my brakes to fail...

Any info or advice would be great. Thanks,



JMH


I too recently tried their pressure bleeder system. By the way it works great. Though I don't have ABS, once I got it all set up, the actual bleeding process was so simple I did it twice. With the car off the ground and wheels removed, I just went around each wheel cylinder again. The second time a small air bubble came out. I was quite sure I let plenty of brake fluid come out the first time even after the new fluid emerged with the clean color. This was the left rear. I just bled the brakes as a maintenance procedure, having been done two years prior by the dealer, so really can't imagine how that small air bubble got in there, unless it had been there all along, or I introduced it through some flaw in my method. Anyway, here's my suggestion to you. Forget about jumpering the ABS pump, and just bleed the brakes again to be sure.

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