Air Bubbles During Power Brake Bleed

import11 · 04-25-2024, 11:02 AM

I was doing a brake bleed with a Motive Power Bleeder and couldn't get the fittings to be totally airtight. I accidentally let the bleeder run out of fluid and small air bubbles were coming out of the line during the front right bleed (Rear brakes finished fine). The reservoir did not run out of fluid. I closed the nipple, refilled the power bleeder, and finished the front brakes with no air bubbles.

The pedal felt nice and stiff after done. I was just reading about introducing air into the ABS system and doing a DSC bleed. If the reservoir didn't run dry do I still need to take it into to have a shop do the DSC bleed using ISTA?

agentrnge · 04-27-2024, 05:15 PM

Even with the motive bleeder empty, as long as your brake fluid reservoir is not empty ( or low to whatever point makes sense ) its not pushing air into the system. its just a little bit more pressurized air in the reservoir above the fluid. I read of a few people noticing air being pulled into the hose at the caliper from a suction/siphon effect from the draining tube if the collection bottle was too low. Could it maybe have been that?

04-25-2024, 11:02 AM	#1
import11 New Member 3 Rep 12 Posts Drives: 2018 Austin Yellow M3 6MT Join Date: Sep 2020 Location: Salt Lake City iTrader: (0)	Air Bubbles During Power Brake Bleed I was doing a brake bleed with a Motive Power Bleeder and couldn't get the fittings to be totally airtight. I accidentally let the bleeder run out of fluid and small air bubbles were coming out of the line during the front right bleed (Rear brakes finished fine). The reservoir did not run out of fluid. I closed the nipple, refilled the power bleeder, and finished the front brakes with no air bubbles. The pedal felt nice and stiff after done. I was just reading about introducing air into the ABS system and doing a DSC bleed. If the reservoir didn't run dry do I still need to take it into to have a shop do the DSC bleed using ISTA? Last edited by import11; 04-25-2024 at 11:19 AM..
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04-27-2024, 05:15 PM	#2
agentrnge Lieutenant 382 Rep 488 Posts Drives: 2018 M3 6MT, 2001 740iL Join Date: Dec 2014 Location: Morris County, NJ iTrader: (0)	Even with the motive bleeder empty, as long as your brake fluid reservoir is not empty ( or low to whatever point makes sense ) its not pushing air into the system. its just a little bit more pressurized air in the reservoir above the fluid. I read of a few people noticing air being pulled into the hose at the caliper from a suction/siphon effect from the draining tube if the collection bottle was too low. Could it maybe have been that?
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