Brake boosters?
JK Jedi
Joined: Apr 2010
Posts: 4,468
Likes: 221
From: SE Michigan
The ABS motor/pump unit (module) is between the master cylinder and the calipers. Each wheel has a circuit within the module that's normally closed tight by a spool. These spools open & close rapidly to balance braking and prevent wheel lockup and vehicle yaw when ABS / ESP(or C) is activated. The scan tool routine opens the spools one at a time and holds them open so any trapped air can be expelled. The routine has you bleed the brakes three times, first time with spools closed to get any air out of the basic system, then with spools open consecutively to expell and air in the ABS module, then a final bleed to remove any remaining air that might have been purged from the module and still trapped in the basic system.
In general if you just open the basic circuit to, for example, replace the flex lines, bleeding the ABS module isn't required. I even replaced the stock master & booster with the Mopar BBK units and didn't need to bleed the ABS. However, if you were replace the ABS module, or leave the system open for any length of time then beeding ABS is essential.
In general if you just open the basic circuit to, for example, replace the flex lines, bleeding the ABS module isn't required. I even replaced the stock master & booster with the Mopar BBK units and didn't need to bleed the ABS. However, if you were replace the ABS module, or leave the system open for any length of time then beeding ABS is essential.
That slight mushy feeling may be that ABS needs it's special bleed procedure. A buddy of mine had similar for a couple years, and had bled the brakes numerous times. He mentioned it while we were replacing an axle, and since I had my scan tool with the ABS bleed function we gave it a try -- No more mushy pedal. Side note, regular bleeding is required after the ABS bleed function to completely remove the air (the scan tool should notify).
Last edited by Rednroll; Dec 4, 2018 at 05:32 AM.
JK Junkie
Joined: Nov 2011
Posts: 2,199
Likes: 218
From: Over the hill
So if the brake lines were bled properly, then how would air trapped in the ABS cause a mushy pedal feel?
Although that's plausible, another possibility is that the base bleeding portion fixed it, and the ABS bleed didn't do anything extra. I try to be methodical and scientific, but there's the little boy inside with a new toy looking for an opportunity with friends to play with it!
Last edited by Mr.T; Dec 4, 2018 at 01:45 PM. Reason: grammar / spelling
JK Freak
Joined: Apr 2009
Posts: 775
Likes: 32
From: Colorado
After selecting ABS Bleed in the menu, the scan tool gave instructions and did some magic with the ABS pump/solenoids. Regular bleeding is performed first if not already done, then the scan tool runs the pump and solenoid valves a few times, reiterates which wheel to bleed next, and waits for a key-press to continue.
JK Junkie
Joined: Nov 2011
Posts: 2,199
Likes: 218
From: Over the hill
Mr T, I got an OTC 3210 and ran the ABS bleed routine. I was surprised it only had me open the bleeders on the passenger side of the vehicle, not all four. Is this what you recall happened with yours? Seems goofy to me. I ran the routine several times. I did get quite a bit of air out of the passenger front & rear when I did the follow up standard bleed routine. I did not have the system pressurized when I ran the ABS bleed cycle as It didn't ask for it to be done. OTC doesn't provide any documentation on the ABS function, so I'm a flying a bit blind here. Your thoughts?
The bleed routine (software) may actually be in the ABS, and the scanner just initiates it and receives status messages.
You mentioned it got some bubbles out, do you notice a difference in pedal/braking?
JK Freak
Joined: Apr 2009
Posts: 775
Likes: 32
From: Colorado
Yes, the brake pedal is depressed and it runs the pump motor, then in two stages it has you open & close first the right front, then the right rear bleed screws. From whay I could see it didn't expel any fluid either time. I was surprised it didn't have me open either of the driver side bleeders. The unit does have the the latest FEDO software version. I couldn't find any info online about the procedure. I ran the ABS bleed, then followup routine bleed routune three times. It did expell quite a bit of air from the passenger rear, and a bit less from the passenger front the first time. Repeat procedures didn't really expell any I could see. (I use a Motive Power pressure bleeder.) Pedal doesn't feel much different than before. A good road test where I could trigger abs proved all was working OK.
Last edited by SoK66; Dec 15, 2018 at 02:30 PM. Reason: More info added
JK Junkie
Joined: Nov 2011
Posts: 2,199
Likes: 218
From: Over the hill
Good -- If air comes out, it has to be more better!
I've had the 3210 long enough that I've upgraded it twice, nice that yours came with the latest firmware.
Sounds like the concept is for the ABS bleed portion to transfer the air bubbles to where a regular bleed finally can remove them (from passenger front/rear). A corollary to this is that activating the ABS may transfer bubbles from the ABS to the main system, worsening the pedal firmness afterward.
Edit: ^ Just remembered you said similar back in post #20.
I've had the 3210 long enough that I've upgraded it twice, nice that yours came with the latest firmware.
Sounds like the concept is for the ABS bleed portion to transfer the air bubbles to where a regular bleed finally can remove them (from passenger front/rear). A corollary to this is that activating the ABS may transfer bubbles from the ABS to the main system, worsening the pedal firmness afterward.
Edit: ^ Just remembered you said similar back in post #20.
Last edited by Mr.T; Dec 15, 2018 at 08:23 PM. Reason: Worserned the grammar and added "Edit: ..."