air in the ABS ?
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From: Almost all Skyline Cruises Vettes at Waterside 1-5
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Originally Posted by jabez
Maybe you need to bleed your brakes.
The ABS is a "flow thru" system air in the ABS is like air in the brake lines anywhere.
I've seen comments that you have to have ignition on when blleeeding the brakes to get air out of ABS, but I have never senn it in the GM Manual
What syptoms are you getting that lead you to believe you have air in ABS?
Racer
Joined: Jun 2002
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From: Dallas Tx
The ABS unit has several recirculation circuits operated by solenoids.
There is indeed a bleeding procedure for the ABS unit, which requires a System One controller (or equivalent) to cycle the solenoids sequentially while the brakes are being bled. The Service Manual details the procedure.
Under most circumstances short of replacing the ABS unit, bleeding the brakes in the usual fashion does not introduce air into the recirculation passages, so special bleeding of the ABS is not routinely required. If a soft pedal is encountered while the ABS is operational, then ABS bleeding would be indicated.
There is indeed a bleeding procedure for the ABS unit, which requires a System One controller (or equivalent) to cycle the solenoids sequentially while the brakes are being bled. The Service Manual details the procedure.
Under most circumstances short of replacing the ABS unit, bleeding the brakes in the usual fashion does not introduce air into the recirculation passages, so special bleeding of the ABS is not routinely required. If a soft pedal is encountered while the ABS is operational, then ABS bleeding would be indicated.
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Drifting
Joined: Mar 2004
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From: UNDER THE HOOD
One more time.
How do you bleed the ABS without a service tool ?
This is not routine. There is a problem that I've not encountered in 25+ years of turnig wrenches as a professional and as a racer.
How do you bleed the ABS without a service tool ?
This is not routine. There is a problem that I've not encountered in 25+ years of turnig wrenches as a professional and as a racer.
Team Owner
Joined: Dec 1999
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From: Lacey WA RVN 68-69
NCM Sinkhole Donor
From what the GM Service Manual says, you need a Tech-1 and the plug-in Brake Module to bleed the ABS system. The Tech-1 can send a signal to operate the ABS system while a pressure bleed is being done.
The ABS does a self-test when you start the motor, put it in gear and the car reaches about 3-4 MPH. The pump runs briefly at that point and you should hear a very short buzzing from the system. The ABS may push fluid from the pump into the brake system and pull fluid in at the same time during the test.
I had asked the local Chevy dealer about doing a full brake bleed including the ABS pump and they did not recommend bleeding the ABS pump unless there was some sort of problem with the ABS.
The ABS does a self-test when you start the motor, put it in gear and the car reaches about 3-4 MPH. The pump runs briefly at that point and you should hear a very short buzzing from the system. The ABS may push fluid from the pump into the brake system and pull fluid in at the same time during the test.
I had asked the local Chevy dealer about doing a full brake bleed including the ABS pump and they did not recommend bleeding the ABS pump unless there was some sort of problem with the ABS.
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Originally Posted by Ls1Rat
ttt 
Personally I think the "gravity" bleed is the best way to go and from what I have read in a few places so do Nascar and other race teams.I open up all bleed screws, put a piece of hose leading to a collection pan(s) on each wheel!
Keep a big bottle of new brake fluid nearby and keep adding to the reservoirs before the fluid level gets down to the bottom.
Takes an hour or so, but, during that time you can polish it or just kick back and enjoy a few suds
I forget how much those big jugs of brake fluid hold, but once you have gone through one, you should be done. You can close up front bleeder screws after about half an hour and the let the rear run
Safety Car
Joined: May 2002
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From: Somewhere nowhere
air in the ABS would NOT cause a spongy pedal unless the ABS unit was activating. only then would it introduce the trapped air into the rest of the system. having said that, the ABS unit does cycle at a certain MPH.
and there is NO way to bleed it without the fancy $$$ tool.
some ABS units have a bleed screw on it, some like my 96 do NOT.
I ran my entire system dry while changing brake hoses, but never had to bleed the ABS unit. I just did the standard "wifey pump pedal" bleed.
I think it would be hard to introduce air into the ABS unit without actually removing the lines from the abs unit itself.
and there is NO way to bleed it without the fancy $$$ tool.
some ABS units have a bleed screw on it, some like my 96 do NOT.
I ran my entire system dry while changing brake hoses, but never had to bleed the ABS unit. I just did the standard "wifey pump pedal" bleed.
I think it would be hard to introduce air into the ABS unit without actually removing the lines from the abs unit itself.
Le Mans Master
Joined: Dec 2000
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From: San Diego, Ca
For a C5 or what year? If the problem was there before you replaced it and there's no air in the fluid, there seems to be some other problem. I'd guess the lines or a bum caliper, or maybe a booster check valve bleeding vacuum, but not knowing the system, hard to tell.
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Drifting
Joined: Mar 2004
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From: UNDER THE HOOD
Originally Posted by SunCr
For a C5 or what year? If the problem was there before you replaced it and there's no air in the fluid, there seems to be some other problem. I'd guess the lines or a bum caliper, or maybe a booster check valve bleeding vacuum, but not knowing the system, hard to tell.
sent a PM
Drifting
Joined: May 2003
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From: Lakeport CA
I was taught during an ABS brake repair class that any air trapped in the ABS would be cycled out if you get the system to activate. I do it easily in a big gravel parking lot near me. Car only has to be going about 5 MPH, clutch in & stab the brakes good & hard. You can hear the pump & feel the pedal shudder/shimmy & get a little soft. But after that the pedal is nice & firm. I also have braided lines & DRM master cyl bias spring installed.
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From: Boston, Dallas, Detroit, SoCal, back to Boston MA
WARNING It depends on the year of the car.
On some it's automatic, you'll hear the unit clicking when you fire it up. On others there's a bleeder screw on the ABS unit, and both it and the brake calipers must be bleed in a certain order.
My '95 was different from my friends '94.
On some it's automatic, you'll hear the unit clicking when you fire it up. On others there's a bleeder screw on the ABS unit, and both it and the brake calipers must be bleed in a certain order.
My '95 was different from my friends '94.