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ABS Hot Tip


Well-known member
May 1, 2002
Dayton, Ohio
'95 LT1 Coupe, Comp Yell; C6 Roadster, Vel Yell
There have been some posts lately regarding ABS lights. I found this information regarding brake bleeding precautions on a Volvo site! I am almost certain that these precautions apply to any hydraulic brake system, especially our cherished Vettes. What do some of you Vette experts say? BTW, Motor Service Mag. is a professional publication for USA domestic auto technicians. They are good! I thought this so important that I wanted to spoon-feed you here rather than pointing you to the website. I trust this is okay with you site boss! :)

"Brake Job Tips: Hose Clamp; ABS Sensors.
Forcing Dirty Fluid Back into the ABS:
[From Motor Service Magazine] We believe the biggest brake bungle techs are making today is forcing caliper pistons back without clamping the hose and opening the bleeder. Since the line comes in near the bottom of the cylinder where the sediment is, this forces debris up into the ABS unit, and that will likely result in a comeback for a glowing anti-lock warning light. Just opening the bleeder as you may have done in the past isn't good enough anymore. You've got to choke off that hose. [Editor's note: you can buy inexpensive plastic pliers with rounded jaws designed to clamp rubber brake hoses without damage. Check your auto parts store.]
Wheel Sensor Damage:
Another thing to remember about ABS is that it's easy to damage those delicate wheel speed sensors while doing brake work, or to cause metal particles to attach themselves to the magnet. Either is likely to put the system into default, or make it go permanently into anti-lock mode (called "false modulation"), and turn on the warning lamp. On ABS, speed sensors are at the top of the list of failures. As far as the ABS problems are concerned, the first is speed sensors with metallic particles sticking to the sensor nose. This may cause system default, or make it constantly go into anti-lock mode called 'false modulation.' Make sure the air gaps are correct, and the sensors and tone wheels are clean with no iron filings or debris in the vanes, which can give an erratic speed signal, set a code, and put the system in default.
Another problem on wheel speed sensors is an internal break in a wire. Be careful doing any wheel work because those sensors are delicate. The second thing is rust where the sensor mounts or in the wheel speed sensor bore, which makes the sensor hard to remove. As time goes on, we're going to see more and more corrosion in the electrical parts. Another problem is moisture infiltration into speed sensor electrical connectors, which causes intermittents."



Gone but not forgotten
Jan 30, 2001
Hermosa Beach, CA
1987 Z51 Silver Coupe
compyelc4 said:
I thought this so important that I wanted to spoon-feed you here rather than pointing you to the website. I trust this is okay with you site boss!

Thank you very much for the tips, but I don't understand your comment about it being ok with the Boss: Rob Loszewski.

If it is of interest to the automotive community, of course we'd encourage you to provide a link. By the same token, you may link other sites to us if you feel we have something we can share with the community at large.

Thanks again for posting this. :upthumbs

(Besides, posting a link will save you all of that typing.) :L
Oct 30, 2001
Glen Burnie, MD, USA
1986 Bright Red Coupe
Well, I for one had the 'false modulation' issue when I bought my Vette. Previous owner mentioned (and I saw this on the test drive) that the ABS would sometimes activate for no reason and the light would come on until you shut the car off. While changing wheel bearings, I found the magnets COVERED with metal filings. Cleaned them off, problem solved. Didn't know about the bleeding/clamping (sound like a surgeon here!) issue...

Here's another ABS question - How easily should ABS activate? I was at the track yesterday, and it was damp most of the day (actively raining during my last session). Spent some serious time braking down from 100+ for a hairpin right, and while the car behaved flawlessly (with mild fade) I did not once feel the ABS activate. In fact, except for the abovementioned false activation, I've NEVER felt it come on.

I was going to post this anyway in a new thread, but it seems to make sense here.


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