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Brakes fading, ABS module Question

Don Powers

Full Member
Joined
Oct 28, 2012
Messages
9
Location
Edmonton AB Canada
04 Avalanche, truck sat for about 6 months, put back on road, brakes are fading on application, as if, air in system, put in new master cylinder, primed properly. No difference, completely re bled the system..... no change. Apply brakes, pedal heads for floor, ABS pump kicks in but does stop.  viewed on YouTube, the self repair of ABS module.  Before I start, Is this the problem. Anyone with a solution please chime in.  New rotors and pads 1 year ago all around. If your going to suggest power steering pump ( boost supply).... its OK.
 
2 things come to mind

Check real close for a rusted brake line
Check the rubber brake lines.
 
Does it have a power booster or Hydroboost system? Anytime I replace the master cylinders on Hydroboost systems I have to use a scan tool to "bleed" the system. Then do the gravity bleed. Then a normal bleed to finish it.
 
I really do not think the booster has anything to do with the pedal dropping to the floor. He has a leak some where. After letting it sit for 6 months and it's a kiss of problems.
 
Did you do anything with the calipers? In the past someone had similar issues due to installing new calipers upside down. Your bleeders need to be on the top.

Another issue to check for is pull the calipers and check that the slide pins are moving smoothly. If you don't grease them or the boots tear you can get corrosion which can prevent the brakes from working properly. Doesn't generally cause you to loose pedal but is easy to check and if they are sticking CAN cause brake fade as well due to over heating brake fluid. Your rims likely would be very warm too if sticking. 

If you do over heat your brake fluid due to such an event you need to completely flush the system with new fluid once you resolve the issue.
 
OK guys, I have checked all rotors and pistons, calipers are all moving fine, in correct position. on application the brake pedal goes to the floor and the ABS pump  comes on. No leaks anywhere, no loss in master cylinder reservoir. It is a functioning (but Poorly) system
Has anyone else have this happen to their truck. I am dually blessed, I also  have an Avalanche of the 2007 hatch. Other than the low oil pressure problem, I have no issues. I would love to cure the brake problem on the 04.
 
MS03 2500 said:
I really do not think the booster has anything to do with the pedal dropping to the floor. He has a leak some where. After letting it sit for 6 months and it's a kiss of problems.

I also do not believe it has anything to do with the power booster. However, if it has a hydroboost system and is not bled properly it will have issues.
 
Could be bad speed sensors...

If ABS is engaging it is likely due to bad speed sensors... Just haven't thrown codes yet.

They are prone to getting dirty with rust flakes and read wrong but still in range.

Otherwise no reason your ABS should be kicking in if your pedal is going to the floor but if ABS is releasing the pressure.... Pedal can go to floor.

Guy at work had the same thing happen to him. He ended up replacing the speed sensors and cleaning up the hubs and made it for a while. Normally the fronts are good about that.
 
I would have the brake codes read before throwing more parts at it. Many auto parts stores have a scanner that can read them.
 
MS03 2500 said:
I would have the brake codes read before throwing more parts at it. Many auto parts stores have a scanner that can read them.

(y)

With the sitting and putting new parts on possibility of air in the ABS block.
Hard to get air out and can cause multiple problems. 

 
It could very well be air in the system but the ABS shouldn't be getting involved at all.

The only time the ABS system kicks in is when the tire speeds are different. Regardless if your speeding up and traction control is engaging (on those so equipped) or your trying to stop too hard and it engages to prevent lockup.

As far as I am aware ABS isn't affected by air in the line, bad booster etc...  So if in fact the ABS system IS engaging you will want to focus some time on the speed sensors. I believe the fronts are the ones prone to having issues.

Other issues could be bad flexible lines. They can balloon up or close off when they fail inside without any fluid loss. The same guy who had issues with his speed sensors on his 2002 PU recently had issues with his brake system failing due to contaminants in his fluid. He still isn't sure what happened but he might have gotten some other fluid in his brake fluid can. His rubber swelled up and caused him grief there too. He had to replace all of the rubber components with new one.

Do you have speed bleeders? Some people have had issues with those as well.

Rodney
 
Thanks for the input, guys. Appreciate it, when mother nature gives us some decent weather I will pull the speed sensors, clean up any rust, and check the rubber lines. All new brake fluid, is going in and a complete re bleed. I will give it a shot.
Thanks again and share the knowledge, will report back when issue is rectified.
 
I vacuum bled the brakes on my 1980 TA and found the front passenger line on bled a trickle. The rubber hose failed exactly as described above. I replaced with braided lines and it's back to normal.
 
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