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Old 06-18-2010, 08:09 PM
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Anyone up for a Challenge?

First off. I am posting a hypothetical case study. This vehicle doesn't exist. This is purely an exercise. The purpose of this post is to expose some people to something new and to encourage them to use their brains. The vehicle is a 2004 Gran Prix GTP. The fault or complaint is that the brake pedal drops when stopping at slow speeds. It doesn't happen all the time; but is more consistent when rolling a stop sign or parking lot manuevers. Hypothetically, let's assume that the vehicle just had the brakes fixed at another shop. All four corners were repaired(pads, rotors, and calipers)and also a 4 wheel alignment was done. There are two new tires in the front. The brake system was flushed along with other repairs. Where would you start?

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Old 06-18-2010, 08:26 PM
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Originally Posted by ethn_bert
the vehicle just had the brakes fixed at another shop. *snip* Where would you start?
I would advise them to return to the shop that did the original repairs and give them the opportunity to fix the problem if it was of the shop's making, before I (as a shop owner) would do repairs that I would have to charge the customer for.

The customer has paid for the repairs. If this wasn't present before the repairs were done, it may well have been caused by the shop doing the repairs, and that shop would be obligated to get to the bottom of it. If it was outside the scope of the repair work that was done and is a separate problem, the shop would explain this and be fully within their rights to bill the repair separately.

If the job was supposed to fix this problem in the first place, the job wasn't done correctly, and the first shop is obligated to complete the repair.
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Old 06-18-2010, 09:10 PM
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Very good point. And very close to the answer already. So, Hypothetically the customer goes back. You are the tech at the other shop. Where do you start?
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Old 06-18-2010, 09:15 PM
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I suppose the first thing I would do would be check the fluid level and codes before a test drive.

Is this about how to go about diagnosing a brake problem, or is this some kind of trick question, or? Because I'd expect that most guys in the bidnez already know how to diagnose brake probs.
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Old 06-18-2010, 09:24 PM
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Instead of you answering the above regarding a trick question or whatever it is, I'll just shut the hell up and let this play out- just because I don't get it is no reason to spoil it for everyone else, so I'll just watch.
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Old 06-18-2010, 09:51 PM
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I would advise them to return to the shop that did the original repairs and give them the opportunity to fix the problem if it was of the shop's making, before I (as a shop owner) would do repairs that I would have to charge the customer for.

The customer has paid for the repairs. If this wasn't present before the repairs were done, it may well have been caused by the shop doing the repairs, and that shop would be obligated to get to the bottom of it. If it was outside the scope of the repair work that was done and is a separate problem, the shop would explain this and be fully within their rights to bill the repair separately.

Quote:
Instead of answering the above, I'll just shut the hell up and let this play out- just because I don't get it is no reason to spoil it for everyone else, so I'll just watch.
You are truly a moral and intelligent person. I'm intrigued as to why you defined yourself in this hypothetical situation as a shop owner. I am not being negative. Those responses gave me great insight into your character and aroused my curiosity. It would have been just as easy to assume your position as a technician or an advisor.

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Because I'd expect that most guys in the bidnez already know how to diagnose brake probs.
Being a technician is kind of being like a doctor. We just don't get to bury our mistakes. Have you ever wondered why a doctor calls his business a practice? It is just that. The medical field is constantly changing and you can never be too sure about anything and they certainately don't know half of the answers they want to know. So in essence they are really just practicing. Same with automotive repair. If you don't study/practice or choose to ignore an aspect of the industry the floor will drop out from underneath you.

Therefore, this is an exercise for the experienced and the unexperienced. Both will bring different views and opinions to the table. At this point there is no correct answer. Only questions and procedures that need to be implemented in order to achieve the goal. Fixing the car.

Quote:
I suppose the first thing I would do would be check the fluid level and codes before a test drive.
The fluid level is fine and there are no stored fault codes in any module. The vehicle intermittently behaves as previously stated during your test drive. The car stops, but the pedal drops lower at times.
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Old 06-18-2010, 11:59 PM
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I would suspect air in the brake lines or a booster going bad or leaking.
I have an 03 GP SE SFI 3.1 and have no problem as I have replaced all rotors and pads myself. Being the car in question has a super charger I would wonder about improper vacuum to the booster. I do not have anti lock brakes.

Strange you would bring up the question as I recently drove a 2010 corolla while my GP was in the body shop after an idiot talking on a cell phone slammed into the side of my car while making a lane change.
I noticed that while driving the corolla that if I slowly applied the brakes while coming up to a stop light it would do the same thing. The brake peddle would drop twice as far down than if I waited to the last sec. to stop by stomping on them. That bothered me but I only had to drive it for a week.
I never could figure out why they would drop so far under light braking and not hard braking.
The only thing I can figure out is it must be the program in the computer related to stability control or anti lock-up system.
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Old 06-19-2010, 01:04 AM
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Possible ABS pump being commanded on? Would make sure the new front tires are same size. And they might even need a stagger gauge. Not sure how picky this ABS system is
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Old 06-19-2010, 11:28 AM
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Quote:
I would suspect air in the brake lines or a booster going bad or leaking.
-Nope, a booster leaking would make a stiffer pedal and less efficient brakes(increased stopping distance) not a lower pedal with similar stopping distance.

Quote:
The only thing I can figure out is it must be the program in the computer related to stability control or anti lock-up system.
-It could very well have the exact same problem as the hypothetical car


Quote:
Possible ABS pump being commanded on? Would make sure the new front tires are same size. And they might even need a stagger gauge. Not sure how picky this ABS system is
Almost! The tires are the correct size and type. The abs is actually engaging when it is not needed. But why would the ABS apply in a non-emergency stop?
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Old 06-19-2010, 12:35 PM
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AIR in the lines

There is air in the lines. With the ABS brakes, it takes a pressure bleeding system and a special procedure to bleed ABS brakes. It is nearly impossible to get the air out of the brakes by foot pumping or using the $10 bleeders.

Therein lies the problem! Usually the techs at a auto repair shop furnish their own tools and they are not going to buy a $300+ pressure bleeder when they think they can get away with using their foot.

Before you have an ABS brake system open to the air, ask the shop if they have a pressure bleeder and let them show it to you. Many shops will lie and say they have a pressure bleeder when they really don't.

I would not even bother to take that car back to the shop that was supposed to bleed the brakes. Find a shop that has a pressure bleeder and make sure they have a tech that knows how to use it.
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Old 06-19-2010, 12:49 PM
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Here is a hint. Backprobing the wheel speed sensors at the module found this result at 5mph. Blue=L/F Red-R/F Green=L/R Gold=R/R

What's the problem?
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Old 06-19-2010, 01:30 PM
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Seems the ABS module is getting wrong AC generator signal from rear. I would also maybe look at graphing on scanner with only wheel sensor PIDs selected for fastest refresh. I dunno, hard to say sometimes w/o car in yo bay

There is no discussion topic along with the pics on iATN that I can find

So really, this wasn't a "hypothetical case study". Its as its as real as it gets Did you fix the car for them?
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Old 06-19-2010, 01:34 PM
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[QUOTE=Almost! The tires are the correct size and type. The abs is actually engaging when it is not needed. But why would the ABS apply in a non-emergency stop?[/QUOTE]

Rotor and pad longevity?

Cars with stability control and ABS are designed to make the right decision for inexperienced drivers from over reacting.

With my GP without ABS I brake early from 60mph coming up to a stop light for the purpose of building less heat on the rotors and pads to increase the life of the brakes.
When I drove the 2010 corolla with ABS under the same circumstance, the peddle continued to drop. The next time I tried waiting to the last minute and stopped quickly and the peddle was noticeably harder and didn't drop as far as the light braking over a longer distance.
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Old 06-19-2010, 01:37 PM
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Quote:
Originally Posted by Rexnfx
There is no discussion topic along with the pics on iATN that I can find

So really, this wasn't a "hypothetical case study". Its as its as real as it gets Did you fix the car for them?
Busted! LOL
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Old 06-19-2010, 01:53 PM
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Perhapps it has done it from the beginning and not realizing thats the way it's supposed to be, thought you could fix that Huh?

Maybe they need to quit driving with stiletto's on!
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