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  #1  
Old 10-12-2004, 08:08 PM
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Help! I Can't Figure This Out

I have a 98 ML320 with 57K miles and every few months a strange thing happens when driving it. I call it uncommanded braking of the right front wheel. The vehicle becomes very cumbersome and will hardly move unless you really get on the pedal. When you release the gas, the car comes to a stop as though the brakes were applied. The right front brake disc area and wheel are very hot when this happens. All the other wheels are normal. There are no warning lights that indicate a problem.

Here is the part I don't understand. If it were only the right front brake that was malfunctioning, let's say a caliper sticking, then wouldn't the vehicle pull to the right when this occurs? It doesn't. Instead, it tracks straight ahead. The dealer replaced everything in the brake system, calipers, rotors, brake lines, pads and master cylinder under warranty. That didn't fix it. It still does this every few months and hit me today in stop and go traffic.

I tried going into low range and back out thinking that might help. It didn't. I tried everything I could think of but the only thing the seems to correct it temporarily is waiting for the brake and wheel to cool. When this happens the transmission also shifts normally so I doubt that has anything to do with it...but maybe it does. After it cools she drives fine again.

Of course I'm out of warranty now and would like some ideas on where to start troubleshooting. I've lost confidence that the dealer can fix it..he had a go at it and failed. Any ideas?

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  #2  
Old 10-12-2004, 08:27 PM
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On previous vehicles, I have had a problem which appeared under warranty and was not resolved while in warranty and I pushed the dealer to make it right as it was their misdiagnosis/inability/ineptitude that caused me to be out of the warranty period. If the problem is brought to their attention during warranty, it is theirs to resolve no matter how long it takes.

Tim
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  #3  
Old 10-12-2004, 09:01 PM
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Never heard of this. It would be pretty tough to diagnose if it only happens every few months. To be honest, I'd dump it (while it's not acting up of course).

Gilly
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  #4  
Old 10-12-2004, 09:52 PM
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Dumping it is not an option Gilly. I already tried that on my wife and she won't hear of it. She loves that ML....she and that "truck" have gone thru all the growing pains of the "early ML320s" and now she's is a pretty good vehicle except for this problem.

How about some ideas? The thing that has me puzzled is it doesn't pull to the right and yet that is the only wheel that is very hot. Doesn't make sense!
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Old 10-12-2004, 10:01 PM
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Well designed suspensions don't let the brakes don't "pull" their wheel to that side. No idea what's causing yours to apply themselves.

I've heard that old hoses sometimes start to come apart inside and the loose parts can act as a check valve. This would hold the brake on after it's applied. Sound like yours? Or does yours apply itself without your help?

Could it be a bearing?? Is it the brake rotor that's the hottest part or the bearing housing?

This is a tough one.
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  #6  
Old 10-12-2004, 10:45 PM
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It's definitely the brake disc that is hot, not the wheel bearing. The dealer already replaced the brake line and it continues to act up every few months. I still don't get why it's not pulling to the right if the right brake is sticking. If the other wheels are trying to compensate for the right pull they would be a bit warm too, wouldn't they?
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Old 10-12-2004, 10:53 PM
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I'd be more suspicious of the abs hydraulic unit than any of the stuff they replaced, but I imagine that'd be a darn healthy investment.
I wonder......if it acted up and you had in mind to disconnect the electrical connector to the control unit (part of the hydraulic unit). May set alot of codes, but it may at least answer the question if it affects it or not. If this were the problem component, it may expalin the "no pull" because maybe when it's doing it's trick on you it's also applying just enough brake to the other side to prevent a pull? Well, there's an idea for you. Either that or have your wife take a nice 3 day weekend somewhere with friends, meanwhile YOU find an identical year and color ML somewhere and trade yours in for it. Tell the car lot your mother-in-law died in it, so your wife wants to get rid of it, but yet she still loves ML's........ahem, OK, we'll fix it..........

Gilly
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Old 10-13-2004, 09:10 AM
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Thanks Gilly. Now I've got something to go on. But wouldn't the brake/abs warning light come on if there were a problem with it? I suspect the abs hydraulic unit is very expensive. Any idea what that might cost to replace if defective? Maybe a hefty repair bill would help change my wife's view on trading it for something else. This has happened to her several times and she seems content to let the vehicle sit for 30 min or so and go about her way. Now that I think about it, this anomaly always happens in city driving (stop and go traffic) and never on our highway travels.

BTW, great idea on how to get rid of the thing....you have an active imagination. I'm glad you're in the business of repairing cars as opposed to selling them. Hmmm...now that's an idea, isn't it?
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Old 10-13-2004, 04:45 PM
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Yeah, especially since I don't repair them anymore either. (Actually I never did, I just stayed at a Holiday Inn Express last night)....OK OK, I fixed them for about 9 or 10 years, just keeping my fingers in it since you're all so NICE to me! I thought about the sales thing though, not sure, not really high pressure kinda guy, never saw myself doing that, who knows, maybe when I'm too old to drive a bus.

Anyways, back to your problem, I'm thinking more like that half of the problem is just that:

Quote:
But wouldn't the brake/abs warning light come on if there were a problem with it?
Yeah it SHOULD come on, but there is a problem with it, it does this lock-up thing and plus doesn't "code" itself, or throw a warning light.
Not sure on a price, maybe contact Phil here at Fastlane for a price quote, GUESSING $500ish, not sure.

Gilly
ps See if both you and your wife can familiarize yourself with how to disconnect the big electrical connector on the abs pump, so if it happens she can try disconnecting it and see if the brake problem is gone. You'll STILL have normal power brakes without the pump plugged in, just no ABS.
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  #10  
Old 10-13-2004, 06:56 PM
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I've read through all the posts, and I go along with Gilly's prognosis. Disconnect the ABS and see if that solves the problem. If it in fact does contact the dealer and go with Tim's scenario. It wasn't corrected under warantee as it should have been. If the dealer shines you on, yell him you would like a meeting with the zone rep. If the zone rep doesn't want to work with you, then tell him you have no choice but to go to corporate. At the corporate level you can slip in the fact that you will be forced to resolve this issue as many other MB owners have by buying a trouble free Lexus.

I have been a factory trained MB mechanic for 30 years and have been loyal to the marque, but I have lost faith in the direction of the company. MB no longer produces fine automobiles. They produce garbage for the masses. On some of the newest series they put a sensitive transmission control switch just under the center console. This switch is subject to moisture, but where did they put the cup holder? It is right over the switch. The list goes on with design screw ups. Sorry but I have lost faith in Mercedes.

Peter
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  #11  
Old 10-13-2004, 08:46 PM
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I have seen numerous ABS hydraulic actuators cause this problem but electronic control has never been the issue and disconnectingt the electrical would have done nothing on any of them. If it did it probably would set a light.

The way to find it is to crack loose the hydraulic line in various places till the brakes release. Since it is so intermittant that will be difficult. On a couple of the units that were bad we were able to deduce the problem by electrically activating each solenoid. The one causing the problem was always quiet and probably stuck.
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  #12  
Old 10-13-2004, 09:52 PM
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How do you electrically activate each solenoid? Is this something I can do myself or does this require special equipment? Do you recommend just replacing the abs hydraulic actuator to remedy the problem? If you have seen them do this in several instances as you indicate, maybe that's the approach I should take. This is my wife's car and I don't want her to have this problem again. It is a personal safety issue. I wonder why the dealer didn't replace it when they worked the problem? Thanks for all the great inputs and information. I guarantee it is more than I would have ever gotten from any dealer.

I'll get a quote to R&R it and get your feedback on it. Thanks to all!
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  #13  
Old 10-14-2004, 12:14 AM
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Apparently Steve has dealt with this same problem which adds more fuel to the fire to persuade MB to cover it under warrantee. I'd still suggest following my earlier post about approaching the mfg about picking up the tab.

Peter

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