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grane
Member
Date registered: Jul 2015
Location: New England and Mississippi
Vehicle(s): G500 2002 MBUSA, 2002 Lexus SC430, 2009 G550
Posts: 6
| Front/rear brake bias crisis!
I have a 2002 G500 MBUSA version that I have owned since 44kMiles. I over service the vehicle. Because I work out of the home office I just drive it on weekends so it sits in the garage most of the time. Last yearI had a Stoptech rotor/pad kit installed (available on A*zon). New sensors, caliper pistons ok, new brake fluid DOT 4, slide lubricated. Also had the axle and diff fluids replaced. Truck now has 150kMiles on it.
Now the spring is coming. The gas mileage dropped by 10%.
What I've found that the rear brakes are sticking almost all the time. The front brakes do hardly any braking. Cold front rotors, rears hot as a zinc pistol after a 30 minute drive when I have to brake fairly frequently.
Had the rear slides relubricated. Did not solve the problem.
Took it to three techs. All started waving their hands except one. He recommended that since the truck sits the AWD system needs to have proper lubrication. He recommended I back the car up 100 yards or so and then apply the brakes. I've been doing it several times before setting out on my drives and it seems to help the problem. (There are no error codes on startup or during driving except for the "replace bulb" annoyance but the ABS light does come on briefly on one nasty curve.) All 4 tires are stock size G-Year Dura Traks on 18" wheels.
Some of the metal brake lines do have some rust in the rear. Bad salt around here. But I wash the car frequently. I take the car off-road on dirt roads and logging trails nothing radical but lots of dirt and some mud. I wash the undercarriage afterwards as well as the rest of the car.
Anyone have any ideas so I can fix this without having to go to the dealer?
Edited by grane 3/26/2018 7:53 AM
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Ertech
Veteran
Date registered: May 2016
Location: Montreal CA
Vehicle(s): 2011 G550
Posts: 156
| Re: Front/rear brake bias crisis!
Could be your flexible rubber brake lines
With age they rot from the inside , with the brake pressure brake fluid can pass but fluid is trapped towards the calipers and pressure can not be releassed
Good luck
Erick |
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grane
Member
Date registered: Jul 2015
Location: New England and Mississippi
Vehicle(s): G500 2002 MBUSA, 2002 Lexus SC430, 2009 G550
Posts: 6
| RE: Front/rear brake bias crisis!
Update: Just checked the Rear Brake Proportioning Assembly that is in the middle of the right axle. It seems to be connected electronically to the ABS system. There is no ABS warning or fault code. W463 with disk brakes on all wheels.
With help of an assistant -
1. Turned on ignition.
2. Opened bottom bleeder - NO brake fluid came out whether or not pedal was pressed.
3. Opened top attachment to the brake lines that supplies fluid to the Assembly - brake fluid does come out whether or not the brake pedal is pressed. Therefore brake fluid is being supplied to the Assembly.
So the problem SEEMS to be that the Assembly is clogged in some way internally. Or should I be looking elsewhere?
1. Does anyone have a part number for the Rear Brake Proportioning Valve Assembly?
2. Does anyone know a good place to get the part?
3. I called the dealer and they want $1400 for it.  (They would not give me the part number.)
Help! |
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grane
Member
Date registered: Jul 2015
Location: New England and Mississippi
Vehicle(s): G500 2002 MBUSA, 2002 Lexus SC430, 2009 G550
Posts: 6
| Re: Front/rear brake bias crisis!
Ertech - 3/26/2018 8:22 AM
Could be your flexible rubber brake lines
With age they rot from the inside , with the brake pressure brake fluid can pass but fluid is trapped towards the calipers and pressure can not be releassed
Good luck
Erick
Thank you for the idea. One tech said the same thing. The pistons in the calipers move freely. Would they move if the rubber brake lines are clogged?
I did not check out the (rubber) brake lines from the assembly to the brakes themselves.
Do you have part numbers for these lines?
Given the age of the vehicle, should these be replaced first before I replace the Proportioning Valve Assembly?
Thank you.
Edited by grane 3/26/2018 1:13 PM
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grane
Member
Date registered: Jul 2015
Location: New England and Mississippi
Vehicle(s): G500 2002 MBUSA, 2002 Lexus SC430, 2009 G550
Posts: 6
| Re: Front/rear brake bias crisis!
Ertech - 3/26/2018 8:22 AM
Could be your flexible rubber brake lines
With age they rot from the inside , with the brake pressure brake fluid can pass but fluid is trapped towards the calipers and pressure can not be releassed
Good luck
Erick
I finally got in touch with my buddy who is a Master Mercedes Tech (30 yrs) said to replace the flexible rubber brake hoses first and change the brake fluid. He definitely agreed with you about internal rot. Frankly I think most of the places I spoke to were trying to up the bill. Duh.
He said hose replacement should be done as part of service at 100k Miles. I asked him why he didn't do it on my G!
I'll report back after I have the service done on Friday. I may use OEM parts in lieu of MB because they are 1/10th the price and are made by the same manufacturer!
Edited by grane 3/28/2018 8:38 AM
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Ertech
Veteran
Date registered: May 2016
Location: Montreal CA
Vehicle(s): 2011 G550
Posts: 156
| Re: Front/rear brake bias crisis!
Aftermarket eom are fine
There are front ones also |
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AlanMcR
Expert
Date registered: Apr 2006
Location: US, CA, Los Altos
Vehicle(s): G300DT E300DT 230SL
Posts: 3500
| RE: Front/rear brake bias crisis!
grane - 3/26/2018 8:41 AM Update: Just checked the Rear Brake Proportioning Assembly that is in the middle of the right axle. There is no rear break proportioning device on your G. That was dropped after 1995 (1996 for gas Gs). That function is performed in software with the mechanical aid of the ABS valve/pump body. Other than that, I would agree that replacing the hoses is the first step.
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BlueG
Elite Veteran
Date registered: Aug 2009
Location: DC
Vehicle(s): 2003 G500
Posts: 714
| Re: Front/rear brake bias crisis!
I had sticky rear calipers but the only fix for me was a pair of new calipers. Not expensive or difficult to install. |
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grane
Member
Date registered: Jul 2015
Location: New England and Mississippi
Vehicle(s): G500 2002 MBUSA, 2002 Lexus SC430, 2009 G550
Posts: 6
| Re: Front/rear brake bias crisis!
Ertech - 3/28/2018 1:20 PM
Aftermarket eom are fine
There are front ones also
I replaced the rubber lines and the fluid. That did the trick!
Thank you Ertech and everyone else for help. Guess I am good for another 100k Miles on the hoses LOL but I am going to change the fluid every year since I take the truck off-road.
No I am not a drama queen but when someone tells you you need a $1400 part one begins to question one's sanity.
Now to take out the small amount of rust underneath the truck.Quart of POR 15 replacement (cheaper - the inventor sold out the POR 15 Company and after a while came out with another one), some abrasives, ramps (that I already have) and some paint brushes. About $100 for more piece of mind.
New question!!!!!
Oh, and I have to change the high brake light in the middle top of the rear door. Anybody suggest a 3 color light bar for braking, turning, and flood for backing up at night?  Or should I do some searching on Pointedthree?
Edited by grane 4/2/2018 8:15 PM
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grane
Member
Date registered: Jul 2015
Location: New England and Mississippi
Vehicle(s): G500 2002 MBUSA, 2002 Lexus SC430, 2009 G550
Posts: 6
| Re: Front/rear brake bias crisis!
BlueG - 3/31/2018 3:49 PM
I had sticky rear calipers but the only fix for me was a pair of new calipers. Not expensive or difficult to install.
The pistons retracted manually and slides were lubricated front and rear. The wheels rotated fine front and rear.
When the rubber hoses collapse or rot internally, as Ertech said, the fluid gets trapped and doesn't let the pistons retract, especially in the rear. Because the rear disks are solid they run hotter than the vented disks in the front anyway.
But not that HOT!
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BlueG
Elite Veteran
Date registered: Aug 2009
Location: DC
Vehicle(s): 2003 G500
Posts: 714
| Re: Front/rear brake bias crisis!
No I was pointing out that your calipers are likely on the way out as well. Mine retracted fine when I was looking at them but driving around they would periodically hang up. Keep that in mind if you do run into any other issues. |
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petermerle
Expert
Date registered: Apr 2006
Location: Cape Town ( deep south )
Vehicle(s): W460 *1, W123 *2, W124
Posts: 1315
| Re: Front/rear brake bias crisis!
Wierd the hoses are failing on a 2002 vehicle already - on my W460 they lasted 32 years and some W460's are still operating on original brake lines here - well I guess they don't make 'em like they used to. There was a W463 here a few years ago whose rear brakes caught fire on the highway. I don't know what the cause of that was however |
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