Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help




Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Diesel Discussion

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 01-30-2012, 02:44 PM
Registered User
 
Join Date: Nov 2006
Posts: 56
Brake pedal pulse/groan

'87 300D. When braking the brake pedal pulses and there is a groaning sound just before the car comes to a complete stop. Pads and rotors(front and rear) have been inspected and are ok. Front caliper sensors are in place. No loss of brake fluid anywhere. the master cylinder is about 3yrs old w/ about 30K on it. ABS light does not come on. The system has not been open since I serviced the master cylinder, so there should be no air in the sytem. Car does not pull to one side or the other during braking either.

Any suggestions?
Reply With Quote
  #2  
Old 01-30-2012, 02:49 PM
sixto's Avatar
smoke gets in your eyes
 
Join Date: Jun 2000
Location: SF Bay Area
Posts: 20,787
Does pulse frequency coincide with wheel rpm or is it a mechanical pulse of X-times per second?

Define pads and rotors have been inspected. Did you use a dial gauge? Did you pull the pads to ensure nothing is embedded in the friction material?

Sixto
87 300D
Reply With Quote
  #3  
Old 01-30-2012, 08:04 PM
Registered User
 
Join Date: Nov 2004
Location: Nova Scotia, Canada.
Posts: 6,510
Sounds like rotor warp if the brake pedal feels bumpy when you are applying the brakes.. Have to use a dial gauge on those rotors to find the offender.
Reply With Quote
  #4  
Old 01-30-2012, 08:10 PM
deanot442's Avatar
Diesel Dean
 
Join Date: Feb 2004
Location: Canterbury CT
Posts: 204
I have felt this in my 300SDL, I think it is the ABS activating just before coming to a complete stop. I searched on ABS issues and think my ABS sensor is dirty or acting up. I have yet to pull the wheel or sensor to investigate (too cold in Connecticut). its a possible direction to look.
__________________
Dean
Reply With Quote
  #5  
Old 01-31-2012, 08:36 AM
Registered User
 
Join Date: Nov 2006
Posts: 56
Sixto: visual inspection on pads, plenty pad material left. I did not pull the pads to inspect. Did not use a gauge to measure rotor thickness. Pulsing and groan only occur the second or two prior to coming to a complete stop...5mph or less. No pulsing experienced at other braking times to indicate a warped rotor(s). It's a 1-2 and sometimes 3 irregluar pulses and a groan and the end of the braking sequence to stop.

As I drove home last night, the ABS light came on and stayed on and the pusle and groan stopped completely....no pedal pusle at all during braking. Brake pedal seems firm. Checked again for leaks at the caliphers, master cylinder and ABS unit, with none found.
Reply With Quote
  #6  
Old 01-31-2012, 01:56 PM
Registered User
 
Join Date: Dec 2005
Location: Carson City, NV
Posts: 3,771
I vote warped rotor. Get out the dial indicator and magnetic base and find out which one(s).

BTW, I have a warped rotor on my 300D and have for several months. I'm pretty sure it's the right front, but I haven't actually followed my own advice and checked for sure. I'm trying to hold out until the pads wear out and just do it all at once. At the rate I wear out brakes on this car, that may take a while.
__________________
Anyone who thinks a 300D is fast drives too slow.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 357,xxx miles
08 Triumph Street Triple 24,xxx miles, lowered 10mm in front, Pirelli Angel GT tires, EBC HH brake pads, otherwise stock.
Reply With Quote
  #7  
Old 01-31-2012, 03:14 PM
Can't Know's Avatar
Registered Slacker
 
Join Date: Sep 2010
Location: Sunny CA
Posts: 733
Quote:
Originally Posted by Finster View Post
Sixto: visual inspection on pads, plenty pad material left. I did not pull the pads to inspect. Did not use a gauge to measure rotor thickness. Pulsing and groan only occur the second or two prior to coming to a complete stop...5mph or less. No pulsing experienced at other braking times to indicate a warped rotor(s). It's a 1-2 and sometimes 3 irregluar pulses and a groan and the end of the braking sequence to stop.

As I drove home last night, the ABS light came on and stayed on and the pusle and groan stopped completely....no pedal pusle at all during braking. Brake pedal seems firm. Checked again for leaks at the caliphers, master cylinder and ABS unit, with none found.
I think your rotors are fine given this updated information.

Clean the inside of the hubs (that's where the sensors do their work) as those can fill up with gunk and trigger the abs way early.

Given that your light came on (that means the system is also disabled) and all of your quirky symptoms stopped, it's clear that the brakes themselves are fine.

You may have a bad abs sensor as well, but I'd start with being sure that everything is spic and span on the backside of those hubs. And wipe off the sensor while you're there, too, of course.

Good luck.
Reply With Quote
  #8  
Old 01-31-2012, 03:22 PM
sixto's Avatar
smoke gets in your eyes
 
Join Date: Jun 2000
Location: SF Bay Area
Posts: 20,787
A front wheel reluctor in my 91 300SE somehow got dinged. I filed the couple of cogs back to shape and it was fine. The system can also act goofy when a wheel seal lets go and the reluctor cakes with grime.

Sixto
87 300D
Reply With Quote
  #9  
Old 02-06-2012, 02:37 PM
Registered User
 
Join Date: Nov 2006
Posts: 56
Thanks for the info....Hope to have time this weekend to inspect more thoroughly...between replacing a burned up sump pump in the house, chasing a vacuum leak in my daughters 98 Le Sabre, and installing a new inner and outer tie rods in the wife's minivan, not to mention playing IT specialist when my kids say the computer's broke and I need to do homework, my car gets the last of my attention...
Reply With Quote
  #10  
Old 02-10-2014, 09:08 AM
Registered User
 
Join Date: Nov 2006
Posts: 56
I've rebuilt all 4 calipers with new o-rings and seals...all 4 pistons were pretty grimy. Got them all cleaned up and cleaned out each caliper of gunk and rust...I put new pads on all 4 and new sensors up front, bled the entire system and problem still persists...

I think the rotors are fine otherwise when the ABS light is on and the ABS is disabled, there is no thumping like a warped rotor is prone to do... rotor don't warp then unwarp when the ABS is disabled.....

FYI, the master cylinder and fluid resevoir are only about 2 yr old...

also, just had the fun of replacing the porcupine aka blower motor regulator....fun fun fun
Reply With Quote
  #11  
Old 02-10-2014, 09:59 AM
gatorblue92's Avatar
Save the manuals!
 
Join Date: Jan 2006
Location: Delaware
Posts: 3,354
It is something with the ABS system that is causing the pulse. I have a similar issue on my 300E but it only does it when in traffic i.e. stop and go less than 15 mph or so. I have also noticed the ABS light will sometimes come on and the brakes work normally when the light is on.
__________________
1977 MB 240D 4 speed 145K - Nearly Perfect
1993 MB 400E 212K - New Project
2014 Honda CR-V 85K - Wife's DD
2018 Ford F150 5.slow 15K - My DD

1979 MB 280E 90K - Sold
1983 MB 240D 238K - Scrapped
1984 MB 300D 347K? - Sold
1984 MB 300TD Wagon - 188k - Sold
1987 MB 300E 5 speed 258K - Scrapped
1991 MB 300TE 5 speed 276K - Sold
1993 MB 400E 130K - Sold
1995 MB E320 Wagon 190k - Sold
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 02:08 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page