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 ShopForum > Technical Information and Support > Diesel Discussion

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 01-08-2007, 07:28 PM
Registered User
 
Join Date: Jan 2002
Posts: 18,352
Brake/booster question

Brakes seem to have gotten harder on the 77 300d. It's holding about 18' of vacuum at idle. Step on brakes, and vacuum drops down about 4 inches per pump and recovers quickly.
How do I tell if the booster is doing a good job?
__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
Reply With Quote
  #2  
Old 01-08-2007, 08:59 PM
Registered User
 
Join Date: Nov 2004
Location: Nova Scotia, Canada.
Posts: 6,510
I do not know the answer. Comparison of brake pedal with engine on and off might give a small clue. Or if brakes were as hard to use with the booster disconected at it's vacuum source might give another. It does sound like the diaphram is intact and even the valve is working at least partially internally. Unless someone has the diffinitive test like reading the hydralic output pressure from the master cylinder I would read in the archives. Whatever it turrns out to be please post it as even though the master/booster is the same..
I seem to recall more 77 300d owners mentioning this problem. I even have one 77d not in use right now with a harder pedal than I like but have not got to it yet. I want to leave at least one problem not repaired on all my old mercedes. Or why should I start there with so many other possible options? I used to make lists of things I should get to until I ran out of paper. Have reverted to the first come first served at present. Squeeky wheel syndrome? I honestly almost believe as they are hauling me away to the funeral home it will only be in the middle of repairing something. .Or deciding how.
Reply With Quote
  #3  
Old 01-08-2007, 09:27 PM
Registered User
 
Join Date: Jan 2002
Posts: 18,352
I think the change has been subtle over time. I asked my wife about it and she had been wondering if they had been getting harder to push. I noticed it in comparison with the 85 which I typically drive. My wife drove the 4WD Sidekick today and said the difference in pedal pressure was significant.

I'll try the vacuum disconnect test once the snow conditions improve around here.
__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
Reply With Quote
  #4  
Old 01-08-2007, 09:41 PM
Biodiesel300TD's Avatar
|3iodiesel300T|)
 
Join Date: Dec 2004
Location: Albany, OR
Posts: 4,845
To test the booster, put you mity vac on the main vac line, start the car and read the vac gauge. If the vac pump and booster are good the gauge will read 20"-23" of vac. If it's low try pulling the main vac line off the booster, then seal the end of the line where it used to go to the booster, and see if your gauge jumps up to where it's should be. If it does your booster is shot. I think there is an o-ring in it that you can replace. If the gauge still reads low your pump it going.
__________________
Andrew
'04 Jetta TDI Wagon
'82 300TD ~ Winnie ~ Sold
'77 300D ~ Sold
Reply With Quote
  #5  
Old 01-08-2007, 10:07 PM
Registered User
 
Join Date: Jan 2002
Posts: 18,352
Quote:
Originally Posted by Biodiesel300TD View Post
To test the booster, put you mity vac on the main vac line, start the car and read the vac gauge. If the vac pump and booster are good the gauge will read 20"-23" of vac. If it's low try pulling the main vac line off the booster, then seal the end of the line where it used to go to the booster, and see if your gauge jumps up to where it's should be. If it does your booster is shot. I think there is an o-ring in it that you can replace. If the gauge still reads low your pump it going.
It reads steady at 18" or so. I think that is the result our altitude--a mile high.
__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
Reply With Quote
  #6  
Old 01-09-2007, 12:44 PM
toomany MBZ's Avatar
Registered User
 
Join Date: Nov 2006
Location: central Va
Posts: 7,820
It will take many adapters, but you can hook up your Mity Vac to the booster, and pump, and pump, and pump, and pump some more, it will eventually come up, if it holds it's good, otherwise, there is an "o" ring that can be replaced easily, (remove master cylinder from booster, you'll see it) check again. These boosters run near $300. Good luck.
__________________
83 SD

84 CD
Reply With Quote
  #7  
Old 01-09-2007, 01:04 PM
Registered User
 
Join Date: Jan 2002
Posts: 18,352
There's clearly something wrong. It's taking double or triple the pedal effort to stop the 77 compared to the 85. What could be causing this lack of force from the booster if the vacuum seems ok? It's holding vacuum in the system, the booster seems to consume 3 or 4 inches with each pump, but then the system recovers. At the pedal it doesn't seem that the booster is doing its job but under the hood the vacuum seems to be working.
__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Last edited by kerry; 01-10-2007 at 01:43 PM.
Reply With Quote
  #8  
Old 01-10-2007, 01:43 PM
Registered User
 
Join Date: Jan 2002
Posts: 18,352
TTT

Any other hypotheses?
__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
Reply With Quote
  #9  
Old 01-10-2007, 07:54 PM
Registered User
 
Join Date: Aug 2005
Location: New Hampshire
Posts: 123
Quote:
Originally Posted by toomany MBZ View Post
It will take many adapters, but you can hook up your Mity Vac to the booster, and pump, and pump, and pump, and pump some more, it will eventually come up, if it holds it's good, otherwise, there is an "o" ring that can be replaced easily, (remove master cylinder from booster, you'll see it) check again. These boosters run near $300. Good luck.
I did the pumping, it does take a loooonngg time. But I found that my brake booster held it's vaccum. That is the reason I found my vaccum pump was bad.

On a side note:
Can someone explain how come the brake booster looses vaccum when it is activated? Example: the vaccum pressure drops when the brakes are used. Where does the vaccum go?

DK
__________________
1983 300sd 253,000 + 13,000 (10,000+ on veggie and biodiesel)= 266,000
1983 300sd 390,000 (Leaky windshield seal) Known to me as the shower car. Parts car now!
1 junk 300sd Watch out for the skunk that lives underneith it!
Reply With Quote
  #10  
Old 01-11-2007, 11:50 AM
Registered User
 
Join Date: Dec 2006
Location: Bloomfield, CT
Posts: 42
If you're holding vacuum, your problem may be the master cylinder, not the booster. You could have a plugged orifice (no wise cracks here) Disconnect each circuit, at the MC, one at a time a depress pedal.
Reply With Quote
  #11  
Old 06-01-2007, 12:42 PM
Registered User
 
Join Date: Jan 2002
Posts: 18,352
Replaced the front brake pads and solved the problem. They were quite worn. Perhaps an 1/8" left on the thinnest one.
__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
Reply With Quote
  #12  
Old 06-01-2007, 12:55 PM
Registered User
 
Join Date: Nov 2004
Location: Nova Scotia, Canada.
Posts: 6,510
I remembered when you mentioned this that the caliper will not extend enough to activate the pads. Or limit the action when the pads are way down. Could be a design thing. Anyways it was talked about before. Hindsite is so beautiful. Also this is something that probably should not be.

Last edited by barry123400; 06-01-2007 at 01:01 PM.
Reply With Quote
  #13  
Old 06-01-2007, 01:01 PM
Registered User
 
Join Date: Jan 2002
Posts: 18,352
The odd thing is that I jacked up the car to see if the front brakes were working and they stopped promptly when I stepped on the brakes. No visual distinction between the front and back brakes. This is what had made me put off replacing the pads for so long. But something different was definitely going on.
__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
Reply With Quote
  #14  
Old 06-01-2007, 08:21 PM
Biodiesel300TD's Avatar
|3iodiesel300T|)
 
Join Date: Dec 2004
Location: Albany, OR
Posts: 4,845
Were you spinning the front wheels by hand? If so there isn't much force behind that when you do. You arent' actually stopping the car, you are just stopping the wheel. It doesn't take much to stop the wheels, whereas it take a lot more to stop a 2500 lbs car traveling down the road.
__________________
Andrew
'04 Jetta TDI Wagon
'82 300TD ~ Winnie ~ Sold
'77 300D ~ Sold
Reply With Quote
  #15  
Old 06-02-2007, 03:16 PM
toomany MBZ's Avatar
Registered User
 
Join Date: Nov 2006
Location: central Va
Posts: 7,820
Quote:
Originally Posted by kerry edwards View Post
Replaced the front brake pads and solved the problem. They were quite worn. Perhaps an 1/8" left on the thinnest one.
Glad to hear you got your problem solved. Yet the service limit on the pads are 2mm, about a 1/16 right? But the pads may have had issues.
__________________
83 SD

84 CD
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 09:25 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2011 Pelican Parts - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page