not-front-rule

Vacuum Pump Repair

Welcome to the Mercedes-Benz Club of America Forums
Here, you'll find members en masse who can talk, guide, answer or listen to your Mercedes-Benz related questions and comments. Participation in the forums is free to Club members. If you're a guest of this site, you'll have access to our read-only discussions. Like what you see? Join the Club to get full Q&A privileges. If this is your first visit, be sure to check out our FAQ page.  To start viewing messages, select the forum that you want to visit from the selection below.

Forum Jump

12 replies [Last post]
Member
Walrath's picture
Chippewa Falls, WI
Offline
Joined: January 26th, 1987

Posts:
420

Vehicles
2008 ML320 CDI 4MATIC
2000 ML320
1998 ML320
1978 300SD

1978 300SD with a double diaphragm vacuum pump.
First our symptoms: The engine would not shut off with the key, the brakes had little boost and became rock hard quickly, door locks worked but very slowly, the trunk lock even slower and the fuel door slower yet.
Diagnosis: I began with a MityVac hand held vacuum pump bought at a local retail store. Then I disconnected the line from the vacuum pump to the brake booster at the booster end and applied the MityVac to draw a vacuum and got very little - about 3.5 in. Hg, it should be around 19 in Hg. This indicated the vacuum pump was in poor condition and in need of a rebuild. Note that on this car there are no branch lines off the main line from the vacuum pump to the brake booster. Had there been I would have disconnected them and plugged the connection at the tee in the booster line. I began the vacuum system diagnosis here because if there were no vacuum from the pump it would have to be rebuilt anyway before I could diagnose any other leaks.
Repair: To rebuild the pump I ordered the vacuum check valve repair kit, the diaphragm kit and the vacuum pump gasket. A very handy resource is the genuine MB repair manuals that give step-by-step directions for jobs. To remove the pump required removing the radiator and fan, which are not difficult jobs. Then the vacuum pump was removed, cleaned thoroughly, the engine block area cleaned and the repair kits installed. (A handy tool for locating the bolts on the vacuum pump is a mirror; at least one of the bolts is quite obstructed.) This also is not a difficult job and is straightforward. The only item I had to modify slightly was the pump to block gasket, it did not have two holes for the alignment pins on the pump. A paper punch hole was perfect size. Both diaphragms in the pump were torn around the center hub about one and one-half inches. The pump was then reinstalled and everything else was put back in place.
Result: Everything on the vacuum system worked as well as it had ever done. The climate control works as good and quickly as it ever had. We had forgotten how well it responded because the loss of vacuum had been somewhat gradual. The car is a delight to drive.

I have continually found that this car is very straightforward to work on. Things are done in a logical manner and it is imperative to read the repair manual and do the job the way it says. Short cuts lead to backtracking and redoing. As the saying goes, "There is never time to do the job right, but there is always time to do it over". I hope this information is useful to others who have vacuum work to do.

I would like to thank the forum for all the information and bolstering my courage to tackle the job. The cost was less than $150 plus my time (about 5 hours) as compared to an estimated $700 - 1,000 at a service center, but the biggest benefit is the knowledge I gained doing the project.

Thank you,

Jim W.

Share this
__________________

Member
AnthroProfessor's picture
Glendale, CA
Offline
Joined: April 9th, 2007

Posts:
804

Vehicles
1992 190E
1985 300DT
1984 190D
1981 300D

Thanks for sharing this with us. Its only a matter of time that I will eventually have to rebuild a vacuum pump. I did not know if it was possible for a hobby mechanic to do it, but it sounds like it is definately something a person with some mechanical knowledge can accomplish.

Guest
JIMZ-MBZ's picture
Offline

Posts:
262
Fyi ----

Found this link on thread "noisy vacuum pump" thread:

its a how-to,,, rebuild vacuum pump :

http://www.diymbrepair.com/easley/Rebuild_vac_pump.htm

or about 350.$ at buymbparts

Jim

Former Member
ghoward@goldrus's picture
Offline
Joined: June 27th, 2006

Posts:
432

Vehicles
None

AnthroProfessor wrote:
Thanks for sharing this with us. Its only a matter of time that I will eventually have to rebuild a vacuum pump. I did not know if it was possible for a hobby mechanic to do it, but it sounds like it is definately something a person with some mechanical knowledge can accomplish.

A word of warning: the vacuum pumps on the 60- engines can disintegrate after 200 - 250 Kmi of service, essentially destroying the engine. I believe, and Marshall or Meade can (should) confirm this, there is no rebuild kit for extending this mileage.

Moderator
Maxbumpo's picture
Mount Pleasant, SC
Offline
Joined: February 2nd, 2006

Posts:
4863

Vehicles
1995 E300 Diesel
1987 300TDT

ghoward@goldrus wrote:
A word of warning: the vacuum pumps on the 60- engines can disintegrate after 200 - 250 Kmi of service, essentially destroying the engine. I believe, and Marshall or Meade can (should) confirm this, there is no rebuild kit for extending this mileage.

Actually, the 60x engine vacuum pumps can fail at 200k miles or earlier; I've read Doktor Booth recommend replacing an original pump prior to 150k miles if possible.

There is no rebuild kit.

123 vs. 124: At least the SVO crowd hasn't discovered us yet! ;)

__________________

Max Dillon
Charleston SC
'87 300TD, 334k miles (head is off, getting ready to install a different used head...)
'95 E300 Diesel, 348k miles (daily driving duty)
'73 Balboa 20

Member
Walrath's picture
Chippewa Falls, WI
Offline
Joined: January 26th, 1987

Posts:
420

Vehicles
2008 ML320 CDI 4MATIC
2000 ML320
1998 ML320
1978 300SD

Andre, it is a repair that someone with some mechanical ability can do quite well. When removing the internal pieces it is very important to note how they come out because the position and order of their installation is critical. It is easy to reverse a valve and cause the pump to not work properly, if at all. I use a muffin tin to lay out the removed parts and put them in each cup in the order and position they were removed.

Our 1978 has a different pump, the older style, than the one pictured in the responses, but the idea is the same.

Jim W.

__________________

Forum Jump

Share this