87 560SL - a different door lock system issue

[karburn]

I searched for this particular issue and nothing specific came up, so:
I have a 1987 560SL and after I unlock the car, I can hear the vacuum pump in the back still running, even after the vehicle is started. I checked w/o starting and it stays on for about 30 to 45 seconds. Another experiment was to try to re-lock using the key just after unlocking the car, and I could not turn it to lock against the pump straining to keep it open! When the buzzing stopped, I could lock it again. So the source has been identified.

The question is whether this is harmful and/or indicative of a pending failure of said vacuum pump. The car still locks & unlocks, so if this is just one of those “560SL things”, I’ll just leave it alone. Hopefully the MB CD shows the location of this gadget in case I need to replace it. Thanks to all for your time.

[JFawcett]

vacuum pump is located in the trunk next to battery - open battery door, remove jack and the pump is in the side well in a rubber jacket.....it just kind of sits there......
Don't know if they are prone to going out...I have had three of these cars (83 500SL, 81 SLC, 87 560SL) and have not had to replace the pump. Could be a vacuum leak that it is trying to compensate for???

[karburn]

I received a pretty accurate diagnosis on another forum. There is a vacuum/pressure switch that is internal to the pump, and if it goes bad the pump will run until it is shut off by a limiter switch. If there was a vacuum leak that the pump was trying to compensate for, the door locks would not work right...and they do in this case.

The end result will be a trip to the dealer or a shop that I trust to either repair that pump or replace it. Maybe that's what the R stands for in R107 - repair / replace.

[ctaylor738]

Jeez, it only worked for 21 years.

I think you are on the right track. There are several good posts on how to troubleshoot this. At least on the 140's you can take the cover off the pump and make adjustments that might get you some time. Used pumps come up on ebay, and if you find someone on car-part.com selling parts off a 560, you might find that they would sell you a pump.

[aublutiger]

Make sure you are really careful in the meantime. A friend of mine had the same issue on his 190E. Now he has to replace all lock assembly as well. The vacuum kept running and he kept trying to turn the key in the doors....now the only way he can unlock the car is through the trunk keyhole

[karburn]

Good advice. I learned quickly that I cannot lock the car immediately after unlocking - I have to wait until the problem pump shuts off. I feel fortunate that (knock on wood) the vacuum system on this car is still pretty good. A lot of 107's have problems because the vacuum system deteriorates and performs like a set of leaky bagpipes - too much air and plenty of noise. I've heard that I could get into the pump and check to see if a certain gear/shaft is frozen up, preventing mechanical shut-off, but that sounds like something best left to a knowledgeable mechanic. If anyone on the forum has delved into the vaccum pump and has a photo or two, please send it on. Thanks.