Vacuum Dashpot at Throttle body???

[n/a]

Hi, today I removed the throttle body for service on my 1970 sl (wow, was it gunked up!) and I noticed the very old vacuum dashpot.  Not only was it ancient, but there was no hose connected to it.  Question: What does this vacuum switch do, and could it affect automatic transmission shifting and where do I connect the missing vacuum hose to?  I think I am going to get a new vaccum switch as I am sure the one in the car must be near dead if working at all.

[hands_aus]

Hey James,
Is this the unit on the side of the venturi unit?
If so I think the dash pot does not have a vacuum hose connected to it.
My understanding is that it is there to slow down the return to idle of the accelerator pedal so that there is no harsh shut down of the engine.
These were not on the 230 and early 250 sls.

Bob (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[ja17]

Hello James,
This vacumme dash pot came on some USA delivery automatic 280-SL's. It must be set to work properly or it will cause rough transmission downshift by holding the venturi switch open. You may be best to remove it if it is bad. Reset the venturi and switch afterward. If it is working the set-up procedure for it is in the BBB.



Joe Alexander
Blacklick, Ohio

[n/a]

Thanks Joe.  Pardon my ignorance, but what is the BBB? Another respondent says (see) that there is no hose, but if that were the case why would their be this adjustable dashpot with a vaccum actuated arm that clearly travels (via vacuum)and is meant to do something. Help!

[ja17]

Hello James,
The BBB refers to the very large and very blue factory shop manual or the "Big Blue Book". If you do not have one we  can relay some information needed.

Yes the Vacuum pot is connected to the intake venturi via a rubber tube. Make sure the vacuum pot is good first. It should hold vacuum, or draw inward when the car is running. Adjust the post on the unit so it just touches at idle out of gear. With the trans in gear the throttle lever should open 1-1.5mm. These units were used in conjunction with the slip joint linkage rod on the venturi of these USA cars. Other cars without the dashpot had solid linkage rod here I believe.

Joe Alexander
Blacklick, Ohio

[hands_aus]

Ah Joe,

I have so much to learn.

Maybe my next Pagoda (whenever that is) will have all the mod cons like a dash pot.

Bob (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[n/a]

Thanks Joe, this is great information!  I do have the slip joint linkage and was wondering about it's purpose.  I need to buy a "Mighty Vac" anyway as I own a diesel so I can test the dashpot with it.  Out of curiousity, I checked with a local MB dealer who wanted 285.00 for the dashpot! I am guessing that I can certainly do better that should I need to purchase a new one. Thanks for clearing up BBB.  I used to be into BMW 3.0 coupes and owned four of their blue books which were helpful.  New question:  How good is the CD rom containing the BBB, owner's manuel, etc? Good detail? Thanks again Joe for solving this vacuum mystery. I used to live in Hudson, Ohio many years ago, nice town!  Best-James

[ja17]

Hello James,
Some of these little "trinkets" are extremely pricey! There are a lot of donor sedans around which will keep your project on budget. Even the carbureted sedans of the era used the same dashpot.
If you post your needs you can often times get help from other owners who have collected some spares. As time goes on you  will also find better sources for new and used parts.
I have not seen the CD yet, but the written version is nice to have next to you when you are wrenching. The BBB covers many different models Mercedes so you  have to sift through the information. Mercedes also publishes "Technical Data Booklets" which are around 400 pages of condensed, technical specifications, diagrams and information. These Data Booklets are also available. Yes some of the Chiltons, Haynes, and other manuals do explain things in a simpler format. They may also have some handy charts and tables. I use these as a suppliment to my factory literature. This kind of literature is a good investment in many ways. It can save you  a lot of money and it will retain or increase in value as time goes on!
 Members of this group are also working on a W113 specific technical manual which should be the best information available at some point in time. The archives of this site are full of information, use the search feature and you will be amazed. I have worked on these cars and engines for nearly 40 years and I still learn from the group also.

Joe Alexander
Blacklick, Ohio

[n/a]

Thanks Joe!  I now have vacuum at this dashpot and it works in spite of looking like it should not! Car is idling slightly lower and I have a low idle miss now (may be unrelated)will have to check. I also noticed that a large spring is missing from the linkage arm at the throttle valve, and I ordered this from MB. Still have problems with the venturi switch, see my new posting.  As always thanks for being a great source of information!