What is the Little Vac Box by the Throttle?

[steve kane]

On two occasions now I have had to remove the Inlet Manifold and both times I have managed to dislodge a small dia plastic Vacuum Pipe that connects onto a rubber connector on the N/Side of the gearbox, the result is a very fierce Gear Change, like you would get by just dropping the clutch on a manual car, and its ****** fiddly to re-attach!
Anyway its clear that this Vac Pipe has a great bearing on the quality of changes, it connects the Gearbox with a small component with an electrical connection behind the N/S headlamp, then goes up to the Throttle Mechanism area where it connects to an Aluminum Box, a further Vac Pipe then travels back towards the engine, but I have not yet traced where this goes. Does anyone know what there components are and do?
Steve

 

[240D 3.0VNTi]

Year/model?

 

[brandwooddixon]

It's part of the setup which decreases engine power momentarily when a gear change is required. This is done by reducing the throttle position as the gearchange takes place.

 

[steve kane]

Ah sorry, the Car is a 1995 C250D (non Turbo) part of the reason Im asking about this is that our 1st to 2nd gear changes are rather fierce with it seems to me, the change being a bit slow to occour and the engine going a little to quickly, I wondered if its possible that either the little Electrical gizmo (a valve??) behind the headlight or the Aluminium Box by the throttle might be "sticky" Im also still puzzled by the loose Vac pipe that exits the top of the Aluminium box, its fitted into a rubber elbow which is let into the top of the box, I have prev tried to find out what this is without success, perhaps its just a breather but I cannot see why they would have bothered fitting a stray length of Vac pipe to it? Intrestingly I tried sucking on this stray pipe and there is no resistance at all. I too suspected that the set-up might be a mechanism for momentarily cutting the power at the point of change, does anyone know if its possible to test any of the bits I have written about or is there adjustments that can be made, or is it likly that anyone of these componants are responsible for out fierce 1st change?
Lastly I did wonder what the effect of capping off the Stray loose Vac Pipe might be? my fear is of blowing off the pipe on the gearbox and once again having to fiddle it back on!!
Is the Aluminium Box common to all the cars and if so what is the arrangement with the stray hose I wonder?
Many thanks for your help,
Steve.

 

[television]

Steve,all of the vacuum system for your car is in the links

http://www.detali.ru/cat/oem_mb1.as...910&GA=722.427&GM=717.417&CT=F&Cat=44V&SID=80

 

[steve kane]

Many thanks indeed Malcolm, I will have a look and see what I can puzzle out.
Steve

 

[steve kane]

The diagrams look intresting but do not show any of the Gearbox to Throttle Control Vac pipes and conponants, they are mostly concerned with Headlight Level, seat control, central locking etc, are there any other pages like this on the site?
Steve.

 

[mattkh]

Hi
How about a picture of this plastic box

 

[steve kane]

Well first apologies for my tardiness in replying to this thread, I have been involved in a bit of domestic plumbing, I feel I have to do these things now before the Govt (backed by the Arcane Federation of Master Plumbers) decide to ban anyone without a masters degree in Plumbing from changing a tap washer, as has happened with Electrics,,,I sometimes wonder how long it will be before the Grand Masters Incorporated Assoc of Garage Mechanics convinces the Govt that cars, being already considered lethal weapons, are far too potentially dangerous to let us amatures loose on them,,,
Right enough of the waffle, the Vac system on my old Merc,,I feel sure that our "snatchy" first change is due in part to the change being a little delayed and possibly the Throttle not being "kicked back" at the point of change, I have looked at the Diagrams of the Vac System and whilst these are interesting they fail to offer any explanation of what the components actually do? Does anyone have any idea of the method of operation, esp of the Aluminum Box which sits in with the Throttle Linkage, it has vac pipes both in and out and a loose "vent pipe"(??) exiting the top, should this be loose? Then there is the small gizmo that looks just like a Relay that sits behind the N/S H/Lamp, the Vac pipe from the Gearbox goes through this on its way to the Aluminum Box, there is a single wire on it too, so I guess its an Electric Valve,,but when/how does it work, what does it do? (why am I here!) I feel if I could get answers to some of these questions I might stand a chance of fathoming things out. Thanking you all in anticipation,
Steve.

 

[Bolide]

Do a search for 606 engine or E300 Diesel. It's the same setup. It's all vacuu-controlled

Nick Froome
www.w124.co.uk