Elimination of Vacuum Reservoir W124
 

On my 91 300D, I concluded that my vacuum problem was a bad VCV....so I replaced it. Things were noticeably improved, but I still had the occasional bumpy downshift. So, just for grins, I took the vacuum reservoir offline. And, wadda you know, shifting is perfect.

Especially on a 23 year old car, I'm all for simplifying the vacuum system to the extent possible to eliminate variables. AFAIK http://www.peachparts.com/shopforum/diesel-discussion/300054-w124-vacuum-reservoir-purpose.html, the only purpose of the reservoir is to create a buffer of vacuum for faster flap openings and closings in the climate control....which I can certainly live without.

Anyone else take their reservoir offline? Any noticeable effects?

I know eventually I can eliminate the BFS....but I think I'll leave well enough alone for now.

Drove around a bunch this morning....vacuum functionality is perfect in all respects....flaps open and close immediately and, for the first time ever, headrests retract immediately.

I wonder if one of the reasons for the reservoir in the original design is the extent of the vacuum network....perhaps not nearly as necessary once the stuff on the passenger side of the engine is eliminated.

Do your door locks work?

Yes....but that's a different system, operated by an electric pump.

I wondered if eliminating the reservoir would slow the "response time" of vacuum to the transmission. But when I checked vacuum to the tranny while cruising around I found the supply to be very responsive to pedal travel without the reservoir. Vacuum climbed and dropped almost instantly, as I assume it should.

Still can't seem to smooth very light "throttle" shifts though...

The vacuum reservoir is a completely passive system. Theres not much that can go wrong other than the rubber hose connectors. I would check those, replace whats worn out and move on. I've eliminated a lot of vacuum hoses and devices in my engine bay but the reservoir in the driver's side fender is still there.

I noticed that MB themselves eliminated the vacuum reservoir effective 06/91 with MY92.....looks like they themselves regarded it as unnecessary when they revamped the vacuum system for 1992.

Driver side?

Don't forget about the coolant overflow tank. The hose to mine was corroded in half... glad I found that one

I wonder if I could fill the reservoir as a little back up supply...

The reservoir acts as a buffer when there's a big demand on vacuum, such as when you pump the brakes. I don't see any reason why it would ever be a problem, but people seem to like removing things.

If it's involved in something as critical as braking (which I'm not sure is the case...isn't that what the brake booster is for?), why did MB eliminate it in 92?

MB did not rid of the vacuum reservoir - its installed on my 1995 E300D behind the passenger fender liner and is linked via a brick red vacuum tube that tees off from the Y junction behind the brake booster.

Mine was disconnected because the line was cut, I repaired it with some rubber tubing while I was doing blower motor R&R. It smoothed out the yank of transmission shifting to a firm surge of power and also helped the dashboard flaps to work quicker (I think)

Well, perhaps they added it back in 95. But if you look at a vacuum diagram for the 92, it's not there.

All I can say that is, with mine offline, I have perfect vacuum functionality of everything....except for the passenger side stuff which was intentionally removed.

Adjust your bowden cable.

that problem more sounds like old ATF or bad modulator adjustment.

Fluids good, I've made adjustments with various results.

Something's not right with the rear end that may be the cause. Maybe the axle half shafts.. not sure

Thanks for the tip, you were right I had the cable much too loose from seat of the pants adjustments. Disconnecting the ball socket and adjusting correctly helped smooth the low throttle shifts, although now my car is pretty much in 4th from 30mph onward.

1-2 and 2-3 are still pretty harsh, no where near as smooth as a modern automatic unfortunately; but with the fluid fully warmed, not too bad either. I'll keep tweaking I guess.

Just wanted to give credit where it was due, apologies for being dismissive at the time.

Cheers

If the car shifts too early, tighten the cable and it will hold the gears for longer. The tighter the cable, the further the trans thinks you're pushing the accelerator. The reverse is true for transmissions that want to redline every gear even at mild accelerator input.

The brake booster is just a big surface area movable rubber saucer like thing which responds to vacuum being applied to one side of it which then helps push on the hydraulic piston of your brake system..... it does not produce anything... it is passive.... if you really do not have a container for vacuum then perhaps your electric pump is sufficient... but railroad cars, trucks, all the other cars with any brake boost... which pretty well means ALL those with any disc brakes... due to their lack of self energizing design... have the vacuum saved up for use when needed.

When my vac is disconnected my 93 300D bangs like a SOB going from gear to gear. I haven't seen anything that looks like a reservoir under the hood.

I do not know about your car....but on my cars it has been located behind the rear seat up under the package tray I think.... or on a wagon back towards the rear under the cargo area....

The 90 and 91 have the reservoir....the 92 (and I believe the 93) do not.

any reason adding one to my 93?

If you disconnect the bfs and connect the lines together it will eliminate the bfs
It's helped my 85 with shifting.