I know the FSM says to remove the steering wheel, but I just telescoped it out and the dash slid out over the top of it. It probably isn't that much more time consuming, but I figured why pull it if I didn't have to. I already had enough parts in the second bay of my garage.

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1987 300TD 309, xxx 2.8.2014 10,000 mile OCI


Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss

Good tip, thanks.

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300E 1986 - 117KMi
Sikkens Metallic Azurite Blue
Member #120 of MB Club VE
Caracas, Venezuela

Yes, excellent tip... I forgot about the telescoping wheel. Make sure you telescope it *before* disconnecting the battery. And for models without the telescoping wheel, the clearance may be very tight without the wheel removed. Since it only takes an extra 5 minutes, I'd still pull the wheel, but in either case be VERY VERY careful of the cruise control stalk when re-installing the dash... I broke mine the first time because I didn't notice the dash was hanging up on it, d'oh.

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BTW, is it possible in any way that a vacuum leak caused by a bad AC system pod to influence the air/fuel mixture of the engine making it go leaner then expected? This would be a problem because extra air not accounted for by the air-flow plate would be getting into the engine and upsetting the basic mixture.

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300E 1986 - 117KMi
Sikkens Metallic Azurite Blue
Member #120 of MB Club VE
Caracas, Venezuela

No, the diesel creates its vacuum from an external vacuum pump, not induction air.

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Gone to the dark side

- Jeff

Well, problem is my car is not a diesel (1986 300E), so I'm still wondering if a vacuum leak could cause any mixture problems.

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300E 1986 - 117KMi
Sikkens Metallic Azurite Blue
Member #120 of MB Club VE
Caracas, Venezuela

In theory, yes, maybe. In reality, probably not. The amount of vacuum leak produced by any part of the ACC system would be so miniscule, it wouldn't affect engine operation. You need a larger leak before it would affect the engine... like at the intake manifold, or TBA, or cracked vac line actually at the manifold, etc.

I plan on doing my '92 300E before summer. At least one of the recirc valves high lift is bad as confirmed by using the Mityvac. Just replaced the defrost valve which had a bad high lift. Did this entire job on my 89 300E years ago. I completely agree with how you replace the various valves. I also agree with replacing all the valves and vacuum testing them before putting the dash back in. The best web site I found for vacuum valve prices is www.***************. If anyone has a better website or price, please let me know.

Gsxr

I just replaced all the vacuum pods on my 95 e300d. Before replacing the dash I double checked each pod with a mityvac and confirmed they all work. However, the air still flows only out of the side vents and defrost vents. So I assumed the switchover tree that the lines connect to was bad and obtained a new one. However the problem remains the same:cold air coming out of the side and defrost vents. I have replaced the acc control unit twice with used versions that were loaned to me by a friend and the problem won't rectify. The main vacuum pump at the front of the engine has been replaced, all the lines appear to be connected. The car does shift hard when it hits gear transitions. I'm sure there is a vacuum leak but I'm at a loss on where or how to track this one down. Any suggestions ?

Connect the Mityvac to one system at a time, pump some vacuum and see what doesn't hold vacuum.

__________________

Gone to the dark side

- Jeff

I'd say that taking into account both your hard shifts and the a/c symptoms you describe, that there is a good chance that there is indeed a vacuum leak somewhere. Did you take a system vacuum reading with the Mityvac? Not sure what the specs should be, but I'm sure that reading would be an easy indication of the condition of the system.

Also, I'm aware this is a bit late for you since you already replaced it but what you call the "switchover tree" can easily be diagnosed for any faulty ports with the Mityvac or even by switching around one of the vacuum hoses that is known to be having the desired effect on its associated actuator, and by taking into account which port is activated in which A/C position.

Good luck with your troubleshooting.

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300E 1986 - 117KMi
Sikkens Metallic Azurite Blue
Member #120 of MB Club VE
Caracas, Venezuela

Not sure about the 95 but earlier 124s have a vacuum line splitter with maybe a checkvalve built-in near the brake booster. Follow each branch from the splitter above the engine vacuum pump. One line should go towards the brake booster then split. One line goes into the cabin to the switchover valve bank, the other goes into a vacuum reservoir in the left fender. Make sure there's a healthy vacuum ar the source with the engine running, and that the reservoir it tight. It takes a lot of MityVac strokes to evacuate the reservoir. I don't know how to test the switchover valve bank for air tightness but you can see if vent selection works with the engine running and the MityVac as a vacuum source.

Sixto
87 300D

When I replace my dash (if I can ever find an uncracked blue one) I plan to replace all of the pods, just because. However, I'd like to modify the system so that the center vents are open all of the time. I did that to my W123 car and really love having center vent heat in the cold months.

In the 123, all I had to do was to disconnect the metal rod leading from the pod to the door (the pod was broken) and jam the door open with the rod. I disconnected and plugged the center vent pod vacuum line to prevent leaks. Has anyone ever done something similar to the 124?

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

That definitely sounds like a vacuum leak. There is no easy way to chase this down, but what I would try is disconnecting & plugging one section at a time, at the main supply line above the vacuum pump. The ACC vents will not work correctly if they are not receiving vacuum. You can also verify if there is vacuum present at the inlet to the 7-port "tree" behind the passenger airbag. There should be approx 25 inches vacuum there with the engine running, if not, you need to find the leak and fix it.

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The 124 design makes it difficult to manually jam the center vent flap open. I would tap into the main vacuum supply line, and send vacuum to the center vent pod at all times, if you want it always open. That would be pretty simple to do. To mechanically force it open, you need to pull the dash and remove the top of the heater box, and get creative internally...