'81 300SD How to replace vac switch on steering column lock - PeachParts Mercedes-Benz Forum

tyl604 · #1 03-23-2017, 07:49 PM

http://www.peachparts.com/shopforum/attachments/diesel-discussion/141367d1489624526-81-300sd-hard-shut-down-ignition-switch-steering-wheel-lock-1-16.jpg

My SD will not shut down and I have traced the vac leak (thank you Mityvac) to the two nipple vac switch which is a part of the ignition switch and steering wheel locking mechanism. It is part #11 circled in the pic above.

How do I replace this part; do all the guts have to come out of the dash to replace just that one part? Not replacing the tumbler, elec switch, steering wheel lock - just the two nipple vac switch. For background see my thread called '81 300SD - Hard to shut down. Thanks to Alec300sd and Diseasel300 for all the help on that thread; their help got me to this point.

tyl604 · #2 03-23-2017, 08:38 PM

http://www.dieselgiant.com/repairignitionlock.htm

Here is something from Dieselgiant. I think I see that the vac switch may be attached to the steering col lock by two screws. But the screws face the passenger side and I have no idea how to get a screwdriver in there. How the heck to I replace this thing? Diesel giant says to drop the steering column itself down and remove the entire locking mechanism. Do I have to follow that?

Junkman · #3 03-23-2017, 08:54 PM

The steering column is easy to drop if that's what needs to be done. Remove the bolster and 2 bolts that hold it up are exposed. If the plastic surrounding the needs to come off, you'll need to pull the steering wheel. Horn button pulls off then use a 10mm allen head socket then a couple of obvious screws to remove the trim. Mark the steering wheel so you can get it back in the correct location. The gauge cluster of course comes out the front. Just push on it from behind. The FSM shows little hooks that can be used to grab the cluster but I haven't used that method since learning that it could just be pushed out.

The above is memory from removing the dash. There are some good threads on dash removal which may still have pics of what you're dealing with re the vac switch.

Diseasel300 · #4 03-23-2017, 09:16 PM

The vac switch is part of the ignition lock assembly. See your FSM for a detailed procedure on how to get it out (fairly involved process). While you have it out, consider replacing the electrical part of the switch if it hasn't ever been done. When you take the lock assembly out, you'll understand why I suggest doing it now (you won't want to do it again!)

As I said in your other thread, I doubt the vacuum switch is the issue. It should be tested for functionality before declaring it the culprit.

tyl604 · #5 03-23-2017, 09:56 PM

Yes, I am still hoping something else is bad and not the vac switch.

Still trying to figure out how to test it. Not quite sure.

ROLLGUY · #6 03-24-2017, 10:29 PM

Quote:

Originally Posted by tyl604

Yes, I am still hoping something else is bad and not the vac switch.

Still trying to figure out how to test it. Not quite sure.

You may have already done this, but for others: Put your vac tester on the tube going to the shutoff, and see if it has vacuum when you turn off the ignition. Then test the shutoff with your tester. If the engine stops when you pump, the shutoff is good. If there is no vacuum going to the shutoff when key is turned to the off position, there could be a fault in the vac switch or tubing. Sometimes the rubber tubing that connects the brown plastic tubes to the vac switch go bad. Replacing them is a good idea, even if they are not the problem. I have replaced the vac switch on a 123 without removing the lock assembly, but I don't think it is possible on a 126. Believe it or not, it is easier to remove the entire steering column as a unit to work on the ignition lock assembly, than it is to just remove the lock assembly alone. Removing the lock assembly only without ruining the dash or other parts is hard to do.

tyl604 · #7 03-26-2017, 03:44 PM

Roller - I am moving closer to thinking it is the vac switch. Cannot find it anyplace in the FSM, the procedure to remove. Any idea where it is? I have an old WinXP computer which rather hesitantly will open and read the CD.

sixto · #8 03-26-2017, 04:18 PM

Can you reach the screws with a Philips bit in a 1/4" breaker bar?

Sixto
83 300SD
98 E320 wagon

tyl604 · #9 03-26-2017, 04:51 PM

Certainly a possibility. You are thinking like me that there are only two Philips head screws holding it in. I have been wondering if it can be done.

ROLLGUY · #10 03-26-2017, 04:59 PM

Quote:

Originally Posted by sixto

Can you reach the screws with a Philips bit in a 1/4" breaker bar?

Sixto
83 300SD
98 E320 wagon

The screws are slotted, and not accessible easily with the lock assembly in the car.

tyl604 · #11 03-26-2017, 11:01 PM

What are slotted screws? So these are not Phillips?

ROLLGUY · #12 03-26-2017, 11:19 PM

Quote:

Originally Posted by tyl604

What are slotted screws? So these are not Phillips?

You know, "regular" screws that have been around since Mr. Benz invented the automobile.

Diseasel300 · #13 03-27-2017, 01:20 AM

Quote:

Originally Posted by ROLLGUY

You know, "regular" screws that have been around since Mr. Benz invented the automobile.

Screws that look like a (-) rather than a (+)

tyl604 · #14 03-27-2017, 08:40 AM

Ok. Thx.

pcp · #15 03-20-2024, 03:38 PM

Ouch! The entire steering column? Forget the diagnostics, the mechanic that worked on my 91 350sd said he'd bet it is the $17 "vacuum valve at steering lock." I'd like to buy it just in case but how the heck (or who) to install it? The mechanic in Denver, I'm in the foothills, is a good one on these old cars but is hard to get to and it is understandable that it takes several days.

From a distance the OP's car looks a lot like mine--black/grey. I've been slamming the hood down for 2 years and need to find a solution. Other fixes are beginning to pile up but this one tops them all. Nice car, 135k miles, but maybe it is time to move on. But everything else is doable and the engine has a lot of miles left!

So what happened tyl604?

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