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Old 03-28-2016, 02:12 PM
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w126 Complete Vacuum tub replacement?

Hi I am considering doing a complete replacement of the vacuum tubing and connectors throughout my 81 300sd w126. Most of the parts look like they are original and honestly I thought this would be a good way to simply examine the entire system and be at least a bit more sure that possible leaks are identified and attended to.

Multiple questions:

1. Am I completely nuts for wanting to do this? (this could very well be the case)

2. Is there a complete vacuum replacement kit or listing of parts that I would need to undertake this?

3. Has anyone done this and if so - was it worth it?

Thanks in advance!!

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Old 03-28-2016, 02:26 PM
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I've done most of this on my w123 (all of the engine bay and the HVAC system, vacuum locks are probably not going to get touched). Generally, I think that the hard plastic lines are not worth replacing, I'd suggest just inspecting them and checking for breaks.

The rubber lines are a different story. Generally I've been replacing all of these, as well as most of the T/Y/X fittings and adapters. You can get good quality OE Mercedes rubber lines fairly inexpensively - I prefer the style with 2 white stripes on them, I'd get at least 3 meters, maybe even 4 or 5 (not sure how much you'll need on a w126), plus more of the fittings than you think you'll need. Invest in a vacuum pump and learn how to use it, you can isolate and test each system - though I've been having trouble finding test procedures for some elements. I also purchased something like 160 vacuum hose clamps made out of nylon. These can be squeezed in place with a pair of pliers and should prevent hoses from being disconnected in the future. It's not exactly stock, but I got sick of chasing leaks and disconnecting stuff. I bought 5/16" fittings, though I found some of the fittings under the dash could really have used 3/8". I'll let you find a source, if you want to do that.

I've found that once I disconnected an old line, there was a pretty good chance of that line leaking in the future.
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Old 03-28-2016, 05:49 PM
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Thanks for the input! All very helpful - will focus on the rubber lines first. Do you know if there are diagrams (mainly for the engine compartment) of the vacuum lines and associated connectors needed? Would be helpful to get a count of the pieces before ordering lol.
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Old 03-28-2016, 05:50 PM
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nm quick google search answered my question - Doh!
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Old 03-28-2016, 08:07 PM
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You're totally normal for wanting to replace 30+ year old brittle vacuum lines that, if accidentally broken due to removing and replacing a vacuum tube, can ruin your car's ability to brake, shift and about a dozen other things. These cars are so vacuum-dependent that it would be crazy not to replace these old parts.

That being said, there is probably a thread on this board that discusses exactly how many meters of vacuum tubing you need, what colors of tubing you need (to match the original vacuum tube colors from MB), where you can get them, and exactly how many and of what type/shape rubber vac tube connectors you need as well.

Have fun doing your vacuum tube replacement. All the seniors on this site have all done it to our cars and we all benefit ted from not having to resort to weird tricks like applying propane to where we think there is a vacuum leak to see if there's a surge in throttle.

Yeah. That's real safe to do in a running car
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Old 03-29-2016, 01:35 AM
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I would hesitate to replace ALL. Normally, the vacuum tubes underneath the carpet last a long long time. If you are so inclined then I would recommend to replace all rubber connectors under the hood. Those become brittle due to heat and exposure. Check out the vacuum hose in door pillars as they 'move' when opening or closing the doors. They could become brittle and crack. You can also replace all the doors, trunk, gas cap pods if you want.

The air circulation pods could also give you problem if it leaks. Car won't shut down. In other words, the sky is the limit to change out everything.
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

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Old 03-30-2016, 12:36 AM
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Yes I think I am going to focus on under the hood initially since that seems to definitely be where the most wear and tear is. Start with the rubber hoses, joints and plastic connectors and move into the plastic lines as well as those mostly seem to be approaching 40 years old in the near future
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Old 03-30-2016, 10:22 AM
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Here are a list of Vacuum info threads.

Mercedes Vacuum diagrams

The Vacuum lines under the hood are about the same between the W123 and W126, except for the door lock system.
The W126 uses a Vacuum Pump in the trunk for the lock system.

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Old 03-30-2016, 01:52 PM
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I did my SDL over a period of a month or so. Take a piece off, cut a new piece and put it on - repeat. Its worth it.

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