Question about the brake booster line...

I had to replace mine (read:stupidity), new part arrives and I notice the end that attaches to the vacuum pump has this multi-elbow metal fitting. The previous line was a small flare fitting that connected directly to the plastic line.

This new elbow fitting... I don't know what to make of it, except that perhaps it's for a w123 with a different vacuum pump. With a bit of hose bending and materials yoga I managed to connect it, but it's really in the way now.

I noticed on the broken line that the PO must have been in the same position and replaced the elbow with a barbed flare fitting. I'd like to do the same, only I have no idea how to get that barb into the hard plastic!

I've been practicing inserting the barbed end onto the broken line (before I cut the new line end off)
I tried boiling the end to soften it -not enough heat. I tried heating it with a lighter -too much burning. There has to be a technique for this.
How is it done in the factory?

flare fitting to hard line

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1981 240D 4sp manual. Ivory White.

What I am going to say won't help with your specific issue. From what I have read most people replace the Vacuum Line because the one of the little nipples breaks near the Brake booster. I broke one of mine the first time I did an Oil Filter change. Apparently I leaned on the plastic tubing.

I was able to do a functional repair but always worried I was going to forget and lean on it again and ruin the repair.

What I finally did was replace the Plastic tubing with rubber vacuum Hose. That also allowed me to route a longer hose to between the shock absorber and the fender out of the way and it won't matter if I happen to lea on it.

I know you have a new part and want it to work but if you cut the plastic tube off and replace it with rubber hose you can route it out of the way and there is no reason why the rubber hose should not last like 10 years or more as long as no oil gets on it (rubber vacuum hose is often thicker.)

Or you could use some combination of rubber hose on the fitting barb and run the rubber hose over the plastic tubing.

So my suggestion is to one way or another use rubber Hose.

If you still want to shove the plastic hose over the fitting screw the fitting into the vacuum pump so there is something solid to push at and try heating the plastic tube with a hand held hair dryer. Maybe wrap some duct tape higher up so that you have something your hands can grip onto.
Lube the fitting with something like STP or grease of something.

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84 300D, 82 Volvo 244Gl Diesel

That is actually a fantastic idea.

I'm thinking of a synthesis of these two concepts. I don't really need to insert the barbed end into the plastic, so much as I need an air tight union between them.
Perhaps a rubber sleeve is a better way to go...

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1981 240D 4sp manual. Ivory White.

That line is Nylon. Hot water is not hot enough. Use a heat gun and leather gloves. Heat both the line and the fitting so that it is just plable enough to shove the fitting into it.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

That's it?

I was beginning to think there was a special press or something.
The fitting I'm trying to insert is brass, but there are also plastic vacuum connectors on this line that certainly haven't been heated first.

I appreciate it.

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1981 240D 4sp manual. Ivory White.

Heat up the metal fitting??

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"I applaud your elaborate system of denial"

Tried that, it melted the nylon.

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1981 240D 4sp manual. Ivory White.

Yes, that's it! Practice on a scrap piece first. Do not overheat the Nylon or the fitting. The reason the fitting is heated is to avoid a cold fitting cooling off the heated Nylon as it is shoved into it.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I think sliding the nylon tubing on is similar to what people deal with in modern gas car's fuel tubing, but a much larger OD. In gas cars, you submerge the end of the nylon tubing in boiling water (just the end), then quickly slide it over the metal barbed fitting. I like the idea of heating the metal fitting, especially if off the vehicle. If really stuck, the vacuum distribution is just a simple plumbing problem, so one could redesign much of it w/ parts from Home Depot.

When replacing rubber vacuum hoses in my 300D's, I use silicone hose since it lasts almost forever, and blue for bling. I have a few rolls of various sizes I use on all my cars. Ditto for silicone hose when replacing heater hoses. I even re-plumbed the Rube Goldberg heater tubing and hoses in my 1985 with silicone hose and aluminum tee, so need not worry about sourcing those special curved rubber hoses in the future.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Haven't done this before, but the following should work:

Warm the end of the nylon hose in a mug of boiled water.
Place the metal fitting in a socket, put both in the oven.
Heat the oven to about 300 degreees or so.

Remove the heated parts with curved pliers.
Push the warmed up end of the nylon tubing onto the warmed up barbed fitting.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

Well dang, today I learned something!

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-Typos courtesy of my mobile phone.

This is great. Still haven't bought a heat gun, might give this one a crack.

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1981 240D 4sp manual. Ivory White.

It works well to put the fitting in a vice with the barbs facing up and then heat the tube and fitting and push the tube down on the barbs. Should slide right on. I don't know if boiling (212 degree) water is hot enough. But a heat gun is if you apply the heat carefully and not get it hot enough to burn or become more than pliant. I believe the stiffness of the nylon is required to maintain the correct vacuum to the booster for the volume of vacuum spec'd. It would be too flexible to use a fuel hose or other rubber hose. Others here may know the exact reasons for the stiff nylon tube.

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DS
2010 CL550 - Heaven help me but it's beautiful
87 300D a labor of love
11 GLK 350 So far, so good
08 E350 4matic, Love it.
99 E320 too rusted, sold
87 260E Donated to Newgate School
www.Newgateschool.org - check it out.
12 Ford Escape, sold, forgotten
87 300D, sold, what a mistake
06 Passat 2.0T, PITA, sold

Las Vegas NV

The heat gun is also good for peeling paint on houses in conjunction with a scraper. Tedious and it works best on flat surfaces.

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84 300D, 82 Volvo 244Gl Diesel

Finally bought a heat gun and completed this repair. On the broken line, it took 7 attempts to figure out a system and muster the confidence to proceed onto the new line.

For you future readers, the trick is laying the heat gun on a table while rotating the fitting in front of it. Every few seconds give it a pinch (leather gloves) and feel how pliable it's becoming. If you go too far, the line collapses while inserting the barb end.

Thanks to all who contributed

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1981 240D 4sp manual. Ivory White.