RE: a 1984 123 sedan. I attempted to pressure bleed the brakes on this car with a Snap-on hand pump style bleeder. The device attaches to a common "screw-on" metal cap with a male adapter which screws onto the plastic reservoir neck. For some reason, the black metal cap isn't screwing on to the plastic neck correctly. It only turns two or three rotations (consistent with a wrong thread pitch match). I know that 1981 and prior model years had a different thread pitch. I thought that anything post 1982 was all the same universal thread. I believe it's a M45 x 3.50, standard for ATE brake reservoirs (even up to model year 1992!). After applying 15 p.s.i. of fluid pressure, the fluid began to hiss out the side. I rescrewed the cap onto the neck four times, still the same. Does anyone know if the reservoirs are different in 1982/1983/1984/1985 model years???

All the same as far as I have ever seen, is the rubber gasket there?
I have seen replacement caps FS. The one on PowerBleeder fits fine.
WHOA just a minute . . . . 15 psi? I never went over about 5 psi. Maybe you have it pumped up too high?

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

45 mm cap Adapter fits most Euro cars
http://www.motiveproducts.com/03adapters.html

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

the bleeder we use at our shop runs at about 20-25 psi

I worry about the brake reservoir level sensing switches, you know the two black buttons atop the reservoir. I saw fluid blow out of one of them once with pressure up 10 or 15 psi since then I have kept the pressure under 6 or 8 psi. There can be quite a head of air above the fluid in the Power booster, that is what is compressed.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

we usually replace the rubber caps and the rubber grommets where the reservoir attaches, i personally never had one leak or blow off the master cly.
for alot of the newer cars to bleed correctly sometimes you need at least 25psi

Yes the rubber gasket is inside the metal bleeder cap. The cap is engraved with "do not pressurize over 15 p.s.i." and the pump-up tank recommends 15-20 p.s.i. too. It just seems to screw on two turns (as if it's crossed) and then stops. The threads on the plastic reservoir are all intact though. I don't get it.

If it threads on a full two turns, it's not crossed. You sure you are not at the end of the threads? Those caps don't have much thread once the gasket is in place.

Pull out the gasket and test the cap again. See if it goes on further. Naturally, don't pressurize the system in this condition.

Good idea to remove the gasket - will do. Typically it turns more than twice (I'm trying to think back). When something is crossed, it usually turns nicely one or two revolutions. My Volvo isn't here at the house to check that option. On that car it turns more than twice...

I went through the same thing.

The only way I could get it to hold pressure was to cut up a latex glove and make an extra gasket to fit in the threads. That rubber gasket in there didn't make any difference if I took it out or if I left it in.

I think that the problem is that the threads are the same "angle", but they are not the same "size". I don't know the technical terms for it.

Knowing what I know now, I'd get the cheap one with the flexible plastic cap that screws over the brake fluid reservior (which I think stands a better chance of making a good seal), instead of the inflexible metal capped one that doesn't make a good seal.

- Patrick

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1982 240D. 198k, Marine Blue/Blue, 4 Speed, Crank Windows, No Sunroof, No Rust, No Oil Leaks
2001 TDI. 197k, Lagoon Blue/Black, 5 speed, Chip, G60/VR6

Interesting... never experienced/heard of this problem before. Thanks.

I finally figured out why the fluid would hiss out of the reservoir when I applied 15 psi to it with a hand-pump brake bleeder. The fluid wasn't coming from the threaded adapter... it was leaking out of the both of the black buttons that you press to test the circuitry of the brake fluid level indicator. I can't believe I didn't see that before. It was bubbling/hissing out from under the pushbutton which means that the seal below that is gone. It wasn't easy to see either.

A simple solution is to source and modify a reservoir cap by drilling an appropriate size hole to allow the use of a tire valve stem that will be pulled thru the hole and will self seal. I have use the same one for the past 10 years on a number of 123 ch. that I have owned with excellent results. A hand held bicycle pump will provide sufficient pressure to allow bleeding of the brake system.

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DDC/MTU....Setting the pace
1985 300cd
1983 300d...aka "The Yummymummymobile"....Wifes ride
2006 Wesmac 38' Sportfisherman, Single DDC/MTU 12V-2000 1500 hp