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  #1  
Old 05-20-2005, 02:23 PM
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my hydraulic line exploded. why?

so, i went to flush, fill, and change the filter for the self-levelling suspension system in my '80 300TD.
i removed the line at the bottom of the reservoir, emptied the reservoir, changed the filter, reconnected the line to the bottom of the reservoir, filled the reservoir to the brim with mercedes spec hydraulic fluid, started the car, went to the rear of the car and cracked the bleeder until i saw the old fluid start to drain into a jar.
i went back to the front to check the fluid level, and there was hydraulic fluid spraying out of new pinholes in the pressure hose!
i just ordered a new hose for $136 (!!!!) and really need to know what i did wrong before i install the new one. opinions?

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  #2  
Old 05-20-2005, 04:19 PM
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Well, are we talking about the original hose that came on the car 25 years ago ?
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  #3  
Old 05-20-2005, 04:40 PM
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indeed

don't know how old that hose is, as i'm not the original owner. all i know is that it was functioning fine until i did the system flush and whatnot, so i figured i screwed up somehow.
wondering, when i disconnected the line at the bottom of the reservoir (which is the supply line for the pump, i believe), did it fill with air? and then, did that air stay in the line when i hooked it back up to the reservoir, and get sent to the pump, and cause the problem?
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'83 300CDT (286k)

former proud owner of:
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'80 mercedes 300TD
'77 mercedes 280e
'80 mercedes euro 250
'82 mercedes euro 250
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  #4  
Old 05-20-2005, 04:44 PM
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When you freshened up the system, it probably increased the pressure, and probably cleaned out some crud that was built-up in the lines, and caused it to leak out of the old, dried up hose. It's probably a good thing that it happened now, instead of a few months from now, possibly far away from home.

Mike
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  #5  
Old 05-20-2005, 04:47 PM
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try analysis, file the pin holes and see if they open up into some corrosion inside the line.
You are lucky it wasn't the reservoir that you had to replace. Last time I messed with one of these the nipple for the return at the bottom of the reservoir cracked where it comes out of the body. No way was I gonna try to glue that stuff together. Luckily I know someone that has a bunch of parts and he had one (cheap). Buying a new one would not make me happy!
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  #6  
Old 05-20-2005, 05:52 PM
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Is this a steel line? Is it rusty? This is very common on old rusty hydraulic lines, brake lines and fuel lines. They get rusty, sometimes only in one hidden spot covered by a clamp or behind a cross member. Or sometimes they are rusty all over. But they are on the verge of blowing out a rust hole. The only thing stopping this from happening is a scab or rust flake, or the last paper thin bit of sound metal. When you disturb the line suddenly it starts leaking or in extreme cases, snaps off in your hand.

This is so common that nowadays if I have a leaky brake line or hydraulic line I never try to fix it, I replace it and check and replace every other line in the system while I am at it because I know they are going to blow as soon as I fix the first one, if they are anything less than perfect.
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  #7  
Old 05-20-2005, 08:37 PM
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the line

what sprung a leak was the rubber pressure hose that goes from the pump to the steel lines. never leaked a drop in the past, and looks good on the outside (not deteriorated or anything) and is still flexible and whatnot.

anybody have any input on the idea that if air got in the pump hydraulic fluid supply hose (that comes out of the bottom of the reservoir), it could translate into the pump "running dry" for a while, producing some kind of increased pressure that caused the pressure hose to spring those holes?
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'85 mercedes euro 300TD
'80 mercedes 300TD
'77 mercedes 280e
'80 mercedes euro 250
'82 mercedes euro 250
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  #8  
Old 05-20-2005, 09:05 PM
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The hose is 25 years old for crisakes. It doesn't owe you anything. It wore out through old age. When you pulled bent and flexed it, the holes opened up. But those weak spots were already there and were an accident waiting to happen. Be glad it blew in your driveway when you were right there with your tools not on the hiway in the middle of the night in the rain.

Check your rad hoses, fuel lines, vacuum hoses, rad hoses and every other hose under the hood. They are past their best before date too. You may need to replace all of them, every 25 years.
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  #9  
Old 05-20-2005, 10:05 PM
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Exclamation Also

There is a "Full Line" on the resevoir, it should not be over filled to the "brim". This may, or may not be the issue. But, check the fluid level.
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  #10  
Old 05-20-2005, 10:09 PM
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When hydraulic lines get old they blow. I wouldn't trust any hose 20+ years old.
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  #11  
Old 05-20-2005, 10:21 PM
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fluid

Can I use standard hydraulic fluid or do I need to use the $10 per qt Febi fluid?
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  #12  
Old 05-20-2005, 10:30 PM
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John Olson who publishes the SL Market Letter markets a fluid that costs less than Febi and which is compatible with the seals in Mercedes systems. I have never heard anybody say they had a failure that was definitely because of the wrong fluid but most caution to use the approved stuff for compatability with the seals. Much the same as using MB or equivalent coolant.
You can beat 10 dollars a liter by shopping around as well as the Olson stuff.
I have seen an eBay guy called RNRN or something like that who sells cheaper than $10.
Saving a buck or two versus replacing a strut for leaky seals is the tradeoff.
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  #13  
Old 05-21-2005, 09:29 AM
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"The hose is 25 years old for crisakes."
LOLOL
That is what I was trying to HINT at... So if it was a newer hose he could speak up.... LOL
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  #14  
Old 05-21-2005, 10:39 AM
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Thanks leathermang. That was the point. My posts are usually emphatic, because I find that otherwise it is too easy to miss the point. It is not my intention to offend, or insult anyone. And if it is you will know it LOL.

Incidentally there is no need to pay $136 for a hydraulic hose. You can get one just as good at any good auto supply store for $15 to $20. They measure your old hose and make one up by cutting the hydraulic hose to length and swaging on new fittings. This service is available anywhere, even small towns, because of the number of tractors and other machines that use hydraulic hose. I even had a power steering hose made this way for a 1952 Chrysler.

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