Diesel RVs: [diesel_mercedes] Re : W-126 300 SD Vacuum & Wipers

Not to worry Barton ;

Most vacuum pump failures are the check valves and they're pretty easy to replace on the car ~ you just need to be *very* diligent about _ALWAYS_ using two wrenches when loosening or tightening the various vacuum pipe connectors ~

I did Tom's W-126 , the phenolic valve disc had shattered and was bouncing 'round inside the pump proper , he was in a rush so I just installed a junkyard takeout check valve and the result was : every few days the debris would clog the valve and he'd have to use both feet to stop the car as the brake booster stopped from lack of vacuum .
The fix was dead simple : remove the primary vacuum pipe and check valve , start the engine and hold it revved up to about 2,000 RPM's (there's a governor in the Injection Pump so you cannot over rev. the engine) then _wait_ and after a few moments a couple - three tiny bits of junk flew out the open pump , stop engine and replace the check valve & vacuum pipe , all was well until the next valve failed , then I had to remove the whole vacuum pump and remove it's cover and replace the other check valve , since then it's been fine as far as I know ~ the main thing is CLEANING everything before you try to take it apart , this includes scraping the accumulated crud out of the 5 MM hex headed screws so you don't strip them out whilst taking the pump off the engine .

I didn't even need new pump to engine gaskets because Mercedes doesn't use cheapo gasket materiel .

The wiper linkages should be the same as gassers and yes, there are gassers in the Boston Metro junkyards or on some rust bucket in a back yard in Malden or on The North Shore , you just need to get busy with the Want Advertiser / Craigslist etc.and find it .

If you buy a used vacuum pump or wiper transmission off the Internet , be sure to ask for all the attaching hardware as you'll surely drop one or two fasteners or the 5MM socket head screws will be stripped etc.

These jobs are DIY do - able @ home , over some CLEAN PAVEMENT . maybe some thrift store bed sheets if you only have grass or dirt to work on ~ this will allow you to find the dropped screws , brackets etc.

Have you tet used your cheapo Harbor Freight vacuum pump to diagnose the vacuum problem ? . if it builds vacuum slowly or the vacuum signal is jerky , it's almost assuredly the pump's check valves .

I do not recommend using junkyard check valves unless you find some that are gold colored , this indicates they're replacements, being anodized when new .

I hope this helps .

-Nate
Barton wrote :
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> Had Sylvia into the local shop for a run down on the broken wiper transmission/carriage and to track down a vacuum link - oh, and also a quick fix for the temp sensor lead which recently detached itself from it's wiring. The diagnosis (from the shop's point of view) is to replace the wiper transmission w/ a used part ($250.00), that I need to replace the vacuum pump ($375), and about 5 hours of shop labor (4 for the wiper assembly alone). Total parts, labor and tax is estimated at $1600.00 - which is *way* more than I want to put into this beast right now. (Maybe had it been trouble free for another year, then maybe...). So, I know it's oft quoted, most expensive car you'll never service, or the cheapest car you'll own if you DIY. I'm pretty sure I can do these things on my own, modulo parts and time.
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> The point of this post? Probably most of all to moan and whine - then to shamelessly ask if anyone has a spare wiper transmission? I knew I should have taken it out of the donor car, but as I said before, ran out of the all too rare spare time to do it before the wrecking truck came to take it to the atom smasher.
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> Have started looking online - one or two sources claim to have used wiper mechanisms, have not made any calls or inquiries thus far.
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> I can't see (much) wisdom in installing a salvage vacuum pump, but think I've read/heard of some people rebuilding them. If the remove/replace procedure isn't too hard, I'm perfectly fine with fitting a new one, or attempting a rebuild if it can be done. It's the wiper assembly that has me most worried - in terms of time to locate one, cost of a used unit (new from MB is $650 list), and whether I'll get it right the first, second, or third time.
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> Depending on which way this goes, I'm almost ready to put this thing up for sale - and you can be sure this will be the first place it's offered - there's too many new parts in it to scrap it - but it would have to go someone who wants the car and knows how to deal with it. Still need the odo fixed and the locks working...low priority compared to the above....
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> Wish we had more PAP's with available inventory in the greater Boston area - might make this current predicament seem less vexing...
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> So that's it for now - thanks in advance for comments/advice/heckling from afar and peanut gallery input.
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> -Barton
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