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Old 06-08-2008, 09:31 PM
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Vaccum-1987 300TD-and other questions...

I have been troubleshooting a rough shifting tranny, but before I buy or rebuild my vaccumm pump, I would like to know what the vaccum generated by the pump should be. Currently, with all of the circuits blocked off and only the vaccum gauge attached I am getting a reading of 12mm Hg. With the circuits attached, the best I was able to get was 8 mm Hg. This was done at idle and at up to 1500 to 2000 rpm. Is there a repair kit for this pump or do I have to bite the bullet and purchase a new or rebuilt pump? I see where check valves are offered but I believe that they fit other models and years.
I would also like to simplify my vacumm system by removing all that is not pertinent to the operation of the car. I have read articles about removing the EGR valve, but see that there are other items that could be eliminated (if doable without causing harm) such as the recirculating air valve, the vacumm transducer for the EGR, the vacumm transducer for the recirculating air valve, etc. In other words, I want to clean up the engine compartment without doing harm to the engine. BTW, I am currently converting this car to run on waste veggie oil.
I also have access to a waterjet and a complete machine shop so I could reasonably have any block off plates built for this project. Thank you


Last edited by scootertrs; 06-08-2008 at 09:32 PM. Reason: misspelling
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Old 06-08-2008, 11:33 PM
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Join Date: Jan 2006
Location: Northeast Indiana
Posts: 10,765
Best to take it to the diesel forum, this is all covered extensively over there.

The vacuum pump original design (smooth front cover vs the later with bolt heads on the cover) is considered by many to be a bad design that can without notice drop bearings into the timing chain and destroy the engine. Search the diesel forum for more info.

The EGR and ARV are not critical for the operation of your year engine, again covered on the Diesel forum, but the standard response is to buy an F vacuum-splitter to replace the 5-way in front of the engine and eliminate the ARV, EGR, and all associated plumbing on the exhaust side of the engine.

EGR blocking plates were being made by a member, not sure if they still are. Nice look, probably should get some some day for my engine.

Vacuum troubleshooting is tricky as you might already know. Best to isolate circuits and test for vacuum-holding capacity one circuit at a time. The most common vacuum problem is the (brown hose) HVAC (ACC) system. If you have air-conditioning coming through your defrost vents at all times, can't get cold air through the center dash vent, or can't get heat out of the footwell vents, these are all signs of bad vacuum actuators (pods) in your system which are leaking air (vacuum). You can try disconnecting/pugging the brown line to the dash to see if it will alleviate your problem.

Thinkng, ... I believe it is brown, or is that the shut-off to the ignition switch/IP? Which brings up another question: Does the engine shut down immediately when you turn off the key? If not, an indicator of low vacuum. That line comes from a Tee connection on the brake-vacuum check valve (separate feed on the vacuum pump). If it is good, probably a good vacuum pump.
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Last edited by babymog; 06-08-2008 at 11:39 PM.
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Old 06-08-2008, 11:39 PM
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Join Date: Dec 2005
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Welcome to the MercedesShop forum. If you use the search feature you will find many threads regarding vacuum issues. Here is one that should help.
Your readings sound low. Even if the pump is working correctly, if it doesn't have 4 torx screws on the face, you should replace it. The old ones fail and if the ball bearings stop the timing chain your engine will be toast.

Also if you post in the diesel forum you will get more responses on diesel related issues.

Chris
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Old 06-09-2008, 12:00 AM
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Here is the thread on the EGR blocking plate. I believe Brian still has kits available.
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1987 300TD 309, xxx 2.8.2014 10,000 mile OCI


Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss
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Old 06-13-2008, 09:10 PM
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replacing pump... found bad actuators...

I like doing things once... maybe twice if I did not get it right the first time... I will be following one of the many forum writeups which basically stated to replace all of the actuator diaphragms... once the dash is out anyway... gotta keep in mind that the rubber is over 20 years old and probably very tired... New pump is now coming my way and I will be removing most if not all of the unnecessary vacuum gadgets. Thanks for the info all...

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