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  #1  
Old 11-23-2011, 02:55 PM
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Another vacuum pump thread- help needed!

Hi all. Although I've searched and used this forum probably a hundred times in the last month, I'm still sort of a newbie. I bought a 1985 MB 300D Turbo Diesel with 254k miles about a month ago. I knew next to nothing about diesels before buying the car, and I hadn't worked on a car in almost 20 years. Using this forum and the FSM, I was able to successfully: change all filters and the oil pan gasket, replace the primer pump, replace the front brake pads, perform a diesel purge, and check the vacuum system for leaks.

From the latter, I found that the pump was putting out only 10" of pressure, which I have read is very low. As a result, the engine is not shutting down properly and the transmission is shifting rather harshly. There are other vac problems too (door locks, a/c), but I think these are due to a leak somewhere behind the firewall. I'll get to those later.

I tried to inspect the pump check valve, but was unable to get it off. In searching this forum for help, I found several threads discussing pump breakdown and the devastating effects it can have on the engine. So I pulled off the vac pump. What a major PITA! There was caked-on oil and grease all over down there. I don't know if this is from the pump or something else. And whose bright idea was it to hide a bolt under the unit with a fan, belts, and a wire in the way?

When I inspected the pump, I didn't find any signs of breakage or pending breakdown. The rocker arm, spring, piston, and bearings are all intact. There were no metal shavings or shrapnel. Despite spraying the valve with lubricant, I am still not able to get it off. I did test it though, and it seems to be working well.

The concern I have is that the spring and piston are extremely stiff. I am not able to push them down at all. I read somewhere (here or other forum) that the piston should be relatively easy to move. With the one on my pump being so stiff, does this mean the pump is broken? Is there a way to loosen up the piston without a rebuild? Lastly, are there any ideas on how to get the valve off?

Any help you can offer is greatly appreciated. I have many other questions, but I will reserve those for future threads.

Averyphilly
'85 Mercedes 300D Turbo Diesel
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  #2  
Old 11-23-2011, 05:48 PM
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Quote:
Originally Posted by averyphilly View Post
I read somewhere (here or other forum) that the piston should be relatively easy to move.
Not with the spring installed.

Quote:
Originally Posted by averyphilly View Post
Lastly, are there any ideas on how to get the valve off?
You don't really need to take it off. Unless you can see all the way through it, it should be okay. It causes problems when its internal parts fall out and block air flow.
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Old 11-23-2011, 10:29 PM
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Quote:
Originally Posted by averyphilly View Post

When I inspected the pump, I didn't find any signs of breakage or pending breakdown. The rocker arm, spring, piston, and bearings are all intact. There were no metal shavings or shrapnel. Despite spraying the valve with lubricant, I am still not able to get it off. I did test it though, and it seems to be working well.


Any help you can offer is greatly appreciated. I have many other questions, but I will reserve those for future threads.

Averyphilly
'85 Mercedes 300D Turbo Diesel
There are three more check valves inside the pump. You should have checked those too. They look like watch batteries. The inside of those valves are plastic and they break. One of the three on mine had a crack and i was wasnt getting enough vacuum.
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Old 11-28-2011, 07:50 PM
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Hi again. Thanks for the replies and advice, tangofox007 and my123ca. I removed the back cover and you were right, my123ca, one of the three check valves was cracked. I ordered a repair kit and will be replacing the valves and o-rings. Hopefully I will get much better vacuum then. I'll report the results after I put it all back together this weekend.
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  #5  
Old 11-28-2011, 08:31 PM
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Quote:
Originally Posted by averyphilly View Post
Hi again. Thanks for the replies and advice, tangofox007 and my123ca. I removed the back cover and you were right, my123ca, one of the three check valves was cracked. I ordered a repair kit and will be replacing the valves and o-rings. Hopefully I will get much better vacuum then. I'll report the results after I put it all back together this weekend.
Save the Old O-rings. Some kits have O-rings that are too thin in cross section to seal the Valves.

You might find a past thread on that; something like "Rebuilt Vacuum Pump but it is not holding Vacuum".
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Old 11-28-2011, 09:12 PM
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Thanks, Diesel911, I will hold on to the old o-rings, which appear to be in good shape.

So other than the cracked internal valve, do any of you think there are other problems with the pump? Is the piston moving as it should? Is it possible that the pump caused the massive oil build-up on the engine block? If so, does this mean it wasn't tightly sealed?
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Old 11-29-2011, 01:53 AM
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I haven`t taken a Vac pump apart yet for a rebuild, but here is some links for you.

Vacuum Pump Rebuild Thread

Charlie
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Old 12-05-2011, 09:52 AM
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Hello again. I wanted to provide an update on my vac pump issue. I replaced the internal check valves and put it all back together this weekend. Before the semi rebuild, I was getting 10" of vacuum. Can you believe that I am now getting 23"?! I am so happy about this! Now may of the systems that were not working properly or at all are now working quite well. Thank you all for your help!

I took her for a drive yesterday, and now I'm having another slight problem. With the front and rear defrosters on, one of the engine belts is now squealing. Did I tighten the power steering belt too much or too little when I put the pump back on? I've heard of "belt dressing"- is this recommended to stop the squealing?

Again, thanks for your advice and help.

Averyphilly
'85 MB 300D Turbo
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  #9  
Old 12-05-2011, 10:18 AM
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I would suspect that you have a slightly loose alternator belt. Without looking at my car, I think that is a matched pair of belts. Make sure they are a matched pair. A matched pair should have matching numbers and is cut from the same manufactured piece of belting at the same time. Then they are packaged and sold together. Anyway, if you are sure they are the correct belts, better snug them up a little.
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  #10  
Old 12-07-2011, 05:28 PM
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Quote:
I would suspect that you have a slightly loose alternator belt.
It turns out you were right. I thought the PS pump belt was too tight, but I had a very loose alt belt. Tightened it up last night and no more squealing.

Thanks all for your help! I have gotten a lot of help from this forum, and I know I will be posting again soon to get more
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