Take a .063" drill bit and very carefully insert it into the plastic nipples that extend from the main vacuum line. You're trying to dislodge any foreign material that's blocking the passage of air. Do this by hand and rotate the drill bit between your fingers. Do it to every nipple that comes off the main booster line.

Is that about the same as a 1/64" drill bit, can I use a 1/64"?

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Steve
1984 300SD
1987 300E
2000 Harley Road King
2006 Honda Accord EXL
1971 Chevrolet C-10 Pickup

1/64" is so tiny that you'll probably snap it.

.063" is 1/16". See if you have that.

Hey Brian, Tonight I tried the drill bit in the two small outlet lines from the booster line , both were unobstructed, I did not try the larger line that comes from the white fitting just before the brake booster.

I unhooked the booster line near the pump, it had no vacuum at first then after several times of plugging the mityvac in and pulling it out it started to pull 24" of vacuum rapidly. Last night it was real slow getting to 23". It pulled 21" of vacuum at the two small lines that I checked with the drill bit, one of those went to the "Y" line that feeds the transmission.

Remember, I did not retrieve all of the guts to the check valve last night when I replaced it with the new one, only the metal part with the hole in the center. Is it possible that the rest of the check valve parts are in the pump and causing it to work intermittely?

It worked tonight several times for engine on/off and for several miles of driving...then on vacuum again. I had to raise the hood to stop the engine when I got home.

I have checked and rechecked all the vacuum lines except the ones that go into the cabin. When the pump works everything works as it should and when it doesn't...well nothing works. Do you think I should get another vacuum pump and try it?

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Steve
1984 300SD
1987 300E
2000 Harley Road King
2006 Honda Accord EXL
1971 Chevrolet C-10 Pickup

Something just doesn't seem correct.

A vacuum pump is not the type of device that can provide good vacuum one minute and then provide no vacuum the next day. I cannot fathom how it could offer up such behavior.

But, if you're quite sure that your results are based on the output from the pump and that no leaks are clouding your results, then, I'd have to say that there's no other option.

I hate to tell you to replace the pump.........only to find out that your testing procedure is flawed in some way.

Sarthur9,
I'm going thru the same thing ewith my '79 300SD. There is a large vacuum line from the vacuum pump to the power brake booster. Put a vacuum gauge on that line and see if the pump is pulling about 18 to 21 inches. If not, the pump is bad. If the reading is good, you have a leak in the car's internal vacuum system.
I have a brand new (new model) Pierburg pump that I thought would fit my '79 but won't. The Pierburg stock number on the box is 7.20547.50.0. The M-B paprt no is 0002301365.
I got it from Europarts Direct on Ebay. Ebay # 290070599389 is the same pump.
I paid $333. plus shipping. Now they've lowered their price to $310 incluing
shipping. I'd be happy to get $250 plus shipping for it.
BTW, local M-B stealership quoted me their list price ...over $1200 plus
installation.
Check the part numbers and let me know if you can use it.
IF so, email me at jackw3306@tx.rr.com.

Have you checked all the things that need vacuum to operate like door locks, HVAC, Vacuum control valve, etc to see if they are leaking?

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

jackw3306,

Thanks for the offer but I already have a pump on order. You should have no problem getting $250 for yours, most I saw were $310 and up.

Steve

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Steve
1984 300SD
1987 300E
2000 Harley Road King
2006 Honda Accord EXL
1971 Chevrolet C-10 Pickup

I'm not sure that I need a new vacuum pump, my problems seems to be intermittent. I have checked the line to the transmission and it holds vacuum, the brake booster also holds vacuum and I have bypassed the EGR system. The door locks work.

How do I check the vacuum control valve for leaks?

How do I isolate the HAVC system so I can check only engine functions?

Is it any other places I should check for leaks and what is the procedure before replacing the vacuum pump?

My car has been out of service for three weeks now, any suggestions would be greatly appreciated. Thanks, Steve

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Steve
1984 300SD
1987 300E
2000 Harley Road King
2006 Honda Accord EXL
1971 Chevrolet C-10 Pickup

The problem is the brakes. None of those consumers can leak sufficient vacuum to kill vacuum to the brakes. The climate control connection is just to the side and ahead of the fuse box. I believe the line is red with a stripe. You can disconnect and plug the line and confirm that it makes no difference to the brakes.

The VCV can leak 100% of the time and the only symptom will be very hard shifts. It cannot affect the brakes.

GREAT NEWS!!!

Just got the new vacuum pump installed on my 300SD and all is well again, brakes work, engine shuts down.....with hood closed. It appears that a vacuum pump can operate on an intermmitent basis.

Many thanks to Brian Carlton for his untiring assistance. Without him no telling how many $$$ I would have spent to find and repair my problem.

Thanks again, Steve

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Steve
1984 300SD
1987 300E
2000 Harley Road King
2006 Honda Accord EXL
1971 Chevrolet C-10 Pickup

Good job.

This is one for the books. I don't think any of us have seen a vacuum pump work perfectly one minute and then have no output a few minutes later.........only to work perfectly yet again.

Glad you've got it solved permanently.

Are we sure? Remember, the problem was intermittant.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13