Is this vacuum diagnosis reasonable? - PeachParts Mercedes-Benz Forum

bodyart27 · #1 06-16-2009, 10:55 PM

Hello! Yes I'm still alive. Just no tinkerin' time with a 14 mo old daughter.

So here's the situation. 84 300SD has been sitting for over a month with a vacuum issue. The symptoms are: car won't shut off with the key (have to use the stop lever on the IP), brakes go hard at low rpm, transmission slams down a gear coming to a stop, dash (A/C) vents only open at highway speeds (high rpm) otherwise flop to "default" defrost mode.

This situation started suddenly after coming off the highway on the way to work. No telling signs of something slowly failing. Probably two months prior I had checked all the switchover valves in the climate control (all good) and found a bad easter egg vacuum pod near the glove box. I think this is unrelated since I did the following testing with climate controll off AND at high rpm (highway speeds) I get all my dash vents to flop open an nice A/C

. NO door lock issues.

So tonight I did the following testing:

I started at the shut off valve at the back of the injection pump. I could kill the motor by hand vac suction or using my mouth on a line to the shut off valve. So - that seems good.

Then I put a guage on the brown line going to the injection pump shut off valve and moved the ignition switch to "off" with the motor running. A measly 2-3 in of vacuum. At this point I was thinking the ignition switch but then I moved upstream to see what vacuum I had on the other side of the ignition switch (the other brown line).

I looked at this post on diesel giant: http://www.dieselgiant.com/mercedesvacuumtroubleshooting.htm
and disconnected the big line going to the brake booster and checked the vacuum at idle - again, a measly 2-3 in at idle. According to Diesel Giante it should be 20+!. The vacuum will rise with higher RPM.

Just for fun a checked the three-way up stream from the brake booster by disconnecting the brown line (for the ignition - right?) at the three way: 2-3 inch vacuum. Checked another line going to the three way that goes to the switches on the valve cover - 2-3 in as well.

Well crap. Now I'm thinking vacuum pump. What do you think?

I'm not seeing oil in the lines. I have a clear filter right before the shut off valve - no oil.

Or, is there anything else I need to check?

Jeremy5848 · #2 06-16-2009, 11:20 PM

Sounds like you have worked through the possibilities pretty well. Try removing the main vacuum line at the pump and fabricate a tight connection from the pump to your vacuum gauge. That will eliminate everything except the pump (and the gauge, of course). If there's still only a couple inches of vacuum, the problem is definitely the pump. In that case, caution is advised, since you don't want a failed pump to scatter metal bits into the timing chain.

bodyart27 · #3 06-17-2009, 12:12 AM

well crap. I disconnected the fat vacuum line at the hardline (near the PS pump) that snakes down to the vacuum pump. It was hard to get a good reading but the results were clear - 3 in at the v-pump hardline.

So - that's terminal - right?

And regarding your question about the guage - I bought it today at sears and I can pull 10-15 in easily with my mouth (no comments from the peanut gallery!). So I'll take that is operating OK.

I noticed (and reading some posts tonight) that there are TWO rebuild kits. Combine the costs of the two rebuild kits and your closing in on the price of a new pump. Is is SAFER to just get a new pump? Of course I'm doing my overkill / rationalizing here (am I the only one that does that?), but a "swap out" would be a heck of a lot less time and effort than to do both rebuild kits.

Thoughts?

Diesel911 · #4 06-17-2009, 01:03 AM

Quote:

Originally Posted by bodyart27

well crap. I disconnected the fat vacuum line at the hardline (near the PS pump) that snakes down to the vacuum pump. It was hard to get a good reading but the results were clear - 3 in at the v-pump hardline.

So - that's terminal - right?

And regarding your question about the guage - I bought it today at sears and I can pull 10-15 in easily with my mouth (no comments from the peanut gallery!). So I'll take that is operating OK.

I noticed (and reading some posts tonight) that there are TWO rebuild kits. Combine the costs of the two rebuild kits and your closing in on the price of a new pump. Is is SAFER to just get a new pump? Of course I'm doing my overkill / rationalizing here (am I the only one that does that?), but a "swap out" would be a heck of a lot less time and effort than to do both rebuild kits.

Thoughts?

Good job troubleshooting!

There are 3 valves in or on the Vacuum Pump.
The one that the Hard Plastic Hose connects to and 2 side by side inside of the Vacuum Pump.
1 or all of them could be gunked up and not closing.
I would clean the Vacuum Valve/Check Valve (shown in the thumbnail pic) first. Remove the Hard Plastic Hose and Unscrew it from the housing and inspect it. Shoot some WD-40 inside and blow it out gently with some low pressure compressed air. Put it back on and retest.

If that does not help there is a good chance it is something inside.
Remove the Vacuum Pump and take a look recording which way the parts go.

Some members have reported that the O-rings that go under the internal valves that you get in some kits are not thick/fat enough (info in threads) so do not throw out the old ones until you know the new ones work.

bodyart27 · #5 06-17-2009, 09:54 AM

Is it the piece I have highlighted in the attached pic?

I noticed the check valve by itself is $50.... which looks to be included in the whole new pump (can you tell I'm leaning towards getting a whole new unit?)

SD Blue · #6 06-17-2009, 11:48 AM

I wouldn't bother with a whole new pump unless you have some sort of mechanical damage with the older one. I pulled mine with 300K+ miles on the clock and there wasn't a hint of mechanical wear.

Once the vacuum pump is removed, (the hardest part of the whole job, due to all of those little hex-drive bolts holding it on, some you can barely see) you replace the piston o-ring, insert new check valves with spacers (note the "direction/orientation" of the original valves!)& install the cover with a new gasket. IIRC, the pump-to-block gasket has to be ordered separately.

There are two versions of the basic rebuild kit, and since your car is nearly identical to mine, order the later version. The extensive rebuild kit, with mechanical parts, I didn't find necessary unless you have mechanical wear.

bodyart27 · #7 06-17-2009, 01:27 PM

There are some posts on catastrophic pump failures, so I guess I was thinking a new pump was better from an "insurance" standpoint.

http://www.peachparts.com/shopforum/showthread.php?t=231260&highlight=vacuum+pump+failure

There is old pump vs new (I think beinga 617 motor I'm "new" style?) Are those more bulletproof (and better just to rebuild).

So many posts to sort through I'm getting confused...

Here is an excerpt from the thread (post #71) that is making me think just replace and be safe:

Torx-head bolts on the external cover indicate that the pump is likely not original, especially on 1986/87 engines. I am not sure what year the Torx screws appeared in production by Pierburg. However, I believe Aaron confirmed that the early Torx-screwed pumps may still have the "bad" open bearing internally. This doesn't seem to be very common though, most pump with the Torx screws on the front cover also have the improved bearing design. I suspect the first improvement to the pump design was the front cover screws, which helped sealing, and reduced oil leaks. The second improvement was the enclosed bearing. There may be others as well, but those are the two I am aware of.

In general:

1) The presence of four Torx screws on the front cover simply means the pump is not ancient - but if you have never removed it, it would be good to do so and see if the bearing is open or not. If it's the old open-style bearing (with exposed balls), replace the pump ASAP.

2) I believe all pumps without the Torx screws will all have open bearings, and these should likewise be replaced ASAP.

3) The date code stamped into the front cover should tell you the year of manufacture, which can be useful in determining the miles on the pump, if at least some maintenance records are available.

4) Based on my "new style" pump explosion, as detailed in this thread, and also based on the data below... I would recommend proactive replacement of even a new-style pump when it reaches the 150-200kmi range, regardless of age, even if it otherwise appears to be working ok. It's relatively cheap insurance, given the potential for catastrophe when metal parts drop into the timing chain cavity & oil sump at freeway speeds...! Besides, there is precious little evidence that these pumps last much past 200kmi.

kerry · #8 06-17-2009, 01:36 PM

Quote:

Originally Posted by bodyart27

There are some posts on catastrophic pump failures, so I guess I was thinking a new pump was better from an "insurance" standpoint.

http://www.peachparts.com/shopforum/showthread.php?t=231260&highlight=vacuum+pump+failure

There is old pump vs new (I think beinga 617 motor I'm "new" style?) Are those more bulletproof (and better just to rebuild).

So many posts to sort through I'm getting confused...

617's can have either new or old style pumps. I think an 85 SD should be a new style.

Shawn T. W. · #9 06-17-2009, 08:35 PM

If you decide to rebuild it . . . takes pictures . . . as you take it apart, an easy way to remember how it all goes!

bodyart27 · #10 06-17-2009, 09:45 PM

Well I'm back at the house and there is a "Made in Spain" stamp on the pump. This tells me it is a replacement pump, and NOT the preferred german Pierburg model. That's all I need to know.

Photo credit goes to "sixto" from the above referenced link.

If I have time I'll do a write up. No promises, my life with a new kiddo is unbelievably busy!

SD Blue · #11 06-18-2009, 10:30 AM

The link for a failed pump is for a 603, which is a different pump from the 617. The 617 pump is beefier by far.

HammerWerfer · #12 09-12-2009, 06:12 PM

On my W123 300DT

Tested the vacuum output of my system a week ago to start figuring out why the vacuum system in the car did not work. You know the symptoms, hard shifting, no center vents. As an expirement, I took the MityVac and connected it directly to the Tranny modulator. Used all the vac hose I had to get it into the cab. Had my son pump up the vacuum to 10"Hg while we were driving, and the car shifted much more smoothly. We tried several different vac levels, and the shifts were much better. Don't think this is a good long term solution.

Isolated the vac pp to booster, attached mity to just this part and pumped as furiously as we could, and got no vacuum in the system. Best number we saw was 5"Hg, just as it fell off to Zero.

Pulled the Vac Pump Check valve and found the check valve spring half way out of the bottom.

Wonder how long its been like this.

HammerWerfer