More vacuum q's....... - PeachParts Mercedes-Benz Forum

Douge · #1 12-19-2007, 07:09 PM

First, I have been searching prior to asking q's but I don't seem to find all the info I need.

I got a vac gauge, not a mytvac but similar. The line out of the Pump registers 22in of lift, the line to what I believe is the engine or fuel cutoff to stop the motor has no vac. The vac lines are small diameter hard plastic tubes with larger ruber couplings. The rubber couplings are obviously degrading.

Rather than checking all of the lines, even though there are not that many and trying to isolate a single leak, as if there would only be one

, I think it would be better to just replumb it all. Stupid, or good idea with poor execution?

Also, the small inline plastic thingies I think are maybe pressure regulators or modulators ?????? Are those easy to find? Is there a pre fab kit or should I just buy the hose and cut it myself, that sounds cheaper????

kerry · #2 12-19-2007, 07:32 PM

Are you creating the vacuum yourself or are you measuring the vacuum the engine pump creates? If measuring the existing vacuum, you should only be getting vacuum on the brown shut off line when the key is turned to off.

Much easier and simpler to trace down a leak. The system can be isolated into sections and tested independently. Systems are brake booster, door locks, climate control, and shut off valve.

hangit · #3 12-19-2007, 08:05 PM

Visit www.dieselgiant.com. He has a pictorial on checking vacuum. Also there are links near the top of the diesel discussion forum that should help.

John

Douge · #4 12-19-2007, 08:14 PM

Kerry, I measured the vacuum at the the line coming off the pump while the engine was running. I then undid the line at the booster and plugged the two tees to ascertain if there was vacuum at the booster and there was. I then cut a small deteriorated section off of one of the rubber couplings and then checked for vacuum downstream at the cut off and the three lines that go through the firewall and they had vacuum. I then shut the car off and it properly activated the cut off. I took the car for a short drive and to my delight the brake booster was working. It only lasted about 1.5 miles before I lost it again. I checked it when I got home and no lines had come apart so I assume there must be another leak. The lines are degraded and I think my best bet is to re plumb.

From what I see, there is the main line that goes to the brake booster, two lines tee off of that line, one going into the cabin and another that goes to the cut off and some engine control functions??? Even if I found a couple leaks, I don't think I would be confident with any of the rubber couplings, they are simply worn or wearing out. What do you think?

I think the transmission was shifting better too.

I filled my SLS reservoir and looked at the system, The back area is very clean, no degradation of the lines and the pump looks clean, I need to get it up on jhackstands though, the ass is so low I cannot get under there to get a good look.

Your help is very much appreciated!!!

#5 12-19-2007, 08:45 PM

Start buy looking at the vacuum diagrams so you understand what goes where:

http://www.peachparts.com/shopforum/showthread.php?t=192440

You will need to isolate sections of the system until you track down the leak(s). It does not make sense to replace all the hard lines, but the rubber connectors and fittings are cheap and available:

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1CQ0J3JZ429618D9FX&year=1981&make=MB&model=300-TDT-001&category=All&part=Vacuum+Hose

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1CQ0J3JZ429618D9FX&year=1981&make=MB&model=300-TDT-001&category=All&part=Vacuum+Hose+Connector

It's not really difficult just tedious, you need to be systematic.

Douge · #6 12-20-2007, 08:36 PM

I replaced all the connections in the engine bay with new hose/couplings. I have vacuum from the pump, the brake booster line is OK, the line that runs through the firewall is not holding vacuum. I replaced one of the two four ways under the passenger footwell.

So I guess I replace the second one and then start going through the HVAC system?

I must be doing something wrong. This shouldn't be so hard, any hints?

The good news is that once I have corrected that, I have an exhaust issue (bad bracket) that should be an easy fix and have to do something with the intake and then I can move to aesthetics.

Biodiesel300TD · #7 12-20-2007, 08:42 PM

You need to take on one system at a time. The green line is the HVAC system and the yellow one is the door locks. I would start with the door locks. Go through the system completely looking and fixing leaks. Then look at the HVAC system.

Douge · #8 12-20-2007, 08:57 PM

Quote:

Originally Posted by Biodiesel300TD

You need to take on one system at a time. The green line is the HVAC system and the yellow one is the door locks. I would start with the door locks. Go through the system completely looking and fixing leaks. Then look at the HVAC system.

Thanks, can't get yellow/red stripe to hold vacuum.

#9 12-20-2007, 10:50 PM

Quote:

Originally Posted by Douge

Thanks, can't get yellow/red stripe to hold vacuum.

Yellow/red is the circuit to lock the doors (yellow/green is unlock). The circuit starts in the drivers door at the master switch and feeds the other three doors, the fuel door and the trunk. The branch to the LR door is under the drivers side floor mat (check that one first). The branches to the RF and RR doors are under the passenger's floor mat. The common branch to the fuel door and the trunk lock are also under the passenger's floor mat. Just follow the circuit until you find the leak. My fuel door actuator has been replaced twice due to leaks, that may be a weak spot.

Edit: I just noticed you have a TD, so some of the details my be different than mine.

Douge · #10 12-21-2007, 12:21 AM

Quote:

Originally Posted by Craig

Yellow/red is the circuit to lock the doors (yellow/green is unlock). The circuit starts in the drivers door at the master switch and feeds the other three doors, the fuel door and the trunk. The branch to the LR door is under the drivers side floor mat (check that one first). The branches to the RF and RR doors are under the passenger's floor mat. The common branch to the fuel door and the trunk lock are also under the passenger's floor mat. Just follow the circuit until you find the leak. My fuel door actuator has been replaced twice due to leaks, that may be a weak spot.

Edit: I just noticed you have a TD, so some of the details my be different than mine.

Thank you Craig!

Sbean · #11 12-21-2007, 01:29 AM

If you find a leaky vacuum pod (split or cracked rubber) you might try repairing it with wet-suit repair glue and a bit of rubber glove. I've had some success with this in my '80 300 TDs. Steve