300D Vacuum Pump - PeachParts Mercedes-Benz Forum

Tubber · #1 10-28-2006, 07:21 PM

Hi,

New here, great site for the MB enthusiast. I"ve got an 85 300D (turbo) with 225,000 km. I've read the posts here on the subject and can't figure what I've done wrong.
When I got it in the spring, the pump was making sporadic vacuum; between 0 Hg-15 Hg bouncing back and forth. I checked vacuum right at the pump with a gauge. Eventually after driving for 20 minutes, the transmission shifted nicely, and there was no more "clunk" from the rear during that last 20 ft of braking to a stop; a vacuum had built up making operation smooth. But for the first 20 km, it shifted hard and clunked when braking. I decided to rebuild it.
After the rebuild, there was no vacuum at all. I checked the forum again, and found that some had problems with the small diaphram rubber gaskets were differing in height, so when I tore it apart the second time, I checked the gaskets that came with my kit and the original ones; they were both the same size. So, I double checked all the other parts (gaskets and diaphrams) along with the piston "ring" and also the "arm" and bearing; all were fine. I re-installed and still no vacuum.
Two questions. How tight do you install the piston nut down? And does it matter which side up the spring is installed? These are the only two things I can figure may need addressing. I was wondering if the piston nut was some sort of adjustment piece, as I have tightened it down fully. Does this result in the bearing not contacting the cam lobe? If so, how much does it need to be tightened down? I was wondering if one or both of these questions will result in the pump not making vacuum possibly due to a non-contact issue between the bearing and cam lobe.
Hope some can understand my explanation.

I can't drive it until I address this issue due to no power brakes.

Thanks all for the help

Blaine Taylor

Larry Delor · #2 10-28-2006, 09:42 PM

First thing that I would check is to make sure I have the check valves going in the right direction. Two face the same way, the 3rd faces the other way.

Tubber · #3 10-29-2006, 08:55 AM

Great Larry, all three check valves are facing the same way! I'll switch the one and see how it works. I guess I should have paid more close attention when I took it apart initially.

Thanks for taking the time to read and reply to my thread

Blaine Taylor

Tubber · #4 10-29-2006, 04:48 PM

Ok, switched the single check valve over, and I'm back to making sporadic vacuum as in the beginning, at least its a start.
I've searched to forum posts to try to find the Hg specs for my 85 300D, and haven't found it. What should it be pulling?
When I say sporadic vacuum, testing right from the top of the pump, the gauge reads between 10-25 Hg, but the needle bounces back and forth rapidly. I was wondering if the gauge should show 25 Hg constantly and not be bouncing?
Any other suggestions as to why directly at the pump, my vacuum would be sporadic like this even after a rebuild?

Thank you all

Blaine Taylor

Tubber · #5 10-30-2006, 04:10 PM

Sorry folks, it looks like its a much talked about subject that someone can help me with....vacuum pump. As stated above, its sporadic, any ideas as to why? Keep in mind I am checking Hg RIGHT AT the pump itself and NOT a line coming off of it. Can't figure out why. 85 300D (turbo).

Or, can someone steer me toward something I can use to reference/troubleshoot myself? I've checked through the archives/search and haven't gotten my answer.

Thanks again

Blaine Taylor

Larry Delor · #6 10-30-2006, 07:47 PM

Trouble is... I don't remember which way the valves face - they are one-way valves....so you could have them reversed now.

I'll look around and see if I can find something further on this.

You might want to post in the Diesel discussion too - a lot of people who are in the know there.

-Larry

unkl300d · #7 10-31-2006, 12:14 AM

are you sure the new membrane is intact? I believe there is a special way for installing these. The piston has to be fully extended, then you install membrane and bolt down.
not sure so check the archives.

Good Luck

whunter · #8 10-31-2006, 12:43 AM

This thread should have all the data you need.

Engine Mechanical:
http://www.peachparts.com/shopforum/showthread.php?t=142400

Vacuum Pump Rebuild Thread
http://www.peachparts.com/shopforum/showthread.php?p=1927867

Have a great day.

Jim W. · #9 10-31-2006, 09:32 AM

Obviously it is too late in this case to know the parts positions at the vacuum pump's first disassembly, but it is a good lesson for anyone else who does this job. It is highly criticial to note the order, position and location of each component at disassembly so that reassembly is just a reverse of it. Good idea to have the diagrams available.

Jim W.

Tubber · #10 10-31-2006, 10:21 AM

Quote:

Originally Posted by unkl300d

are you sure the new membrane is intact? I believe there is a special way for installing these. The piston has to be fully extended, then you install membrane and bolt down.
not sure so check the archives.

Good Luck

Are you referring to the membrane that goes around the outside of the piston, like a type of piston ring? Its a type of "paper-like" material. I'm not sure its still intact. I placed it around the piston, and gently snugged it in the cylinder from the top using a little oil to lube it. I then pushed the arm through (compressing the spring) the top hole of the piston, and tightening the bolt onto the thread. I tightened the bolt down fully. Anything wrong with what I've done? First however I'd like to make sure my check valves are oriented correctly, then move on from there.

Thanks for your help

Blaine

threehunnertdee · #11 10-31-2006, 11:17 AM

I'm about to rebuild mine, I think. I have 5" reading at the brake booster at idle (with the check valve stuff removed and plugged). Revving the engine will bring it up to about 12". It seems to hold there, but leaks in the door/acc/etc are too much for it. When I first brought the car home it had 20" or so at idle off of the main line check valve.

Oh, does anyone know what the thing on the firewall under the driver's side wiper blade is? It has a black with red stripe vac line going to it (others as well, and some wires too) from the line with the little green dashpot near the IP. Sorry, I don't have a picture handy. That thing seems to be losing a lot of vacuum in my system.

Larry Delor · #12 11-01-2006, 07:00 PM

There are two types of pumps used. The earlier ones used a large round rubber membrane that was easy to get to and fix.
The "improved" design, is the one giving Tubber his troubles.

Sbean · #13 11-01-2006, 11:52 PM

You can drive a car without the brake booster functioning. You just have to push extra hard on the pedal. I did it for a while until I rebuilt the vacuum pump. Mine (1980 TD) has just 2 check valves, and you can tell by inspection which way each one faces. Steve

Tubber · #14 11-02-2006, 12:48 PM

Ok,

I'm still unclear about couple of things:

How tight do you tighten down the nut on the piston.

What way the check valves are oriented.

The vacuum appears to be the same pre and post rebuild; sporadic. This is causing rough shifting and the central locks don't work either. The pump is making enough vacuum that the engine shuts off with the key. I would just like to address the pump, then move on to other vacuum issues later.

I am almost positive that the check valves are oriented properly. I have no idea as to why I still have this problem. I've checked the link for rebuilding the 617 vacuum pump on this site and there seemed to be a problem with it leading to a wrong site. I understand its being worked on.

I am aware you can drive the car without the vacuum pump working properly, but the brakes are hard to depress and I think commuting that way would just set me up for problems......CRUNCH!!

Help!!!!!

Blaine

rrgrassi · #15 11-02-2006, 01:22 PM

Have you tested the check valves to make sure they are doing their jobs? They can crack from the heat and time spend in the engine compartment.

Do the locks work? Do the air vents blow properly, or do you get air flow through the defrost vents on the dash as well as the center vents?

When did you check the vacuum, engine hot or from a cold start?

Does the car have an EGR valve with out the test BB? Also, how are the lines in the black box on top of the valve cover?

Did you find engine oil in the lines? Have you tested the brake booster? IF engine oil was found in the lines it will wreak havoc on the booster.