1976 300d fuel filter - PeachParts Mercedes-Benz Forum

1976300d · #1 10-01-2008, 02:10 PM

hi there...

can anyone tell me how to replace the main canister filter on a 76 300d?

it is the older body style not the 123...

once you clean and replace the filter and fill the canister with diesel, do you have to bleed it?

if so, where is the priming pump on these things? what does it look like?

thanks for any help

Diesel911 · #2 10-01-2008, 03:41 PM

Do not start the car until the air is purged out.
You will need to bleed the air out of the system. The Hand Priming Pump is on top of the Fuel Supply Pump on the side of the Fuel Injection Pump.

To find the Fuel Supply Pump trace the hose from the filter back to it. The Hand Primer will look like a 3 inch long Aluminum tube with a hard plastic knob on it. Unscrew the knob only and pull up on it. Pumping it up and down pumps fuel through the Filter and Fuel Injection pump. When you are done push it all the way down and screw it snug to prevent air leaks.

If you do not see the 3 inch Aluminum tube you may have the updated type of hand primer covered with a Black or Gray rubbery substance. With this on you only have to push down on it and let the return spring bring it back up and keep doing that to prime the system. When you are done just leave it alone.

How many times to pump? If you listen carefully you will hear a buzzing or faint squealing sound as the air is purged out. After you hear that sound and it is quiet you can stop pumping and start the car.

If you want to see what the parts look like try going to one of the online parts sellers and doing a parts search; they often have pictures.

Diesel911 · #3 10-01-2008, 04:07 PM

How to replace:
From the pic (not the spin on filter) at this site it looks like you open the Drain bolt on bottom of the filter and drain out the old Fuel into a suitable container and close the plug back on.
You remove the central bolt and remove the cover to gain access to the Fuel Filter Element. Yank out the old filter and put in the new one. Put on the new gaskets/O-rings as needed. Install new filter and fill canister with clean Diesel Fuel (or prepare to do a lot of pumping with the hand primer). Put the Filter Housing Lid back on with the proper gaskets/O-rings and the Central bolt tight.

http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=123130&M=617%2E912&GA=722%2E118405&GM=716%2E005++++++++++++++717%2E400&CT=M&cat=143&SID=07&SGR=120&SGN=04

The Fuel Supply Pump is item #305 and the thing sticking up from the supply pump is the Hand Primer.
http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=123130&M=617%2E912&GA=722%2E118405&GM=716%2E005++++++++++++++717%2E400&CT=M&cat=143&SID=07&SGR=045&SGN=01

Palangi · #4 10-01-2008, 09:18 PM

A 76 300D might have the disc style primer pump, mounted on the side of the filter canister.

1976300d · #5 10-02-2008, 02:42 AM

ok thanks 911 and palangi... i will take a look tomorrow...

also, it doesn't look like there is a prefilter where the manual says there should be one... is that installed by mercedes, or is it an aftermarket thing when running biodiesel?

pizzachef · #6 10-02-2008, 10:06 AM

I have a pre-filter on my '74, I would think you'd need one to protect the lift pump, a small clear plastic in-line filter right before the lift pump. You'll need a short piece of fuel line and two more hose clamps to install a filter there if you don't already have one.

1976300d · #7 10-03-2008, 04:37 PM

hi again...

thanx for the responses so far....

i'm trying to post some pics here to see if anyone can help me further...

pic 1 shows what i am pretty sure is the manual pump, attached to the canister filter...

pic 2 shows a picture of something that looks like a prefilter, but my knowledge of engines is dismal, so i don't know what it attaches to...

pic 3 shows another identical filter-type thing, which looks like it goes to the manifold?, so makes me wonder if the filter in pic 2 isn't a fuel filter...

any ideas?

1976300d · #8 10-03-2008, 04:38 PM

sorry i think the pics are in reverse in previous post ie pic 1= pic 3

Palangi · #9 10-03-2008, 08:49 PM

The third picture (merc fuel filter 3.jpg) the arrow is pointing to the primer pump. Push down on it to pump. The other pictures show check valves in the vacuum lines.

Diesel911 · #10 10-04-2008, 01:45 AM

The hose going to the Power Brake Booster is a Vacuum Hose/Line.
The Hose comming from the Intake Manifold to the front of the Engine and most likely the Inlet/Intake Air Hose/Line for the Vacuum Pump.

The 2 hoses with the; the ones the other Member said have the check valves in them should go to the Vacuum Pump. Click on the picture and enlarge it.

http://www.***************/search/product.aspx?sid=hzo31d5550ncxx553jidel55&makeid=800016@Mercedes&modelid=1193666@300D&year=1976&cid=vacuum@vacuum&gid=5172@Vacuum%20Pump

pizzachef · #11 10-04-2008, 09:47 AM

Okay, you have the different style primer pump, so I can't say for sure, but in the third picture...with the arrow pointing to the primer pump...there is a banjo bolt on the side of the primer pump to which a fuel line is attached. The other end of that fuel line should eventually disappear under the car and go back to the tank. If you need a pre-filter, this is the fuel line that should have it. It goes upstream of the primer pump to protect it.
However, I don't have the same kind of primer pump as you, so I can't say for sure if you have/need the pre-filter...I assume you would.
Fastlane has a part listed here.

1976300d · #12 10-05-2008, 03:48 PM

ok... thanks again for all the help...

i'm gonna follow the line that goes into the manual primer pump back towards the fuel tank to see if there is a prefilter along there somewheres...

if i have to replace the prefilter, how do i prime it?.. do i just fill it with diesel before i put it on and pump the priming pump afterwards to bleed any air?

do these priming pumps auto-bleed somewhere or do i have to open a bleed valve somewhere to let the air out?

Diesel911 · #13 10-05-2008, 07:43 PM

The pre-filter should be between the Fuel Supply Pump on the side if the Fuel Injection Pump and the Fuel tank. On later models it is within 6 inches of the Fuel Supply Pump. Assuming it is a plastic fuel filter like the later models there is no way to prime (pre-fill it) other than to pump on that Primer on the Filter Housing.

If you fill up the large filter housing with Diesel when you change the filter and pump a lot on the hand primer that may get all of the air out or it may not.

If after you have done the above and your car still dose not want to start; loosen the Fuel Injector Hard Line Nuts at the Injectors and crank the engine to bleed the air out. you will see fuel coming out up by the Injectors. When you see that tighten up the Injector nuts and start the car.

While the Fuel Injection Pump can bleed off small amounts of air (more so if the Engine is already running) I would not say it is self bleeding. If you get Air in the Fuel Injection Hard Lines between the Fuel Injection Pump and the Injectors it is extremely difficult and hard on your battery/starter to bleed that air out by cranking the engine.

The reason is that the Injector works like spring loaded. The Valve/Injector will not open until the pressure it is set to (in your case I believe it is 115 bar).

Air in the Injector Hard line is trapped between the Injector and the Fuel Injection Pump and when the Fuel Injection Pump Plunger tries to push the Air out it mostly compresses it and pushes little if any out of the Fuel Injector.

To get the air out of the Fuel Injector Hard lines as I have said above: you loosen the Injector Hard Line Nuts and crank the Engine until you see a good amount of fuel coming out. Since the Injector Lines are open at one end the Air is no longer trapped and the fuel can move through the line.

The first time you do this it is nice to have a Battery Charger or another running Car with a good battery that you can get a "Jump" from incase your Battery gets low.

bhahl · #14 10-06-2008, 10:47 AM

The other filter you are looking for is hard to find. I just found mine this year when I was doing a diesel purge. If you look down past the canister filter you should be able to find it, otherwise you might have to remove the battery to get a better view.

1976300d · #15 10-07-2008, 05:18 AM

ok thanks again for all the help...

i am off to help my buddy with his house 14 hours from here... i was hoping to take the mercedes on its first trip, but it will have to be the next one... i put about 10L of bio-diesel in to half a tank of regular ol' stanky diesel, so i guess that makes it about 25% mix?

will try to find the prefilter under the battery when i get back, get all that changed out, get it insured and let you guys know the results...