Mercedes-Benz Forum banner

1 - 14 of 14 Posts

·
Registered
1986 Unimog U1700L (435 series)
Joined
·
302 Posts
Discussion Starter #1
Hello,

I notice that the bell housing has what appear to be 3 plugs (same size as oil drain/fill plugs in the transfer case/gearbox housing).

Two at low level and one part way up.

Does anyone know what they are for. I could hazard a guess that two of them are to drain any crap that could get in their from leaking seals? But whats the one that's almost 1/2 way up for I wonder? Maybe an inspection hole? What would I be looking for?
 

·
Registered
1988 U1300
Joined
·
52 Posts
The PTO box on my 1300 has two drain holes and of course one fill. One of the drains is at the lowest and narrowest portion of the casing and is hard to find unless you're crawling under the truck with a good light. I cannot access the lowest plug with an allen wrench without removing a suspension piece. So that's 3 for the PTO box. If you are looking at another lower drain on the front facing of the bell housing, that one is an inspection port for the clutch. The advice I took away from my reading here is that you are encouraged to leave this one open with the plug in the truck unless you are fording. Keeping it open, or opening it often. allows any residue from an RMS leak to find atmosphere vs nesting in your clutch goodies.

At first I was reluctant to fill the PTO box when completing the fluid change, so looked at some photos of PTO boxes on this site's predecessor (now that it's been new and improved I can't seem to find anything) to confirm that I wasn't filling the clutch with hydraulic fluid.
 

·
Unimog Moderator
250GD Wolf
Joined
·
13,074 Posts
Picture is worth a thousand something or others, but if I remember right, there is one drain, and two fills, one fill is for "when installed in MB Trac", but that should be cast into the housing.
 

·
Registered
U1450L DOKA
Joined
·
9,589 Posts
Here are some shots of dismounted PTO boxes. You can see the MB TRAC / UNIMOG designations, cast into the housing.
2606723
2606724
2606725
2606726
2606727
2606728
2606729
2606730
2606731
2606732
 

·
Registered
U1450L DOKA
Joined
·
9,589 Posts
By contrast, here are some shots of the standard Bellhousing, which is in place on UNIMOGs that have neither
2606735
2606736
2606737
2606739
2606741
2606742
2606743
2606744
2606745
the PTO box nor the Claas Overdrive.

And, a couple of shots of the clutch and that side of the equation.
 

·
Registered
1988 U1300
Joined
·
52 Posts
Super crappy photos that I took when I got the truck and was wondering as Jason is 'what was what'. Following up on my comment regarding two drain and one fill holes on my 1300, the photo with two plugs visible shows the fill (covered in fluid toward the right of the photo and was like this when I got it), and the dry one is the drain. Getting gear oil in unless the bed is off can be a PIA and it was likely spilled on an earlier fill.

The other photo shows the bottom drain under the smaller portion of the PTO casting that juts out as per Trucktor's first photo. This one I cannot get a tool on without removing pieces from the suspension. I drained from the side mounted drain hole and filled the proper capacity of gear oil into the higher one so I think I got it right.

Hopefully there's no 2nd fill hole cuz' that means I overlooked filling somewhere. But I've not used the pto so there's still time to avoid an expensive bonehead event.

Cheers!
mainptodrain.JPG
clutch.jpg


2606759
2606760
 

·
Registered
1986 Unimog U1700L (435 series)
Joined
·
302 Posts
Discussion Starter #7
Hi everyone. According to wonderful photos by Truktor of inside casings:
  • The two on the rear end of the housing (photos 994 and 995) must be oil fill and drain respectively for the drive output. Fill plug having 'Unimog' embossed next to it.
  • The lower plug in photo 998 appears to on be the actual clutch housing. This one is presumably the inspection (and for draining any seal leaks etc).
  • Then I found a 4th plug hidden up above the sway bar (photos 999 and 555 (I copied one of Truktors photos)) on the PTO gear area. Its an oil drain plug and not visible in the photo, but its there. As Daytonecoupe66 mentions, its impossible to get at without removing the sway bar. However, I could not see a fill point for this gearbox (unless its filled by the plug in photo 994 ?).
Descriptions in the manual to pick from are: Hydrostat 17 Litres, PTO shaft drive 5.75 or 8.0 litres, lock up torque converter (sounds like an automatic version ?) 17.5 litres. Photos are in the order I first mention them above.

InkedPICT0994_LI.jpg InkedPICT0995_LI.jpg InkedPICT0998_LI.jpg InkedPICT0999_LI.jpg Inked555_LI.jpg
 

·
Registered
1986 Unimog U1700L (435 series)
Joined
·
302 Posts
Discussion Starter #9
Hi Chas,

I guess what you are saying is that the PTO takeoff gearbox section is joined internally to the gearbox section on the rear of the clutch, and both get filled by the one fill point which is marked with 'UNIMOG' embossing.

My next step is to try and work out the oil quantities for each, so I can publish it on my web site. The below photo is of the Unimog filling capacities. Its clear as to what most assemblies are (eg: engine, main gearbox/transfer case, axles, steering, brakes, grease and winch) but the PTO/clutch gearbox are a mystery for me still. It should not be this hard to figure out.
PICT1001.JPG
 

·
Registered
1991 1250L Doka Unimog, 2002 ML320
Joined
·
1,183 Posts
I'll look it up in my books, but, basically fill until it is full. Like many things on the Mog, I fill slowly until it starts coming back out the fill hole. I'm thinking it was 11 or 12 quarts/liters. It's dark and cold here so when the sun comes out I'll check if I have my amounts. Others much smarter than me can chime in.
Chas
 

·
Registered
1991 1250L Doka Unimog, 2002 ML320
Joined
·
1,183 Posts
Here are a couple really bad photos.....I'm no TRUKTOR......

Not sure why the two different amounts. Mine took the higher.
IMG_5977.JPG
IMG_5978.JPG

Chas
 

·
Registered
1986 Unimog U1700L (435 series)
Joined
·
302 Posts
Discussion Starter #12 (Edited)
This table of details, is where I am up to.
As one will note, I am still unclear about the clutch converter (if thats what its called, also seems to be called a hydrostat ?) box and for PTO transmission box? They seem to be listed as two different boxes, but discussions on this site imply that they are joined inside. If joined inside, then the PTO box only needs a drain (which is located just above the sway bar). If however, they are different boxes, then the PTO box must have a fill plug somewhere?

InkedU1700 oils summary for web site_LI.jpg
 

·
Unimog Moderator
250GD Wolf
Joined
·
13,074 Posts
If that's Hydrostatic in the oils listing, its a whole different monster, if you do not have a joystick to drive forward and reverse on your dash then you do not have a hydrostat. you can ignore that as well as the torque converter clutch which I assume is that other one (torque converters are often found on aircraft tug unimogs or train shunt unimogs). The manual might be covering all options, some of which your Unimog might not have.

Some good reading on SBU/MBU hydrostatic systems here:

 

·
Registered
1986 Unimog U1700L (435 series)
Joined
·
302 Posts
Discussion Starter #14
Thanks tkv000.
I think I'm sorted now. I'm assuming that the 5.75 litres is for the combined clutch and PTO.
 
1 - 14 of 14 Posts
Top