Differential leak - PeachParts Mercedes-Benz Forum

psaboic · #1 05-25-2019, 12:07 AM

Folks today, after being parked for about an hour after a 25 mile drive, I noticed about a 1.5 to 2 inch puddle of gear oil under the car. Crawling under and taking a look, it appears the Differential front (pinion) seal is leaking. Is there a good DIY somewhere I can use to go about changing the seal? I know all about the special socket needed for the flange nut, and loosening the driveshaft (especially since I just replaced the center driveshaft bearing about 350 miles ago), but once the flange nut is removed, does the flange slide off, or is it pressed on?

Or would it be less hassle (yet more costly) just to swap out the whole damn differential.

psaboic · #2 05-25-2019, 12:08 AM

Oh yes, this is on my 1983 300D

Squiggle Dog · #3 05-25-2019, 04:59 PM

In most cases the yoke slides right off by hand. If it happens to be rusted on, I imagine it would only take a blow or two on the back of the yoke with a hammer. BEFORE you remove the yoke nut, remove the rear wheels and make sure the brakes aren't dragging, then take a lb-in beam style torque wrench and put it on the yoke nut and turn it clockwise slowly and steadily and write it down the amount of force it takes to rotate it. When you install the nut back on, you'll want to tighten it down until there is the same amount of resistance read when turning the yoke nut.

Unfortunately, if the bearings have worn (which is likely), then they are probably too loose right now, and when tightening the yoke nut so the yoke has the same amount of turning resistance as there is now, the bearings will likely also be too lose again. But, the problem is there is no way of knowing if your yoke bearings were too loose before without removing the axle shafts, so all you are doing is setting the friction to what it was before, even if it was too little.

When I replaced my pinion yoke seal, I did it with the axle shafts removed. The manual wants you to do it with the internal gear set removed as well and to set the friction between 50-100ncm for used bearings, but I found that the gear set only adds about 25ncm of friction to the whole unit, so setting the bearing friction between 75-100ncm with the gear set installed should be fine.

In my case I found that my pinion bearings had no preload on them at all, so I'm glad I had the differential removed, because I would have had no way of knowing this otherwise.

I got this Performance Tool lb-in torque wrench at AutoZone for $25. The Massive flange too was useful for holding the yoke when cranking down the yoke nut, which requires a lot of force.

Be aware that the yoke's seal surface can wear a groove into it which can cause leaks, even with a new seal.

psaboic · #4 05-25-2019, 09:26 PM

Squiggle Dog: Thank you for the great advice and pictures. It looks fairly straight forward for the most part. I guess the thing that aggravates me the most is that I am going to have to remove the driveshaft or at least disconnect it again after just replacing the center bearing and mount less that 500 miles ago. I checked the diff when I did that job and it was dry, so the leak just started in the last 100 miles or so.

One question, it looks like the job can be done with the differential on the car. Do you happen to know if you can remove the slotted flange nut on the car, or is it cranked down so tight you need a breaker bar and something to hold the flange from turning to get it off.

Squiggle Dog · #5 05-26-2019, 03:48 PM

You might want to check the breather valve to make sure it's not clogged and causing pressure to build up which is forcing oil out of the seals. But, it's still likely the pinion seal needs replacing.

Removing the slotted flange nut shouldn't be a big deal. I had a really hard time unstaking the nut because I couldn't get anything underneath the tab to bend it out. But, after putting a screwdriver against one of the slots and hitting it with a hammer, the nut rotated without much force. You'll want to have the rear wheels on the ground or the parking brake engaged to keep the yoke from turning if you don't have a way to hold it.

When it comes to tightening the yoke nut, you'll probably want a yoke holder because it requires a breaker bar and tremendous force to tighten the new nut before you stake it. You'll have to constantly check the friction by turning the pinion with a lb-in beam type torque wrench until you have the same amount of force required to rotate it as it took before, under the same conditions (wheels off the ground and parking brake released).

Be aware that very tiny increments of tightening can make a huge difference in friction, and if you go too far, you can't simply loosen the nut and try again, because there is a crush sleeve behind the yoke which compresses with tightening, and it would need to be replaced--however you have to take the gear set out of the differential in order to do so, which may require a tool that stretches the housing.

psaboic · #6 05-26-2019, 11:02 PM

Never thought to check the breather valve.....In fact, I never even looked for it when I was under the car. Is the breather valve on the top of the differential case? How hard is it to remove? I have one on a 65 Corvair that was a real Beee-atch to remove.

Clemson88 · #7 05-27-2019, 03:35 PM

I changed the yoke on a w126 while on the car. The FSM says to remove the wheels, brake calipers and rotors and set the axles on jack stands level with the differential to measure the rotational friction.

I had to make a device to hold the yoke while I loosened the nut. It looked a lot like the one in the FSM but it was made of aluminum angle.

psaboic · #8 05-27-2019, 10:54 PM

Correct me if I am wrong. I was in a discussion with another MB enthusiast today and was discussing my current differential issue. I mentioned that outside of possibly different ratios, 300D/TD/CD differentials interchange, as well as 300D and 300SD/SDL differentials. In fact, they have the same part number for the differential case, cover, etc.....

They told me I was crazy....

Squiggle Dog · #9 05-28-2019, 02:10 AM

Quote:

Originally Posted by psaboic

Correct me if I am wrong. I was in a discussion with another MB enthusiast today and was discussing my current differential issue. I mentioned that outside of possibly different ratios, 300D/TD/CD differentials interchange, as well as 300D and 300SD/SDL differentials. In fact, they have the same part number for the differential case, cover, etc.....

They told me I was crazy....

Yeah, just as long as the gear ratio is the same, it should fit (unless it's a second generation W126 which uses a different mounting configuration). Some people like to upgrade to a taller gear ratio, though. The differential in my 1980 W116 300SD came out of a 1981 W126 300SD. There are different widths of differentials which require different axle shaft lengths, BUT that seems to have more to do with the gear ratio than the chassis. Axle shafts are different lengths between the W123 and the W116 and W126 as they have a wider wheel track.

Also, the breather valve is mounted at the top of the differential cover. To remove it, you just need a 17mm wrench, I think. I think it also has tapered threads and no crush washer. You can clean it in diesel/biodiesel/degreaser and blow through it from the bottom with compressed air until it flows freely.

psaboic · #10 05-28-2019, 10:45 AM

Yep, got the breather valve out. Looked ok, but didn't flow a lot of air, so I cleaned it out. Flows better so I re-installed it. We shall see.......my game plan is this.......see if the breather valve helps. If not, next is do the pinion seal. If that turns out to be a huge PITA with the nut, preload, etc......I'll just look for a replacement differential.

Diesel911 · #11 05-28-2019, 11:00 AM

You need to be carful of your newish Drive Shaft Support when manipulating the Drive Shaft. I tore the rubber on mine moving the Drive Shaft so that I would have room to one of the Trailing Arm Bolts.

Concerning the special Nut on the Pinion. If you obtain a new one people have said the new ones are the normal hex head type of nut that you won't need the special socket for.

Once you know you have a solid source of the normal hex nut you can use a punch to loosen the special Nut. That will deform it but you already know where you can get the new hex type that does not need the special socket.

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Diesel911 · #12 05-28-2019, 11:01 AM

Before you drain out the Differential Oil be sure you can loosen the Fill Plug as it is often a tough job to loosen it.

psaboic · #13 05-31-2019, 10:24 AM

Ok, So I am gathering all the parts and tools together to replace the leaky pinion shaft seal. My question now concerns the special nut that holds the flange on to the pinion.

I would like to take the nut off using a punch and hammer vice paying for the special tool. Since this method is apt to damage the nut, can anyone tell me where to score a replacement nut, preferably the normal hex head type?

That is the only thing (besides time) that is holding me back right now.

Thanks

Diesel911 · #14 05-31-2019, 02:13 PM

Quote:

Originally Posted by psaboic

Ok, So I am gathering all the parts and tools together to replace the leaky pinion shaft seal. My question now concerns the special nut that holds the flange on to the pinion.

I would like to take the nut off using a punch and hammer vice paying for the special tool. Since this method is apt to damage the nut, can anyone tell me where to score a replacement nut, preferably the normal hex head type?

That is the only thing (besides time) that is holding me back right now.

Thanks

Did Pelicanparts have it?

vox_incognita · #15 05-31-2019, 04:54 PM

A1233530072 - nut
115 589 01 07 00 - pin wrench socket
Nut can be had for $8-$15
Socket - $60 and up.
Or (have smb.) build your own,dimensions are everywhere.

I personally would not hammer the flange nut.

P.S.It must be on this forum that I've seen the idea of a grooved disc attached to the flange+a cord+ a fisherman's electronic scale for measuring the friction (better consistency of reading especially if it "holds" the peak value).