differential leaking

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Meagnew

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hello,
Gotta leaky differential problem in my '70 2800cs. I bought the car about a month ago and it had been leaking just a few drops in the garage. After a 150 mile trip to the city this past weekend, the diff seemed to leak more so I decided to inspect. I checked the level and it was real low so I changed the oil and added new washers on the drain plug bolts. The oil was so low only 1/2 quart was drained when changed. It was very dark colored and had a burnt smell to it. Hopefully there is no serious damage to the differential resulting from low oil. It never seemed to make any bad sounds, however oil is all over the rear muffler and drive shafts.

After a de-greasing job I think I found the leak. It seems to be where the propeller shaft attaches to the diff. I know it is a pain in the ass to change the seal in there from reading the repair manual. Also, the previous owner changed the seal already. He told me that it might be leaking from the top of the differential from the venting tube, although he admits that he might be thinking about his Porsche differential he had worked on. I think it might be leaking from both places since there it lots of oil on top.


My diff is the original one that came with the 2800cs (3.45). The car now has a ’85 535i engine and transmission. So my question is: take out the differential and repair the seal myself or find one to replace? Considering that the previous owner had already replaced the seal and it might be on the verge of failing, I think it might be time for a new one. What ratio would work best with the 5 series engine and transmission? Thanks for your help.
-Max
 
Hi Max

I'll throw some stuff out for you to think about

If the oil smelled "burnt" do you have a limited slip differential in the car?
If you do you must use LSD oil in it or it won't work properly.
Several checks here include looking for an "S" painted or stamped on the casing.
A tube from the top going to a "can" and back in
Jack the back end off the ground turn one wheel, does the opposite one turn in the same direction - yes you have an LSD no - you don't
Sounds like the output shaft seals are leaking too.
They don't actually hold that much oil - can't remember exactly how much right now maybe.... a litre... sombody will know

Next

Yes your right - to change the seals on the diff is a pain in the behind but to make life much easier remove it from the car!!!
1.. Jack up car at rear support really well!
2... Mark relationship between propshaft and flange on diff.
3... Mark relkationship between drive shafts and diff output flanges
4... Unbolt driveshaft flanges at diff
5... Unbolt propshaft from front of diff
6...Support diff with trolley jack.
7... Unbolt diff from rear subframe 8 bolts
8... Unbolt from rear bush
8... lower diff to ground.




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NOTE : I removed the driveshafts completely but you should not have to do that

In the immortal words of the Haynes manual - assembly is the reverse of dissassembly!!!

Oh dear was it that long ago? :roll:

Next

In regard to ratio's it depends on the driving your doing, and your style of driving. However to find complete, good diffs is getting harder and many have lots of miles on them, I believe you can get them exchange.

While E9 casings are different to later BMW ones many of the internal parts are the same, thus it is possible to fit a crown wheel and pinion from say an E28. However there is a lot of set up work to do and you need a lot of special tools etc

HTH
Malc
 
Diff Seals

You should be able to change the output seals without removing the diff. remove the half shafts (6 bolts each side). The side shafts on the diff can be pryed off by placing a pry bar between the flange and the diff body.

The seals can be removed and new ones pushed back in place. Be careful not to dent the seals when installing. Insert the side shafts back into the diff and rotate slightly to align the splines. Tap back in until you feel them snap.

Tom
 
Leaker

It would be a shame to scrap a diff that may not be shot. However, since the PO indicated that he changed the seals and it's still leaking, something doesn't sound right. Since there are unknowns in your case, I think a close inspection is in order. Remove the diff, remove all seals and INSPECT ALL SEALING SURFACES CLOSELY for nicks and irregularities on the shaft where the seal makes contact. If there are deep nicks, scratches and/or grooves you may have to use a "speedy sleeve" to bring back the surface finish to where it should be. Sometimes the use of a different manufacturers seal will bring the contact point on a "fresh" surface of the shaft. But, above and beyond that, you should check all aspects of play in the shafts as they relate to the amount of backlash(lost motion in rotation) in the gearing as well as radial play indicating wear characteristics and proper bearing clearances. All the numbers are in the manuals. If you notice anything extreme backlashwise, then you may suspect some compromise of the gearset which can only be confirmed 100% by cracking the case open and then really having some fun.

Good Luck!
 
Re: Diff Seals

You should be able to change the output seals without removing the diff. remove the half shafts (6 bolts each side). The side shafts on the diff can be pryed off by placing a pry bar between the flange and the diff body.
Click to expand...

There's a bolt in the middle of the flange that has to come out to pull the output shafts. You're right, output shaft seals are an easy job.
 
Thanks for the help

pulled out the diff and changed all the seals. I think it was only leaking from the driveshaft input seel. The main bolt holding the input flange was not torqued properly. It was no where near the 108 ft-lbs. So this is why it was leaking. Hasn't made a drop yet, hope it lasts. Thanks again for all the help
-Max
 
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