BMW Differential - Have you had oil leaks from the output seals?

[Geoff Brown]

IMPORTANT UPDATE - DECEMBER 2016

At the Club Tech Forum held in November at Donington, Christine (Club chairperson) tabled a question on my behalf about the problem to Simon Lambert, Caterham Chief Technical Officer.

His reply indicated that CC are aware of the problem & that it is on the "to do list".

CCs investigation has highlighted that the very, very tiny float on the drive shafts pulls oil through the lip seal & that this occurs at low speeds.

My experience counters this as a slow-ish 20 mile trip round the block produces no dynamic leakage but a full bloodied, 'balls out blat' of about 50 miles or so produces said leakage.

Advice? None at the moment from CC as work in progress but  check that the hub nuts are tight at 274Nm.

 

Original Start of Thread

I am asking this question as not only have I experienced this problem but I think so have a few other members?

The latest occurrence is a brand new car fresh from IVA with less than 500 miles on the clock booked in at Williams Autos for rectification. This car belongs to one of my area members. Not happy.

The E46 Diff as fitted to BMW M3s has a history of slightly weeping from the output seals that can be lived with until a reasonably high mileage. The splattering of oil on the surrounding underbody  or indeed pooling on the lower part of the casing then dripping on to the ground when the car is static does not occur but seems to when fitted to a Seven..

So it would be great to tabulate any occurrences as I feel Caterham need to know.

I am not saying there is a conspiracy of silence from Caterham but there is a polite denial that the problem exists.

As with the lack of lubrication on pre-assembled front uprights that I high lighted some time ago once a thread is started the can of worms duly opens.............

FURTHER COMMENT:

I have been doing some research after comment about the fill quantity recommended could be 800ml.

The Diff is mounted in BMWs the other way up ie with the filler plug pointing down. So the installation in the Seven makes the BMW Diff upside down?!

This means the fill level is altered. Installed in a BMW the oil level when it dribbles out of the filler is JUST BELOW the output seal level & equates to about 800-900 ml. In a Seven the fill level is above or at the output seal level. Caterham quotes that the fill is 1.1-1.2 litres.

So are we overfilling our BMW Diffs? And of course some of us are then unlucky to get a leak.

I intend to suck out the existing Diff oil & refill with approximately 800ml & see what the results are. I understand that checking the oil level at service time could be difficult (no dribble) but I am going to concoct a flexible dip stick to enable me to check the 800ml mark. 

I estimate that the 800ml level is approximately 10-15mm below the filler point in the Seven installation..

Will post again in the near future with the results....leak or no leak.

UPDATE.

Sucked out 1l of existing Diff oil. Approximately 0.1/0.2 L has leaked out. Replaced with approximately 0.8 L of new oil & went for a 20 mile drive. STILL leaking but not as badly (due to the lower oil level).

Sigh...nice job changing both Diff output seals this Winter. Well what else would I do!

FURTHER UPDATE (16/10/2016)

With regard to Dave_H34s comment on page two. I ordered two replacement output shaft seals & they have the flexible spring 'Gitz' type seal installed to keep the lip in contact with the rotating shaft. Having a solid type lip seal support would not be practical.  I cannot see that the statement is correct?

In preparation for the seal change I have found that a 56mm socket is the perfect installation tool. Along with a two pound lump hammer for that precision fit!

UPDATE (16/11/2016)

Early start & changed output seals. Car back together in about 6 hours. Trouble is I did not just throw it back together but cleaned & lubricated everything as necessary including the roll bar drop links. So realistically the job for both sides could take about 4 hours without any hitches.

Car looked very majestic but 'fragile' high up on axle stands set at the third hole!

The must have tool to remove the seals is the  Draper Seal Puller available from Machine Mart. Looks like a double ended ice pick. Leverage against the casing pops the seals out. All I need now is a new windscreen to be able to test drive. (Pheasant strike at 50 mph which smashed glass & bent top of frame). 

ANOTHER UPDATE (11/07/2017)

As stated above the output seals were replaced on 16/11/2016 @ 13,150 miles. Car now at 14,535 only 1,385 elapsed miles but I am constantly monitoring the seals! No signs yet.

THREE YEAR UPDATE - (Nov 2019)

It has been three years & 10000 miles since the output seal change & all is still OK.

In my opinion several factors have determined why the replacement seals have not leaked:

• a subtle difference in the lip seal design
• a more robust metal flange which could resist flexing
• the new seals positioned further in to the casing as far as they could go against the originals which were almost flush with the outer rim of the diff seal housing
• new seal position being more inboard could have reduced the wear effect upon the lip seal caused by shaft rotational variation.

[aerobod - near CYYC]

The BMW diff used on the E46 M3 and E85 Z4M is not the same as the BMW diff used by Caterham (as used on BMW 316/320/520 and similar models). That being said the 90,000km I put on my Z4M left not a spot of oil on the output flanges, neither has any oil exited the output shaft seals on my 22,000km R400. Check that the seals are not pushed further than flush into the diff casing and that the diff is centred in the chassis such that there is even spring tension from the CV joints holding each drive shaft against the bearing face in the diff and fully seated in the seal.

[Jim 123]

Geoff, this may not be relevant, but I have some experience on Beemers where the diff will tend to leak if there is any small excess of oil inside the casing. Indeed I have seen BMW Service Instructions to the effect that on some models, a service refill of an existing diff should be less than the spec volume because of oil remaining inside the assembly. This might be a factor with Caterhams,  

As you know, the easiest way to access the filler/level plug is with a rear wheel removed, but if this is done with only the rear end in the air and not the front as well, you can put too much oil in.  When I initially filled my diff, there was a partial fill of oil already in the unit when it came out of the box. With all 4 wheels sitting level, I filled the diff and the unit took 0.2 litres less than the spec volume to come up to level. With only the rear wheels raised the unit would have swallowed 1.2 litres on top of what was already in the casing ex factory.

Having said all of the above, you've got me worried and I'm off to have a look under my car.

[Geoff Brown]

I am trying to create a dialogue about this problem as I know there is one but there is not much fact based evidence at the moment.

I am aware of all the consequences of not having the diff centred or the output seals not flush but these are not an issue with my car or that of others.

The oil level issue is interesting as I have been thinking that the tried & tested Diff oil level check with the car level  for oil to dribble out of the filler/level point may be incorrect. So I am considering allowing the oil to continue to leak until it stops which does not suggest that there is no oil in the diff but that the level is now 'correct'.

This suggests that the tried & tested Diff oil level check may be actually overfilling the Diff.

None the less I will change the seals over the Winter & then see what transpires.. 

[mikecocker]

When I was supplied with my latest backplate 3 years ago, it came with instructions to only use 800ml of oil and not to use the fill hole as a level. From memory, it was about 10 mm below the plug.

[Dave J]

it's a 1 series diff not M3

to test before going to all the hassle os changing seals - why not suck the oil out and refill with the specified amount ?. I wouldn't gamble with running it possibly dry.

[Jim 123]

Ebay has 200ml syringes with plastic tube attachments which are pretty handy if Dave's suggestion is an option to be explored.

[ScottR400D]

My R400 has now done 3500 miles. From build it was filled to the edge of the filler hole with Comma oil. A couple of weeks ago I refilled with Redline, again until it overflowed. 

Cars done 3 TDs in its mileage, including one last week, after the oil change  

No leaks, so far. 

 

[Dr Slotter]

My car was one of the first to be fitted with the BMW diff and never had any leaks. It's been refilled at least once.

[dave_h34]

Yep mine leaks. I'm pretty sure it didn't with the open diff the car came with but after fitting an LSD 6 weeks or so back I now get 1 or 2 drops on the underside of the diff after a drive with the fluid having come down from the drive shaft seals. It doesn't drip onto the garage floor, and doesn't leak when not in use. I'm not sure what to do about it tbh, the place that fitted the diff said 'yeah, that can happen'.

[dave_h34]

And btw Dr Slotter, how old is your car? Would my 2009 car have had the BMW diff from build?

[Dr Slotter]

Mine was built in May 2009 and CC seem to think it had the old-style Ford diff in it for a few months and then got swapped (previous owner).

[wjblundell]

I built my car in 2010 and the kit came with the Ford diff which I found to be appallingly noisy. After a number of visits to CCM I did a deal with them for the BMW replacement which required a mounting adaptor to fit the smaller unit. Problems arose around this adaptor with cracks, loosening bolts and in my case a damaged brake line on top of the DeDion tube. A mk 2 adaptor was fitted to all the Academy cars and were made available for others. After hearing about a mk 3 adaptor I decided to wait for this solution on the basis that the mk 3 would be an improvement on the mk 2 and so it proved. CC provided the kit to Kenricks in Llangollen who fitted it at no cost to myself. It has been used since then without any problem, so much quieter than the Ford unit and certainly no oil leaks. I'm sure plenty of posts can be found around 2011/12 providing more info.

 

 

 

[DJ.]

I built my car in 2011 and it has a Ford diff, they announced the change after my kit was delivered.

[dave_h34]

Curious! On a different but related note, where is the breather on a BMW diff?

[Dr Slotter]

Presumably CC definition of a 'few' is more than mine is! It certainly had it by the end of 2011. My car went through a similar process at CC Midlands to the one wjblundell described a few posts ago.

[BurwellSupersport]

Hi,

Same problem here.  Local (non caterham specialist) has had my Supersport back 5 times in the last 12 months after they identified the leak on the output seals of my BMW diff.  After replacing the seals each (and every) time we ended up modifying the breather to make the hole bigger and add a decent length of pipe, unfortunately it still leaks.

Am intregued about the idea of reducing the amount of oil in the diff, yes it would take it below the level of the output seals  (eliminating the opportunity for leaks?) but how would you then check whether it had lost further fluid?

I'm not sure if I compound the problem by storing the car slightly nose high (circa 10 degrees).

Incidentally I also have a slow gearbox leak which may also be influenced by the attitude of the car.

Mike

[dave_h34]

Received some more information on this today. Apparently when the diff is installed in a BMW there's a spring spacer/circlip type arrangement to keep pressure on the seal as the driveshafts move. In the Caterham installation this is omitted and replaced with a plane spacer. Therefore if the driveshafts are moving, I guess bumps, hard cornering, donuts(!) etc, a small amount of oil can ease out. No cure apparently as the driveshaft would need to be modded to include the spring element.

[BurwellSupersport]

This fits with my thinking as whenever the garage take a test drive (after replacing seals) its fine and yet when I drive it (maybe slightly more energetically) it leaks.  I guess the question is 'what happens next' just accept it and top up occasionally?

Your news does help though as it puts my mind at rest about volume of oil being lost and the risk of running it dry.

Thanks!

[dave_h34]

Anyone have further info or revelations? Following the 60th event the chassis and fuel tank on my car are now both liberally coated in diff oil!

[Geoff Brown]

Get those drive shaft output seals changed !

dave_h34 if you want advice or guidance on the job PM me.

[dave_h34]

They're only 9 months old! Did you have success after changing yours Geoff?