Final Drive fluid capacity

[Illini]

I've got an 06'RT that had a whole driveline replaced when I had a seal blow out in the original final drive. (The original had the drain plug in the 9'O clock position and had to drop the final drive down to drain completely-The newer final drive has the drain plug at the 6'0clock position for a better drain. I disconnected the drive line anyway to moly lube the splines) I'm doing a fluid change and asked my dealer for a capacity spec. and was informed that the fatherland is no longer recommending 22ml (7.2 fluid oz. for USA) but rather 18ml through a PUMA (????) bulletin. Seems the 22 ml. was building up too much pressure and causing seals to fail. Can anyone with access to service Bulletins verify this?? I've done a search and this didn't pop up. Thanks in advance

[Twisties]

[Marty Hill]

Verified on advrider a week ago by two dealer employees. Go there and see the multi page thread in g-spot.

[Illini]

Sorry but my capacities are way off, let me try again (I can't seem to edit my original post) It should read 212ml or 7.2 Fluid OZ. (not 22ml) AND THE PUMA DISCUSSION RECOMMENDS 180ML (NOT 18) 6.086524 fluid oz. SORRY FOR THE INCORRECT FIGURES!

 

I just returned from my dealer and he showed me the PUMA which discussed heat build up and pressure from too much fluid in the final drive. So BMW has revised it's refill recommendations. On a normal fluid drain and refill use 180ml not 212ml!

[mneblett]

Sorry but my capacities are way off, let me try again (I can't seem to edit my original post) It should read 212ml or 7.2 Fluid OZ. (not 22ml) AND THE PUMA DISCUSSION RECOMMENDS 180ML (NOT 18) 6.086524 fluid oz. SORRY FOR THE INCORRECT FIGURES!

 

I just returned from my dealer and he showed me the PUMA which discussed heat build up and pressure from too much fluid in the final drive. So BMW has revised it's refill recommendations. On a normal fluid drain and refill use 180ml not 212ml!

 

Just a nit correction -- I eye-balled both the old and new maintenance docs over my service manager's shoulder (when I asked him about the change, he wasn't aware and wanted to check it out himself). The original fill level was "0.22l" (220 ml). The 0.18l (180 ml) number is spot on.

 

Best,

Mark

Illini Class of '80

[JayW]

So BMW has revised it's refill recommendations...

 

I am now a believer, and used the new recommended lower volume with my most recent FD fluid change.

It seems legit.

 

Jay

[Redbrick]

It's 180 ml's now which looks like maybe 6 tablespoons full.. ......But I couldn't stand it; put in 200 when I changed it a couple of weeks ago....

[RodB]

According to the R1200 maintenance DVD purchased from a member here; the capacity is 250ml - so now you say it has gone done to 180ml; that is quite a difference.

[JayW]

Yeah, I'm not sure where Jim got that 250cc volume from. I am not aware of any other source that ever recommended that much. He is pretty knowledgeable though, so he must have gotten it from somewhere he trusted. It is no longer valid either way.

 

Jay

[marcopolo]

The service bulletin with the new fill volume was posted on the MOA forums. Indeed the new amount of fluid for an oil change in the FD is 180 ml, and the interval is every 12,000 miles, or two years. I copied the service bulletin and saved it. I also have a service bulletin from early 2005 concerning the hexhead FD. The fill quantity in that 2005 bulletin was 250 ml for an initial fill, i.e., a new drive, and 230 ml for an oil change.

 

For those who are really keen, here's the text of the latest bulletin:

 

Measure no. Subject

 

US 23342824-01 Increased wear in the rear-wheel drive

 

Status date (mm/dd/yy) Status PQM Problem reference

 

4/15/09 Accepted

 

Date created (mm/dd/yy) Created by Organization

 

4/15/09 Rainer Wanninger US, MOT

 

Release date (mm/dd/yy) Approved by Dealer release

 

Allow automatic release

 

Vehicles affected

 

E series Engine Body

 

K25 K25/02 K25/03 K25/11 K25/12

K25/HP K26 K26/02 K27 K28

K29 K29/HP K40 K40/11 K43

K43/11 K43/HV K44 K44/31

 

Production period (from/to) Feedback (all cases relating to

(mm/dd/yy) Comment on production period measure up to) (mm/dd/yy)

/

 

Complaint

 

The rear-wheel drive displays premature wear in the form of leaking shaft sealing rings or an increased bearing clearance.

 

 

Cause

 

1. Increased temperature and high pressure lead to premature wear on the shaft sealing rings.

2. Metallic abrasion, which is constantly increasing when the vehicle is in motion, significantly shortens the lifetime of

the bearings in the rear-wheel drive.

Measure

 

 

For point 1: The gear oil capacities have changed for initial filling and when changing the oil in the rear-wheel drive.

The new capacities:

For initial filling: 200 ml

For changing oil: 180 ml

(The new RSD 05/2009 contains this modification)

 

 

For point 2: Regular oil change in rear-wheel drive:

At 600 mi.

every 12,000 mi or every 2 years

(This service interval is all ready in place)

 

 

Fault

 

Fault location Nature of fault Condition

 

Drive, Drive train, Rear drive Noise While driving

 

 

Defect

 

Main group

 

33 rear axle

 

Subgroup

 

10 Rear wheel drive

 

Location

 

00 Rear wheel drive

 

Defect code Defect description

3310002100 Rear wheel drive Excessive

 

tooth backlash

Module Area Fault code

 

Powertrain

 

CIP / DIS

System State Version

___________________________

Tech. Office report

__________________________________________________ ______________________________

Report no. Subject Link Condition

23344826 Increased wear in the rear-Approved

wheel drive

___________________________

Measure AG

__________________________________________________ ______________________________

Measure no. Subject

AG 23342824-01 Increased wear in the rear-wheel drive

[smiller]

2. Metallic abrasion, which is constantly increasing when the vehicle is in motion, significantly shortens the lifetime of the bearings in the rear-wheel drive.

 

...

 

For point 2: Regular oil change in rear-wheel drive: At 600 mi., every 12,000 mi or every 2 years

Who would have thought?

 

I guess a BMW engineer must have infiltrated a Honda tech session and took away some secrets.

 

 

[xoomerite]

So, should those of us who have putting 230 ml at the changes, drain it down to 180ml?

[BeemerLover]

Complaint

 

The rear-wheel drive displays premature wear in the form of leaking shaft sealing rings or an increased bearing clearance.

 

Cause

 

1. Increased temperature and high pressure lead to premature wear on the shaft sealing rings.

2. Metallic abrasion, which is constantly increasing when the vehicle is in motion, significantly shortens the lifetime of

the bearings in the rear-wheel drive.

 

 

 

Several years ago before I bought my R12RT I asked a wise old BMW tech what he thought the reason was for seal failures in the new final drives. He said he didn't know for sure but suspected it was pressure build up as the newer units were sealed units. He said the pressure builds up and forces oil past the seal but then, when the final drive cools off there is a slight vacuum that forms and air is pulled back into the drive. Over time with repeated cycles, oil passes out of the drive and the seal breaks down. He said there was no problem like this with the older drives as they were not sealed.... He said the problem could be fixed if it were possible to drill a small pressure equalization hole somewhere. He said he didn't know where that could be done, that if it were too low the oil would just leak out but if it were up high the oil would get slung out anyway as the drive turns. He indicated that maybe a fill plug could be outfitted with a hole and some sort of flexible rubber cap that would allow expansion but not leak.

 

 

[Ken H.]

He indicated that maybe a fill plug could be outfitted with a hole and some sort of flexible rubber cap that would allow expansion but not leak.

Considering the 'fill plug' is the ABS sensor, that would be, uh, "interesting."

[Ken H.]

So, should those of us who have putting 230 ml at the changes, drain it down to 180ml?

Personal opinion - yes. Overfill is a bit of a no-no on the hexhead FDs.

[BeemerLover]

Hmmmm.... I meant the drain plug....

 

 

[xoomerite]

230 ml is overfill only since the new recommendation of 180 ml.

[steve_tech]

Just changed my final drive oil and thought I would do an experiment.

180ml is about 3/16 inch below the "drain plug" hole on my 06 RT with the bike on the center stand, the hole being at 9.00 o'clock of course.

I used a bent plastic tie as a dipstick due to the gear being somewhat in the way but it is still possible to fill it from here.

[Mister Tee]

Sounds jolly and all, but there appears to be the same amount of dismantling and reassembly required to drain and fill the final drive. Maybe instead of using a horse syringe and tubing I can just fill it with the tip of the oil bottle like I did my transmission.

[kdiver]

This seems a bit confusing. More oil would provide more cooling. The increase in pressure of a gas (the volume in the final drive not filled with gear oil) is directly related to the temperature increase (and has nothing to do with the initial volume since the volume is NOT changing). Conclusion: less oil might in fact increase the temperature, increase the pressure and possibly increase the seal failure. The obvious solution is to provide better cooling to the assembly. It will be interesting to watch this situation to see how it develops.

My 2006 r1200rt is filled with the original oil capacity and is only ridded one up. the final drive temperature after a triip of 300 miles in 90 degree temperature was just slightly warm to touch, maybe 100 degrees.

[kdiver]

A qualification to the statement above: if for some reason the slightly lower quantity of gear oil does in fact lower the operating temperature of the final drive assembly, then the pressure would also be lowered. Pressure equalization mentioned earlier is also a way to minimize seal failure.

[SirAubergine]

No need for confusion. Let's look at a couple of factors:

 

What are the sources of heat? Friction in bearings, in the meshing of gear teeth, between oil seals and shafts and whatever heat is conducted via tire/wheel/ambient air and drive shaft.

 

Oil provides lubrication and acts as a heat transfer medium. Once enough oil is present to minimize friction and transfer it to the final drive case, where air flow carries it away, there is no need for more oil.

 

Any additional oil will present a greater thermal mass, and the drive will therefore take longer to attain operating temperature, but the additional oil will not provide any additional cooling. Friction of excessive oil being whipped by gears could actually add heat.

 

Air in the final drive case will be displaced by adding more oil, thereby reducing the free air volume in the case. As the drive assembly warms to operating temperature its components and oil expand in volume, compressing any free air in the case.

 

An expanding larger initial oil volume will compress the smaller remaining air volume to a higher pressure at normal operating temperature, and higher yet if the added oil is acting as a heat source.

 

The additional pressure appears to be the primary factor in seal failure.

 

Hope this helps!

[mneblett]

This seems a bit confusing. More oil would provide more cooling. The increase in pressure of a gas (the volume in the final drive not filled with gear oil) is directly related to the temperature increase (and has nothing to do with the initial volume since the volume is NOT changing). Conclusion: less oil might in fact increase the temperature, increase the pressure and possibly increase the seal failure.

The faults in this logic are the assumptions that the mass of the gas in the vapor space is constant, and that the temperature of the drive will be different at different fill levels.

 

If, as the gear oil heats up, some of the oil constituents are volatilzed, the pressure in the vapor space increases more than just the amount dictated by Boyle's law (PV=nRT). The presence of this addtional gas will increase pressure.

 

As far as running cooler with more oil, the short answer is no. For a given cruising speed, there is a fixed amount of energy being deposited into the final drive (the couple % of power loss through the gears). While it may take slightly longer for the drive with more oil to reach a steady state temperature, it will ultimately reach the same temperature as the lower-level drive -- regardless of how full or empty the drive is, the heat being input into the drive is being dissipated over the same surface. With a fixed energy input (HP loss through a gear drive being only ~97-98% efficient), and a fixed heat radation/convention surface, at steady state the temperature in the drive will be the same, regardless of the oil volume.

[kdiver]

Great discussion. I think that using boyles law can explain most of the pressure increase. if we assume that the initial pressure is 1 atm (14.7 psia) and the initial temperature is 50 degrees (510 degrees absolute) and the running temperature is 120 degrees (580 degrees) the final drive pressure will increase to: 14.7 times 580 divided by 510 = 16.7 psi. which means that the final drive has increased by 2 psi. if the shaft seal cannot hold a seal at 2 psi a leak will occur.

 

The solution has to involve minimizing temperature and venting of any pressure increase.

 

My initial post was to address the thought that reducing the oil volume by 1 fl oz can have such a significant effect on the operating temperature. If it does then I remain confused.

[mneblett]

My initial post was to address the thought that reducing the oil volume by 1 fl oz can have such a significant effect on the operating temperature. If it does then I remain confused.

It doesn't, so no confusion.

[kdiver]

If we agree that the slight reduction in gear oil quanity does not reduce temperature and therefore does not reduce the pressure, what principle is at work to improve seal life, bearing life and overall final drive life?

[marcopolo]

FWIW, someone posted this in the MOA forums:

 

The book "Systematic analysis of gear failures" (I love google!) states:

 

"Excess lubrication presents some unusual problems in a gear train. The churning effect resulting from excessive lubrication can raise ambient temperatures, because the energy involved in cutting the shear plane of the oil is reabsorbed as heat. A continual churning of the oil, along with increasing temperatures, will tend to solidify the oil. In some instances, high vaporization pressure has broken seals, evolving a leakage problem."

[SHIMHEAD]

Let's say pressure rise is causing seal leakage and eventual drive failure. Let's say someone drills a vent passage and installs a small fitting in the final drive to which a vent hose is attached and said vent hose is attached to the clean air side of the airbox through another small fitting. Let's say this fixes the issue of pressurization in the final drive finally!

Brilliant! Ride on!

 

SHIMHEAD

[kdiver]

Venting the final drive will prevent pressure buildup, but using the clean air side of filter will be at a slight vacuum depending on the cleanliness of the filter. This slight vacuum may not be a problem. An interesting comparison is my Mercruiser outdrive which uses a system that keeps the ENTIRE gear train (lower foot and top case) FULL of gear oil (no air space) and has a hose to a remote reservoir which is kept nearly full but is VENTED. The drive can become very warm after running at high rpm because most of the drive is in fact out of the water, yet with proper maintenance the drives are fairly dependable.

It has been mentioned that older BMW models used vented final drives.

 

 

 

 

 

 

 

 

 

[SHIMHEAD]

Just checking to see if anyone was paying attention. Of course a slight vacuum could be created in this configuration. Also, if left up to BMW to design a vent system, there would be at least 7 parts...such as banjo bolts, seal rings, labyrinth vent chamber, pressure sensor, switchover solenoid valve, spring clamps for the hoses. Oh, and don't forget the obligatory, dealer only, maintenance schedule and reminder lamp. Continuation of your warranty would be dependant on that ink stamp in your maintenance manual!

 

SHIMHEAD

[JMR]

The notion of venting a final drive is nothing new, wonder why BMW didn't do it to begin with?

Here's a schematic of a 1993 Honda ST1100 final drive, part #3 is a "breather cap". ST1100's were well designed and built...bulletproof IMO. I'll agree the "breather cap" is kinda wart-lookin' up on top of the gear housing and all, but the only ST1100 final drive problem I ever heard of was caused by lack of proper maintenance regarding O-rings for the moly on the gear splines. Caused pre-mature wear out of the gear splines, technically not really a "failure".

[Tech1]

I know for a fact that having more oil is not necessarily better. It causes extra "windage" from the gears and bearings, which creates more heat (drysump engines try to remove unnecessary oil from rotating parts to reduce horsepower loss and heat). A misconception is that more oil can help with cooling, but only the oil directly contacting the parts and then contacting the bare area of the case will help with cooling and I would bet that everything is "wet" when it is turning. A lot of the cooling in the case of a final drive will be direct from the bearing contact to the case.

The change in level discussed is small, I think the main benefit is not a change in temperature (windage reduction would be small), but an increased air volume will lower the pressure changes on the seals. Under continuous high load and speed(touring, 2up), oil temps in the final drive will increase significantly from higher bearing and gear mesh contact loads. I believe this is the situation that would have the most risk and benefit from the change. I think they intended the level to be at the plug, not above, but they overshot a little in determining the amount listed in the manual. This is the first product I have worked on that had a plug that certainly looked like it was intended as a level check. This wouldn't be the first mistake in a service procedure and/or capacity in a manual. If the plug was only intended as a drain, why not put it on the bottom! Venting would probably be the best fix, but it is difficult to do right in a small contained part like a final drive. It also lets moisture in.

Too bad I don't have an extra final drive laying around to put a temp and pressure sender in and run on our spin fixture to determine the optimum level!

[SWB]

This whole discussion reminds me of a concern I've always had when servicing either final drive or transmission, i.e. mechanical areas with close tolerances which take relatively little fluid. I can measure 180ML, and I can ensure most of it ends up in the final drive, but how do I guarantee that there's not 50ML left over inside (again, a few tablespoons), or 60ML, or 30ML, after draining the FD? I'd almost feel better if I could run some sort of solvent in there to clean all fluid out the FD before adding new fluid, but then of course that would contaminate both the FD and new fluid.

 

Certainly if one were not careful, he might overfill the FD by failing to adequately drain it. If BMW Motorrad believes that an extra 50ML is destroying well engineered BMW final drives, it's reasonable to expect that some of those failures might be caused by an inadequate fluid-removal design (say, like neglecting to add a drain plug in the first place) rather by an excessive fluid replacement spec.

 

Since my 2005 RT has always been serviced by BMW, it hasnever had a FD fluid change, I picked it up at 42K miles and added the FD fluid change to my priority task list for the 48K mile service, due in about 2K miles (or perhaps a month) from now. I'm now thinking that I may just drop the fluid this weekend and get it done early (or late, depending on one's perspective). I'm curious as to the condition (but on the other hand, maybe I don't want to know).

 

In any case, I'll take my time draining the FD, will "shake, rattle, and roll" it, and maybe even add a little heat to get all the fluid out of there.

 

My son suggested retrofitting a drain plug in the FD. The idea's definitely crossed my mind, but that's probably only reasonable during a FD disassembly/rebuild, i.e. too much chance of leaving metal shavings inside from drilling unless the FD is disassembled. If adding a Zerk fitting is possible, it can't that much harder to retrofit a drain plug, can it?

 

- Scott

[JMR]

I'm now thinking that I may just drop the fluid this weekend and get it done early (or late, depending on one's perspective). I'm curious as to the condition (but on the other hand, maybe I don't want to know).

 

You can expect to find some metal shavings on the speed-sensor, at least the first time you pull it anyway, .....trust me, you will have metal fuzz on the sensor. I've not had any metal on mine since the first time I pulled it. (Maybe it has been such a small amount it didn't show itself very well?) When I started changing my final drive oil, I switched to synthetic and IMO it's the way to go; especially now that it's recommended to reduce the amount of oil used. JMO there. Once you do it the first time, there's really not much to it. It may be overkill, but I change my final drive oil everytime I change tires. I do it as much to moly-grease the shaft splines as much as to change the oil. Certainly doesn't hurt anything, doesn't cost much at all, doesn't take much time to do, and the oil I've dropped since the first time hasn't even been close to how dirty and dark that first oil drop was. (Actually, the last change was mostly clear.)

[marcopolo]

...I switched to synthetic and IMO it's the way to go; especially now that it's recommended to reduce the amount of oil used.

 

Not sure I understand that statement since BMW has always specified synthetic gear oil for the hexhead final drives: 75W90 synthetic GL-5.

[mneblett]

...I switched to synthetic and IMO it's the way to go; especially now that it's recommended to reduce the amount of oil used.

 

Not sure I understand that statement since BMW has always specified synthetic gear oil for the hexhead final drives: 75W90 synthetic GL-5.

I don't believe he was saying that synth is recommended, but that the lower fill level is now recommended.

[kdiver]

I recently did the service on my r1200rt final drive and filled it to the level recommended by my service manual. This past week i found this thread and today decided to: 1. ride the bike at 70 mph for 100 miles in 93 degrees weather.

2. at the end of ride the final drive was warm to touch. 3. placed the bike on the center stand 4. i slowly loosened the drain (leaving it at the 9:00 position)

5. if found that there was a slight very brief pressure release when the plug was removed

6. i caught the excessive gear oil and measured the overflow quantity to be approx 1 tablespoon. 7. i let the unit cool and then replaced the plug.

 

I will run the bike with this new fluid level and continue to monitor temperature and pressures.

 

The bike has 13,000 miles. I did not find any metal on plug during service or today. the final drive never feels hot just warm . the rear wheel side play is essentially zero.

[codinn]

The oil will expand as the temperature increases. This will compress the air in the housing. Less oil, less total volume expansion and the expansion is working over a larger volume of air affecting it less on a percentage basis.

 

The fuller the cavity, the greater the effect. We see a similar phenomenon filling wine bottles. Fill the bottles too full and if they warm up even a little, there is either leakage or a pushed cork.

[kdiver]

One thing is for sure: the increase in temperature causes the pressure to slightly increase in the final drive.

 

Some believe it is the expanding oil

Some believe it is explained by gas laws (which I believe) and can easily be calculated.

 

But pressure venting would be beneficial no matter which theory you believe in.

My test today proved that there is a small pressure build up after the temperature is increased by riding the bike.

 

It would be interesting to know what pressure the oil seals are designed to handle.

[JMR]

...I switched to synthetic and IMO it's the way to go; especially now that it's recommended to reduce the amount of oil used.

 

Not sure I understand that statement since BMW has always specified synthetic gear oil for the hexhead final drives: 75W90 synthetic GL-5.

Well you got me on that one, I didn't realize that. Until my warranty expired, BMW did all the service work and I didn't get too involved. I looked up the oil weights and such when I started doing my own service but don't remember synthetics being specified. Not saying it wasn't there, just saying I don't remember; knew I was going to use synthetics anyway so maybe I wasn't looking too closely beyond oil weights.....they say your memory is one of the first things to go.......what were we talking about?

[BeemerLover]

Can someone brainstorm a way to make a drain plug (9:00 position) that has some sort of device that would absorb the pressure, either negative or positive? I envision a hole down the center of it with a balloon on the end. I know that a balloon is not feasible but...... Hmmm maybe a flexible rubber membrane inside the plug?

 

Or maybe drill a 1/8" hole in the top of the drive and glue a flexible cover (Rubber?) over top?

 

Or just a small hole that is vented to the atmosphere but in a place where oil is not slung out?

 

Maybe drill a hole, put a brake bleeder nipple in it with one of those rubber covers on it?

 

(Can you tell I'm grasping for straws...? )

 

I understand that older BMW final drives were vented. How was that done? Can we do it that way?

 

 

[mneblett]

I understand that older BMW final drives were vented. How was that done?

If you look at the older drives, there's a thumb-size metal cap on top of the drive housing. The cap covers a vent on the top of the housing.

 

Given the proximity of the crown gear under the top edge of the current housing, I doubt there's room for any sort of oil-catching labyrinth in the housing, so something would have to be added to the outside of the housing.

[SirAubergine]

Given the proximity of the crown gear under the top edge of the current housing, I doubt there's room for any sort of oil-catching labyrinth in the housing, so something would have to be added to the outside of the housing.

 

This, I believe, is the real source of hexhead final drive troubles. In an effort to simplify and save weight everywhere on the bike, the final drive case was made much smaller than on previous models.

The smaller case has little clearance between the rotating parts and case itself. With such small clearances, oil level becomes critical. Too little oil and one risks heating and failure due to insufficient lubrication and heat transfer. A little too much oil and heating and pressure buildup due to oil churn becomes a problem.

 

I suspect the actual pressure in such an overheated drive is pretty high. It will take more than a few psi to force an oil seal out of the housing. A vent will relieve the pressure in the housing, but with little clearance volume, BMW may have eliminated the vent because they found it difficult to keep oil in the drive. Air/oil separation becomes more problematic when venting a drive with small clearance volume.

 

It would be interesting to have somebody cc a final drive - fill it completely full of oil, and then remove and measure the oil removed to restore proper oil level. We'd then know just how much clearance volume the drive has.

 

[kdiver]

A good guess is that the void volume is approximately equal to the oil quantity. When i opened the plug at 9:00 the oil level was slightly higher than this point. The plug seems to be very close to the center line of the drive. (void would be 7 to 8 fl oz.)

[mneblett]

A vent will relieve the pressure in the housing, but with little clearance volume, BMW may have eliminated the vent because they found it difficult to keep oil in the drive. Air/oil separation becomes more problematic when venting a drive with small clearance volume.

I suspect that things happened in a different (sorta opposite) way.

 

If you've ever seen the inside of the older drives, you'll know that there was quite a bit of annular space around the crown gear, with a wall just outside of the gear to define an oil-separating space between the crown gear and the outer wall of the housing:

 

I suspect that this annular space was eliminated to reduce the size of the drive, based on a determination that a vent (and thus, any need for oil separation) could be eliminated with a sealed, life-of-the-bike drive design. If BMW had been right, it would have been a great solution; but since the seals aren't surviving, they now have to figure out how to put a vent into a drive that no longer has sufficeint space to accomodate it. I wouldn't be surprised to see a slightly larger, vented drive in the future.

[kdiver]

Do you have the drawing on the current final drive assembly?

Also, where is the vent on the schematic shown above?

The old style does have the advantages you mention. Maybe BMW will acknowledge the problem and send us all a newly designed final drive, and put an end to the problem and the discussions.

[Redbrick]

................ Maybe BMW will acknowledge the problem and send us all a newly designed final drive, and put an end to the problem and the discussions.

 

I'm not holding my breath.....

[mneblett]

Do you have the drawing on the current final drive assembly?

Also, where is the vent on the schematic shown above?

The old style does have the advantages you mention. Maybe BMW will acknowledge the problem and send us all a newly designed final drive, and put an end to the problem and the discussions.

I don't have a good pic; this will have to do for the time being:

 

Unfortunately, the hole for the vent in the older drive isn't visible -- it is direcly behind the bearing race that is shown in the drawing aligned with the top edge of the housing.

[Twisties]

I guess I'm a little confused. So if we think that the pre-change void volume is about the same as the fill volume, a reasonable estimate IMHO, then we have a 230 - 250 mls void volume. The change from reducing the fill to 180 ml would make it 280 - 300 mls, or an increase of about 18% in void volume. I think, all else being the same, this would result in an 18% pressure drop. Doesn't seem like much to me.

 

Maybe that's enough, or maybe that's all that's achievable (and we'll take what we can get), or maybe I'm wrong, or maybe all else is not the same, or maybe we're completely misunderstanding this.

 

My gut says that it isn't just about increasing void volume to reduce pressure, although that may be a factor.

 

 

[JMR]

Is there any informations as to the overall percentage of hexhead final drives that have failed?(Wondering how many are not failing and why they're not failing?)