Interesting. I just looked up a 1 Series (E82 120i assumption) diff oil on realoem.com and got the BMW part number 83222295532. 83222295532 is Hypoid Axle Oil G1 SAE 75W-85. Genuine £20 per 0.5 liter, but you need 0.8 liter, so a £40 experiment plus LSD additive (which I already have). Surely that will make it as quiet as possible.
My detailed build blog
My BMW diff with Titan LSD is quieter with 75w140 than it was with 75w90, both Redline GL5 full synthetics with LSD additive already in the oil.
BMW specifies 75w85 for all current open diffs, 75w140 for ///M LSD equipped diffs.
So just fired my brain read about SAE grades. If I have this right, a 75w140 is the same when cold, but thicker when hot, than 75w85. In comparison to a straight 90, which is only measured when hot, 75w140 is thicker when hot, but the 90 would be thicker cold.
This might explain why,
a, The 90 is quieter for road use
b. Why the Motul 75w140 is described as competition gear oil, i.e. get it hot.
Knowing 75w140 is BMW's spec for M cars, and Motul 75w140 is Titans recommend diff oil I suppose I will be sticking with that for now. Every time I think that diff sounds loud I will have to remind myself its because I am not pushing it on hard enough.
Well it would seem that the issue of oils for transmissions needs a DIFinitive answer. No apology for that will be given. I am not a tribologist, nor a transmission specialist, however Road and Race certainly are. In dialogue with R&R, they have provided a lengthy but comprehensive explanation, as follows:
" Both the BMW 168 and the Sierra 7" differentials used in the Caterhams require an SAE 90 GL5 oil. The most crucial part of this is the GL5, this refers to the level of extreme pressure additives in a GL5 compared to a GL4. As a rough rule of thumb, a GL5 requires twice as many EP (Extreme Pressure) additives as a GL4. It is these EP additives that provide the largest amount of gear protection when compared to any other additives for viscosity. The viscosity does not directly equate to gear protection, however it is also crucial to get this correct, as it is important when relating to flow. An oil too thin or too thick, can increase or decrease the flow respectively. This will not allow the oil channels to circulate the oil as effectively as designed, which can lead to decreased bearing life and decreased crownwheel life. The differential manufacturers, in this case BMW & Ford, will have spent millions designing the casings, gears, choosing the bearings and then the oil, for everything to work as effectively as possible. It is for this reason, even when LSDs or ATBs are added, you should always follow the original grade of oil.
Gear oil viscosity is usually specified in two grades. For example a 75w90 or an 80w140. This initial grade, the 75W or 80w, refers to the thickness when cold. Modern manufacturers specify this to take advantage of advances in oil technology which allows for a thinner oil when cold. This will increase efficiency and emissions before the car warms up to operating temperatures. The cold weight in differentials is not as important as they warm up very quickly. It is far more crucial in gearboxes where it can make the gear change "notchy" when cold. The warm viscosity (the second number) is important in both. I will touch on why we opted to go for a single grade later.
The GL grade is the single most crucial grade for a differential and gearbox. As previously mentioned, it refers to the level of EP additives, and therefore extreme pressure protection an oil can offer.
Differentials require a much higher level of this than a gearbox due to the hypoid gears they use. This means the gear pressure angle is more aggressive, and requires greater strength to stop the gears from touching. When the gears touch, in any scenario, (gearbox or differential) this metal on metal contact generates localised heat and prematurely wears the gears. Stopping this metal on metal contact is why it is so important a GL5 is used in differentials, as it provides the protection a GL4 does not. Unfortunately, you cannot use a GL5 oil in a synchronised gearbox as the EP protection would stop the synchronisers from working. It forms a barrier and the synchro rings can't effectively slow down or speed up the engine to match the road speed, resulting in crunching and wear of the synchros. This is why gearboxes use a GL4, as it provides a balance of gear protection (they are at less aggressive angles) and still allows the synchros to function through friction. Some modern oil manufacturers combine a GL4 and GL5 by using EP levels that pass the tests for both, while being at the higher end of GL4 and at the lower end of GL5. We don't generally recommend these as there is a huge compromise on strength and protection. This is likely to cause bigger issues on older gearboxes and differentials as they are more sensitive to oil.
When it comes to LSDs and reducing the plate noise from these, various friction modifiers are used in oil marked as "for LSD use". These effectively allow for smoother sliding of the clutch plates in the LSDs, without affecting the lockup at full throttle. As some of you will have noticed when using various oils, some will make the Caterham LSD "clunking" worse or better. This is due to the type of additive, and the amount used. It is not a requirement for plated LSDs to have these additives in them and they can be used without them. In front wheel drive gearboxes, you can't use any LSD additives as their friction modifiers don't allow the synchros to work, in the same way as excess EP additives. However, in applications where they can be used (such as differentials), it is beneficial to do so. It increases plate life, quietness when making low speed turns or reversing and benefits high speed cornering stability as the LSD locks/unlocks smoothly. Conversely, you should not use LSD oil or any LSD additives with ATBs as the helical gears work much better with higher friction levels.They require internal friction to bias torque effectively.
When designing oils, roughly 90 % of the oil is made up from a base oil ( mineral, semi-synthetic or synthetic). This is regardless of it being used as an engine oil, gear oil or some other lubricating oil. The main difference is what additives are chosen to form the remaining 10%. With mineral and synthetic oils being as good as each other now, but their molecular compounds being different, the choice of base oil largely depends on what additives you need to use. Some additives work better with mineral or synthetic oil bases. With this 10% (additives) you need to have a balance of friction reduction, extreme pressure protection, thermal protection, viscosity modifiers,foam inhibitors,detergents, the list goes on. Because of the need for so many components, and the sheer cost of these chemicals, designing an oil is a compromise with no single "right" way to do it., but plenty of wrong ways. When we designed our LSD oil, we wanted gear protection and the effectiveness of the friction modifier to be at the top of our priority list. We opted to use very high quality chemical components, but even so, we decided not to add in the viscosity modifiers to give a thinner cold weight. It was not necessary, and we did not want to compromise on the quality of the rest of the oil.This is one of the reasons that you shouldn't pump excess levels of friction modifiers (LSD additives) into oils, as you run the risk of reducing the % amounts of the other chemical components to a level that will reduce their effectiveness.
With specific regard to the Titan LSDs used in Caterhams ( sintered plate version) the sintered plates are very high quality, high friction and have a good longevity. It is their high coefficient of friction that causes the "banging" that is common. This coupled with the cost of additives, type of friction additives, and compromises on various chemical component percentages, is the reason that so many oils from major manufacturers struggle to keep them quiet during cornering. Neither Caterham or Titan should be deviating from the recommended oil grade BMW or Ford give, as they have not designed or changed the crownwheel & pinion, or made any changes to the internal oil channels, or use different bearings. The addition of an LSD does not require a different viscosity oil, only an oil with the appropriate friction modifiers.
I will also address the confusion in BMW differential oils. The part numbers that BMW specify for for the differential oils used in Caterhams is 83222365987 or 33117695240 which is a 75W90 GL5. BMW do use a 75W140 GL5 for their more powerful vehicles as they use bigger differentials with larger teeth, and larger oil channels, so a thicker oil is necessary. There are other oils that they have recommended for various years, but the 75W90 GL5 and the 75W140 GL5 are the most common."0
Well I did warn you this was a lengthy post!
Personally I have found this a very interesting summary of the technical issues and objectives, so thanks to Road and Race for it. I now know exactly why my sintered plate Titan LSD is so much quieter with RR oil installed.
The oil story is not easy and not helped by a mish mash of classifications over the years...... as GL6 oils are said to be in excess of GL5, although the test procedure is obsolete, like wise new oils can't be graded GL4 for the same reason - test procedure is obsolete, which makes a mockery of the classifications.
The GL was originally for the US market,
Ford Sierra was specified as follows:
5 speed gear box SAE 80 EP
Final drive (non LSD) SAE 90 Hypoid
One final point to note Pete,
The banging in the Titan LSD is caused by excessive design movement in the ramp blocks, (poor design) which allows them to impact and deflect the bellevilles through their entire range (again which they are not designed to do) resulting in the bellevilles eventually fracturing which makes the banging worse still coupled now though with a reduction in static preload.
Thanks for that, The more complete the understanding of any subject, the better.
A slight aside, RR also mentioned that they consider a torque test of the LSD when the car is serviced is sensible. If down to 20ft/lb its advisable to have diff stripped and re-set at fairly low cost. If the reading is at or below 15ft/lbs .... impending doom and high cost repair! I didn't ask what the "as built" torque should be, and probably should have. Any views?
PS: My father was a tribologist for BP and worked on the development of BP Visco Static ( yes that long ago) and was also heavily involved in solving the piston ring seizures of Lanc Merlin engines during take off with a full bomb load. I think of him when subjects like this arise, he would engage with knowledge and enthusiasm in spades.
Viscous Static was my Dads oil of choice - I remember it well !
I grew up near the Lancaster practise area for the Dambuster raid - the sound they make over Howden and Derwent is magical
In a Caterham I wouldn't even have the preload set that high, never mind any higher...
my ZF is set at 5lb - it just drags the opposing wheel round when there both off the ground....
Any pointers for the testing process?
For the preload torque...?
Jack up one rear wheel, handbrake off
Torque wrench applied to hub nut and see what torque is required to turn the wheel hence you are over coming the resistence of the preload on the clutch pack.
A dial torque wrench is easier is you have on, but clicky type can be used too, set it low and repeat until the wheel turns without clicking.this will be your threshold.
Having been trying to minimise the driveline noise and shunt in my 2010 (Sierra open diff) car (including a rebuilt diff by R&R now filled with their oil, plus new driveshafts) I'm surprised to read that it seems the same issues exist with the BMW diff and Mazda gearbox set up, since I'd been led to believe that the 'they all do this' was due to the recon diffs and gearboxes used by Caterham when mine was built.
My Dad's 33 year-old, 30,000 mile BDR HPC isn't noisy at all. Either that's just luck - be interesting to hear from other owners of early De Dion cars - or there is something else going on with the newer cars for this to be accepted as normal.