by Diff Boy, UK
Since 2010 the BMW 168 differential is the Caterham preferred original equipment fit. If a limited slip differential then it will have the Titan limited slip unit (LSU) fitted.
Up to model year 2015 the Titan possessed carbon faced clutch plates. Later plates have a sintered metal finish for longevity but to some extent create more noise, vibration and harshness (NVH).
Seven owners in the UK have been alarmed to find that the carbon faced plates have worn out more rapidly than expected. Some owners have experienced a total loss of Titan functionality in as little as 3000 miles (4830 Kms).
A minority have experienced the Titan 'surviving' for upward of 20000 miles (32190 Kms) over a period of six to seven years.
Evidence gathered from UK owners has revealed that the average life of the carbon faced plates and that of the Titan as a whole can be little more than three years or 9000 miles (14484 Kms).
A Titan that that appears to have longevity may have ceased to function as a credible LSU many years or miles/Kms previously. Inevitably it is a gamble as to when the internal components fail especially if one is unaware of any danger signs.
This is an issue that Caterham Cars sadly overlooked. Quote: 'on the serious matter of longevity of the carbon plate – type differential, this is something that I am trying to dedicate resource to investigate. Ironically, carbon plates where introduced to reduce noise, but we switched back to sintered plates some time ago when reports of premature wear first started to appear.............I continue to have very few reports of issues but understand anecdotally that it is a wider problem than first understood and I am committed to finding a solution'.
During LSU operation plate surface finish degredation alters the set up and tolerances of the internal components which can adversely effect the integrity of the conical 'Colleville Springs' and shims. The result is that these components fracture often failing in several pieces distributing debris within the casing. Unless detected at an early stage failure of the differential is guaranteed. During this period the removed carbon mixes with the differential oil creating a fine grinding paste which effects bearings, seals and possibly the Crown Wheel and Pinion.
So why is this problem occurring? Titan as the manufacturer recommends an overhaul 'Every 12 months, race season, or every 10000 road use miles (16000 Kms)'. Take into account higher mileage or track days then the threshold of 10000 miles or 16000 Kms will reduce. In fact for a Seven used purely on the road the overhaul period could repeat itself in as little as two years.
Unfortunately no information regarding service requirements or intervals was ever officially offered to owners. Neither at the point of sale or by publishing in the Owners Handbook Service Schedule table.
The reason? Quote - 'We do not want to make ownership onerous, but in the respect of the differential it is increasingly apparent that the team at the time got this wrong....it needs to be corrected and I would be first to admit it is taking an extraodinarily long time'.
But the recommendations of the Titan manufacturer have always existed, readily available and straight forward.
How can the owner help mitigate this problem? Simple – preventative action:
Wheel rotation check
With the rear of the car raised rotate one wheel. The opposite wheel should turn in the same direction. Non rotation or rotation in the opposite direction of the opposite wheel indicates a possible reduction of functionality of the LSU. Non rotation means you have the same operation as a 'normal' open differential and a failed LSU.
Magnetic filler plug
Fit to monitor the differential & LSU health. (Gold Plug Magnetic Plug M22 x1.5 AP22).
Carry out annualy. If dark, black or contains very small debris suspect the worst.
Dependant on annual mileage/kms driven, vehicle use or type of oil. Consider changing every two to three years.
Differential Pre Load Check
If there is real cause for concern then this check should be carried out.
There are two options:
(a) Raise the rear of the car. Remove a rear wheel. Carefully balance the vehicle on the three remaining wheels ensuring adequate support & chocks in place. Apply a torque wrench to the exposed hub in the direction of rotation until the axle breaks away. A digital wrench is ideal.
(b) Raise the rear of the car & support on axle stands. Remove a rear wheel. Brace the remaining wheel by placing a suitably sized piece of wood through the spokes & carefully against a chassis bar. Apply a torque wrench to the exposed hub in the direction of rotation until the axle breaks away. A digital wrench is ideal.
40ft/lbs = satisfactory
20ft/lbs = consider a service
15ft/lbs or less = failure could be imminent
This link may be usefull: Differential Preload Check – Caterham 420 Detailed Build Blog
Listen to your differential. An indication of a loss of function of the Titan is often accompanied by chattering and knocking noises increasing during cornering. Vibration and harshness may increase as well. The car may start acting strangely in the handling department when pressing on, not feel so stable in corners or unstable when accelerating in a straight line especially from rest. These attributes indicate that you may now have an open differential.
Oil. This is an important component to preserve the BMW/Titan differential. The subject of which to use has differing opinions. Consideration should be given to local climatic conditions and driving habits when choosing an oil.
SAE 90 GL5 LS oil.
Suitable for use in the UK and likely compatible for most of 'temperate' Europe. Two UK differential and LSU overhaul workshops recommend a mineral SAE 90 GL5 Limited Slip oil for the BMW/Titan. This oil type will operate across a wide ambient temperature spectrum. Dependant on use and being a pure mineral oil it will probably break down quicker than a synthetic so changes will be more frequently required to preserve the differential.
75W/140 LS Synthetic oil.
This viscosity and type of oil is recommended by Caterham Cars. Suitable for repetative track driving, racing and extremes of ambient temperature.
This type of oil does include friction modifiers and in the opinion of one well known UK LSU and differential overhaul workshop the addition of friction modifiers is deliberately designed to camouflage and flatter NVH created by design weaknesses of the Titan and other LSU.
Can I get my Titan overhauled? Yes.
Titan Express LSD Rebuild Kit – Titan Express a kit of parts for this process but unless you have in depth knowledge it is advised to leave the process in the hands of a transmission specialist. Unfortunately there may be more work required than just attention to the LSU.
Caterham Cars also provide the same: REBUILD KIT BMW LSD - Caterham Parts
Are there alternatives to the Titan? Yes.
Caterham Cars retail replacement Titans.
Tracsport (SPComponents) an independent UK transmission specialist offers a well proven, robust, well designed and engineered unit that utilises molybdenum surfaced plates for durability and longevity.
Drexler Motorsport offer a solution for BMW differentials.
Expense ! All figures are approximate
Titan Express overhaul kit = £345/Euro 395
Caterham Titan overhaul kit = £515/Euro 590
Caterham Cars replacement Titan = £996/Euro 1142
Caterham Cars replacement BMW LSD (3.64) = £2340/Euro 2683
Titan overhaul with differential service = £1565/Euro 1794
Tracsport LSU upgrade and differential service = £1800/Euro 2064