SouthernBM provide many services for their extensive list of clients. Apart from servicing BMWs, SouthernBM also specialises in performance modifications for all modern BMW models.
One of the most popular upgrades is shown on this M140i - a Quaife Limited Slip Differential (LSD) retrofit.
What is a Limited Slip Differential?
An LSD is described as: “a differential that allows its two output shafts to rotate at different speeds but limits the maximum difference between the two shafts. In an automobile, such limited-slip differentials are sometimes used in place of a standard differential, where they convey certain dynamic advantages, at the expense of greater complexity.“
The Quaife Automatic Torque Biasing LSD is a unique type of limited-slip diff that substantially improves traction for powerful vehicles using only gear mechanisms. This clever design revolutionised the differential market - offering a superior level of performance and warranties compared to its competitors.
Quaife themselves are a British based operation and specialise in components to upgrade the driven parts of a vehicle such as driveshafts, diffs, and steering racks.
What are the benefits of a Limited Slip Differential?
The Quaife LSD unit specified for this upgrade allows for a driver to further exploit the mechanical ability of the car, whilst built so it fits inside the existing differential housing. This means that it will look factory fresh, and requires no extra engineering or modification. The differential ring gear also remains the same meaning there is no change to your final drive ratio and no reprogramming of the engine management computer required.
Andrew Brien, the owner and director of SouthernBM, explains that the extra performance a Quaife LSD provides allows for a car that's easier to control and is able to apply its power to the tarmac with maximum effect.
He says that in comparison to a normal diff, an LSD provides more mechanical grip across a varying range of conditions and gets more of the engine’s output to the driven wheels. This makes driving the car an easier and safer proposition.
Andrew then explains that the process to install the Quaife LSD into the housing requires some specific machining and mechanical work. In older vehicles the mechanism that makes up a differential and the process to disassemble and reassemble were, in comparison to today, far easier.
Manufacturers moved to provide a set and forget mechanism by welding components (crown wheel and carrier, says Andrew) together. This made for both strength and longevity, plus brought the manufacturing costs down. However, to replace or upgrade requires the components to be worked upon to separate them.
Limited Slip Differential Retrofit Process
When supplying a new LSD, the existing crown wheel requires some mechanical machining to accept the new Quaife ATB unit. This machining ensures the crown wheel and LSD are a bolt together fit, and will sit snugly, where possible, inside the existing housing before being refitted to the car.
This process has taken extensive research and development on SouthernBM’s part. Specific computer programs were written to suit the machinery used and this ensures millimetre perfect tolerances when drilling bolt holes to mount parts together, for example.
Andrew describes the Quaife unit fitted as a helical gear cut unit. These require less servicing, are quieter, and is torque biasing. Quaife describes this process as: “the limited slip differential automatically biases the torque across the axle to the wheel with the most grip.”
On high torque, turbocharged, rear wheel drive machines such as the BMW M140i, this dramatically improves rear end grip. This makes cornering on a slippery road surface driving safer and on a dry road, allows a driver to really utilise the full power and torque delivery of an engine.
SouthernBM clearly go the extra distance to provide a bespoke mechanical and upgrade service. Be sure to lodge an enquiry below if you have any questions.
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Thank you once again to John, Andrew and their team. Have been bringing our cars to them for several years now and have complete trust and faith in their workmanship and honesty.
Excellent service at reasonable prices. The shop is very nice too, you almost feel like you're at BMW.
Fantastic customer service from the team at Southern BM. Expertly repaired my 2011 323i and did so without the attitude and excessive cost of a dealer. Thank you and I will be back for all future servicing.
The guys are great, definitely take your BMW there.
Seriously great service and people. Honest and fair. Would happily recommend anyone to them.