This project was probably the most complicated single batch we ever made for a customer. It was a very large limited slip differential casing for a rally car. The manufacturing instructions ran to around seventy pages and the part required around seventy five separate operations. If you count each hole and each sub operation then the total runs to over 1000, every one of which must be correct. You can do 999 out of 1000 operations correctly, but get just one wrong and the whole thing is scrapped. Reworks are not allowed on such highly stressed components.
We made a batch of around 50 of these and never scrapped one. The secret was great attention to detail with manufacturing drawings and written instructions being produced, issued and used for every stage, operation and piece of tooling required.
Amanda with Thomas The Tank Engine pretending to use the phone
Limited Slip Differential components
Over a period of ten years our company tried several methods of producing the plates shown which form the heart of a limited slip differential. We developed manufacturing methods which produced plates that were flat to exceptionally fine limits, had neither sharp edges nor chamfered edges, were dimensionally correct and contained both internal and external splines. The photo also shows the barrel which contains a stack of plates and the hub which transmits power from the device.
The two views above show a typical gear carrier for a limited slip differential and the third photo shows a typical gear of which eight would be needed.
The differential gear is a vital part of virtually every car ever produced and was invented in Coventry by James Starley. The story goes that he had an accident on a tricycle which he was manufacturing and sought a way to allow the rear wheels not to scrub on bends in the road. He invented the differential gear which was a key element in paving the way for the development of the automobile.
Harry Ferguson was a dynamic inventor and businessman who made Massey Ferguson tractors in Coventry between 1948 and 1998. He invented many devices allied to vehicles and one of his companies played a key part in developing the limited slip differential.
Our company produced thousands of components for limited slip discs between 1980 and 2000.
These are two more examples of differential cases that required extensive planning and production control to manufacture them to extremely fine tolerances and high tensile specifications.
This was one of the most complicated items we ever manufactured. It shows two halves of a single case which had to fit together perfectly and over which the lower gear was then fixed by its internal splines. The half cross holes for holding the gear shafts were not evenly spaced and the internal carrier gear had an uneven number of teeth. This was an exceptional piece of work. Ten were made.
This shows another project which included a machined casting, an extension housing, a proprietary GKN bevel diff set and numerous other in house designed and manufactured drive components.
A variety of differential output shafts which take the power from the gear set to the universal couplings.
Colin Walker 2012
