“Recently, whilst replacing my 7-year-old Brompton’s rear mudguard, I noticed play in the rear triangle pivot. Some on-line research suggested that the pin retaining screws cannot readily be unscrewed and would have to be drilled out. A replacement pin is available as part of a kit, but there were ominous references to expensive tooling to deal with the frame bushes. I duly drilled out the screw heads and pushed out the steel pin, which indeed showed some wear at the ends where it runs in the bushes.
To my surprise, the bushes appeared to be only slightly worn and I was able to make up a replacement pin from some over-size silver steel rod.This is now installed and the play has disappeared so I did not need to find a dealer to do the repair.
Assuming the pivot does not seize through lack of lubrication, I doubt if a degree of wear matters much, except when it causes those not used to the Brompton’s rear end bobbing to ask if something is wrong!
George Winspur
Professor Pivot replies: Your observations are entirely correct, George. Brompton does insist that the new bushes be reamed to size using a precise and rather specialist tool. Only a limited number of UK dealers, and distributors in Spain, Germany and the USA are equipped with these tools, so – besides the Brentford factory – these are the only outlets able to undertake a full rebuild.
However, the Brompton functions well with a surprising amount of wear.This can be measured by sitting the bike in the part-folded position and rocking the back of the rear wheel. From my experience, 5mm of play has little or no effect on handling. If modest play has developed, the life of the hinge can be extended by adding a few drops of heavy oil at regular intervals, particularly after riding in the wet.There’s no need to do anything else until play reaches about 10mm, which should take 10,000 miles, or even more. By this time, the bike may feel a bit nervous, particularly on fast reverse curves.
A complete rebuild will probably be needed, but as you also correctly observe, most wear occurs on the pin, so it is often permissible to replace the pin alone. For those with an engineering background, the complete kit (including pin, replacement screws and even a suitable drill should the old screws be seized) costs £11.84 from good Brompton dealers, or the factory.When fitting the pin, make sure the bushes are well coated with grease, but take care to keep grease clear of the threads, both on the screws and the inside of the pin.The screws must be locked in place with a suitable thread sealant – if left dry, they can unwind in use, and ultimately cause the pivot to collapse.
For machines ridden in extreme conditions, the life of the pin can be extended by fitting a grease point, which not only allows grease into the heart of the assembly, but expels grit or water that may have worked its way in.The expert at this treatment is Steve Parry – tel: 01934 516158 or email: spbicycles@aol.com
