F-Frame Rear Suspension
Before discussing rear suspension work, a little historical background may be useful. Owing to Alex Moulton’s suspension work for the British Motor Corporation (incorporated on Mini, 1100/1300 and other cars in the 1960′s), he was able to use production facilities at the Kirkby, Liverpool, Mini car plant for mass production of Moulton cycles between 1963 and 1966. This should have been a great solution, after being turned down by Raleigh, who later came to regret their short-sightedness. However, quality control at Kirkby was appalling, with none of the personal commitment found at the Bradford on Avon workshops. As a result, we can disassemble a Bradford-built Deluxe within an hour, whereas a similar machine from Kirkby may take several weeks! The main reasons for this were the complete lack of greasing when built, bad or insufficient brazing, overheating when CO2 welding, and undercutting of inner sleeve linings in rear fork blades. Later Series I rear forks incorporated an extra plate under the brake bolt area, but this did not avert the twisting and cracking that appears there. Only the more angular, finned, Series II forks overcame these problems.
Bearing these problems in mind, we can now work through the dismantling process of an early Moulton’s rear suspension.
Firstly, disconnect the rear brake and gear cables, and remove the chain and rear wheel so that nothing impedes the removal of the rear forks. Remove the brake from the forks and also the mudguard. Sometimes the mudguard screw is seized where it is attached to the centre of the rear forks, between the blades. It may be necessary to saw through the bolt, using a junior hacksaw and taking care not to score the underside of the forks with the length of the hacksaw blade. The nut retaining the brake bolt also sticks and is best treated with a box spanner. Three self-tapping screws must now be removed. Two are at the base of the white rear carrier support strut, just ahead of the sides of the rubber suspension block. The third is directly under the frame. This one is usually seized by road dirt and rust and removal should not be attempted until the screw has been soaked in Plus Gas because, once the head is damaged, you will have no choice but to saw off the head and drill out the screw.
With the three screws out, turn your attention to the pivot bolt. Soak first with Plus Gas, preferably for some days, before dismantling (Plus Gas is far superior to WD40 for this purpose). Loosen one nut until it is flush with the bolt end. Then tap the nut and bolt towards the frame: it should move. If so, keep tapping, winding the nut back and eventually off, until the bolt is tapped through and out of the frame, using a similarly sized bolt to push it out in the later stages. If the original bolt had been greased at production, it should just slide out. If it hasn’t, curse the Kirkby lads and prepare for battle.
Presuming the bolt is removed, the forks can be tugged out from the rear. Tap out the pivot sleeve using a similar piece of cylindrical tubing. Put a screwdriver into the pivot tube of the frame, passing through one of the bushes and gently positioning the blade tip behind the other; tap the screwdriver handle to push out the bush. Repeat the process to remove the other bush.
So far, we have described fork removal on a polite, well brought up Moulton. On a neglected bike, things may well be different. The pivot bolt, sleeve and bushes are likely to be seized together with rust and rusted into the frame tube too. Avoiding the rubber area, soak the whole unit in easing solution for up to a week before trying again to tap out the bolt, lying the frame on its side and supporting it with chocks of wood. Hammer the bolt hard. If it still won’t budge, turn the frame onto its handlebars and saddle; remove the bolt nuts and, using a junior hacksaw, saw through the pivot bolt on the inner edge of the fork blades. You can then pull the forks out from the rear of the frame. The remaining stump is now stuck in the frame. If the bushes are nylon, a blowtorch will melt them out, leaving the sleeve and bolt stumps to be easily tapped out. The earlier bronze bushes can be impossible, and it’s usually necessary to bore through them with increasingly larger drill bits – a laborious and excruciatingly noisy process. Wear headphones – the bike may squeal with pain, and I’ve yet to find the correct anaesthetic!
Now that the parts are all removed, you can survey the need for further action. If the rear forks need brazing or respraying, the rubber suspension block will need removing first. You will need a 1/8 inch drill bit to drill off the 4 pop rivets holding the suspension’s metal plate to the forks. Once drilled off, gently prise up the lower edge of the metal plate from the fork plate and, using a wide screwdriver as a wedge, lift the suspension block away from the fork plate, lifting free of the top edge. Avoid any unnecessary bending, as at this time replacement suspension units are totally unobtainable, and if the plates fail the unit is useless.
Some plates have rusted and will reject the rubber bonding. It is possible to recondition the unit, temporarily at least. Presuming the rubber and metal have separated, thoroughly clean the rubber face with a degreasing agent, then score with a blade. Use Rust Eater (by Turtle Wax Ltd) on the metal face, then rub with emery cloth and score. Apply a flexible adhesive like “Uhu Action +” to both surfaces and clamp for at least 24 hours prior to refitting. The unit will most likely serve for many more years as it operates in compression and is only stressed when the bike is lifted or hung. So never suspend Moultons for storage, nor use Araldite-type adhesives which will simply crack away when the suspension flexes.
To re-rivet the suspension to the forks, see that the fork rivet holes are clear of the old rivets or braze flux; use a pop riveting gun and four 1/8 inch pop rivets; position the holes on the suspension plate to the holes on the fork plate, using a small-blade screwdriver, and rivet home. The suspension plate edge may be slightly puckered after riveting and should be tapped flat using a hammer gently. It may be prudent to run a little Uhu Action + adhesive round the upper and lower rubber and metal joints for protection. Once re-built, I spray the rubber with furniture polish, as I have found that the rubber responds well to silicone coating, which protects it from road dirt too.
Points to consider when re-fitting the rear suspension
Ensure that all new pivot parts are greased, including the back end of the main frame, the suspension’s metal components and 3 self-tapping screws. See that the pivot sleeve is flush with the new bushes in the frame. When re-fitting the forks, you will be ‘fighting’ against the suspension rubber. It is best to position the frame with the head tube to the floor, rear end up. Introducing the forks down onto the frame is best done as a 2 person job. One exerts shoulder pressure down onto the forks, while the other introduces a thin screwdriver through the fork and frame pivot holes, to pull them into alignment. It is wisest to put in the 3 self-tappers at this point to keep the alignment, but often the bolt hole is still off true. Prepare the bolt, look to see which side of the frame hole shows the best alignment and introduce the bolt, shouting orders at your red-faced partner, to exert more or less pressure on whichever side of the fork blades needs to come down to align with the frame pivot hole. Once in line, begin to tap in the new pivot bolt, but stop as soon as any resistance is met, and adjust fork/frame alignment again until the bolt passes through, otherwise you could damage the bolt threads. Once the bolt is in place, fit the pivot bolt nut, but don’t over tighten it, as this will create too much lateral stress and the bolt may snap after some use. This is entirely my own opinion, based on 20 years of experience. There are varying views on whether pivot assembly parts should be held tightly or left mobile, and my view is that they should be firm, but not over tight