MyVincent.co.uk

Wheels Brakes and Steering

Wheels Brakes and Steering

General

There should be just-detectable play at the rim if the hubs have been correctly shimmed; 1/32-in. is a fair value for a cold hub; it permits hub expansion as the light-alloy warms up with running. Clearance can best be tested with the wheel removed and the spindle clamped rigidly in a vice.

If resetting is required it can usually be done very simply. The two inner races of the taper roller bearings are carried on a hollow axle and abut against shoulders. The distance between the races is the deciding factor and this is controlled by shims inserted between the inside of the races and the shoulders. Removing a shim reduces the shake at the rim, adding a shim increases it.

To exclude dirt and water, the brake plates must abut as closely to the drums as possible without touching; contact is audible when the wheel is spun. To move the plate outwards, shims are inserted between the inside face of the plate and outboard of the inner bearing race. When adjusting rim 'shake' do not remove or add shims - transfer them from one side of the bearing to the other. In this way brake plate/drum clearance remains undisturbed.

Felts are normally used to seal the bearings. These are supplied new as plain discs. A few miles use is sufficient for them to take on the right shape to seal the bearings. Bearings are packed one-third to one-half full with high-melting point grease.

An alternative type of hub seal is the racing pattern which consists of a brass turning in the form of a shouldered plate. These offer less friction than do the felt ones which must, and visibly do, wear the brake plates. They are intended to be a tight fit in the bearing housing.

Bearing outer tracks can be removed and replaced by heating the housing carefully with a gas jet and tapping out gently; four indentations made with a chisel retain the tracks also and these must be peened back before bearing removal and new indentations made after replacement. For a while during 1949-1951, taper roller bearings were in short supply and some machines were fitted with metric ball-journal nearings. Servicing of such hubs is really a professional matter.

Brakes

Brake drums are secured to the hubs by eccentrically-headed bolts and self-locking nuts. The six boles drilled in the corner between the drum flange and the braking surface are intended as drain holes; they also exhaust small quantities of air. They get blocked with lining dust and should be cleaned periodically.

There are two types of brake plate - steel or magnesium alloy. The former are standard and not fitted with provision for air scoops. The racing-type plates offer better braking and less unsprung weight but are expensive compared with the plain steel ones: They have self-lubricating cam bushes pressed in, whereas the steel plates are unbushed and feature a grease nipple; grease sparingly, otherwise the linings may be contaminated.

Service-exchange brake shoes undoubtedly offer the best method of renewing brake linings. The owner relining his own however, will find that linings are not supplied ready drilled and countersunk, as shoes are not jig-drilled during manufacture. Pull-off springs should be offered up on to the bare shoes and the whole, as a sub-assembly with cam, slid into place in the brake plate.

The cam spindle terminates in a square shoulder and a portion threaded 3/8 C.E.I. By means of the squared end and the serrated cam arm attachment, it is possible to set the cam arm at the correct angle. It should not pass a right-angle when the brake is fully applied. The two front brakes are compensated whereas the rears, when two are fitted, are not.

The rear brakes are operated by rods which in turn are actuated by a cable working on a cross-over linkage. With the Series 'D', one brake only is used and this, when in good condition, is normally sufficient, though of no more than 7 in. diameter. Trouble is sometimes experienced in synchronizing twin rear brakes; here is one method. Release both brakes fully and screw one adjuster down until the wheel can only just be turned with the utmost difficulty. Now screw it back until the brake just fails to rub, and count the half-turns. Screw up the other adjuster until the almost-locked condition is achieved. Back it off the same number of turns as used for the first brake. If the brake still binds, back both off the same number until all binding ceases. Then screw off a further five half-turns.

The brake application rods and motion blocks in the cam arms are made of stainless steel and no protective finish is needed.

Steering

Whether the front wheel is out or not, the head bearings can be tested for tightness or slackness. The former is apparent on the road to some degree but will show up plainly if the front wheel is off the ground, the damper is slackened fully and the steering is turned from lock to lock. There should be no tight spot, and the steering must fall freely from centre to side.

Slackness will show up on heavy braking though it can be confused with wear in the 'Girdraulic' bushes. With a machine as fast as the Vincent it will pay to renew the bearings if in doubt. The cup-and-ball system is used, the cups being a simple interference fit in the steering-head casting; be careful not to crack the races if new ones are drifted into place instead of being pulled up with a bolt and washers etc. No tilting of races is permissible.

It is possible to get 21 1/4-in. dia. balls into each race; no more than 20 must be used under any account. High-melting point grease is specified for this hearing because of the heat rising from the front cylinder when the machine is stationary. Overgreasing via the nipple provided will result in grease running out of the downward- and rearward-pointing tunnel in the head casting; it will foul the front head. The trouble can be prevented completely by blocking the tunnel with a large cork.

Bearing adjustment is by means of the large hexagonal-head nut immediately below the steering-damper knob; but the head-clip is secured on the head-stem by a pinch-bolt which must first be released. Do not overtighten afterwards or it may break.

A later specification steering damper can be readily fitted and this is claimed to be self-locking, overcoming in this way the tendency of the one-frictionplate type to slacken off. It is a useful plan to mark the knob in some way so that one can tell at a glance how much damper is applied. The damper should always be well-tightened at speeds over say 75 m.p.h. and slightly biting at lower speeds. To obtain precise steering, considerable correction is built in through the trail and the 60 degree head angle and so forth; this has been known to cause steering wobble on a bumpy road. The steering damper is the perfect answer as it lessens the rate of correction but not the amount.

It will be noticed that the damper reaction peg is a loose fit in the hole in the bottom of the head casting. This is intentional. Check that the damper does actually tighten properly and that it is not an illusion caused by rusty or damaged threads on the through-rod-they are 1/4 B.S.F. See that the rod is not bent. A ball peened into the damper notching mechanism and acted on by a captive spring mates with depressions and provides 'click-by-click' adjustment. The ball must, obviously, he free which means that the spring must not be allowed to become rusty or clogged with road dirt. An effective damper is essential for sidecar work to overcome the low-speed 'shimmy' that tries to build up at about 25 m.p.h.

With these things done, and the footrests set at equal heights, the machine should have hairline steering provided that the wheels have been aligned. But a wobbly seat mounting on the 'B' and the 'C' can have a bad effect. If this fault is present, make sure that the front pivot is free from slop and also that the rear friction-dampers do not need renewing. The latter consist of strips of Ferodo trapped in adjustable clamps. Overtightening or binding of these can bend and even break seat supports; auxiliary dampers that squeak may be oiled - but at some expense of friction.

Failure of the machine to handle correctly can now only be attributed to one of three things: the upper frame member or forks may be bent; the tyre(s) may be defective; the wheels may be out of alignment.

A bent frame may result from a twisted upper frame member, that is, the oil tank in the case of the 'B' and 'C'. Or it may originate elsewhere. If, with the wheels aligned, the machine pulls steadily to one side on an uncambered road when ridden 'hands-off' at 45 m.p.h., this means that the model has to be leaned over to bring the steering head vertical when viewed from the front. If the lean is slight it can be ignored or, at worst, countered by moving the rear spindle a couple of clicks out of alignment towards the side to which the rider has to lean - but this is a last resort.

A defective tyre, the result of a manufacturing error, is a rarity indeed. But in the search for an elusive steering fault nothing can be ignored. Check that, with the fitting line true to the rim, the tread peak is central. There have been isolated instances of moulded fitting lines being out of position as a result of poor tensioning of the cover canvas.

Most suspect handling can probably be attributed to riders using machines with the wheels out of alignment though believing the tracking was perfect. Setting the wheels with the aid of a straight edge, or string, is simple enough after making due allowance for the different widths of the front and rear covers normally employed. And maintaining this condition is simplicity itself with the Vincent, thanks to the unique 'click-by-click' knurled adjusters provided. Turning each an equal number of times must maintain the correct adjustment once it has been obtained.