Information normally required when carrying out routine maintenance.
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Loosening of wheel nuts may not be as common as it was in the days when CFs were in production - there aren't so many around now and annual mileage often is low - but being aware of the possibility can save a lot of pain in the wallet if not prevent loss of a wheel.

The symptoms of a loose wheel can vary, from squeaks and clunks to rattles and vibration, and easily can be missed or mistaken for something else such as oval brake drum if vibration only is noticed under braking.

The remedy is simple: check the tightness of the wheel nuts on a regular basis. However, there is no one simple answer to how often wheel nuts should be checked for tightness; what 'regular' comprises will depend on are axle weight (i.e. load), tyre pressures, style of driving, suspension stiffness and vehicle condition and maintenance.

AXLE WEIGHTS

The weight of the payload must be properly distributed over both the front and rear axles, although not necessarily evenly. The maximum weight the front axle can carry and the maximum weight the rear axle can carry are shown on the Vehicle Identification and Weight Plate.

Note that the sum of these may be greater than the GVW, so that it is not necessarily proper to load both axles at the same time to the maximum capacity shown for each.

The GVW rating represents the weight of the complete vehicle taking into consideration the payload, engine, transmission, frame, spring and tyre capabilities.

Actual front and rear end weights at the ground can only be determined by weighing the vehicle. Care should also be exercised to see that the payload is distributed on both sides of the centre line of the vehicle as equally as possible.

To determine front and rear axle weights first weigh the complete vehicle on a weighbridge. This is the GVW.
Then weigh the front axle only with the wheels positioned as close as is possible to the centre of the weighbridge.
To weigh the rear axle similarly turn the van around in order to compensate for any deviation in ground level.
The sum of axle weights may or may not equal the GVW.

Add together the two axle weights then divide each axle weight by the total.

For a GVW of 2250kg, front axle weight of 1000kg, rear axle weight 1300kg -

1000/(1000+1300) = 0.4348

1300/(1000+1300) = 0.5652

Now multiply the GVW by each result to obtain the axle weights -

Front axle weight = 2250x0.4348 = 978.3kg

Rear axle weight = 2250x0.5652 = 1271.7kg

These figures will be within specification for a short wheelbase model (CF230, CF250) and, all other things likewise being within specification, loosening of wheel nuts should not be a problem.

When axle loading exceeds specifications there is a risk of wheel nuts loosening due to stresses on wheels, nuts and bolts beyond design limits. There is a margin of safety if only to cater for shock loading to be expected as wheels traverse road surface imperfections but using up this margin by over-loading enhances the probability of loosening of wheel nuts.

This can happen on any CF model but CF280 models with 5-stud hubs and large bodies (campers, ambulances) a particularly affected. Indeed, some ambulances based on the CF280 chassis were fitted with 6-stud hubs for spigot mount wheels to avoid this problem.

TYRE PRESSURES

Tyre pressures given in Owner's Manuals and elsewhere are for vehicles in a fully laden condition. If the vehicle is to be operated in a partly laden condition then tyre pressures should be adjusted in accordance with the tyre manufacturer's pressure chart.

The standard tyre pressures given are for vehicles operating in the UK. In some overseas countries permitted payloads may be increased or decreased according to local regulations which could affect tyre pressures.

Tyre pressures should be checked at least weekly and maintained at the correct pressures according to vehicle load. Do not overlook the spare wheel.

Radial ply tyres have an appreciable bulge where they contact the ground even when inflated to the correct pressure. This does not denote under inflation.

Tyre pressures in excess of specifications will increase shock loading on the wheel, nuts and studs as well as the suspension. This can be readily experienced as a harsh ride and likely many rattles and clunks besides if any load is loosely stowed.

Excessive tyre pressures often are avoided just for the sake of comfort once a driver becomes accustomed to the vehicle and its limits. Going too far the other way (under-inflated tyres) will waste money in fuel cost and tyre wear: don't rely on how a tyre looks or feels hard when kicked. Avoid doubt by using a good quality tyre pressure gauge, e.g. PCL pencil type (type TPG1H01, or TPG4H01 for twin rear wheels).

STYLE OF DRIVING

The intrinsic stability of the CF due to independent front suspension and relatively wide wheel track dimensions allows for an amount of uneven loading side to side. This also lends itself to hurtling about at the limits of tyre adhesion if the load is compact and has a relatively low centre of mass. Indeed, a laden CF can out-pace many a van of similar size and vintage (and even much younger) when tackling twisty country lanes at a lick but that's somewhat extreme.

Heavy-hoofed driving of all descriptions can loosen wheel nuts on any model CF, even when unladen and more inclined to slide and skip around tight turns than go where pointed. A lot else can shake loose or fall off too.

Remedy is obvious ...

SUSPENSION STIFFNESS

In this context tired springs allowing suspension travel to the bump stops on uneven road surfaces can be as effective as up-rated suspension in shaking loose wheel nuts. Distinction can be made between steel and air suspension upgrades, the latter being superior for stability but bringing with it a tolerance of heavy-hoofed driving as well as adjustability for even ride height regardless of axle load.

As a general rule any increase in suspension stiffness beyond specifications can cause loosening of wheel nuts whether or not axle loads, tyre pressures etc. are within specifications. Original suspension bushes and attachments also may suffer, particularly on CF350 models with heavy duty suspension (CF350L or CF350 with Code 580) where the swinging shackle is prone to fracture.

The problem here usually is down to age and constant laden state of much of the surviving CFs, predominantly motor homes and ice cream vans. Interventions aimed at restoring ride height of a CF gone soggy at the rear must be carefully thought out starting with checking for over-loading be it due to additions and alterations in the van or its payload over its life.

If the axle weights are within specification and the problem boils down to tired single taper leaf springs then proprietary kits usually will suffice. Multi-leaf springs can be repaired and re-tempered and helper leaves can be fitted to any leaf spring arrangement (as is the case for CF350L or CF350 with Code 580). The aim should be to restore ride height for the maximum axle weight allowed, not compensate for over-loading.

Special bodies (motor homes, ice cream vans etc.) often lend themselves to alterations and additions to suit individual circumstances, a merit of old technology put together with bolts and screws rather than made up of sub-assemblies of floor, sides, ends and roof stuck together mostly with glue. The demerit of course is the weight, timber frame construction being relatively heavy, but this would be offset by the use of lightweight materials and construction.

The margin for loose payload will be limited especially if there is much of a body overhang beyond the original chassis rear panel. With some motor homes the margin can be next to b-all but usually this normally applies to top-end gin palaces (of the 1970s anyway) already provided with all mod cons for the number of beds fitted. A life of several owners with their own individual (and sometimes misguided) ideas about what constitutes an improvement can tip the balance all too often: witness the tired old things that have suffered a re-vamp using B&Q chipboard which may well be aesthetically pleasing but far too heavy a material to replace original doors and worktops.

Coachbuilt bodies with inter-panel seams, either lapped edges or butt edges overlaid with trim, have another feature: they are prone to water ingress due to deterioration of joint sealant. If water leaks into the body are evident then the body frame and insulation could be so waterlogged that the rear axle is overloaded even when all loose content has been removed.

Better to deal with any overloading than create more problems by tinkering with the suspension; fuel consumption should improve too.

VEHICLE CONDITION AND MAINTENANCE

Wear and tear over about 40 years of use alone can lead to wear of wheels, nuts and bolts even without any abuse and improper maintenance meanwhile. Often wear is not significant or may not be noticeable especially if wheels, nuts and, or, bolts have been renewed in the past, e.g. when loose bolts or worn nuts found during normal maintenance.

Slight wear of wheel nut cones and conical recesses in the wheels usually can be accommodated by re-tightening of the wheel nuts soon after wheel replacement to allow for cones bedding in to recesses. If the recommended tightening torque for wheel nuts is adhered to when a wheel is disturbed then this re-tightening usually can be left to about 1000 mile after initial tightening.

One exception is when brake drums are disturbed especially if a drum has been particularly stubborn about coming off: the drum may not fully bed against its hub flange until the vehicle has been driven a few miles. Twin rear wheels are another exception especially if mating wheel centres are rusty or the conical washers against the brake drum have been disturbed and don't lie perfectly flat on first tightening of the wheel nuts.

If normal service procedure is followed when carrying out regular maintenance then the first re-tightening should occur after a road or roller test and in fact this operation is listed on the CF service checklist. Note however that re-tightening should not be done if brakes, hubs or wheels are hot: allow them to cool to ambient temperature. A Wheel change notice can be used as a reminder to re-tighten at about 1000 mile.

Over-tightening of wheel nuts, whether in a misguided attempt to cure loosening without investigating the cause or over-enthusiastic use of an air wrench, must be avoided in order to prevent 'thread stretch' of nuts and damage to cones or wheels or loosening of wheel bolts, on CF350 models often accompanied by fracture of the bolt head and commensurate damage to the hub flange.

Use of any lubricant on bolt and nut threads also should be avoided: threads should be clean and dry. The only lubricant necessary is on wheel nut cones particularly on 6-stud hubs to aid tightening to the specified torque.

Best fit of a wheel nut is achieved when marking of the nut indicates contact with the full width of the conical depression in the wheel. Ideally the contact area should be towards the leading edge of the cone on the nut.

Attention is required when a wheel or a nut becomes so worn that the contact area is higher up the taper, the ultimate limit being when the nut bottoms against the hub flange or brake drum or a wheel brace slips off for lack of purchase on a sunken nut.

If a wheel nut binds on any wheel bolt indicating damage to the leading threads (i.e. nut will spin on backwards until the binding threads meet the wheel bolt) then check for other indications of a wheel running loose such as rust stains around wheel nuts and rounding of the contact area between nut and wheel.

Slight wear of cones and seatings usually is of no consequence: nut and wheel are malleable enough to bed in together after proper tightening and re-tightening especially if worn nuts are dispersed about the vehicle.

Nuts that are badly worn or creak and shriek on the wheel bolts before being tightened (along with some bad language more often than not) ideally should be replaced. Indeed, if a wheel nut binds enough to jerk and crack as it is turned then remove it before it can jam and loosen the wheel bolt. Until a nut is properly tightened the wheel bolt is vulnerable, as can be demonstrated by the ease with which wheel bolts often can be knocked out with a single hammer blow when replacement is required.

New wheel bolts MUST be pressed or drawn into the hub flange until the head contacts the flange. DO NOT hammer in new studs. Wheel nut tightness must be checked frequently after renewing bolts until all residual movement ceases and the required torque setting is maintained.

Particular care must be taken when fitting alloy or other non-standard wheels.

Alloy wheels MUST be fitted using appropriate wheel nuts, i.e. with cones or loose conical seatings suitable for the particular wheel. Cones or loose seatings required often are larger in section than standard cones and sometimes have a different taper angle (standard taper angle is 60°).

Steel wheels with thicker section centres than standard also may require flange type nuts with larger section cones (e.g. Ford Capri, Escort etc., dome or open type) if only to ensure that sufficient of the flats remain above the surface of the wheel centre for proper tightening and ease of removal.

Banded steel wheels and wide profile tyres ordinarily won't affect wheel nut security but if the wheel centre offset is much away from standard it is wise to bear in mind the possibility of this being a cause of loosening of wheel nuts if no other cause is found. Here the use of acorn nuts (7/16-inch UNF thread) tall enough to stand well proud of the wheel centre will aid removal and tightening especially if 13-inch wheels are fitted to the front axle. A bit of chrome plating wouldn't go amiss either. :)

Last but not least: if wheels are to be refurbished then ensure that there is no build-up of paint or other coating around mounting holes or on any part of a wheel in contact with hub flange or drum or other wheel.

SUMMARY

Check your nuts. :)

If you don't have a torque wrench or any inclination to get grubby then get your local garage or tyre fitter to re-tighten wheel nuts if you have had to change a wheel yourself, e.g. after a puncture.

In theory the original wheel wrench should be adequate for loosening and tightening wheel nuts at the roadside with the proviso of checking the tightness with a torque wrench at the first opportunity. In practice something a bit more substantial may be needed but that's more a measure of lack of maintenance than anything else.

Even if wheels and hubs are removed together for brake inspections (front hubs with drum brakes, fully floating rear hubs with twin wheels) the wheel nuts should be checked at every service nonetheless (i.e. security, condition) and at least slackened then re-tightened so that it is possible for normal people to loosen them with the original wheel wrench.

If you maintain your own CF then invest in a torque wrench and follow normal service procedures especially the first re-tightening after any wheel is disturbed.

Be sure to investigate further according to which of the factors of axle weight, tyre pressures, style of driving, suspension stiffness and vehicle condition and maintenance may apply to your CF if wheel nuts persistently work loose or if you find rust staining around wheel nuts -

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or worse -

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Postby admin » Fri Jul 08, 2016 6:04 pm