Vetting a Used Vehicle
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by Edward Meeson, M.I.R.T.E.
A Systematic Method of Inspection Which Should Provide the Prospective Purchaser With a Sound Bargaining Background .• Judging from a Road Test
IN inspecting a used commercial vehicle, there are two important features to observe. The first is to have a knowledge of what to look for and, secondly, to work to a system.
I attach great importance to carrying out a road test, because if the vehicle proves to be unsatisfactory on the road, then it may be a waste of time to subject is to a mechanical inspection.
Any such road test should be for at least 10 miles, by which time excessive oil leaks, overheating and other bad symptoms, can be expected to show themselves. Any such test should also include an average main-road hill.
Before setting out, it is advisable to check tyre pressures as any great differences in the front tyres may give a wrong impression of • the steering.. At the same time, the tyres should be
examined for condition. '
Assuming that the vehicle is equipped with an electric starter, it should be noted whether this operates. quietly and with reasonable smoothness, or whether an excessively harsh, racking sound is emitted as the engine is turned over. In the latter case, it is likely that the teeth of the flywheel ring gear are badly worn and it should be remembered that such a replacement is fairly expensive. Should the starter have any great difficulty in turning the engine, this will almost certainly indicate nothing more serious than a discharged battery which can either be recharged or replaced according to its general condition.
When the clutch pedal is depressed. R40 it should be noted whether the first gear can be engaged quietly and easily. Ii not, and the gear has to be forced in, with resultant crashing of the teeth. this 'Will point to faulty clutch-control adjustment which is usually a simple matter to correct. Should the trouble be in the clutch mechanism itself, this is a more serious matter. A wobbly feeling on the clutch pedal when the foot is applied usually indicates wrong adjustment of the toggle levers.
Dial Readings Important
Ignition and oil-pressure warning lights, if fitted, will be checked for correct functioning before taking the vehicle on the road, and if there is an ammeter, this should also be checked. Oil-gauge readings should be noted when the engine is hot and checked against the maker's figures.
At the first opportunity the brakes must be given a quick test to see if they are reasonably safe. If their condition is not satisfactory, the road test should be delayed until any faults have been corrected.
Regarding the gearbox, a good way to test this is to change up and down through the full range of gears 'several times, observations being made of the quietness, or otherwise, of the intermediate ratios. A noisy gearbox indicates worn gear teeth, or excessive wear may have taken place in one or more of the bearings. In the latter case, it would probably show up in the form of excessive leakage of. oil from the inputor output-shaft bearings, as oil-seals quickly become .faulty when the bearings t are badly worn.
To test whether the gears are inclined to jump otit of mesh, the vehicle should be accelerated smartly from a low road speed and ,.as suddenly decelerated from a higher, speed, this test being applied to all the gears, If jumping-out occurs it may indicate either worn gear teeth, which is Serious, or weak selectorrod retaining springs, which is not.
There is little that.can be done about testing the rear-axle beyond noting•that it is not unduly noisy, either on the drive or the over-run. A test for the steering gear is t6 attain a speed of about 28 m.p.h. and to note whether the steering feels reasonably light, or whether it drags and appears heavy. Such a condition could be caused by lack of lubricant Or excessive Wear in the king-pins and bushes.
If the vehicle tracks properly it should be possible to release the steering wheel momentarily and observe whether the vehicle shows any tendency to veer to the right or left. This test should be carried out on a flat road, or on the crown of one which is cambered. A tendency to deviate from straightahead travel would indicate incorrect alignment of the front wheels Or, possibly. there is some fault in the steering layout.
Should there be a tendency for the vehicle to weave, as opposed to veering to one side., the cause might be traceable to excessive wear in the steering-rod joints, or to the steering box being loose on the frame, or a combination of the two. An incorrect castor angle of the king-pins will result in the vehicle having to be pulled hard round a corner, with the result that the vehicle has to be straightened out with considerable physical effort after the vehicle has taken the turn. This would be a case for an expert both to decide, and to rectify.. .
Before attempting to test the brakes • make sure that there are no vehicles following close behind. Note first of all whether the vehicle pulls up squarely. on all four wheels. With straight.
mechanical brakes, incorrect adjustment or faulty compensation of the linkage may result in one wheel locking. Similar trouble could be caused by uneven wear of the brake facings.'
In the case of hydraulic brakes, compensation cannot be at fault and therefore if one wheel shows a tendency to lock it will be due to the faulty condition of the brake facings or to seizure, or partial seizure, of one of the bisectors.
Unsteady Braking
Should the vehicle show signs of stewing to the righter left during an emergency brake application, faulty compensation or had condition of the facings is probably reSponSible. There are two faults peculiar to hydraulic brakes, one being 4 spongy feeling when the pedal is..pressed, and the other when ".double pumping' or two or more brake applications in quick succession are required to make the brakes effective. In the former case, it indicates the presence of air in the system, the cure for which is known as bleeding.
In the second case, the -trouble may be due to faulty adjustment of. the shoes or that the facings need replacing. On some vehicles there is a 'rubbercovered inspection hole in the brake back-plate, through which the Sides of the facings can be seen. It will also be possible to see if the facings are soaked in oil when, of course, the brakes would cease to function. It should be made clear that bleeding the system will not effect a cure if the trouble calls for double pumping. Unless the hy.dratilic, fluid, has been allowed to become excessively -low which would permit air to •enter through the Master-cylinder, bleeding of the system is rarely necessary.
Note should be taken of the security of the driver's seat when fullbrake applications are made. A faulty seat
could lead to a .serious accident. •
The hand brake is frequently overlooked. It should be .capable of holding a vehicle on any -main-road hill under full load conditions. 11 would be as well to examine the teeth and pawl of the-. hand 'brake lever, and if these cannot be easily seen, the lever should be pulled, on slowly, one click at a time, to see that each tooth engages firmly. If the [eller can be pulled for, mOre than three7quarlets of its full travel, the brake ,'mechanism' is in need of adjustment: • • " With the assistance of • the: following suggestions, it should be within the scope of an intelligent driver to assess the performance and capabilities of the engine. To lest the compression, the engine should first be well warmed up. Compression of each cylinder should be gauged by use of the starting handle. If the compression is good, it should be possible to bounce the handle; but if turning the engine produces a hollow blowing noise and there is mi bounce, it points to a compression leakage past the piston and rings. On the -other hand, the valves may be faulty, but, in this Case, the trouble will nbt proclaim itself by the same hotloW blowing sound, as when the fault is due to the pistons and rings.
Poor compression, due to faulty valves, can -easily be remedied, but in the other case it may mean that the cylinders need reboring: At the same time as this test is 'being carried out the opportunity Shatild 'be taken .to make an inspection for excessive oil leakage atsump. joints, -gearbox and back axle -Engine Test
. A _good testfor the general con . . .
.dition of the engine is to take the vehicle on to a -reasonably level road, get into tOp 'gear and allow the engine to pull :tt, a fairly slow speed. With top gear still engaged, the•engine should be gently accelerated when, if the carburation is correct and the ignition timing is in accordance with the maker's setting, not only should the engine run smoothly -bin it should respond to the accelerator nmi pick up speed without' Under these conditions an engine that is well eatboned-up and illtuned Wilt probably pink eXcesSively --and show signs of Missing.
• Should a governor be fitted it is, important to see that it is functioning'
at the correct road speeds -each gear. The vehicle maker's -handbook will give the Toad speed ineach. geiir at which the governor should cut in.
The test should be carried. out on a fairly level road. Assuming that the cut-in speed in third gear is 26,1114xh. and it is possible 'to exceed this speed before it does so, then the engine is being over-revved. Conversely. if the governor cuts in at, say, 22 m.p.h. then power is being lost because the engine is incapable of reaching its peak power output on the respective gears.
Governor Cheek Governor action should he positive in cutting in and cutting out and provision for adjustment is made. Tests have now been made of the engine, clutch, gearbox, rear axle, steering and brakes and if none of the faults referred to is found to exist then the prospective buyer can he reasonably sure that he is taking over a reliable vehicle. It should be remembered that as the road test will probably be conducted with an unladen vehicle, should the performance be poor it is likely to be particularly bad under full-load conditions.
There is, of course, the static mechanical test, the:procedure in connection with which will be detailed in an article to be published in our next issue.