One of the most common of transmission troubles is noise in the operation of the gears, generally a grinding sound. This is heard more in bevels than in spurs, but in old transmissions and on the lower speeds it is heard frequently. A good way to quiet old gears, after making sure that they are adjusted rightly and meshing correctly, is to use a thicker lubricant. If thick oil is being used, change this to a half-oil half-grease mixture or even go so far as to use an all-grease mixture of fairly thick consistency.
In this respect the repair man or amateur worker may take a leaf out of the book of second-hand car men, who are said to "load" an old and very noisy transmission gear with a very thick almost hard grease in which is mixed some shavings, sawdust, cork, or similar deadening material. When this is done, a graphite grease is generally used, so that the shavings, cork, etc., would not show in case it was necessary to take off the gear-box cover. This material will fill up all the inequalities of the gears and shafts so that temporarily, everything fits more tightly, and in addition all the sounding-board, or echo, effect is taken out of the transmission case. This sounding-board effect is fully as important as the former, for many really insignificant noises are magnified, by poorly shaped gearcases, so as to appear very loud, indicating serious trouble which needs immediate attention, when such is really not the case.
Another source of gearset noise is a shaft out of alignment, caused either by faulty setting, by worn or loose bearings, or by yielding or cracking of the case. If it is properly set at one end and is out at the other, the trouble will be more difficult to find and remedy.
Heating is a common trouble, too, but usually this can be traced to lack of lubricant in an old car, of too large shafts or too small bearings in a new one. Sometimes the grease used will cause heating, particularly when long runs are made with the transmission working hard. This is most noticeable when the grease or lubricant is of such a consistency that the gears simply cut holes in it but do not carry any around with them, or do not otherwise circulate the lubricant. This can be remedied by making it thicker so the gears will cut it better, by making it thinner so they will splash it more, or by changing the nature of it entirely to a form which is more sticky and will adhere more tightly.
Fig. 79. Types of Gear Pullers.
One of the principal necessities for transmission work is a form of gear puller. These are like wheel pullers, except that they are smaller and more compact. In Fig. 79, a pair of these are shown. The one at the left is very simple, consisting of a heavy square bar of iron which has been bent to form a modified U. Then, a heavy bolt is threaded into the back of this or bottom of the U. This will be useful only on gears which are small enough to go in between the two sides of the puller, that is, between the sides of the U, which in use is slipped over the gear, the screw turned until it touches something solid as the end of the gear shaft, and then the turning continued until the gear is forced off.
While not as simple as this, the form shown at the right has the advantages of handling much larger gears, and also of being adjustable. As the sketch shows, this consists of a central member having slotted ends in which a pair of L-shaped ends or hooks are held by a pair of through bolts. Then there is a central working screw. To use, the hooks are set far enough apart to go over the gear, then slipped around it and hooked on the back. The central screw is turned up to the end of the shaft, and then the turning continued until the gear comes off. There are many modifications of these two, in fact practically every repair shop in the land has its own way of making gear or wheel pullers. At any rate, every shop should have one.
(The repair man should use a great deal of care in doping out or diagnosing the trouble in a transmission, for frequently what appears at first to be at fault turns out to be all right; or else something is back of the first trouble which must be corrected before a remedy can be applied. Thus, recently, a repair man figured that a new gear was needed to repair a transmission. This was received from the factory three days later, and when he started to put it in, he found that a bearing was defective; in fact, the defective bearing caused the wear in the gear. This necessitated a further delay of three days in order to get a new bearing.
A common transmission trouble is poor gear shifting. This may be due to a number of different things. For one thing the edges of the gears may be burred so that the edges prevent easy meshing. When this is the case, any attempt to force the gears into mesh only burrs up more metal and makes the situation worse. Whether this is the trouble can be determined very quickly and easily by removing the transmission cover and feeling of the gears with the bare hand; the burred edges can readily be distinguished. If this is the only fault, the transmission should be taken down, the gears taken out and placed in a vise, and the burrs removed with a cold chisel and file.
Poor or worn bearings or a bent shaft or one not accurately machined may cause difficult shifting. If the bearings are worn, the difficulty of shifting will be accompanied by much noise, both in shifting and after. The bent shaft is more difficult to find and equally difficult to fix, a new shaft probably being the quickest and easiest way.
Sometimes the control rods or levers bind or stick so that shifting is very difficult. In case the gears are difficult to "find" or will not stay in mesh, the fault may be in the shifter rod in the transmission case. This usually has notches to correspond to the various gear positions, with a steel wedge held down into these notches by means of a spring. The spring may have weakened, may have lost its temper, may have broken, or for some other reason failed to work. Or with the spring in good working condition, the edges of the grooves or notches may have worn to such an extent as to let the wedge slip out of, or over, them readily.
In the Ford transmission band assembly there are three springs, which it is difficult to assemble because of the trouble in holding so many things at once. To eliminate this trouble the tool shown in Fig. 80 can be constructed, this being made from flat bar stock. The handles, if they could be called that, are pivoted together and carry at one end a kind of flat jaw with three notches. When the two of these are squeezed together by means of the screw and handle at the other end, the flat plates will hold the three springs tightly enough so that all can be inserted in their proper positions at once, and by using but one hand. Tools of this kind, which save a great deal of the workman's time and thus save both time and money for the owner of the car, should, and in fact do, distinguish the good well-equipped repair shop and garage from the old-fashioned kind which is only in the business for the money, and not too particular how to get it.
In transmissions of the planetary type, there is little or no trouble except with the bands. If these are loose, the gears will not engage and the desired speed will not result. If they become soaked with grease, oil, or water, they will not work as well as if kept clean, and in the case of excessive grease, will slip continually. If the band lining becomes worn, it should be treated just as a brake lining is. When inspected for wear and found not badly worn but slippery, it may be cleaned in gasoline and then in kerosene, after which a saw, hacksaw, or coarse file may be used to roughen it. Sometimes greasy bands can be fixed temporarily - say, enough to get the car to a place where tools, materials, and] facilities for doing the work are available - by sprinkling on powdered rosin or fuller's earth. The former should be used sparingly because it will cause the band to bite or grab hold when forcibly applied, and at times has been known to cut into and score a cast-iron drum. In general, as stated previously, planetary transmission bands should be handled in the same way as ordinary brake hands, as to lining and relining, roughness of surface, lubrication, etc.
Fig. 80. Handy Spring Tool for Ford Assembly.