Failure Analysis
Contents
1. Gear mechanical part to transmit motion 16 Gear Jumping shift lever movement out of a selected position Gear Locks device to keep a gear engaged Hard Shifting use of excessive force to move the shift lever Offset Spalling caused by a bearing being subjected to extreme overload conditions in a short period of time Oil Seal device used to confine oil to a certain area Pitch Line location of a gear tooth midway up the tooth Pitting resulting marks when the endurance limit of the material is exceeded Proper Lubrication describes a transmission that has the proper oil level and recommended oil type Root Diameter innermost part of a stress concentration such as the bottom of a groove Scoring resulting marks caused by excessive heat generation in the gear mesh Seized condition caused by a lack of lubricant and the presence of high heat Shockload violent impact on a gear tooth that ususally causes the tooth to break Torsional Vibration twisting action that may be either reversed back and forth or unidirectional one way2. E Improper Installation e Use of improper tools e Improper installation of the oil seal in the bearing cap seal cocked in bearing cap bore e Installation of damaged yoke or input shaft with burrs or nicks E Storage and Handling Damage E Improper storage of oil seals E Improper protection on output yoke or input shaft sealing surfaces E Improper method used to prevent sealing surface from rusting E Excessive Heat e Breakdown of lubrication e Use of improper lubrication e Use of lubricant not compatible with seal material 13 NON WARRANTABLE CONDITIONS Product Warranty IubricationFailure A transmission product warranty covers repairs when the product proves defective in normal use Normal Wear All components will wear to a certain degree under normal operating conditions New units have an initial break in period in which compo nents wear until mating with one another result ing in greater contact surfaces The most impor tant factor in keeping wear to a minimum is adhering to proper maintenance schedules and including an inspection of transmission compo nents and lubrication If components with exces sive wear are found check and replace them as needed Replacing worn parts is less costly than replacing an entire unit later Pitting scoring and galling can occur when the gear NOTE Always use the correct maintenance material endurance limit is exceeded Lubrication problems manual and genuine
3. in wrong gear too high a gear e Review shifting procedures e Driver training E Starting the vehicle while the brakes are still applied e Driver training E Popping the clutch e Driver training E Overloaded vehicle e Check gross vehicle weight specification WE Backing into a loading dock e Driver training WE Tires spinning then quickly gaining traction e Avoid spinning wheels if possible F A L U RE 8 A fourth common cause of gear failure is clash shifting When a driver shifts a transmission before the engine and transmission speeds are matched or before the synchronizer can do its job a clutch collar is forced into gear The result is worn clutching teeth that can lead to the transmission jumping out of gear See Figures 8 and 9 Gears collars or shafts with worn clutch ing teeth or gearlocks should be replaced x lt SHIFTING CAUTION Improper shifting of the transmission will result in worn clutching teeth which may lead to the transmission jumping out of gear If the transmis sion jumps out of gear there could be a loss of power In order to avoid worn clutching teeth you must 1 assure that the driver receives training and adheres to proper driving tech niques 2 inspect the vehicle and replace any worn gears collars or shafts Figure 8 Failure to use the clutch can cause worn clutching teeth a major cause of transmissions jumping out of gear Shown here are worn clutching teeth left and n
4. leave in sand see Figure 5 Generally bending forces on the gear teeth will create cracks in the tooth s surface Over a period of time the crack will continue to grow Causing a beach mark design fracture pattern Finally the tooth is weakened to the point where it breaks off The surface of the failure is generally smooth and will have con toured lines which show how the failure pro gressed A fatigue failure such as this is caused by loading the vehicle beyond its specified gross weight or by abusive operation on the vehicle on rough terrain Gear teeth that have rolled over are an additional sign of heat and lubrication problems During a teardown always inspect gears for signs of pitting scoring galling cracks and rolled teeth Replace any worn or damaged gears If one gear shows signs of trouble also check the mating gears for possible damage Use a magnetic particle crack detection system to do this Figure 6 A broken shaft and missing gear teeth indicate shockload C OM PON EN T Figure 7 A twisted mainshaft indicates shockload A gear tooth that has broken below the root line is a good indicator of shockload Usually mating gears also show signs of the shockloading Always replace the damaged gear and the mating gears even if they do not look damaged Also check the rest of the transmission for dam age from the broken gear tooth traveling through the unit Common Causes of Shockload E Starting
5. leaving metal deposits 11 C OM PON EN T Figure 23 Discoloration is a sign of heat which is related to lubrication problems Improper driveline angles or offset out of phase universal joints will cause torsional vibrations severe enough to break down oil film For more information on proper lubrication see the Heat and Lubrication section of this publication page 2 and review the specifications in your service manual A third big cause of shaft failures is shockload ing see Figure 5 DX See VIBRATION WARNING and LUBRICA TION CAUTION pgs 2 and 3 12 S Transmission seals are the most common cause of problems in vehicle transmissions If the Front Bearing Retainer amp Seal problem is not repaired properly major transmis sion failure can result Spicer transmissions have hen installing the front bearing seals with an improved design that use new tame and seal in the transmission sealing materials use the red plastic sleeve to prevent seri ous damage to the oil seal Failure to use Causes of Seal Failure the seal sleeve will void the seal warranty E Contamination e Dirt e Oil e Grease e Water M Faulty Repairs e Damaged output yoke e Incorrect diameter yoke sleeve e Seal lip damage during installation e Output yoke seal surface not machined properly e ee manual repair of yoke with emery clot e Output bearing wear and or failure causing excessive runout or endplay
6. Figure 19 the shaft must be replaced to protect against gear jumping Figure 19 Worn shaft gearlocks can lead to gear jumping Oe On et aes O N ee 7 lis Figure 20 Worn gear locks on the clutch gear can lead to gear jumping Also examine gear locks on the clutch gear Worn gear locks on mainshaft clutch gears contribute to gear jumping see Figure 20 If gear locks are worn replace them Also check for proper clutch adjustment and verify that transmission lubrication is correct Also check the output end of the shaft for signs of end yoke vibration This is indicated by a shiny area on the output yoke shaft splines see Figure 21 This problem can be avoided by tightening the yoke nut to the specifications listed in the Spicer service manual Fretting corrosion is a common type of surface damage that occurs when two materials rub while vibrating very slightly Such corrosion is common at surfaces of splines and other close fitting parts that are subject to minute relative movement Figure 21 Shiny areas on the output yoke splines indicated end yoke vibration Gear seizures and discoloration of the shaft especially a blue hue indicate heat problems see Figures 22 and 23 Heat problems can be traced to inadequate lubrication using the wrong type of lubricant or not changing the lubricant frequently enough Z See LUBRICATION CAUTION pg 3 Figure 22 A gear seized on this shaft
7. SOME COMMON TRANSMISSION COMPLAINTS Hard shifting When hard shifting is reported the first thing to be inspected is the clutch An improperly operat ing clutch will interfere with the shifting of gears in any transmission And don t overlook the obvious Spicer transmissions require the correct lever ratio to shift properly This ratio is calcu lated from the fulcrum both up and down Syn chronized transmissions require a shift lever ratio of 8 to 1 for proper shiftability Next examine the remote control linkage for proper adjustment worn bushings bent rods or lack of lubrication If none of these are the prob lem remove the remote control from the trans mission By removing the remote control and shifting the transmission into gear with a pry bar you can determine whether the transmission is at fault If the shift rods move readily into position the trouble is somewhere in the external linkage If not consider these possible causes of hard shifting E Worn or bent shift rods or shift rails e Replace as necessary E Broken springs or elongated poppet holes in shift cover e Replace springs shift cover or both WE Clutch collars tight on mainshaft splines e Check for twisted mainshaft and replace E Free running gears seized on either the thrust face or the shaft diameter e Use correct type of lubricant at the proper fill level E Broken thrust washers or snap rings e Replace and check for vibration mM Exces
8. Spicer transmission parts to CaM RgO COUE O ERE CORGO ensure a proper repair Shockload Non Warrantable Conditions The following photos show examples of non warrantable conditions These conditions are due to misuse negligence improper maintenance or improper operation A broken shaft and missing gear teeth indicate shockload 14 NON WARRANTABLE CONDITIONS Torsional Vilbration Worn clutching teeth indicate a clash shifting condition Vibration can cause the brass ring to separate from the rest of the synchronizer Sheared synchronizer pins are also a sign of vibration Over Shifting Torsional Vilbratiion Wl _ 5 T 3 a Whe Fork pad wear is caused by over shifting and clash shifting Torsional vibration caused these worn teeth LES e L O S S A R Y Addendum portion of a gear tooth between the pitch line and the tip of the tooth Beach Marks visible lines on a fatigue fracture that show the location of the tip of the fatigue crack Contaminate to make impure by foreign mate rial Clutch Collar device used to engage from one gear to another Dedendum portion of a gear tooth between the pitch line and the root of the tooth Fatigue Failure minute cracks that grow under the action of fluctuating stresses Fracture break or separation of a part into two or more pieces Fretting Corrosion surface damage that occurs when two materials rub while vibrating slowly
9. as well as to scoring and galling is improper lubrication Improper lubrication refers to lubrication break down improper lubricant levels and contami nated lubrication Any breakdown of the lubrication or reduced oil film can increase the possibility or acceleration of tooth surface distress More importantly inadequate lubrication for a sustained period is likely to cause the distress to advance to more severe stages Common causes of inadequate lubrication are E Low lube level E Inadequate lube viscosity E Use of incorrect lube E Use of oil beyond its functional life This can lead to alternate welding and tearing of metal from gear teeth surfaces see Figure 3 gt lt See LUBRICATION CAUTION pg 3 C OMPONENT As the hardened gear teeth surfaces begin to wear away failures arise A sudden shockload failure shows clean break lines see Figure 4 Figure 5 A beach mark signals a fatigue failure that has developed over time ha 7 y u ye Re 3 3 at Along with lubrication problems and normal Figure 4 A clean break indicates a sudden shockload wear another cause of gear damage iS failure shockload Shockload failures may occur imme diately after the initial shock or at a later date The mainshaft can also be damaged see Fig ures 6 and 7 A gear failure that occurs over a longer period of time has oyster shell or beach marks These marks look like the pattern ocean waves
10. detent position are two obvious causes of fork pad and fork shoe wear see Figures 13 and 14 A third cause is using the shift lever as a hand rest Prevent these prob lems through driver awareness and training See SHIFTING CAUTION pg 6 Figure 11 Seized bearing Figure 13 Fork pad wear Figure 12 Lack of lubrication to the pocket bearing resulted in a bearing seizing to this input shaft note the ring of metal If a bearing isn t properly lubricated bearings may seize see Figures 11 and 12 Discolora tion especially a blue tint is a sign of heat Heat is generally caused by improper lubrication This can mean the wrong type of lubricant not enough or too much lubricant using lubricant past its useful life or using contaminated lubri cant Figure 14 Fork shoe wear See LUBRICATION CAUTION pg 3 C O MPON EN T A fourth less obvious cause of fork pad wear is a loose output nut A loose output nut will allow the mainshatt to move back and forth This motion not only can damage the shift forks but can crack or break thrust washers To prevent this always tighten the output nut to the torque speci fications listed in your Spicer transmission ser vice manual Synchronizers Some of the leading causes of synchronizer failure include improper shifting techniques vibration and lubrication problems Starting the vehicle in the proper gear An empty truck can be started
11. e transmission i e aero body configurations low front bumpers deck plates skirting or an exhaust pipe near the transmission E Any vehicle application that has high transmis sion shaft speed at low ground speed or runs above 250 F continuously E Geographical locations in which the vehicle is to be operated such as mountains or in high ambient temperatures E Transmissions running a PTO in a stationery application LUBRICATION CAUTION Proper lubrication of the transmission is critical to the life of the transmission and safe operation of the vehicle Lubrication problems can result from too much lubricant too little lubricant or the wrong type of lubricant Improper lubrication can result in excessive heat and seizure of the bear ings in the transmission A seizure of the bear ings can cause the vehicle to lose power In order to avoid these problems it is important that the instructions for proper lubrication are care fully followed Proper Lubrication Help your lubricant protect your equipment by following these guidelines E Always fill Spicer transmissions to the proper lubricant levels Using too much lubricant causes it to churn foam and overheat This prematurely breaks down the lubricant Too little lubricant allows heat buildup and prevents adequate coating and protection of components The lubri cant should be level with the transmission oil fill plug E Always follow the
12. ew clutching teeth right C O MPON EN T F A LU RE Bearings The service life of most transmissions is deter mined by the life of its bearings Many premature bearing failures are caused by vibration or contamination If bearings are stored it s very important to coat them with a rust inhibitor and keep them tightly wrapped to prevent contamina tion Other reasons for bearing failures include WE Lack of lubricant or contaminated lubricant E Improper assembly E Overloading E Misalignment Offset spalling see Figure 10 is caused by Figure 9 Worn clutching teeth misalignment of the transmission in relation to other drivetrain components To prevent clash shifting Make sure the driver is familiar with both the shift pattern and the required RPM changes between shifts WE Establish correct clutch adjustment to prevent inadequate clutch release or dragging W In air shifted transmissions make sure the pressure regulator is at the proper setting usually 55 60 psi See SHIFTING CAUTION pg 6 Figure 10 Offset spalling is caused by misalignment Offset spalling is similar in appearance to de structive pitting but craters are larger in diam eter and shallower in depth Spalling occurs over a short period of time when a bearing is sub jected to an extreme overload condition C OM PON EN T F A LU RE 8 Forks Clash shifting and over shifting going beyond the shift rail
13. haft or clutch gear gearlocks e Replace e Inspect mating components for damage SOME COMMON TRANSMISSION COMPLAINTS Vibration Vibration problems are often difficult to trace and isolate While the effects of vibration will often cause transmission problems the vibration itself usually originates somewhere else Intermittent vibration can be isolated under specific conditions of engine idle or RPM gear selection load and speed Constant vibration should also vary with engine RPM load and speed to provide clues to its source Some possible causes of vibration include E Loose output nut which is sometimes indi cated by shiny areas on the output shaft caused by yoke movement e Tighten nut to specifications e Check output shaft for wear E Rough idling engine e Use dampened disk clutch E Loose or broken engine mounts e Replace Sometimes vibration originates in the driveline Potential causes include improper universal joint working angles out of phase shafts shafts that arent balanced and excessive driveshaft lengths If the driveline is the source of the vibration these conditions must be corrected Figure 1 Torsional engine vibration could cause worn clutching teeth lt N VIBRATION WARNING Vibration can be an early indicator of a problem with the vehicle driveline Potential causes of driveline vibration are excessive operating angles out of phase shafts unbalanced shafts or excessive shaft length
14. lubrication blocker neutralizes automatically and the clash free shift is the result It must be noted that a Another aspect of improper shifting involves steady pressure on the shift lever helps the vehicles with power take offs PTOs Never shift synchronizer do its job quickly from one gear into another while the PTO is engaged The PTO will act like a brake slowing countershaft and input shaft rotation The syn chronizer will try to match the mainshaft speed while the PTO will work against it See SHIFTING CAUTION pg 6 C OM PON EN T F A LU RE 8 Vibration is another big cause of synchronizer failures Broken or sheared synchronizer pins are a very common sign of vibration see Figure 17 The brass synchronizer ring may also be pushed off the pins due to vibration see Figure 18 Figure 17 Sheared synchronizer pins are a sign of vibration Figure 18 Vibration can cause the brass ring to separate from the rest of the synchronizer Refer to the Vibration section of this publication page 2 for information on causes of vibration It is also important to maintain proper lubrication levels See the Heat and Lubrication section of this publication page 2 for more information xX See VIBRATION WARNING and LUBRICA TION CAUTION pgs 2 and 3 Shafts When gears clutch collars clutch gear or synchronizers show signs of clash shifting carefully examine shaft gearlocks If they are worn see
15. recommended grades and types of lubricant for your Spicer transmission Never mix and match grades or types of lubricant they may be incom patible Lubricant specifications are pub lished in Spicer service manuals E Always follow the recommended oil change schedule for your Spicer transmission WE Use only quality lubricants E When changing oil check it for contamina tion If debris especially metal chips are found it could be a sign of internal trans mission damage In any case replace contaminated lubricant and further exam ine the unit if it is indicated WE Check the angle of the transmission Too steep an angle could prevent lubricant from reaching the input shaft pocket bearing C O MPON EN T Gears andClutch Collars As you examine a gear you may notice hob marks or scallops on the tip and root of the gear teeth These are normal and acceptable machining marks They do not indicate a prob lem with the gear see Figure 2 Figure 2 Hob marks are acceptable However over time gear teeth will wear as they mesh with mating gear teeth When the endur ance limit of the gear material is exceeded the result is pitting see Figure 3 If a gear with pitting over 50 of its tooth surface is allowed to remain in service it will eventually fracture gear material endurance limit is exceeded Lubrication problems can also contribute to these conditions Another contributor to pitting
16. s These conditions must be corrected immediately Driveline vibra tion can cause damage to the transmission and can also result in separation of the driveline from the vehicle Separation of the driveline from the vehicle can result in serious bodily injury or death In order to avoid driveline vibration you must have the vehicle examined immediately by a qualified mechanic who is experienced with proper driveline application and installation Heat and Lubrication A continuous operating temperature of 250 F should be considered as maximum for reason able drain intervals A rise in temperature of 20 F over 250 F doubles the oxidation rate thus shortening the effective life of the oil Short periods over 300 F don t indicate a transmission problem but will still affect oil life SOME COMMON TRANSMISSION COMPLAINTS Certain conditions can cause a temperature increase and therefore make an oil cooler necessary These include E All direct main transmissions behind engines rated at 400 HP gross and above E All overdrive main transmissions behind engines rated 350 HP gross and above E All main transmissions direct and overdrive where vehicle GVW GCW exceeds 90 000 Ibs All auxiliary transmissions where vehicle GVW GCW exceeds 80 000 Ibs WE All auxiliary transmissions behind overdrive main transmissions regardless of engine horsepower WE Vehicle configurations that restrict air move ment around th
17. satisfactorily in a higher transmission gear ratio than when partially or fully loaded If auxiliary transmissions or two Me S speed axles are used they must be in the lower Figure 15 Improper shifting techniques cause worn ratios for satisfactory starts Drivers should be ey Omer CRCnING 2ert shown what ratios can be used for safe starts when the truck is empty or loaded Don t let drivers find out for themselves they can damage synchronizers If the truck is diesel powered a good rule of thumb for the driver to follow is empty or loaded select the gear combination that lets you take up the slack and start moving with an idling engine or if necessary just enough throttle to prevent stalling the engine After the clutch is fully engaged the engine should be accelerated to near governed speed for the upshift into the next higher gear When shifting a synchronized transmission it is important to move the shift lever in one motion until the shift is completed Stabbing the shift lever will result in gear clashing Another result will be worn clutching teeth see Figure 15 and metal chips embedded into the brass synchro nizer ring see Figure 16 When the synchronizer ring makes contact with the desired gear the blockers automatically prevent the shift collar from completing the shift until the gear and Figure 16 Metal chips are cause by clash shifting or lack mainshaft speeds are matched At that time the of
18. sive end play e Shim to correct end play E Loose mainshaft nut e Torque to specified rating E Worn or seized pilot bearing in flywheel e Replace worn or damaged components e Use correct lubricant M Oxidized or overheated lubricant e Follow recommended lubrication procedures E Metal particles imbedded in brass or GYLON coated synchronizer ring e Replace synchronizer e Check lubricant for contamination and replace e Check for other damage that could result from clash shifting Gear Jumping Gear jumping is caused by interference in the shifting mechanism or some other malfunction which results in the clutch gear or shift rod moving out of its selected position during opera tion When a problem occurs inspect the shift lever first Make certain it moves freely and completely into position Also check the floorboard opening driver s seat or anything that could prevent full clutch gear engagement Other potential causes of gear jumping include WE Heavy shift lever extensions e Use a shift lever that doesn t have a top heavy extension E Broken poppet springs e Replace E Worn shift rod detents e Replace shift rod E Bent or sprung shift rods or forks e Replace E Worn clutching teeth on shift collars e Replace e Inspect mating components for damage e Make certain the driver Knows and uses proper shifting techniques E Broken thrust washers e Replace E Broken snap rings e Replace E Worn corners on mains
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