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Manual Transmission Diagnosis

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  1. Manual Transmission Diagnosis

  2. Lubrication • Most manual transmissions are lubricated by the splay and spray method • Proper oil level is essential • Too high: churning and foaming • Too low: insufficient lubrication • Some transmissions have a trough to deliver oil to rear case bearing • Input bearing retainer may have oil holes for front bearing lubrication • Align correctly • Ensure correct oil is used • 80W-90 • 10W30 • ATF • Syncromesh

  3. Diagnosis • Possible problems • Transmission jumps out of direct drive only • Transmission jumps out of gear • Transmission shifts hard • Gear clash during shifting • Transmission sticks or locks in gear • Bearing noise • Gear noise • Leaks

  4. Diagnosis • Transmission jumps out of direct drive only • Excessive input shaft endplay • High gear synchronizer worn or broken • Worn front case bearing • Shift linkage not fully engaging • Worn shift forks

  5. Diagnosis • Transmission jumps out of gear • Shift linkage worn or misadjusted • Insufficient spring tension on detent springs • Misaligned or loose transmission or bellhousing • Pilot bushing badly worn • Shift fork, lever, or shaft is bent or badly worn • Badly worn bearings • Worn synchronizer hub or broken keys (inserts) • Excessive main shaft play • Bad transmission/engine mounts

  6. Diagnosis • Transmission Shifts Hard • Clutch free travel excessive • Clutch does not release fully • Sliding gears or synchronizer rings binding • Synchronizers worn or damaged • Damage teeth caused by insufficient clutch disengagement, bad blocking rings or damaged slider • Shift mechanism binding, worn or out of adjustment • Low lube level or incorrect (to thick) lubricant • Bellhousing misaligned

  7. Diagnosis • Gear clash during shifting • Clutch not releasing • Synchronizer has worn blocking rings and/or cone surface • Broken blocker rings • Excessive output shaft endplay • Detent springs weak or broken • Gears seizing to main shaft • Input shaft binding in pilot bearing

  8. Diagnosis • Transmission sticks or locks in gear • Clutch not releasing • Stuck interlock or detent plugs • Shift linkage out of adjustment • Sliding gears tight on splines • Peened over teeth on synchronizer sleeves • Blocker rings seized on gear cones • Lack of lube

  9. Diagnosis • Bearing noise • In all gears except direct drive • Front main shaft bearing (pocket bearing) • Countershaft bearings • In all gears (only when vehicle is moving) • Rear case bearing • With clutch engaged (transmission in neutral) • Front case bearing • Countershaft bearings • With clutch fully disengaged • Pilot bearing

  10. Diagnosis • Gear noise • Whine in one gear only • Worn gear • Clunk in one gear only • Broken main shaft gear or counter gear • Clack in one gear only • Cracked gear • If cracked gear is found check all gears for cracks • Transmission noisy in all gears • Incorrect or inadequate lubricant

  11. Diagnosis • Leaks • Oil level too high • Vent overflows • Seals damaged • Front and rear seals, shift shaft seals • Gaskets missing or damaged • Bearing retainer, side cover, extension housing • Loose bolts • Plugged vent • Pressure builds up forcing lube out of seals and gaskets • May be caused by excessive RTV on mating surfaces