Car Tuning Drivetrain and Transmission 5 — Questions and Answers
Question 1: When converting a FWD vehicle to AWD, what major structural challenge must be addressed beyond the drivetrain components themselves?
- The front suspension geometry must be converted to MacPherson struts
- The unibody floor pan typically has no tunnel or mounting provisions for a rear differential or driveshaft (Correct answer)
- The engine must be remounted longitudinally
- The ABS system must be completely deleted
Correct answer: The unibody floor pan typically has no tunnel or mounting provisions for a rear differential or driveshaft
FWD unibodies are designed without the transmission tunnel, rear differential mounts, or driveshaft clearance needed for AWD conversion, requiring extensive fabrication.
Question 2: In a transmission rebuild for a turbocharged application, what internal modification helps prevent gear failure due to shock loading?
- Replacing steel gears with aluminum for weight savings
- Shot-peening gears to induce compressive surface stress that resists crack propagation (Correct answer)
- Using standard OEM gears but with synthetic fluid only
- Removing the 5th gear to reduce weight
Correct answer: Shot-peening gears to induce compressive surface stress that resists crack propagation
Shot-peening gear surfaces creates compressive residual stress that significantly improves fatigue life and resistance to the shock loads from turbocharged power delivery.
Question 3: What is 'clutch pack stack height' in a limited-slip differential, and why does it matter during a rebuild?
- The total diameter of the clutch discs
- The combined thickness of friction and steel discs that determines preload and bias ratio (Correct answer)
- The height of the differential housing from the axle centerline
- The distance between the ring gear and pinion gear
Correct answer: The combined thickness of friction and steel discs that determines preload and bias ratio
Stack height controls how much preload is on the clutch packs; incorrect height results in either too little bias (acts open) or too much (creates harshness and binding).
Question 4: A builder notices excessive driveline shudder only during light throttle at highway speeds after a transmission swap. What is the most likely cause?
- The transmission fluid level is too high
- The driveshaft phase angle (U-joint phasing) is incorrect, causing speed fluctuations at low torque (Correct answer)
- The clutch disc is contaminated with oil
- The wheel bearings are worn
Correct answer: The driveshaft phase angle (U-joint phasing) is incorrect, causing speed fluctuations at low torque
Incorrect U-joint phasing means the joints are not canceling each other's speed variation, causing cyclic driveline vibration most noticeable at low torque cruise.
Question 5: In a performance automatic transmission tune, what is the purpose of adjusting 'shift firmness' or 'clutch apply rate'?
- To increase transmission fluid operating temperature
- To control how quickly clutch packs engage, balancing shift feel and clutch pack durability (Correct answer)
- To delay torque converter lockup until higher speed
- To modify the stall speed of the torque converter
Correct answer: To control how quickly clutch packs engage, balancing shift feel and clutch pack durability
Clutch apply rate determines engagement speed; too fast causes harsh shifts and shock loading, too slow causes clutch slip and heat damage.
Question 6: Why do some high-power drag builds use a 'spool' instead of a limited-slip differential in the rear axle?
- A spool provides smoother cornering by allowing wheel speed differences
- A spool locks both rear wheels rigidly together, eliminating any differential action for maximum straight-line traction (Correct answer)
- A spool reduces unsprung weight by removing all clutch packs
- A spool allows torque vectoring between rear wheels
Correct answer: A spool locks both rear wheels rigidly together, eliminating any differential action for maximum straight-line traction
A spool permanently locks both axle shafts together, ensuring 100% of torque goes to both tires equally, which is ideal for straight-line drag racing.
Question 7: When calculating the correct pinion depth during a ring and pinion gear installation, what tool is used to measure the critical distance?
- A dial indicator with a depth micrometer or pinion depth gauge set (Correct answer)
- A feeler gauge placed between ring and pinion teeth
- A torque wrench set to bearing preload spec
- A straightedge and ruler across the differential housing
Correct answer: A dial indicator with a depth micrometer or pinion depth gauge set
Pinion depth is precisely set using a dial indicator and depth gauge to position the pinion the correct distance from the ring gear centerline, ensuring proper tooth contact pattern.
Car Tuning Drivetrain and Transmission 5
When converting a FWD vehicle to AWD, what major structural challenge must be addressed beyond the drivetrain components themselves?