Tto be a serious threat at the drag track, it is necessary to upgrade your gearing to at least 4.10 gears. Most late model Mustangs and many other sports cars come equipped with standard 3.55 gears in their rear differential, however by adding 4.10 gears they can effectively make their drag times faster and deliver more power to the wheels faster.
Gear ratio has a great deal to do with how your car performs and handles under load. The gear ratio is the ratio of how many times your engine has to turn the crankshaft to turn the rear wheels one rotation. Therefore, the higher the ratio (4.10 gears compared to 3.55 gears) the higher the gearing and the greater number of rotations before the rear wheels turn. This equates to a greater amount of power transferred to the wheels.
Installing 4.10 gears improves the car’s performance on the track but with negligible effects to the highway driving. If your car is equipped with an overdrive, you may not even notice a difference in gas mileage with the new higher gearing. Depending on the transmission that you have installed, you might even be able to adjust the overall gearing so that the final drive of your car is nearly the same while in overdrive, but allows you to take advantage of the new gearing in the lower transmission gears.
The main negative aspects of installing 4.10 gears lie in performing transmission modifications in general. If the gearing in your differential is changed in a significant way, then the speedometer calibration is likely to be affected which will make your speedometer inaccurate. The new gearing can affect transmission shift points as well (on automatic transmissions, but this is a non-issue for manual transmissions). Custom tuning by a qualified speed shop is normally a good fix for both of these issues.
Switching from a gear set of 3.55 or 3.73 to 4.10 gears will affect your gas mileage slightly as your engine will be turning more times to rotate the rear wheels once. In most cases you can expect to see a drop of 1 to 2 miles per gallon.
On that same token, there are a few telltale signs that can indicate when a manual gearbox or automatic transmission is in trouble. In both automatic and manual transmissions smooth operation is ideal. Odd noises and rough gear changes may be the first indication that something is beginning to fail internally. Taking quick action when things start to feel a bit funny can help to keep repair bills to a minimum.
In a manual transmission, a grinding noise that occurs when shifting may be the result of a worn synchronizer. It could also be an indication of a low fluid level, so having the fluid level checked at the first sign of noise is a wise move.
A manual transmission that is difficult to get into gear could have issues with the linkage system connecting the shifter to the gearbox. In some cars these linkages can be realigned to restore trouble-free shifts. This could also point to an issue with the clutch hydraulic system, so a little troubleshooting may be needed to find the real culprit.
A slipping clutch is usually indicated by a climb in engine RPM without any increase in vehicle speed. Luckily, there is a simple test to check for this condition. It is conducted by accelerating from a low RPM through the engine’s peak power band (where it makes its optimal horsepower and torque) in fourth gear. Liberal use of the throttle in these situations will generally cause a weak clutch to slip without any real risk of damage.
Automatics can be a little trickier to diagnose. Just as with their manual counterparts, a flare in RPM during acceleration may indicate a slipping clutch. Since automatics use a number of different clutches, the problem may be isolated to one gear.
Excessively rough shifts in all gears may indicate problems as well. Luckily, modern automatics are computer controlled, which means they can be interrogated with a technician’s scan tool. This is an excellent way to begin diagnosing any shift concern.
The overwhelming variety of transmission designs and configurations means that shift quality and feel will be very different from car to car. This is why it is important to become familiar with the way a particular transmission (manual or automatic) feels when it is working properly. If something feels off in a vehicle you use every day, odds are something may not be right. If such issues are given prompt attention, the early action may reduce future headaches.