About Repairing a Transmission

Gearbox replacement is often eaiser than repair.

The transmission, or gearbox, is one of the most complex components on a vehicle, so manufacturers spend a great deal of time and money engineering them to be more reliable. But overheating, lack of maintenance, or vacuum leaks can cause a transmission unit to fail.

Symptoms

If your transmission is not shifting correctly or you feel it slipping (between drive and neutral) there may be a problem with the clutch if your transmission is manual or a vacuum leak if your car has an automatic transmission.

Leaking Gearbox

Transmission fluid is usually red in color, so it is good practice to check out your driveway after driving the car. If any red fluid is on the driveway where you park your car, then your transmission unit might need to be resealed. Jack up the car as high as possible, secure on axle stands, and determine exactly where the leak is coming from. Purchase a reseal kit. It is possible to remove the old seal, clean the area and fit a new seal with the transmission in place, unless it is the front seal that attaches to the engine. In this case, the unit will have to be removed, making it a more difficult and time-consuming job.

Replacing Gearbox Parts

You can remedy sloppy gear changes by replacing the gear-linkage rubber mounts and greasing the movable parts. You can perform these maintenance procedures without removing the gearbox. Other procedures will require you to remove the gearbox.

Overhauling the Gearbox

After the arduous task of removing the gearbox--you usually have to remove a cross-member and the exhaust system--and opening the transmission case on a clean table, you can set about looking at the parts. Using this opportunity, you can inspect each part for wear, check the seals, and clean the transmission thoroughly. Rebuilding the transmission requires a methodical approach in cleaning and refitting, but once you have completed the rebuild, your transmission should last for hundreds of thousands of miles longer.

Repair or Replace Gearbox

Always weigh the cost and time required to rebuild a gearbox with the cost and time of replacing a gearbox. You can get some transmission units cheaply; replacing a transmission is often cheaper and easier than rebuilding.

References

• USA Transdoctor: GMC Transmissions
• Family Car: Transmission