Transmission Rebuilds: When & How

Automatic transmissions are delicate mechanisms designed with precise clearances between the moving parts. Rebuilt TransmissionParts that move, of course, wear down. And when the wear gets so bad the gears no longer mesh correctly, the vehicle will no longer shift as it should. Well before this point the transmission should be rebuilt or replaced.

Signs of Trouble

Some initial transmission symptoms may not indicate the need for major work. Replenishing low fluid solves some problems. If topping off does not help; draining the unit, changing the filter and replacing seals and gaskets may coax a tranny back from the edge of failure if it has only minor symptoms like these:

  • Leaks
  • Fluid is dark or smells burnt
  • “Check Engine” light is on

A few more serious trouble indicators almost always indicate the tranny should be replaced or rebuilt:

  • Slow or no response to change in engine speed
  • Resistance to shifting into park or drive
  • Hesitation when gears change on the road
  • Shimmy during gear changes
  • Metal shavings in fluid
  • Tranny-related noise

Rebuilding Procedure

A rebuild begins with jacking up the vehicle or raising it on a rack. The mechanic then drains the transmission, takes it apart and lays it out on a bench. Each part in turn is cleaned and inspected for wear. Professionals will use new replacements for worn parts, but home mechanics may wish to consider carefully selected used parts from local sources, especially for the more expensive components.

Some parts should always be replaced during a rebuild. The clutches and bands, for instance, work by friction and so undergo tremendous wear. Seals and gaskets should also always be changed out. The torque converter, the fluid coupler that transfers rotational energy from the engine to an automatic transmission, is subject to large amounts of stress in operation and is quite susceptible to damage during the removal process. Many mechanics replace the torque converter as a matter of course.

Cautions for Do-It-Yourself-rs

A rebuild can be a challenging proposition. It involves removing several hundred pounds of dead weight containing nasty liquid from a vehicle over the mechanic’s head, and there often is no plug to facilitate drainage. After, all the delicate parts covered in toxic goo must be disassembled in an environment free dust…and the whole put back together with replacement parts as appropriate. Then the rebuilt tranny is put back on the vehicle and filled with fluid. At this point the used fluid must be disposed of properly.


Do-It-Yourself mechanics, particularly those with the proper tools and a good deal of experience, can and do rebuild automatic transmissions with entirely satisfactory results, and many do enjoy the process. An owner at a lower skill level, however, or someone who does not have the time or the tools to do the job right, should consider having it done professionally. This usually involves purchasing a new or rebuild transmission built from a reputable specialist like Rocky Mountain Driveline who performs exhaustive test to ensure perfection. You may still do a self-install, though this still means dealing with the weight and proper disposal of the old fluid. As an alternative, the installation can be handled by just about any local shop.

Transmission failure can make a vehicle unusable or worse, lead to an accident. Investment in a rebuild keeps cars running better and longer. Whether a home mechanic rebuilds the tranny out of the vehicle or a shop replaces it with a purchased rebuild, taking care of tranny problems saves time and trouble in the long run.

Rocky Mountain Driveline is your local leader for rebuilt transmissions. Stop by or call today!

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