It is extremely rare to replace any gears when rebuilding an automatic transmission. Most of them are built onto other components and rarely fail. It's the clutch plates and internal and external seals that normally get replaced. Those parts will cause slipping when they're worn or leaking.
If you have your transmission rebuilt, you will typically be charged for all needed parts to make it operate as before. Most of the more expensive shops will also replace any parts that have new and improved versions that became available since your car was built. This is a custom repair meaning it is tailored to the needs of your car specifically.
When you buy a rebuilt transmission, typically it comes from a shop that does nothing but these rebuilds. A number of people rebuild many of the same model at the same time. They use the same tools, replace the same parts, and follow the same procedures at the same time so there is less chance of overlooking something. They first replace any defective parts, then they install any new and improved parts. Since this is more like an assembly line, costs are generally lower. Your mechanic's labor cost might be a little higher because he has to transfer brackets and external parts to the new transmission but that higher cost will likely be offset by the lower cost of the rebuilt transmission.
Automatic transmissions have to be kept extremely clean inside to work right, and it is very easy to overlook little things that can cause incorrect operation. There are a lot of really good transmission specialists out there but that's one advantage of installing a professionally-rebuilt transmission from a specialty shop. Most independent repair shops don't even get involved in transmission rebuilds. If you want to have your transmission repaired, they will just remove it and reinstall it, but they'll send it to a transmission shop for the actual rebuild.
The transmission specialty shops typically have one set price for a transmission for a specific car. That makes it easy to provide a fairly accurate written estimate.
Any worn or collapsed mounts will be replaced when the transmission is reinstalled but they are not considered part of the rebuild. There's only a few external seals. During a rebuild, they all are replaced. During a transmission repair when the transmission does not have to be removed from the car, only leaking seals are replaced and those that seal against parts that are being replaced.
Thursday, June 7th, 2012 AT 7:28 AM