When it *might* be viable:
* Specific, known problem: If you've definitively diagnosed the problem as *only* the 2nd and 3rd synchros, and the rest of the transmission is in good working order (bearings, gears, etc.), then replacing just those assemblies is a cost-effective repair.
* Mechanical aptitude: This is a fairly involved repair requiring significant mechanical skill and specialized tools. If you lack the experience, you'll likely cause more damage.
* Availability of parts: Finding replacement synchro assemblies for a YJ transmission might be challenging, depending on the age and specific transmission type.
When a transmission swap is generally better:
* Multiple problems: If other transmission components are worn or damaged, it's usually cheaper and less time-consuming to swap in a rebuilt or used transmission. Trying to piecemeal repairs on a worn transmission often leads to more frequent breakdowns down the line.
* Labor costs: The labor involved in disassembling a transmission, replacing the synchros, and reassembling it can be substantial, potentially exceeding the cost of a transmission swap.
* Uncertainty of diagnosis: If you're unsure of the exact cause of the transmission problems, a complete swap eliminates guesswork and potential for additional, unforeseen problems.
* Time constraint: A transmission swap, while still requiring time, is often quicker than completely disassembling and reassembling a transmission for a specific repair.
In short: Replacing only the synchros is a *possible* repair, but a thorough inspection of the entire transmission is crucial before committing to this approach. Unless you're extremely confident in your mechanical abilities and have accurately diagnosed the problem, swapping the transmission is usually the more practical and reliable solution in the long run, especially considering the labor involved. The cost difference might be surprisingly negligible if you factor in the time and potential for further repairs down the line with a partial rebuild.
