* Heat damage: The intense heat from welding can warp the transmission case, damage the gears inside, or even melt or weaken the surrounding metal. This would likely require a complete transmission replacement, costing far more than attempting a repair.
* Removal of the nut: Welding often makes nut removal *more* difficult, especially on a hardened steel nut like the one on a fifth gear. The weld might crack or break off, leaving the nut even more firmly stuck.
* Professional Expertise: Even if you're a skilled welder, working on a transmission requires specialized knowledge and tools. The risk of damaging the transmission far outweighs the potential benefit of a quick fix.
Better Alternatives:
Before resorting to welding, try these methods:
* Penetrating Oil: Apply a generous amount of penetrating oil (like PB Blaster or Liquid Wrench) to the nut and let it soak for several hours, or even overnight. Tap the nut gently with a hammer to help it penetrate.
* Heat: Carefully apply heat to the nut with a propane torch (avoid excessive heat). This can help expand the metal and break free any corrosion. Be extremely careful not to overheat the surrounding parts. Let it cool *slowly* after applying heat.
* Impact Wrench: An impact wrench provides significantly more torque than a regular wrench and can often loosen stubborn nuts.
* Gear Puller: A specialized gear puller might be necessary to remove the gear itself, which might allow easier access to the nut. This is a more complex procedure.
* Professional Transmission Shop: A qualified mechanic with experience working on transmissions is the best option. They have the right tools and expertise to remove the nut without damaging the transmission.
In summary: While welding might seem like a quick solution, it's a highly risky approach that could lead to significant and expensive damage. Exhaust all other options before considering this as a last resort. The cost of a professional repair is almost certainly less than the cost of replacing a transmission due to welding damage.
