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I have a 1984 Toyota Supra that is now exclusively a track car. The last round out we let some less experienced drivers take the wheel and they basically destroyed the transmission. Nothing but 4th gear works now.

We've been making the rounds at some local junkyards looking for a replacement, but have yet to find one. I've seen that there are rebuild kits available online for a couple hundred bucks, but I'm a little scared of cracking open a transmission. I've nearly taken the entire car apart and put it back together including swapping out a cracked block, but the head and transmission are the two pieces I try to stay away from touching for fear of not being able to get them back together correctly.

Given the fact that the transmission can barely be forced into gear and 4th is the only gear that works at all is it even worth trying to rebuild? And secondly, is rebuilding a transmission something that a non-professional should attempt to do on his own? And if so are there a lot of special tools that will be required?

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It's not something I've ever attempted, but I know people who have...

The innards involve a lot of small springs, shims, etc (mainly in the synchros), and these can often have a habit of flying off when released! It is something that should only be attempted in a decent, clean workshop/garage so you can keep track of all the bits as you take it apart, and do so carefully.

I suspect from your description that it probably isn't worth trying to rebuild as the gears are probably wrecked, but if you have the facilities it might be an interesting learning experience to try taking it apart - I imagine you'll find some badly damaged gears and bits of teeth and swarf in the oil, but you might be lucky and find that it is rebuildable.

Source another, then have a go at dismantling this one - if you get lucky and it can be rebuild, then you've got a spare next time someone wrecks it, and if not, you've not lost anything except your time.

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    The most important part for reassembly will be photos and more photos. If the gears are trashed this may be a good time to upgrade the internals. Many times heavy duty components are available that may be louder (not much of a concern in a track car) but much stronger.
    – mikes
    Commented Jul 13, 2012 at 10:38
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    Nick posted exactly what I was going to say: purchase a replacement and then investigate this broken transmission. Here are a few images that will give you a hint as to what a rebuildable transmission should look like: supramania.com/forums/…
    – Bob Cross ♦
    Commented Jul 13, 2012 at 12:10
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Rebuilding a transmission often requires the use of a multi-ton press to get gears and bearings on and off a shaft. It's possible to take the shaft and parts to a garage and ask them to do it for a nominal fee, but it can be a hassle. I second the recommendation to source a replacement and only tear into your trashed one for educational purposes. Personally, I'd pick up a rebuild/upgrade kit and have a shop install it, that way you know what you've got (as opposed to picking up something of unknown abusage at the local U-Pull-It).

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To put things into perspective: The Subaru workshop manual tells you how to completely disassemble the engine, overhaul it and put it back together. But the section on the transmission recommends that you "leave it to the pro's". I know you don't have a Subaru, but Subaru engines are more complex than the Supra engine, and they think it's easier for a non-specialist to take apart and reassemble and entire engine than to rebuild a transmission. I don't mean "easier" as in "less time", I mean easier as in: less special tools and skill required.

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It is possible that the shift forks are bent or broken. These are not so hard to replace. Take a peek inside the tranny to see what is going on, move the lever around and see what is binding. The gears themselves may be perfectly fine (even if the synchros are smooshed).

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I used to work as a mechanic many years ago and I find that the manual is easier over the automatic. Automatic transmissions have many more parts than the manual transmission does. I know this is late but it may help others who are asking this same question.

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