1977, c4 transmission no forward gears

[21drivers]

So I just bought a 1977 thunderbird for $1200. Amazing deal. No rust, body damage, etc.
The catch is that the c4 transmission has no forward gears, and the engine is in need of main bearings, rings, and maybe an oil pump (oil light is on at idle) but it does run right now.
I'm expecting to have to pull the transmission, but I'm curious what causes the forward gears to go out? It needs to be rebuilt (probably), but what actually goes wrong to cause this?
It still has reverse.

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[74 Harley]

It could be bad clutches, broken bands, planetary gears, the list goes on.
Good luck with your project, keep us updated with pictures!

 

[mcm51]

I can't help much on the tranny, could be all kind of stuff, and I've seen through the years, no forward gears but reverse works....From your photo, it looks like you got a great project car to start, I like that color, side molding looks good, front grill looks good, front bumper maybe tilted down a tad but in great shape, this Bird would look great with the locking spoke hubcaps, if you can find them........You did'nt mention if it was a 351 or 400 ? auto on floor or column..........Keep us up on how things go...............