Put car in reverse felt like i had run over something then made odd noise now will not move in reverse but will go forward ok.Car will roll freely in neuturl.

S80s use 3309 fluid, not Dexron! But even with a flush, I am afraid you may be in need of another tranny.

Klaus
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Proud owner of a 1967 220S. If I had more room, I would have more Volvos.

The 4 speeds use dex.3 and 5 speeds use 3309
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Jake

Unfortunately, it sounds like you've had an internal failure in the transmission. Not too much to do in a case like this from outside the transmission. S80 transmission failure isn't all that common to my knowledge, so I'd feel safe with a low miles used unit.

Actually, a lot of S80s have trans failure. Reason is, Volvo calls the fluid "lifetime fluid" but it is not true at all. The fluid gets very old and gunky with age. It eventually prevents the trans from performing well.
Give this a try first.
First off, when you put it in reverse, does it say R on the dashboard? If not, you could have a linkage problem. You could try giggling it and seeing if the R appears.

If thats not your problem, I suggest you flush the trans and change the filter. You can DIY or have Volvo do it.

Heres a guide:
http://www.matthewsvolvosite.com/forums/viewtopic.php?f=11&t=20278&sid=c5c5e825420b2721a05477a47e08aeee

Good luck. And use Dextron III or equivalent fluid.
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Jake