transmission clunking
 

I have a 1998 XC70 AWD that at 40-mph the cars starts to clunk in and out between 3 and 4th gears. First noted going down hill and now intermittently on flat roads after acceleration. Dip stick shows clean fluid.
New tires and the angle gear was replaced 20K ago.
I did some searching on this site and came up with "valves are faulty".
What valves.
Any help will be appreciated.

transmission clunking
 

Well I found out the transmission fluid was low.
Seems ya got to check it with the engine running . Put 3/4 of a liter of ATF in the tranny and the problem "seems to be gone" - at least from, one test drive on secondary roads and a few miles on the highway. Shift and stays in gear and does not over rev.

Time will tell.

Thanks

The technique for engine running is reverse flow out the transmission pipe with green collar at the radiator. This would mean it gets all the fluid flushed from gearbox. But, I have a question with that: do you refill at same time so transmission does not run dry? Or, because sitting in neutral no fluid is in needed in the gearbox while engine running?