Volvo 850 2.5 auto TDI - Help! Is my gearbox doomed?

Firstly, merry xmas everyone! I've just got my first 850, and up until a fortnight ago I was really pleased with it - quick for a big diesel car, good fuel economy, great auto box. However, all of a sudden problems have arisen, and the 2 dealers I've tried are struggling to identify what's wrong. From being smooth and picking up well, the engine now sounds really strained, doesn't pick up at all at low revs (well, any revs really) and my mpg has plummeted from roughly 38mpg at 70 on the motorway to 25/26. This is confirmed by my range setting on the dash which after a full tank would read 660ish, now it's 450-500ish (same journey every day). The engine sounds like it's trying too hard for the speed it's doing (usually a crawl) making exiting junctions 'interesting', with the engine revving away but the car hardly moving.
The garages have been concentrating on the engine, but after reading a few other posts, I noticed someone describing the effect of a 'torque converter' failing on the auto box which gave the effect of a clutch slipping - this sounded a lot like my symptoms.
What I want to know is (and I'm a total auto simpleton I'm afraid) is can the garage check if the torque converter is at fault without replacing it, and is there any way it can be repaired without fitting a new unit? (which I suspect is a big job and very expensive). Can these things be adjusted, or do they just 'go'.
Sorry for the mammoth first post, but any advice would be greatly appreciated!! Cheers!

[Ben O Brien]

Hi,

It does indeed sound like a torque convertor, i believe they can be bought reconditioned or you could chance getting a second hand one but for the amoumnt of labour involved it might be worth getting a new one.

Hope this helps.

[sholtby]

I've experienced several cars with failed TCs. Each time it was like a slipping clutch that within a matter of a week or so was barely drivable.
You maybe able to check if a TC is faulty by connecting a pressure gauge to the gearbox and checking hydraulic pressures.
Auto boxes are very complex items and even the best of garage mechanics will know very little about them. Your best bet would be to find a garage that specialises in autobox repairs, its a business in itself. Look in the yellow pages. I'm sure they could tell from experience if there is a problem straight away.
Have you pulled the fault codes from the gearbox ecu and the engine ecu?
Have you checked the gearbox oil level? Usually this is done with the engine running, oil quite hot and the car in park.
You cant adjust or repair a TC. You'll need a new one if it has failed. There is also a risk that if it has broken up that it could have sent schrapnel throughout the gearbox, but unlikely.
I know an excellent specialist in the NE of england if that is where you live.

Simon

[warthog]

I'll second what has already been posted and add that if you've driven the car much in this state, it's very probable that the increased energy that's been absorbed by the torque converter/gearbox has been transferred directly to the gearbox oil, causing the oil temp to go through the roof. This will almost certainly have fried internal gearbox seals and caused a loss of oil pressure causing the clutch packs and brake bands to slip. In my experience (several different makes of box going the same way) once you have these symptoms it's time for a rebuilt box and converter.

Make very sure that whoever does the job thoroughly flushes the oil cooler and lines before connecting them up to the box (even better, fit a new external cooler) as they'll be contaminated with detritus from the box/TC

If you're anywher around the Bristol area I can recommend a very good independant gearbox specialist who renewed my T5 box and converter.

Cheers

[DieselDoNicely]

Volvos diagnostic computer aallows you to read the efficency of the torque convertor. The dealer should plug it in and have a look for you for a moderate fee. Haggle, they charge about £5 to £15 to reset the service light.

DDN