I've got a 97' 850 AWD that appears to have bevel gear failure and I was curious if anyone has experience with changing the gearset in an M58 trans or if I would be smarter to try and find a complete trans from a newer V70?

 

its not the tranny that has failed. its the bevel gear. its a separate unit, and can be changed separately.

you should be able to use a bevel gear off another 850 (rare) or any 98-99 v70 awd which come up as parts cars quite often.
the only problem with going used is you never know how long it'll last. dont pay alot for it. if you want to pay alot, buy it new.

edit: how do you know its your bevel gear?

 

I'm told by the previous owner (I just inherited the car..) that it made some fairly loud rude noises and then was awd no more.... the coupler at the back of the driveshaft appears alright as the shaft turns when I spin either rear axle.
I was most interested in what is involved in changing out the bevel gear as I have yet to find any such specific info in any forums of otherwise.

 

Bevel gear (box) changeout not too complicated, but a fair number of things to do:

Remove passenger side axleshaft.
Disconnect driveshaft. Be careful with hex-head bolts. Make sure your socket fits tight in the hex bolts. Stripping the heads is not an option.
Remove bolts holding the bevel gearbox to side of transmission.

You may need to create some room to get the box fully disconnected/removed by:
Moving or removing downpipe. There is a tab that is bolted to the transmission with the bevel gearbox.
Removing subframe bolts to enable subframe to drop at rear attachment points.

Replace the seals and fluid in the box you're putting in.

I hope this helps!

 

You may want to pull the angle gear and inspect stuff.
On the newer AWD cars the collar between the trans and angle gear strip out.
I have seen many of them. They are also a pain to replace. If you have the right tools I hear it is not to bad. But without the proper tools it is a major job.

 

Here is a pic of one I changed on a S60R
This is before I removed it.

 

If you google "V70 bevel gear" you will get probably a billion links. I did when I was looking to buy a V70 XC. VolvoSpeed for example - maybe half of V70 postings are on this issue.

 

Thanks very much for the help!

 

what are the symptoms of a Bevel gear going bad? Just curious.

 

They are usually really noisy when going bad.

 

What else can break and cause the rear wheels to not engage? Winter driving has made me realize that something is broken, but the drive line is not making noise. I'm also a new owner of the car (850 AWD), and don't know all of its history.

 

I was in the same situation with a car that I didn't really know the complete history, I found with my car that the bevel gear wasn't working by first lifting the rear wheels off the ground. With the car in gear spin the back wheels and if the front to rear driveshaft is turning then there is a dis connect in the bevel gear. I have the bevel gear that I pulled out of my car if you want to have a look at it. Apart from the bevel gear it could be the viscous coupling or the lockout clutch.