In short my 1996 960 rear end (leaf spring version) was making noises. My mechanic decided to swap in the rear end from a 1994 960 (non-leaf spring).
All went smoothly until about 10 miles into a test drive, when dash warning lights came on and the car started to run poorly. I'm aware the final drive ratios are different and we are hoping to somehow override the "rejection".
We have the donor car (1994) and need advice on how to modify my 1996 to accept the changed rear end.
Thanks in advance for any advice.

Dear craigclark57,

Hope you're well. Which warning lights came on? In what specific ways did the car "run poorly"? What OBD codes have been set?

Did you try to clear any codes, by disconnecting teh negative battery cable clamp, from the negative battery terminal?

I ask these questions, because the Volvo pocket data booklet: Cars, 700,850,900 (1991-1996) shows some overlap in 960 rear end final drive ratios. Up to and including the 1994 models, final drive ratios were 3.54, 3.73 and 3.91. In the 1995 and later models, these ratios were 3.73, 3.91, 4.10. As a result, there may not be a difference in final drive ratios between 1994 and 1996 models.

You should find on the differential housing, a label with the part number and possibly with the final drive ratio. I own 940s, so am not sure exactly where this label would be on a 960.

Hope this helps.

Yours faithfully,

Spook