If you go this route, be sure to get return rights if the new rear end assembly turns out to be bad.
There are a LOT of variables in swapping gears: first, it depends a lot on which rear end you surrently have, and its ratio.
I have a PV544, with a Spicer model 27 differential. The current gear ratio is 4.11:1 (called "411") and the only other gear set that will fit this carrier is a 3.73. This would give me a slightly higher top speed with a corresponding loss in take-off power. I'd love to have a rear end in the low 300 range.
To change to any other gear ratio (and there are perhaps eight different ones?) the carrier would also need to be changed. This involves removing all the guts of the differential and putting in a new carrier. In doing this, you need special tools to set up the spacing between the gears, to avoid severe wear and a lot of howling noise.
Basically, you can easily swap in any Volvo rear axle assembly for the model you have: except for needing to bleed the brakes, it's a very simple job. You can almost always find a small tag on one of the cover bolts that will have the gear ratio stamped into it, so you'll know what you have. Otherwise, you can turn the wheel one complete revolution and count the number of times the drive shaft goes around. If it makes 4 and a small fraction turns it should be a 411, etc.
You also have the option of installing a rear axle from a different make of vehicle, but that usually requires welding skills to install the diferent mounting tabs on the axle so it will fit your Volvo. Ford Ranger seems to be a fairly popular swap, but I understand that the axle tube on one side must be cut down to fit the correct track width. Stock, the Ford unit has an offset pumpkin, so besides shortening the long axle tube, you'd also need to have an extra short axle to install on that side. I believe that FOrd has the same wheel bolt pattern as Volvo, though, so that's a plus!
I'd recommend first trying to find a rear end assembly that you can install yourself. Barring that, I'd take it to a good shop and have them do the gear change. Maybe not cheap, but certainly easier!
Good luck!
Steve
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