What is the rear end gear ratio of a 1985 k5 blazer with 305?

There's no single answer to the rear end gear ratio of a 1985 K5 Blazer with a 305 engine. The ratio varied depending on the options selected by the original buyer (e.g., towing package, off-road package). Common ratios included 3.08, 3.42, and 3.73. To know the specific ratio of a particular vehicle, you'd need to:

* Check the vehicle's data plate (often located on the driver's side doorjamb). This *might* list the axle ratio, but it's not guaranteed.

* Look at the casting number on the differential housing. This number can be cross-referenced with GM parts catalogs or online databases to determine the gear ratio.

* Physically count the teeth on the ring and pinion gears. This requires removing the differential cover and is the most definitive method, but it's also the most labor-intensive.

Without looking at the specific vehicle, it's impossible to say for certain.