Can you switch from 75w-140 to 75w-90 rear end fluid?

Yes, you can switch from 75W-140 to 75W-90 rear end fluid, but it's important to consider the specific requirements of your vehicle's differential. The viscosity difference means that 75W-140 is thicker at higher temperatures, providing better protection under heavy loads, while 75W-90 is suitable for lighter conditions. Always refer to your vehicle's owner manual or consult a mechanic to ensure compatibility and optimal performance.