windstar98

On a 87 bronco11, if I change the rear diff do I also need to change the front one.The number on both rear diff don't match.

 

GypsyR

Yes. You need to run the same ratios front and rear or you will tear the transfer case apart the first time you put it in 4wd. That said, a transfer case will tolerate a slight difference, such as a 4.11 paired with a 4.10. Something like a 3.73 versus a 3.08 equals destruction for sure.
If you absolutely have to, then take the front driveshaft off. Then you can drive around on your new rear gears until you get around to the front gears without a chance of destroying something.

windstar98

thank you, ended up changing both.