# Swaping rear ends **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [July 31, 2008, 11:56pm UTC](https://community.cartalk.com/t/swaping-rear-ends/17516 "2008-07-31T23:56:44Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![IceMeister](https://avatars.discourse-cdn.com/v4/letter/i/258eb7/32.png) [@IceMeister](https://community.cartalk.com/u/IceMeister)\ **Post date:** [July 31, 2008, 11:56pm UTC](https://community.cartalk.com/t/swaping-rear-ends/17516/1 "2008-07-31T23:56:44Z")
Hi All, I am going to swap out my sons Jeep cheerokee axel and have a used one to put in. I opened the back plate and counted the teeth on the ring gear at 39 and the pinion gear at 21. I think that I devide the large number into the smaller number to come up with the right ratio. I am looking for it to work out to 3.55 but am not shure how to get there. Can anyone help an old guy out on this. IceMeister ---
**Author:** ![ken\_green](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/ken_green/32/816_2.png) [@ken\_green](https://community.cartalk.com/u/ken_green)\ **Post date:** [August 1, 2008, 12:02am UTC](https://community.cartalk.com/t/swaping-rear-ends/17516/2 "2008-08-01T00:02:23Z")
count again. and remember if it’s a 4x4 you must also change the ring & pinion in the front. 39 divided by 21 is 1.86. not a ratio I’m familiar with. ---
**Author:** ![IceMeister](https://avatars.discourse-cdn.com/v4/letter/i/258eb7/32.png) [@IceMeister](https://community.cartalk.com/u/IceMeister)\ **Post date:** [August 1, 2008, 2:02am UTC](https://community.cartalk.com/t/swaping-rear-ends/17516/3 "2008-08-01T02:02:06Z")
My math says 1.77. When doubled it comes out 3.55 but I am not clear that I did it right. Or it is the right way to do it. The old rear end is 3.55 as to the Id plate. I was just trying to confirm that the new/used rear end is the right gearing so I would not have to change the front end as well. The junk yard took off the Id plate on the rear end when they sold it to me. Made me wonder why. Just want to be safe before going through all the work to make the go again. IceMeister ---
**Author:** ![IceMeister](https://avatars.discourse-cdn.com/v4/letter/i/258eb7/32.png) [@IceMeister](https://community.cartalk.com/u/IceMeister)\ **Post date:** [August 1, 2008, 2:04am UTC](https://community.cartalk.com/t/swaping-rear-ends/17516/4 "2008-08-01T02:04:52Z")
I made a mistake on the first post. the numbers were 39 and 22. Not 21 as I had written. Sorry for the error. Old hands do bad stuff. Ice ---
**Author:** ![Caddyman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/caddyman/32/23_2.png) [@Caddyman](https://community.cartalk.com/u/Caddyman)\ **Post date:** [August 1, 2008, 2:26am UTC](https://community.cartalk.com/t/swaping-rear-ends/17516/5 "2008-08-01T02:26:39Z")
Count the teeth again…You divide the pinion into the ring number. If the ring gear has 39 teeth, then for a 3.55 ratio, the pinion must have 11 teeth. ---
**Author:** ![Caddyman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/caddyman/32/23_2.png) [@Caddyman](https://community.cartalk.com/u/Caddyman)\ **Post date:** [August 1, 2008, 2:28am UTC](https://community.cartalk.com/t/swaping-rear-ends/17516/6 "2008-08-01T02:28:29Z")
Because of the twist in the pinion gear teeth, you must be counting them twice… ---
**Author:** ![IceMeister](https://avatars.discourse-cdn.com/v4/letter/i/258eb7/32.png) [@IceMeister](https://community.cartalk.com/u/IceMeister)\ **Post date:** [August 1, 2008, 3:18am UTC](https://community.cartalk.com/t/swaping-rear-ends/17516/7 "2008-08-01T03:18:05Z")
I will recount the teeth. Thanks Ice ---
**Author:** ![IceMeister](https://avatars.discourse-cdn.com/v4/letter/i/258eb7/32.png) [@IceMeister](https://community.cartalk.com/u/IceMeister)\ **Post date:** [August 1, 2008, 4:09am UTC](https://community.cartalk.com/t/swaping-rear-ends/17516/8 "2008-08-01T04:09:12Z")
Well Caddyman, You were right. I did count the teeth twice. Which confirms that the ratio is 3.55 and I now feel much better about going ahead and installing the rear end. I thank you very much for your help. IceMeister