Rear differential gear ratio

I recently bought a 1997 ex cab V6 that I am working on. The Prior owner put a new rear axle in but I noticed after working on the truck the axle has 342 written in paint pen on it. The vin sticker on the door is BO6A which is 391. Is there an easy way to verify what rear axle ratio is for sure. 342 and 391 are too far apart and would damage the transfer case when in 4wd correct?

 

First I did a sas on my 95 runner. Both axles 5.29
they I decided to go 60 and 14 bolt.
I ran 538's in the 14 bolt and 5.29 in the front toy axle.
did not even feel any difference. I think you will be fine.

If I'm not mistaken mud trucks run different ratios

 

You need both axles to be the same ratio if operating in 4X4 or you could break something.

I have a brother in law who picked up an ancient IH Scout for a few hundred bucks to use as a toy. It had different ratios front and rear which he didn't know about until after he bought it. He considered it 2 wheel drive and only engaged 4X4 after getting stuck to help get out. In extreme poor traction it won't matter if the front and rear wheels turn at different speeds since all of them are spinning anyway. Anywhere else and something is going to break.

 

I defiantly agree ^^^^ when in mud and offload the slightly different ratios would not matter.

 

Thanks Thats what thought. what is the easiest way to verify for sure what my rear axle ratio is?

 

If you have a floor jack and some wheel chocks it can be done in a few minutes

https://www.quadratec.com/content/how-check-your-gear-ratio-without-removing-cover

 

Thanks it’s already on jack stands I’ll try it

 

I already had the truck on jack stands since I’ve been working on it. I locked one of the rear wheels so it wouldn’t spin and put reference marks on the other hub and on the driveshaft. Turned the hub 10 revolutions which equaled approximately 19.5 revolutions on the drive shaft.

19.5 x 2= 39
39/10= 3.9

So it looks like it’s a 3.91 like the vin tag says it should be.

 

Yep. My mom jumped in my old jeep at the lake, I had just swapped an axle into. Had it in the sand just to put the boat in the water and she decided to jump in it and get on the road for a minute while I was out on the boat. Kaboom! I knew the ratios were different, she didn’t know but she verified it.

 

Sounds right to me!