Full locking rear differentials

[Volvo8873]

Hi, I do need to be educated somehow about full locking rear ends for my semi...

When I swap both my differentials to locking type can do I still retain the inter axle lock? So I would have 3 switches total if I wanted to pick whatever one I so desire?

Can I just swap out ONE axle whether it be front or back for a locking differential along with the interaxle lock to make it kinda like a "3 wheel wonder"???

I switched paths and now do a lot of construction and truss deliveries going into jobsites wherever so that is the reason for change.

[Rawze]

No need to try to re-invent the wheel that the industry has already figured out ...

If you go full lockers, you need to do both axles ... otherwise there is little to no point to it.

For the same reasons, Also, only 3 positions should be used ...

OFF> none
A> inter-axle lock position (only lock driveshaft between the front/rear diff)
B> full lock everything position.

OFF, A, or B.

People who run in the mud also report ...

++ It is handy to also have a fairly quick way to air up tires on the truck (via a hose on the catwalk) ... as sometimes you have to let half the air out of them for more grip to get out of a hole if its bad enough. That or always have a stack of sacrificial moving blankets handy to throw in in front of the tires as a last resort.

++ That the back axles need tall lug, open shoulder tires too. This helps a lot to keep from getting stuck, which indirectly means that your fuel mileage is going to suffer all the time too.

[marek4792]

Assuming you have a Volvo, my previous truck only had two switches for interaxle and interwheel(full lockers). Good to have if you go to odd places all the time, but on a highway application is kinda eh..

[Rawze]

(07-11-2026 )marek4792 Wrote:  Assuming you have a Volvo, my previous truck only had two switches for interaxle and interwheel(full lockers). Good to have if you go to odd places all the time, but on a highway application is kinda eh..

I agree with the highway statement. People do not realize that the spider gears in them wear over time even if your not engaging them. This means that if you only use them maybe once a year or so,.. or less, they are not likely going to be worth it so much, as they likely could be worn out after 6-8 years, and only actually needing them that many times.

[Volvo8873]

Thanks for the insight. I run a 2015 Internatianl Prostar nowadays. I think for now I will look into open shoulder tires for now. Never thought of the letting the air out of the tires for better traction. It’s simple things like that I never think of! Lol

[JimT]

(07-15-2026 )Volvo8873 Wrote:  Never thought of the letting the air out of the tires for better traction. It’s simple things like that I never think of! Lol

It's not a common thing to see done on class 8 trucks, at least not outside of specialized situations, due to the gross weights involved. Probably more useful when empty. However under inflation is a very common thing in the 4x4 / off-roading world. Especially when driving over sand (beach, dessert, etc...).

[Ricky]

(07-15-2026 )Volvo8873 Wrote:  Thanks for the insight. I run a 2015 Internatianl Prostar nowadays. I think for now I will look into open shoulder tires for now. Never thought of the letting the air out of the tires for better traction. It’s simple things like that I never think of! Lol

My ProStar is stretched out to 296 inches center of drives and it gets stuck pretty easy. I consider locking drives because all I do is steel for construction, but every time I get stuck there's always something there to push or pull me out.

[Rawze]

(07-23-2026 )Ricky Wrote:  

(07-15-2026 )Volvo8873 Wrote:  Thanks for the insight. I run a 2015 Internatianl Prostar nowadays. I think for now I will look into open shoulder tires for now. Never thought of the letting the air out of the tires for better traction. It’s simple things like that I never think of! Lol

My ProStar is stretched out to 296 inches center of drives and it gets stuck pretty easy. I consider locking drives because all I do is steel for construction, but every time I get stuck there's always something there to push or pull me out.

if your delivering steel regularly onto job sites with off-road conditions then yes ... a set of double lockers would be appropriate. Just take into consideration of what was mentioned above so that your not going into it blindly.

[DVT873]

Volvo, you might look into Automatic Traction Control (ATC) for your ABS. It works fairly well. I had a customer who ordered some single-axle straight trucks for job site work. He disengages it when he goes onto the site. If he starts to get stuck, then he engages it and tries to back away from where he is. He says it works well for him. I realize this is not quite the same as your condition.
You say this is only a few times a year, and you usually can get pulled out. Maybe leave it at that. The full locker setup is going to cost a lot of money, reduce mileage, and wear out quicker. Keep in mind that if you get that combination stuck, you will be really stuck. All 4 wheels spinning and digging holes. And if just one finds traction at the wrong moment, bye-bye rear end.
A long time ago Pennzoil ran some barrel trucks near me. Tandems. They ran normal power dividers but had Detroit Lockers in the rear rear diff. I got to know the mechanic there. Sharp guy. He said that combination worked out pretty well for them and that was all he wanted. They had tried some full lock-up setups. Drivers would forget to disengage.
—an expensive mistake. This was before electronic controls. And some still got stuck.
So they settled on the Detroit Locker in the rear. Fairly simple to add IIRC. It replaces the existing spider nest. Downside is they can be noisy.