Air Lockers - OEM vs ARB?

na3s

Active member
I've been curious about this for a while...

Based on what I've read, both seem to be well regarded, reliable, and robust, any reason to favor one over the other beyond the pros and cons I could come up with below?

OEM
+ Cheap, can be found for +/- $100-300 for complete axles w/pump
+ Already set up, no need to have a diff rebuilt/backlash set if offered in the gearing you need; 4.22 & 4.636 correct?
+ Simple low pressure pump, I've read aquarium pumps have been used as replacements

- Parts are either no longer available or difficult to source and service
- Can be hard to track down if no local yard and expensive/heavy/bulky to ship
- Diff must be rebuilt/backlash set if going w/4.9 gears
- Requires the factory shortened axle shaft if swapping only the 3rd member; driver's side?
- No front option


ARB
+ Currently in production w/warranties and available parts/service/distribution worldwide
+ High pressure pump can be used for airing up/tools/etc
+ No extra to change gearing while setting up
+ Matched front option that can utilize the same pump for both front and rear

- Expensive, +/- $1,000 per diff, +/- $200-$560 for pump, plus install
- Diff must be set up by someone with the skills to set gear backlash/etc
 
  • Like
Reactions: plh

billiebob

Well-known member
I have never read a bad review on lockers, factory, ARB, Eaton, or other. Lockers tend to be too small a market to attract the off shore invasion. This is more personal choice, product availability, price? peer advice.

The big choice is air vs electric.
 

Toasty

Looking for that thing i just had in my hand...
I don't believe that there is an electric option for Monteros
Harrop is our electric option, the aftermarket lockers are a lot stronger than the OEM. Not that the OEM is weak but if you're not careful you can shear the teeth on them and it no longer functions as a locking diff. The latest Mitsu diff sold here is still serviceable for now (1997+) but the older ones are no longer serviceable.
 

plh

Explorer
Harrop is our electric option, the aftermarket lockers are a lot stronger than the OEM. Not that the OEM is weak but if you're not careful you can shear the teeth on them and it no longer functions as a locking diff. The latest Mitsu diff sold here is still serviceable for now (1997+) but the older ones are no longer serviceable.
ah yes, the 8" rear, 9" rear and 8" front.

 

offthepath

Adventurer
Although on a gen 3, I have arb front and rears in mine. If I were to do it again I'd get harrop elockers.

The rear arb had an internal air leak. After pulling the diff 3 times over the course of a year to replace the same seal again and again, arb finally gave me a new locker. Knock on wood, it has been leak free, but I'd take the simplicity of electricity over a system relying on leak free high pressure air to function.
 

Michael Brown

You followed me, so now we're both lost
ARB makes a very good locker, but you are at the mercy of the compressor and lines for it to function. Most manufacturers have moved towards electronic style lockers to reduce the bill of materials for production or advanced traction control systems. The OEM air locker has the benefit of the low pressure operation, but you still have a pump and lines to maintain.

Labor cost to set up the differential for the non-OEM options will also be a large part of the cost. At $1500+ just for quality locker systems, this is also not a place where one can afford to attempt to save money.

Also, there is a difference in engagement time. Pneumatic lockers engage/disengage immediately once air pressure is applied as long as the wheels are stationary or both moving at the same speed (eg. straight line). E-lockers require some rotation to activate the ramped mechanism, so expect a little wheel spin right before it fully engages.
 

Kmrtnsn

Explorer
ARB makes a very good locker, but you are at the mercy of the compressor and lines for it to function. Most manufacturers have moved towards electronic style lockers to reduce the bill of materials for production or advanced traction control systems. The OEM air locker has the benefit of the low pressure operation, but you still have a pump and lines to maintain.

Labor cost to set up the differential for the non-OEM options will also be a large part of the cost. At $1500+ just for quality locker systems, this is also not a place where one can afford to attempt to save money.

Also, there is a difference in engagement time. Pneumatic lockers engage/disengage immediately once air pressure is applied as long as the wheels are stationary or both moving at the same speed (eg. straight line). E-lockers require some rotation to activate the ramped mechanism, so expect a little wheel spin right before it fully engages.
Since having onboard air for airing tires up and down is a given with most vehicles that are driven off-road regularly a compressor isn‘t something that wouldn’t be there already or would be purchased anyway, as for air lines to the lockers this is hardly much different than running electrical wires to an E-locker.
 

plh

Explorer
Although on a gen 3, I have arb front and rears in mine. If I were to do it again I'd get harrop elockers.

The rear arb had an internal air leak. After pulling the diff 3 times over the course of a year to replace the same seal again and again, arb finally gave me a new locker. Knock on wood, it has been leak free, but I'd take the simplicity of electricity over a system relying on leak free high pressure air to function.
I don't see on the Harrop web site that they have an option for the Gen 3 9.5" 35 spline rear. The 8" 28 spline would work in the front.
 

offthepath

Adventurer
It's been a few years, but I'm pretty sure they had them. I considered going harrop, but it was about $500 more than arb ( including the compressor) as I recall.
 

Michael Brown

You followed me, so now we're both lost
Since having onboard air for airing tires up and down is a given with most vehicles that are driven off-road regularly a compressor isn‘t something that wouldn’t be there already or would be purchased anyway, as for air lines to the lockers this is hardly much different than running electrical wires to an E-locker.
This is a good point, but may not be true depending on the person, geographic location, or wheeling expectations. It also may be a cost or budget issue. It is hard for some to justify a $200-300 air compressor on a $5-10k vehicle without installing lockers. Anyone installing a locker would benefit from having the onboard air system, but they should already have been carrying an air source before wheeling at all.

There are a lot of people who use a portable air compressor in place of the on-board units. I typically carry my M12 air compressor (rated up to 120psi) for air duty since it was cheaper and can be moved between my vehicles. Before that I used the compressor built into the Stanley jumpboxes that I keep in each vehicle. These also have the benefit of not needing to find a permanent mounting point in the vehicle. I can even carry it to a vehicle on the trail without needing to park next to it or get a long hose.

ARB has a proven design, and I do not believe their large components (locker or pump) would fail. However, if something damages a high pressure air line, I am not sure of an easy trail fix besides carrying spare line. The ARB locker engages at 70psi and they recommend supplying 100-150psi. A cut or tear to this line, although unlikely, could happen. This cannot be fixed with duct tape or even rescue tape to get it to engage again. The damaged section has to be cut out and replaced with new line and couplers, which is exactly what ARB sells as their trail service kit. At least the OEM low pressure system is 4psi which I can get to hold with enough gorilla tape or spare vacuum hose (usually rated to ~10psi) until I get off the trail. The E-locker would just need the wires reconnected to a 12V power source or spliced back together, which could be done with pliers and butt splices (as long as a smart installer leaves a little excess in case of repairs). Tree branches jab at weird angles, rocks seem to sneak up on weak points, and a random sharp object could be anywhere.

I would also be interested in seeing the total price of each system installed on the same vehicle. E-lockers requiring 2 differential installs, switches and a 12V connection, and the ARB with on-board air. I think they may be closer in price since the E-lockers tend to cost a little more, depending on the installer charges. DIY install, I believe ARB is cheaper.

I considered both, but I will stick with the rear hybrid LSD and traction control. I have yet to get stuck or need to turn around, and the largest boulders I have had to cross were the ones near Rabun Bald Mt. If I leave the east coast, I would probably reconsider these options again.
 

Michael Brown

You followed me, so now we're both lost
Here it is......
May just be my work firewall, but this doesn't open for me.

Also, I have become aware that the OEM rear locker is available on Gen 4 3.2 DI-D models in Germany. I am curious what components are available and what the install would require since they are LHD models with an automatic. I know the ratios are different. I shall dig more, but this probably should be listed under things I shouldn't have found out.
100th Anniversary for Sale

Pajero 100th RD lock.jpg
 
  • Like
Reactions: plh

Michael Brown

You followed me, so now we're both lost
Done digging for now. PartSouq lists numbers and diagrams, but nothing in stock. Perhaps some diffs and pumps make their way to salvage yards, perhaps those salvage yards have access to eBay, perhaps someone is as crazy enough to try it.
I have not confirmed any part numbers or any compatibility with US spec models, but here are links I was looking over if anyone else is curious.

2018 Diff w/lock Diagram
2006 Diff w/lock Diagram
2006 Diff Lock Pump Diagram

Seems less difficult than an SAS swap, but don't hold me to that. Remember, I give all answers for free, correct ones cost extra.
 
Top