This modification came about for two reasons:
One, I have always felt that the Jimny’s low range is not low enough, I often found myself stalling on trails when I had my foot flat on the power, and I hardly ever used 3rd, 4th or 5th when in 4L.
Two, when doing very rocky sections of trails, I found the Jimny was always going too fast, you had to get it to 3000/4000 rpm in order for it to not stall, and by then you where bouncing over rocks, there was no possibility of you just idling through an obstacle or trying it as slow a possible. This always felt very cow-boyish and it was a matter of time before something was going to break, snap or bend.
After agreeing to do Baboons Pass in Lesotho (an extremely rocky trail at a high altitude), I decided that it was indeed time to do the ultimate modification and put in transfer case reduction gears. These are generally designed for guys running 30″/31″ tyres on their Jimnys.
I oped for a kit that gave a 17% reduction in high range (both 2H & 4H) and then a 86% reduction in low range (4L).
This meant that I could put larger tires on the Jimny and not experience any power loss, and at the same time this would fix my low range problem. In fact, this kits Low range is so low that you can actually refer to it as crawler gears because in 4L-1st gear the car barely goes anywhere, which is fantastic for attempting very rocky tracks.
Remove the transfer case from the car
This step is fairly easy,
First, put the car into 4H and make sure that it is engaged, then put the car up on the Jack and start removing:
- Front & Rear prop shaft (TC side)
- Input prop shaft (TC Side)
- Remove the electrical connectors
- remove the 3 nuts holding the TC Down.
This shouldn’t take more than 15 -20 minutes to do. Once this is done you should have something that looks like this:
Install the new gear set
Next up, we have to remove all of the accessories on the transfer case, (Make sure to put all the bolts & goodies in a secure container).
- Remove the 3 locking nuts on the prop flanges
- Remove the 3 prop flanges
- Remove the shifter actuator
- Remove the shifter position sensors (and small ball bearings)
- Remove the speed sensor
Lastly, remove the case bolts, and gently crack open the transfer case housing. You should see the following:
The next few steps are super technical & rather complicated, one essentially has to dismantle all the shafts & gears, then using a press, remove the bearings & old gears from the shafts, and then press on the new shafts & bearings.
One of the steps involves grinding away a small portion of the transfer case housing in-order to make more space for the larger gear. The key thing here is to make sure you clean the housing out super well afterwards. The last thing you want is stray metal fillings mixing with your oil and new gears.
Once all the new gears have been added to the existing bearings & shafts, one then essentially undoes everything you did earlier by putting the accessories etc all back onto the transfer case.
Put the transfer case back into the car
Simply bolt the transfer case back into the vehicle, making sure you tensioned all the bolts correctly and reconnected all the electrical cables.
While the car is still on the lift, try and change the car back into 2H and check that transfer case is still all working fine.
I was lucky enough that we had put everything back incorrectly and the car worked perfectly. Next thing up.
Testing the new gears
The first thing which I did as I drove out of the workshop was to hold down that 4L button and see just how low the new low range gears were, and wow they are LOW. My immediate thought was that these will be amazing off-road… I unfortunately didn’t have many places to play around with them so I put her back in 2H and headed off home.
It was a long 60 Km highway trip home. It was a very interesting trip driving getting used to the new ratios. (remember I have a 17% reduction in high range, and I was still running stock 205/70 tyres). Initially, I was very impressed with how the car pulled, it felt like it had more power, which it did, in theory have (at the cost of higher RPM). However, nomad was just flying. I got to 120km/h in no time. Very chuffed with my self I carried on cruising home.
That was until I remembered than the kit also corrects the speedo for larger tyres. So even though the speedo was showing 120km/h the GPS speed was more like 98km/h this is when I had a good laugh at my self. However long story short, I was pretty much able to cruise at 100 – 110 km/h on the highway the whole way home, I never had to gear down to 4th once, not even on the uphills.