What is a part time kit?
A part time kit converts a constant four wheel drive vehicle into a rear wheel drive vehicle with manual locking hubs at the front. In other words, while you drive on bitumen the vehicle is two (rear) wheel drive. When you need four wheel drive, you get out of the vehicle and lock the front hubs, and engage the centre diff lock (now the 4WD button).
What is the point?
Part time kits are fitted for a variety of reasons. Having 2 less wheels driving means the wear and tear is greatly reduced, the fuel economy is increased and in many cases the handling is better. In older vehicles, there tends to be a lot of backlash when you add all of the working components together. By fitting a part time kit often that slack is greatly reduced, making it easier to change gears and reducing any jolting that occurs on rapid throttle position changes.
Vehicles that will take part time kits
The most common vehicles that part time kits are fitted to are 80 and 100 series Land Cruisers. However, I have heard of them being fitted to Land Rover Defenders, and no doubt other vehicles that are constant four wheel drive.
How does the part time kit work in an 80 series?
80 series Land Cruisers run a centre diff, which allows the front differential to be connected to the rear one when it is engaged. 80 Series that have a lot of backlash can be difficult to shift gears without them crunching and will often jolt back and forth if you rapidly change throttle positions. By removing the front driveline from the equation on bitumen roads, most of the backlash is removed. The part time kit in an 80 series stops the front tailshaft, differential and axles from turning unless the manual locking hubs are engaged. To engage 4WD, simply stop the vehicle, lock the front hubs and press the centre diff lock button on the dashboard. This button turns into your 4WD button.
More about the 80 series
Please note that by fitting a part time kit to a vehicle with ABS, it will be non operational unless the hubs are locked. Also, some models come with a viscous coupling in the transfer case, and some don’t have the centre diff lock button in the cab, which means it would need to be replaced.
A number of different companies manufacture part time kits. The most reliable and well known is Marks 4WD Adaptors. However, you can purchase them from 4WD systems, eBay, Lokka and Ashcroft Transmissions. The prices vary (all around $600), but remember to check the individual parts out in each kit. The hubs vary considerably in quality, and some brands are much more reputable than others!
Fuel economy gains
I haven’t driven my 80 series enough to tell if it makes a difference. I have heard of increases in economy of up to around 15%, and also heard some people say that it doesn’t make any difference at all. From an engineering point of view it must make some difference, because there are less moving parts. How much though, I will wait and see!
Installing a part time kit
A complete, detailed guide should come with the installation kit (or you can download them off the Marks 4WD adaptors website, including photos). However, a brief description exists below:
To install a part time kit, you are looking at around 3 -5 hours, with two people. To start, remove the hubs on the front, and replace them with the manual locking ones. This only takes about 15 minutes for each side (keep the old hubs as spares if you can; they may come in handy if a hub breaks in the bush!). From there, get under the vehicle and drain the transfer case oil. Remove the rear tail shaft and the rear of the transfer case (unplug the wiring), and the section in front of that too. Remove the centre differential, and be sure to take note of the shim positions.
Take the components to a work bench and thoroughly clean them. Press the tapered roller bearing off the spool, and fit it to the new spool. Fit the new spool, shims and torque the transfer case up to the required level with plenty of gasket sealer. Top the transfer case up and fit the tail shaft back in place. Check it turns smoothly and give it a test drive!
My review of Marks 4WD adaptors part time kit
I purchased a Marks 4WD Adaptors part time kit about 2 weeks ago now, and had it delivered within a few days. The kit has everything you need, including great instructions and good quality hubs. I fitted it with a mate who had done one previously on his car. In total, it took around 4 hours. We didn’t have any real dramas, but took it slowly and made sure things were done correctly. If you have a reasonable range of tools and a good mechanical aptitude I’ve no doubt you could easily fit one yourself. I believe fitting costs at a mechanic are around the $500 mark; quite a saving!
When I bought my 80 series it had some pretty severe backlash (like you would expect with a vehicle that has done nearly 350,000km). If you let the revs drop in second gear to around 1500, and then took off gently it would jump back and forth considerably until it got to around 2000rpm. If you were driving along normally and stomped on the accelerator, jumped off it and then stomped back on it again it would slap so bad that you thought something was going to break. Also, when down changing from 4th to 3rd it would regularly catch and grind, no matter how careful and slowly you did it. This meant driving the vehicle had to be done carefully – let the clutch out slowly, change gears slowly, don’t alter throttle positions rapidly and in general treat it like a car made of glass. It was quite a pain to drive.
Since fitting the part time kit, I have been absolutely blown away. It still surges a little bit at low RPM, but not to the point where you can really feel it. The gear changes are a million times better, and you can now change gears very quickly without any worries of them grinding. It accelerates better, corners more controllably and in general has completely transformed the drivability of the vehicle. I am seriously impressed with the kit, and very happy with the customer service provided by Marks 4WD Adaptors.
Is it worth fitting a part time kit?
If you have a constant 4WD vehicle with slop in the drive train, it is worth it 10 times over. Speaking from personal experience, I love my part time kit. If you want to reduce wear and tear in the front driveline and steering, then it is likely to be worth it. If you want to improve fuel economy, do some research to see if it makes much of a difference and then make a decision. At around $600 for the kit, plus time or $ to install it the modification isn’t cheap! However, looking at 80 series on the road in Perth, and it is a very common modification!
Let me know below if you have had any experience with part time kits, and whether you think they are worth it!