One of the first things that made itself onto the mod list for the new Dmax was underbody protection, or bash plates. The reason for this is simple; there are some very expensive, vulnerable and low to the ground bits of gear underneath the Dmax.
I never had anything fitted on the 80 series Land Cruiser, but that was a totally different beast. The chances of hitting anything vulnerable on the 80 was much less likely, given it had a lot more clearance, and things seemed to be tucked away better (with exception to the differentials, which you are always careful of anyway!).
If you want to see the finished build, here it is - Dmax 4WD modifications for travelling Australia.
Why do you fit underbody protection?
The sole purpose of fitting underbody protection is to protect your fragile radiator, sump and drive line from damage when off road. This can be in the form of sticks and rocks being flicked up while driving along or physical impacts from logs or big rocks that touch underneath. One bad slip off road can cause you hugely expensive repairs, and that's without the inconvenience of being towed home. If you can prevent that by adding a bit of extra weight in the form of plates under your vehicle, you'd be mad not to.
People spend a lot of money protecting the front and rear of their vehicles with bull bars and rear bars, but the gear under your 4WD is just as (if not more) important.
There's no doubt that the Dmax has much less clearance than our 80 series had. I could comfortable roll around under the Land Cruiser, and even sit up in some parts of it. The Dmax has a number of points that are extremely close to my nose when I crawl around underneath, and given it is low almost all the way from the front suspension to rear, its a good idea to fit some protection
Expensive automatic transmissions
The automatic transmission on the Dmax hangs fairly low down, and I could see a sharp rock puncturing a hole in the oil pan, or worse. This was the primary reason for fitting the bash plates, but doing the whole kit covers the radiator and sump too.
What did we fit?
In the end, I went with the full 3 plates kit from Bushskinz, in silver zinc electroplating. Delivered, it was about $430. I did a fair bit of looking around, and decided on Bushskinz to be the best value for money, and that suited our build.
We could have had them powdercoated black for about another $150, but I didn't really see the point.
Installing the bash plates
Even with no instructions, fitting these was a piece of cake. Yep, they are heavy, and yep, the vehicle is low to the ground. A set of ramps is a fantastic way to get under the vehicle, and you can fairly easily hold them up while putting bolts in. They install from rear to front, and make use of the same holes in between each plate, which makes it easy to slot them in.
What should you look for in bash plates?
Bash plates generally come in 3 material types. The most common by far is mild steel that is powdercoated, or zinc plated. Beyond that, you can get stainless bash plates, and aluminium ones.
Mild steel is the cheapest, easiest to be repaired but also very heavy. Stainless is more expensive, will never cause you rust issues, is just as heavy and has a habit of cracking and work hardening.
Aluminium is the lightest, but needs to be thicker to get the same strength, and it also tends to gall, or 'stick' when you drag it over rocks. It's also much more expensive.
For mild steel and stainless, 3 or 4mm is normally the chosen thickness. Aluminium can be thicker - around 6mm to achieve a similar sort of strength.
Everyone seems to go for the thickest available, but it is extra weight and not always required. Some vehicles snap the bash plate mounts off long before they bend bash plates!
I was told by a reputable supplier that 3mm is more than enough, but everyone wants 4mm, so that is what they make!
What does it actually protect?
It's all well and good putting bash plates on, but it needs to function well. The normal 3 plate kit covers the radiator, front differential, engine sump, and transmission. However, you can buy individual plates for select areas, and some places even sell fuel tank guards, differential pumpkins and transfer case. It's worth getting under your vehicle and seeing what is vulnerable, and then getting what you need to suit how you use the vehicle.
Design and work required vs cost
Most bash plates are just bits of steel plate with a few bends and holes in them. These range from about $300 - $430 a set. If its more involved, like the AFN underbody protection for the Dmax, expect to pay a lot more.
How much does it weigh?
Steel plate is heavy. Even thick aluminium has a fair bit of weight to it. Expect a full set of bash plates to weigh anywhere from 30 - 50kg. How is your 4WD in regards to payload?
One thing I am always mindful of is changing the original equipment manufacturers design. Bash plates can dramatically reduce air flow through the underneath of the vehicle, and this can in turn create other problems. If your radiator, differentials, motor, automatic transmission or transfer case don't get enough airflow you can make them run hot, and at the very least reduce their lifespan.
I'm carefully monitoring the temperatures of the Dmax, and feel confident the bash plates will be fine as there is a lot of open area for air to move through. Some designs and vehicles that I've seen though are not like this, and I have heard of overheating issues due to bash plates.
Is it maintenance friendly?
If your bash plates have no holes in them for accessing regularly used bolts or plugs (like your sump and oil pan plugs) then they have to come off each time you want to change the oil. You can't really get away from the weight, but how do they bolt on? If they are fiddly to install and remove then your mechanic is going to bill you accordingly.
Does it reduce your clearance?
You will lose some clearance when you fit bash plates. How much depends on the design of them. Good bash plates create a smooth surface (as much as possible) for things to drag through and out of the way. If the bash plates lower your clearance by a substantial amount though, it could cause you a problem off road.
Will it fit diff drop kits?
If you are fitting suspension lift kits, and you plan on doing a diff drop in the future, make sure your bash plates are compatible, or you will be buying another plate to suit!
How does it mount up to existing accessories?
Before buying something, try and see how it mounts up, and make sure its going to work for your application. Bull bars all have different designs, and not all bash plates will marry up in a way that looks good, is functional and easy to work with.
Facebook is the ultimate place for researching things like this, as you have a wide audience running a heap of different gear. Try the individual groups for best results, like Isuzu Dmax and MUX owners Australia, for example.
What's the downsides of bash plates?
- Extra cost
- Maintenance is more difficult
Do you really need them?
I can't answer that for you. You need to have a look under your vehicle, and think about what hangs low, and how low it hangs. If you hit it with a rock or stick, is it going to do some nasty damage? What sort of terrain do you drive on?
On a vehicle with a lot of clearance and plenty of steel work they are not as important, but consider this; one little mishap off road and you can be up for a LOT of money when it comes to repairs! Factory bash plates are usually 0.5 - 1.5mm thick, and are no where near strong enough to take a decent hit.
The manual version of the Dmax has a much higher transmission, and a bash plate is less important. Auto's hang lower, and have a light weight oil pan right at the bottom!
Who sells bash plates?
You can buy underbody protection from a huge range of places - Bushskinz, Boo's bash plates, Custom Offroad, ARB, TJM, Opposite Lock, Ironman, Roadsafe, Pedders, Brown Davis, Superior Engineering and AFN.
Do you run underbody protection?
What do you run? Why did you install it? Are you happy with it?