Now we have established the need for underbody protection, and the benefits of applying our own underbody protection, and the fact we need all three of the previously mentioned systems for maximum protection, we can begin by cleaning the vehicle ready for underbody application. Cleanliness is next to godliness is a common saying, and its never been more appropriate than with a 4X4, the cleaner it is the more effective our protection will be, but before we clean our underside we need to ensure any work necessary to the chassis is completed as these systems are all highly flammable. Where a vehicle is being converted or modified it is essential to complete any chassis welding, or repairs, or utilise another method other than welding to mount additional brackets for tanks or storage.
Its a nice sunny day, so thats the best time to clean our chassis then? no is the simple answer, cleaning is best done when it is sopping wet as wet mud is soft and easily washed off, particularly inside enclosed sections such as sills, chassis and crossmembers, or other inaccessible areas which can hold mud or other debris. We do need a wet chassis to soften mud, but a dry and clean chassis and underside to apply protection to, so how do we do this? one simple way is to drive the vehicle into a river or stream and leave it for an hour, the running water will soften and remove lots of debris from inside enclosed sections of the vehicle, in reality most people cannot do this. What can be done is to regularly clean the vehicles underside during wet winter conditions, this will remove most of the concealed debris inside the chassis or enclosed sections and leave it reasonably clean in preparation for applying underbody protection.
Cleaning the outside of a chassis, crossmembers, and the vehicles floor is best done by scraping off any loose material with a scraper, an old putty knife is an excellent scraper, and the quickest and easiets way of getting it back to clean metal is with a 115mm angle grinder with a 75mm angle grinder cup wire brush screwed onto it. This will remove underseal and dirt, as well as rust from the outside of a chassis or underside of a vehicle very quickly, and without continually clogging as abrasive papers do. Cleaning the top of a chassis is a little more time consuming and the best way is to use a drill with a flat 150mm wire brush attached, this will clean the top of the chassis and the floor immediately above it, but, this is slower than using a high speed angle gringer, but still very effective.
Cleaning the inside of a chassis is more time consuming, the first thing to do is identify the numerous holes in the chassis and gain access to both ends of the chassis, once this is done it can be blasted with a jet wash or hosepipe from each end, and through the numerous holes to remove the mud and debris. If this is done periodically during the wet winter weather, most of the mud and debris will have been removed and will leave very little inside the chassis to be removed, but, this will not remove any rust. Let the chassis fully dry out then proceed to the next stage.
Removing rust is more difficult, one little trick is to obtain some wire rope about 6mm diameter, and about 2 metres long, one end is placed into the chuck of a drill and the other end is taped using insulation tape about 6" from its end, working from the end you simply seperate the individual strands and bush them out to form an umbrella shape. Push the umbrella shaped end into the chassis and start the drill, you now have a flexible wire brush which will reach about 2 metres inside your chassis to scabble it, and the whipping action of the rope will beat any tougher pieces of rust into submission, work slowly, backwards and forwards until the inside of the chassis is clean. While 6mm diameter rope may be deemed the thicker the rope the better, as the rope is pulled from the chassis it may be whipping excessively so a leather glove may be worn to hold the rope in its centre to control this whipping. Work from both ends of the chassis rails as very few chassis rails are longer than 4 metres, for those that are you can work through the numerous holes already in the chassis to get the middle of a chassis. Your new tool can be used in other enclosed sections such as chassis crossmembers, irrespective of shape as it is flexible enough to go around corners, and inside any other enclosed sections such as sills or chassis outriggers.
Once the chassis has been cleaned internally it needs blowing out, a compressor is ideal as high pressures can be achieved with the numerous blowguns on the market, equally a long thin pipe may be used and you will have to blow down this with your mouth, some may be better than others using this method. If you note the condition and amount of debris being blown from inside your chassis rails, you can determine if you need to repeat the cleaning procedures above, and reinsert your new void cleaning tool to clean it again, obviously the cleaner the inside of your chassis rails the better protection you will get. If you are unsure, clean it again.
When you clean the underside of your vehicle you will need to do this in stages, if you clean it all in one session you may run out of time to apply at the very minimum, one coat of metal paint to protect the cleaned area, so work in small stages, clean, paint, and leave no sections of chassis unprotected for longer than necessary.
Gaining access to certain areas may be a problem, some crossmembers may be fully welded, or spot welded at each end, and they may only have a small (3mm) drain hole to let out water, or you may find only drain holes in sills to let water out, so you may have to find an alternative access, or drill to gain access. Manufacturers often drill holes in the rear of the front wheelarch, or the front of the rear wheelarch for their factory protection, these are then plugged with a rubber or plastic body plug before the factory underbody protection is applied, so look closely to locate these holes. If you find your vehicle has these access holes then fine, scrape away the underbody protection and remove them, you can insert your cleaning tool from one, or both ends to clean inside a sill section, of not then drill an access hole, but ensure you have a suitably sized body plug to replace the removed one.
Where there is no access to a crossmember you need to drill, drill from the outside of the chassis, through the outer rail, then through the inner rail to access the crossmember, remember to measure and mark the outer rail carefully so you do not miss the inner crossmember, and again, ensure you have a body plug or grommet to plug the outer chassis rail. Do not drill holes any larger than required, and do not drill any more holes than necessary. Where you drill any hole to gain access, ensure you paint any exposed metal with a good quality industrial metal paint before fitting the body plug or grommet, you may spend hours protectiong your vehicle from rust, yet fing it rusting where you have drilled, this rather defeats the object.