Shaving A Diff For More Clearance!
There are many choices in making your 4wd more competent when going off-road. The 3 main options 4wd owners usually opt for are; a larger set tyres; fitting of new suspension to allow more lift and articulation, and; lockers to aid in traction.
Eventually you get to the limit of how much lift you can fit in the vehicle because of legalities or center of gravity becoming an issue; tyres can only fit within the guards so there is a limit to how big the tyres can be fitted, and; lockers are only useful when your wheels are on the ground.
There is another option that brings about a great benefit to not only competition vehicles but also the everyday recreational 4wd and this is Diff Shaving. This is a process of removing excess material from the underside of the diff and this will then give you more ground clearance.
If it is possible to remove 1 inch of material from the underside of the diff this would be the same as using a 2 inch larger tyre to achieve the same under pumpkin clearance without changing the legalities or driving characteristics of the vehicle.
Most diffs can be shaved, some more than others; in this tech article we will modify a Toyota Hilux LN106 front diff.
Start by removing the diff from the vehicle. Have the oil drained and completely stripped down.
Setup the diff on suitable stands or bench, in Image 1 you can see I have marked an approximate area that I estimate will be the cuotut.
Remove the 3rd member first then start by cutting a small section out first, you then need to refit the 3rd member in place to see how far you can cut.
Using chalk, re-mark the approximate area to be cutout if it needs to be altered, remove the 3rd member again. Cautiously cut out most of the material that you wish to remove, keep in mind that most pinions sit on a few degrees angle in the vehicle so you must allow for this when cutting. If you just cut square from the 3rd member face you will not remove enough material.
In Image 5 & 6 you can see how much material has been removed. Image 7 shows a ruler used to see how much clearance is available. Another way to check the clearance is the use of a piece of Blue tack. Simply put the blue tack on the gear set and push down the fill in plate, remove the plate to see how compressed the blue tack was pushed, this will give you an indication of how much material can be removed.
Once you are happy with the amount of material removed you can cut the fill in plates, this is usually 5-6 mm mild steel or if you have access to wear plate you can use 4-5 mm. It is recommended to use wear plate because of the extra strength. Cardboard can be used as a template to get the shape of the fill in plate correct.
With the 3rd member removed and your fill in plates cut, it is now time to tack them in place. Refit the 3rd member one more time to check everything is moving freely.
If you have in your workshop an old 3rd member that is of no use it is highly recommended that you install this into the diff housing and properly tighten in place - this will help the housing stay straight in the flange area. If you do not have a spare housing to tighten in place during this process you will risk the diff housing bending and it will not seal properly.
Once all the welding is done let the diff housing with the old third member still fitted cool in still air. Carefully clean the housing and visually check for any cracks, holes or weld defects.
Finally paint the shaved housing, refit the 3rd member and all the associated parts and install back into the truck. Remember to fill it with oil and check carefully for oil leaks.
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Burpengary Queensland 4505
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