The ATV and UTV become more popular sports in the USA now, we drive on the field, trail, rock and mud to enjoy the fun, itís really exciting sport, but meantime some parts is much more easily broken than the street car, like CV axle broken is the most common issues for the owners, and some ones use lift kits and big tires to lift the ATV or UTV, this cause the CV axle failure more often on rocky terrain and mud race, mainly shaft broken. So the needs for the buying CV axle in the market is increasing much now, and on the market there are different grade and price CV axle to sell, how to choose and which is suitable for you?
On the market except extreme heavy duty CV axle like RCV, Turner made in USA, most are from China, and for many years I had worked in China for USA company on sourcing CV axle and accessories for ATV and UTV exported from China to USA, so Iím aware of these product and related market, Here I just want to share my some thoughts with everyone, hope to be a little helpful for your reference to choose the suitable CV axle according to your driving style and have your wallet lean.
On the most current ATV and UTV, they are independent suspension design and use CV axle transfer the force, which include the outer fixed BJ style CV joint connected the wheel, inner plunging DOJ style connected the differential, and the center shaft link the outer and inner CV joint together as the whole assembly CV axle, the engine force transferred from the differential to the wheel by the CV axle, this CV axle just only bear the torque, (on the very few special condition, the bending moment will happen and would have the CV housing crack or shaft bended ), when the torque is overload, the CV axle will be broken, Since the most failure of CV axle is on the shaft broken, so here we mainly talk on the shaft and other main factors.
The shaft raw materials
ATV and UTV driving conditions is hard terrain much more than the street car, the strength requirement is much higher than the street car, but this is very young market and growing rapidly, R&D on it is not mature, so in China the factory still use the same standard of the street car make the CV axle, the factory choose raw materials with the cheapest cost but strong enough within the design, in China 5140 is very common alloy steel for the shaft, easy to buy in the market and the heat treatment technology was already mature, the performance is also very nice ( tensile strength can about 980 MPa after Q&T) and machinability is good，itís heat treatable steel for driving elements as crankshafts, CV axles, steering components.So on the proper heat treating, a 5140 forged shaft is an economical choice, even though the OE ATV they also use this 5140 steel shaft, so almost all the China factories use this 5140 steel to make the shafts for car and ATV and UTV.
(On 300M shaft, RCV and Turner the best steel 300M, which have tensile strength ratings of approximately 1480 MPa, these are for extended long travel for the rock crawling and mud race. No China factory use this materials by now.)
The shaft heat treatment
Actually this 5140 steel is really good enough but the heat treatment must be correct processing, I visited several factories to test their 5140 shaft of diameter 23.3mm strength, the first test the max toque is 3135 N.m, this end is OK within the Chinese CV axle standard of 2900N.m, I found their one heat treatment process is the normalizing instead of quenching and tempering, I asked why, they explained since by normalizing the shaft strength could already meet the country standard, so no need to do by quenching and tempering with added more cost, you know on the ATV shaft bearing the heavy torch and impact load, thequenching and tempering can achieves an extremely fine-grained and homogeneous micro structure and give the high strength and good ductility, so I asked them this must be needed, then the next they use quenching and tempering and surface induction hardening, the testing end improved much better with increasing about 10% to be 3391N.m, this is very nice end.
Max torque 3135 N.m before improving the heat treatment process
Max torque 3391 N.m after improving the heat treatment process
The consistent quality raw materials and correct heat treatment processing is the key for the shaft strength, No one hope that your customers buy from you and found even though in the same batch order the hardness and tensile strength of one shaft is vary a lot to another.
The shaft profile is one of factor to affect the shaft strength, most stress is centered on the neck down step, on the design, should make it smooth and fillet radius as soon as possible to avoid stress raise, this is not big issue, the experienced engineer should consider it, just when you need to develop a new custom axle, remember to remind this!
The OE parts were designed to be just only strong enough for the normal drive, not including for extended long travel for the rock crawling and mud race.
The OEreplacement is almost same as the size of the OE, they just copy.
For the aftermarket, they make the CV and shaft size longer and larger to meet the extended suspension and strength need, usually the shaft diameter is about 10-20% increased due to the working space and angle limited.
The increasing the shaft diameter will affect the CV axle working angles, for most ATV and UTV, the outer CV joint with wheel is fixed joint of BJ style, the max allowance angle is about 49 degree, the inner CV joint with differential is plunging joint of DOJ style, the max allowance angle is about 25 degree. If the shaft diameter increased, the max allowance angle will decrease, special for DOJ CV joint, in order to resolve this issue, we can use the fixed joint with special inside form to replace the plunging joint to achieve the big working angle, and use the shaft traveling with the inner race to achieve the plunging, by this way, the max allowance angle of inner CV joint will be about 44 degree, and the shaft travel is still about 2 inch (50mm), and the lager diameter shaft strength increased than OE.
CV Boot for storing lubricants and avoid dust, water and salt into the lubrication system. Performance requirements must have excellent (high temperature) fatigue resistance, heat oil long-term erosion. Usually on CV axle we use TPEE plastic or rubber CR (chloroprene rubber), TPEE has excellent low-temperature fatigue resistance, oil resistance up to 100 ℃ long-term erosion of the working temperature range is very wide, it can be used in -70 ~ 200 ℃, excellent ozone resistance, weather resistance and anti-aging properties.
Recommend TPEE boot on CV axle!
CV joint grease requirementis with withstanding high temperature and pressure to avoid excessive wear and lengthens the life of the joint.There are different grade and lots of brand grease in the market, some use the same level as the car using, the workable temperature is about -35-120℃, the higher level is about -35-150℃, but for extreme heavy duty ATV axle, the immediate heavy load and to increase the temperature is much higher than the normal, by using the high grade could ensure the CV joint work well and long life, Recommend using the special off-road PYRONOC CV joint grease, itís -40-180℃ working rang, on the picture the left is off-road PYRONOC CV joint grease, after high temperature driving, you can see the grease still attached on the component keep the original condition, almost no change, this is very good lubricate for the protect the CV joint surface when extreme running, the right is lower level grease, you can see it become liquid after driving, this is not good protect.
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From the above information, we knowthere are some difference on the raw materials and technology grade, this cause the different cost and quality, and all will be affected on the end price on the market.
The price from high to lower
Extreme heavy duty, OE, aftermarket, OE replacement
The strength from high to lower
Extreme heavy duty, aftermarket, OE, OE replacement
The failure percentage on normal driving condition from high to lower.
OE replacement, aftermarket, OE, Extreme heavy duty
So now from all the above information, when your CV axle broken, we could combine your driving style and considering the price, strength, failure percentage considering to choose the suitable CV axle on the market for you.
If you just drive on the farm normally as utility, OE replacement should be better for you due to the cheapest price and the strength almost same as OE.
If you are light off road on the field and trail, aftermarket should be better for you due to the strength is stronger than OE and the price is cheaper.
If you are enthusiast on rock and mud racer, no doubt the strength is your first factor to consider, so the extreme heavy duty is your best choice.
Please remember: whatever the CV axle strong, which must be weaker than the differential gear, since CV axle is cheaper cost than differential and you could replace your broken CV axle in the field, but not possible to replace the broken differential gears in the field.
I'd like to exchange more information on the product and market with everyone, please see my linkedIn search name "Bai zhongmin".