| BHPian
Join Date: Nov 2007 Location: Chandigarh
Posts: 376
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| The Axle debate
Hi there,
i thougt i'll start an axle topic regarding what constitutes axle strength. I would need help with inputs from UBS Sir, Arka, Vinod, amongst others, and i know they would help. If anybody has any views, questions, answers, or a different logic, please do post so. I may be wrong, so please do correct me. And yes, please let us all try to keep this topic as clean as possible. And if you can,please do forgive me for any spelling mistakes.
Lets start from the contents of differential pumpkin housing:-
1) Crown or Ring:- This is probably the biggest feature that determines axle strength factors. Quite obviously, the bigger the ring, the more strength factor it has has. but another thing to note is the thinchness of both the teeth surface and the overall thickness of the ring itself. In the Ford 9" axle, even though it has a smaller ring than the seemingly more powerful Dana60, it has more a thick ring. Material strength is also a factor, but lets leave this aside since all axles, except custom made units, more or less use the same kind of materials. Also, all Ring/pinions under sudden torque loads go through a little torsional vibrations, and therefore they lose the strength in doing so, and this is when a great number of axle rings break. Some custom Ford 9" axles have these sort of plug to hold the crown on the opposite side of the ring where the pinion meshes.
2) Pinion:- This is probably the most undermined and neglected, yet the most important factor of axle strength. Naturally, both the thickness and length matter to the great extent, but also the bearing support. The Ford 9" pinion is fatter than the Dana60,70, and probably the 80 too. The GM axle though are known to have more thinkness.
Another factor here, caused by the torsional vibration, affects the pinion too, and axles like the ford 9", and much to my surprise even the Tata 407 has bearings on both sides of the pinion to counter this, whereas the other axles have the bearing just on one side(the input side).
3) Carrier housing:- The thichness of the carrier housing again makes a lot of difference. Since the outer thinkness of a facotry design cannot be changed since firstly, the inner dia. of the ring/crown has to be taken into consideration, and secondly it would interfare with the pinion rotation.
Also i point to note is that all Switchable locker types, like ARB, Ox and others, have to lose some amount of the housing wall thickness since the axtra mechanical for switching the locker take some space as well. This factor to quite some extent is countered by using a better material than the factory units(the factory units don't necessarily use the strongest materials available since neither is there a need to overbuild an axle, and they have to keep the overall cost factor down too).
I have seen photographs if lockable carrier housings breaking, especially an early example of a new pin type locker that broke right from the carrier housing where the ring is mounted. This the the reason why most of the factory locker options, used in military trucks, including the Unimog and the Tatra have a whole new axle design started from stratch, where the locker is locked from outside the carrier housing on the bearing side. For this, they use a much largewr side bearing on the side that the locking mechanism is mounted, with a larger dia. carrier bearing mounting surface, a bigger dia. locking sleeve and thinker teeth(though there are some examples, like the tempo trax do not, and the reason is that are generally designed with as few as possible modification from unlocked axles used for the same purpose, therefore are required to use as many similar parts).
4) Spider and Side gears:- The thickness and diameter of the side gears determines their strength, and the same goes for the Side gears. Also the number of spider gears inside the carrier housing also affects the strength factor. For i.e. both the Dana44 and the Jonga axle have the same dimensions, the almost same ring and pinion dia, the same axle shaft dia(though the jonga unit has slightly thicker shafts = 1.31"), but the jonga axle is the winner here since it has 4 spider gear instead of only 2 in the Dana44 axle, The aftermarket switchable locker versions of the Dana44 too have 4 spider gears.
Also i noted that the jonga side gears have the same outer dia. and about the same thinkness as the Tata 407 gears, and have the same number of teeth too. I could easily fit the 407 side gear inside the Jonga axle housing, but the innder dia., where the axle shaft fits is greater in the 407 due to its much thinker(1.51") shafts, and also the part of the side gear that rests with the carrier housing has a larger dia. than the Jongas.
5) Carrier side bearing mounting tube thinkness( don't remember whatever its called, please correct me) and Bearings:- Even though some of this has been covered above, i'll go into some details.
The side of the carrier housing that is tube shaped to mount the bearing is of quite importance. Firstly the entire load from the ring/pinion, through the side gears and into the axle shafts, is handles by the bearing, and therefore the greater surface that is offered to the bearing mounting, the more stronger it is. Literally, the more the dia. of the side tubes of the carrier, the more powerful the housing becomes.
Also, another factor is that the outer dia of the tube has to be taken into consideration since the inner dia of the tubes has to be fat enough for the axle shafts to pass through. the thicker the axle shaft, the thicker, the lessor will be the material placed between the inner and outer diz of the carrier housing tubes, therefore the outer dia of the tubes has to be compensated. (This is the biggest problem i'am facing by using Tata407 axles in the jonga axle housing. Since i have to increase the inner dia. of the tube to get the axle to pass through it, the material between the inner and outer dia. of the tubes is therefore now lessor than it initally was, and the overall strength of the carrier housing likewise diminished, beating the actual purpose of the mod. I have to use a bearing that has the same outer dia. as it originally was, but the inner dai. lhas to be the size of the bearing used in the 407 axle, but that too will desrease the overall bearing strength, but not to that great an extent as it was with the carrier tubes. another option is to put the axle or the differential pumpkin housing on the lathe, and remove material from the bearing area to make use of a larger outer dia bearing, but that decreases the carrier holding strength of the differential housing. Its always a matter of you lose some, and you win some, and here i think option no.2, of using a smaller but stronger material bearing is the solution).
The bearing as i said earlier, the bigger the difference between the inner and outer dia., the better and stronger it is.
6) The housing tube thinkness: Naturally, the biggest reason the big fat axle/differential housing of the trucks is more powerful than the jeeps is the thinckness of the tubes. This factor is the same regarding both the full-floating and semi-floating axles. There are some tubes that have the same outer dia. as each other, but the inner dai is smaller. The One with the smaller inner dia, has a stronger housing, but a smaller inner dia. also means a smaller dia. axle shaft, so the total strength facter depends on the total housing and axle strength combined. This is usually in case of Semi-flaoting axles and full-cloating axles of the same design, where the full-floaters have a smaller dia. and therefore weaker axle shaft than the semi-floaters, but that factor is counteracted, not necessarily in over all axle strenght as regards to off-roading, but surely in-case of load carrying.
7) Axle shaft thinkness:- Naturally here too the fatter the better, but there are so many new stronger materials in the market that smaller, thinner axle shafts made by them are still as stronger as the fatter ones.
An axle is basically designed to twist, when a big torque load is applied, and thus when you see a broken axle shaft, you would be axle to make out the twisting bends made on them just before it broke.
When an axle shaft is hmade, it is hardened only from the outer side and the inner portion is purposely kept soft, which makes more flexible to twisting forces. Depending on the main purpose the shaft is made for, this ratio of harned, thus strengthened versus flexibility is very precisely monitered.
Also regarding the max thickness of the axle, all axles are goosenecked, as in thinkness of the axle goes down right after the inner spline area and is gradually increased until the outer spline area. How much depends upon the axle. A full-floating axle has more of less the same thickness in at inner and outer splines even though they too are goosenecked. Whereas a semi-flaoting axle would be as much as one and half times as thick as the inner end(there are no outer slpines, except in a few axles. In the jeep Cj3b axle, its held on by a single carter pin at the outer and, so that makes it weaker than the other Dana44 semi-floaters).
Semi-floating Vs full-floating
In the semi-floating axle, there is just one bearing at the outer end to upport the axle shaft. Beyond the outer bearing at the axle tube, the axle shaft is on its own to counter both the weight of the vehicle, and the torque loads. Therefore a semi-flaoting axle shaft is a lot thinker toward the outer end then its inner end.
A full-flaoting axle has no bearing at the outer end of the axle tube. Rather the other end has a flange through which the axle shaft passes, and here the hub, which is supported by 2 bearings, is connected to the axle shaft. Now since the entire weight is on the hub bearing, the flange, and there on the axle housing, the axle shaft does not have to bear any of the load of the vehicle, which is passes ofn ot the axle housing to handle through the flange and the bearings. The only thing that the axle now has to handle is the torque load.
Now the main points here are:-
1) The axle shaft of a semi-floating axle is much more stronger than a full-floaters, thought the overall strenght of the full-floating axle might be much more. The holds true especially for the Dana44 type axle, excluding the Cj3B axle which have a carter pin.
2) The beaings of a full-floater last longer, since there are 2 brearing on each side to hold the weight rather than one is the semi-floater.
3) In case of the Semi floater, the weakest part is the outer part of the axle shaft, whereas in the full-floater its the bearings and the flange. On the jonag rear axle though, which is a semi-floater, its the axle holing nut, twhich have been known to come lose, throwing out the entire axle shaft on a moving vehicle.
Anything else you want to put down here guys. |
16th April 2009, 18:42
(1)
Thanks
