Halfshafts, on the other
hand, are the weakest link in the Midget’s drive train. This is down to
both the material and the spline design, which is an old type which
results in concentration of stress at the ends of the splines and at the
centre of the halfshaft.auto oil seals Fiat.
The halfshafts were marginal for the standard engine’s power output, so if contemplating increased power or competition use it is a good idea, and cheaper in the long run, to do something about the halfshafts.
Here are the options:
Modify your existing halfshaft:
The cheapest way of uprating the shaft is to eliminate the stress raiser at the ends of the splines. This is done as follows:
Waist the halfshaft behind the spline down to the root diameter of the spline so the spline is left standing proud of rather than cut into the halfshaft.auto oil seals Fiat.
Machine the shaft to this diameter for 4”
Then blend out to the original diameter over 6”.
Blend the ends of the splines inwards as can be seen in the photo (it’s a fine-spline photo but the principle is the same.)
It may seem counter-intuitive that reducing the diameter improves the shaft, but that is the case. The simple reason is that the stress is no longer concentrated in the short distance between diff gear and spline end where the shaft is smallest. Instead, the stress is spread over a much longer length of shaft and so the level of stress is reduced accordingly. There are other more complex issues which concentrate stress which are also addressed by this modification.
Note: It’s a good idea to have the shafts at least crack tested and preferably stress relieved before doing this. The material type (which the heat treatment company will need to know to do the stress relief) is EN17 for later halfshafts, EN8 for early ones.auto oil seals Fiat.
Use halfshafts made of stronger steel
There are a number of uprated halfshaft options on the market using stronger steel, but surprisingly most repeat the design error. While the better material represents a worthwhile improvement, if the choice is available it’s better to address the design issue as well – usually at little or no extra cost.auto oil seals Fiat.
There are two separate aspects of the design:
Eliminate the stress raiser at the ends of the splines as outlined above underModify your existing halfshaft. This may be by buying halfshafts already made like this, or by modifying uprated steel halfshafts made to the original design
Change the spline pattern to one with fine splines. Not only does, the greater number of splines means that the stress per spline is reduced accordingly, but the V-shape of them spreads the stress over a greater area of halfshaft, around its periphery rather than focusing it to a small circle in the centre as the original rectangular section splines do. In addition, the smaller splines retain a larger root diameter. Each of these features substantially reduce the stress levels in the steel, combined together the effect is dramatic, particularly when the waisting past the end of the spline is done too.auto oil seals Fiat.
Note that the side gears in the diff will need to be changed to a fine spline pattern as well of course. The LSD’s supplied by Frontline already come with a fine spline option. Alternatively get some made – our ones cost us $NZ70 each to get made.
Our shafts are made from 2767 steel, which is an extremely strong material rated at 100 tons and stronger than EN24, EN30B,EN40B or 4340 which are some of the other steels used. We have them in both the original and fine spline pattern.auto oil seals Fiat.
The halfshafts were marginal for the standard engine’s power output, so if contemplating increased power or competition use it is a good idea, and cheaper in the long run, to do something about the halfshafts.
Here are the options:
Modify your existing halfshaft:
The cheapest way of uprating the shaft is to eliminate the stress raiser at the ends of the splines. This is done as follows:
Waist the halfshaft behind the spline down to the root diameter of the spline so the spline is left standing proud of rather than cut into the halfshaft.auto oil seals Fiat.
Machine the shaft to this diameter for 4”
Then blend out to the original diameter over 6”.
Blend the ends of the splines inwards as can be seen in the photo (it’s a fine-spline photo but the principle is the same.)
It may seem counter-intuitive that reducing the diameter improves the shaft, but that is the case. The simple reason is that the stress is no longer concentrated in the short distance between diff gear and spline end where the shaft is smallest. Instead, the stress is spread over a much longer length of shaft and so the level of stress is reduced accordingly. There are other more complex issues which concentrate stress which are also addressed by this modification.
Note: It’s a good idea to have the shafts at least crack tested and preferably stress relieved before doing this. The material type (which the heat treatment company will need to know to do the stress relief) is EN17 for later halfshafts, EN8 for early ones.auto oil seals Fiat.
Use halfshafts made of stronger steel
There are a number of uprated halfshaft options on the market using stronger steel, but surprisingly most repeat the design error. While the better material represents a worthwhile improvement, if the choice is available it’s better to address the design issue as well – usually at little or no extra cost.auto oil seals Fiat.
There are two separate aspects of the design:
Eliminate the stress raiser at the ends of the splines as outlined above underModify your existing halfshaft. This may be by buying halfshafts already made like this, or by modifying uprated steel halfshafts made to the original design
Change the spline pattern to one with fine splines. Not only does, the greater number of splines means that the stress per spline is reduced accordingly, but the V-shape of them spreads the stress over a greater area of halfshaft, around its periphery rather than focusing it to a small circle in the centre as the original rectangular section splines do. In addition, the smaller splines retain a larger root diameter. Each of these features substantially reduce the stress levels in the steel, combined together the effect is dramatic, particularly when the waisting past the end of the spline is done too.auto oil seals Fiat.
Note that the side gears in the diff will need to be changed to a fine spline pattern as well of course. The LSD’s supplied by Frontline already come with a fine spline option. Alternatively get some made – our ones cost us $NZ70 each to get made.
Our shafts are made from 2767 steel, which is an extremely strong material rated at 100 tons and stronger than EN24, EN30B,EN40B or 4340 which are some of the other steels used. We have them in both the original and fine spline pattern.auto oil seals Fiat.
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