Best 3 speed transfer case?

[Pin_Head]

So, Kurt, does your kit contain the hardened OEM, or a soft idler gear shaft?

Both OEM and aftermarket shafts are hardened and I can't tell that there is any difference. I was just repeating the "lore" that I had heard. In the handful of shafts I have replaced, some were spalled and some were merely worn, so the diffrence in wearpattern may reflect differences in surfacehardening.

 

[dgangle]

...And, as far as the cracking goes, it starts from the top, inside corner, because of a flaw in the casting and a general weakness of radiused corners.

This is exactly what I was thinking too. The gears 'walking' would push on the thrust washer which in turn would push on the inside of the housing in an outward direction. There can't be force on the shaft outward. There is no way this can happen as the idler does not have anything to hold onto on the shaft to push it in the first place. I have not owned the gammet of years of 40's as some but my 75-78's transfercase housings I have broken have always started at the top as Mark describes. I had my own version of a Decker brace before I even know what a computer was let alone the internet. These work to a point but one can break anything if they try hard enough!

 

[IDave]

Both OEM and aftermarket shafts are hardened and I can't tell that there is any difference. I was just repeating the "lore" that I had heard. In the handful of shafts I have replaced, some were spalled and some were merely worn, so the diffrence in wearpattern may reflect differences in surfacehardening.

I'd heard this lore, too, Charlie, and I still wonder, I guess. Sounds like it's sixes, really. I appreciate your help.

 

[cruiseroutfit]

So, Kurt, does your kit contain the hardened OEM, or a soft idler gear shaft?

It is Japanese aftermarket*, but as Pin Head indicated... I truly feel that the "OEM or bust" legend is all lore... I have literally sold hundreds of these kits, and never do I get calls back about the idler...

*as with some of my aftermarket sourced parts, the idler shaft "may" be produced as the same company that makes the OEM ones... The kit has Koyo bearings, etc...

 

[Trollhole]

This is exactly what I was thinking too. The gears 'walking' would push on the thrust washer which in turn would push on the inside of the housing in an outward direction. There can't be force on the shaft outward. There is no way this can happen as the idler does not have anything to hold onto on the shaft to push it in the first place. I have not owned the gammet of years of 40's as some but my 75-78's transfercase housings I have broken have always started at the top as Mark describes. I had my own version of a Decker brace before I even know what a computer was let alone the internet. These work to a point but one can break anything if they try hard enough!

Well if the thrust was is pushing out on the case and the idler shaft is attached to the case then it would move the idler shaft also. It's very clever idea of taping out the idler shaft on the back side and adding a washer. Though I would think more than just a washer would be needed. You could machine a thicker washer that would fit in the original frreeze plug orfice and then spread out maybe a half inch or so with a hole in the center for the bolt.

I don't know about pushing th idler through the case more though that stop tab keeps it from rotating. You might be able to fabricate some sort of cap that goes over the idler shaft but also hold it from rotating. The easiest would be just to cut another notch on the other side and tap a bolt and add a tab to the other side. That way you have both sides of the case working together with double the strength.

But I've also been told this is not where cracks start.

 

[Trollhole]

It is Japanese aftermarket*, but as Pin Head indicated... I truly feel that the "OEM or bust" legend is all lore... I have literally sold hundreds of these kits, and never do I get calls back about the idler...

*as with some of my aftermarket sourced parts, the idler shaft "may" be produced as the same company that makes the OEM ones... The kit has Koyo bearings, etc...

I was told once by an engineer for Aussie lockers how to tell if something has been hardened. If you take a metal file and rake it across the metal and it doesn't scratch then it's been done right. I've got a few idler shafts that I had laying around. One out of a stock case with no aparent rebuild wouldn't scratch and showed very little wear from roller bearing. Another scratched very easy and showed significant wear. Non OEM new from Spector showed no scratches. I guess it's hit and miss.

 

[IDave]

Scratch one for me, Kurt! See what happens!

 

[dgangle]

Well if the thrust was is pushing out on the case and the idler shaft is attached to the case then it would move the idler shaft also. It's very clever idea of taping out the idler shaft on the back side and adding a washer. Though I would think more than just a washer would be needed. You could machine a thicker washer that would fit in the original freeze plug orfice and then spread out maybe a half inch or so with a hole in the center for the bolt.

I don't know about pushing th idler through the case more though that stop tab keeps it from rotating. You might be able to fabricate some sort of cap that goes over the idler shaft but also hold it from rotating. The easiest would be just to cut another notch on the other side and tap a bolt and add a tab to the other side. That way you have both sides of the case working together with double the strength.

But I've also been told this is not where cracks start.

I am certainly no expert on this but my experiences and understanding of why this is happening make me believe that broken housings are the result of the idler gear and its shaft trying to 'move away' from the transmission output shaft/gear under the force of torque. This force is perpedicular to the axis of the idler shaft. When this force exceeds the strength of the TC housing/casting the case breaks starting at the top like Mark says. I still do not see how a bolt/washer could remedy this cause/effect and surmise that a device to externally hold these axis' from spreading apart would be the solution. My solution is a support that goes from the PTO cover bolt to the center of the idler shaft and provides extermal support on these two axis/ from spreading apart. It has worked for me on two different 40's but I don't spin a 33" tire on asphalt like a dragster anymore either. I forget who said it but as I get older I try to make things last longer than trying to see what it takes to break it!

 

[Trollhole]

well said.

 

[65swb45]

I forget who said it but as I get older I try to make things last longer than trying to see what it takes to break it!

If it was me, I said that one of the signs of middle age is when you become more interested in seeing how long things will last rather than how fast they will go.

 

[andrewfarmer]

Let's think this through. If I understand the suggestion correctly, this would involve using washers on BOTH sides of the case, front and back. I have seen many cases and idler shafts that were worn on the front side of the case, so the prospect of stabilizing it would be attractive.

That said, I do not think that this would work. First off, on the four speed trannies, there is simply not enough room for anything larger than the stock freeze plug on the front side of the case.

I've had another look at mine. The washers are manufactured, about 8mm thick in the centre. The one at the front of the case is threaded - the bolts goes into this, eliminating the need for a nut.
It just fits. The washer is about 40mm wide.

 

[andrewfarmer]

I am certainly no expert on this but my experiences and understanding of why this is happening make me believe that broken housings are the result of the idler gear and its shaft trying to 'move away' from the transmission output shaft/gear under the force of torque. This force is perpedicular to the axis of the idler shaft. When this force exceeds the strength of the TC housing/casting the case breaks starting at the top like Mark says. I still do not see how a bolt/washer could remedy this cause/effect and surmise that a device to externally hold these axis' from spreading apart would be the solution. My solution is a support that goes from the PTO cover bolt to the center of the idler shaft and provides extermal support on these two axis/ from spreading apart. It has worked for me on two different 40's but I don't spin a 33" tire on asphalt like a dragster anymore either. I forget who said it but as I get older I try to make things last longer than trying to see what it takes to break it!

Having closely looked at a few (and talked to an engineer who's looked at many), I still beleive the problem is (and definately was when I broke mine) the idler gears moving along the idler shaft and trying to push out of the back of the case. This happens because the gears are helical cut. The through-bolt braces the back of the case by holding it to the front of the case, in effect doubling the strength of it.
Since I upgraded mine this way I've broken lots of bits, but had no problems with the case.

 

[dgangle]

If it was me, I said that one of the signs of middle age is when you become more interested in seeing how long things will last rather than how fast they will go.

Yes, that was it. Credit where credit is due and well said.

 

[dgangle]

Having closely looked at a few (and talked to an engineer who's looked at many), I still beleive the problem is (and definately was when I broke mine) the idler gears moving along the idler shaft and trying to push out of the back of the case. This happens because the gears are helical cut. The through-bolt braces the back of the case by holding it to the front of the case, in effect doubling the strength of it.
Since I upgraded mine this way I've broken lots of bits, but had no problems with the case.

I see your logic but I am an engineer that has looked at a few and I'll stick to my guns. I appreciate your sharing your solution. Wanna little freindly 2F/V8 debate?

 

[cruiseroutfit]

Pics of the bolt solution???

 

[bustanutley]

I've had another look at mine. The washers are manufactured, about 8mm thick in the centre. The one at the front of the case is threaded - the bolts goes into this, eliminating the need for a nut.
It just fits. The washer is about 40mm wide.

Ok I think I finally get it. The idler does in fact float and press against the thrust washers, no doubt. You add washers and bolts to the idler shaft and use shaft to "squeeze" the case. This transmits the outward force on the case to both sides of the case.

little diagram for those that have a hard time visualizing, like me

 

[IDave]

That's a great diagram. Thanks!

 

[andrewfarmer]

Brilliant pic. Yes - you've got it exactly. The helical cut on the gears is what pushes the gear back. On a straight cut gear the force is only 'around', on helical, there is a sideways force as well.

 

[andrewfarmer]

Wanna little freindly 2F/V8 debate?

Sure - I've started a new post for you

 

[andrewfarmer]

Have another look at the diagram and it's not quite right.
There is one LONG bolt that goes from the back of the case through to the front. It is threaded into the 'front' washer.

Here is a pic of mine from the back to gave an idea of washer size.

Note the idler shaft (from memory) is std length. The protrusion at the rear for the lock tab to fit into is the same length as the plug that is in the front. The front washer has an oring set into it for oil control. The rear retains the std oring around the shaft.