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Old 04-18-2010, 11:30 AM
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duncanstives duncanstives is offline
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MORE driveshaft questions

Some of you may remember I posted a topic the other day about my front driveshaft issue... The plan was to take the current one down to republic diesel (my prefered driveshaft shop) and have it repaired or reaced as needed.
Today i happened to be at a junkyard and found an awesome looking front driveshaft... It is a bit shorter than the current one (about .5in) which is good because I have worried about uptravel on my current one, it is significantly thinner but FEELS much heavier like it's made of thicker material (also good... Helps clear the crossmember which might be an issue when get new non-saggy front springs) and most importantly it has a MUCH longer splined section which is also greasable (unlike my current one). All and all it looks awesome except it does not have the double cardigan joint at one end like my current one... Because it's nicer in other respects and it was cheap I thought I would take it and have it shortened to accomidate that joint and then have the joint added. Thing is it SEEMS like it will be fine without the joint... It does not look like it will bind (I am still replacing the ujoints on it but I held it up there and checked) and it occures to me that although my current one had the joint at one end the end WITHOUT the joint would be subjected to the same angle as the end WITH the joint and it seemed fine... I am assuming there is a reason for the joint... What am I missing?

Just looking for a quick answer because if it will be OK that way I would like to stick some fresh u joints on it and get it in before I have to head back to Lexington for the work week.

Thanks.
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Old 04-18-2010, 02:23 PM
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azpackrat azpackrat is offline
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Double Cardin joints are used in the front because the drive train tilts towards the rear, putting the transfer case pinion and the axle pinion both at an upward angle. That combined with the shorter length of the front drive-line (more severe angle) in a full time 4x4 would create vibration and lead to U-joint failure. In a part time 4x4, not so much, before the full time units became popular in the seventies most front drive-lines were single joint.
If your front doesn't bind and you run a part time case with locking hubs you probably wouldn't have any problems. Of course you also have to consider how the joints respond to full suspension droop, but that's true for any drive-line.
One other thing to consider is the shafts construction. You mention that it is thinner but heavier, this does not mean stronger. There is a reason that large trucks use large diameter drive-lines, they're stronger, even if the walls are thinner. The larger diameter makes them more ridged and less likely to twist under torque
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Old 04-19-2010, 08:29 AM
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duncanstives duncanstives is offline
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Thanks.

I did not assume it would make it stronger... In fact I suspect that the new driveshaft might be a bit weaker because a thicker driveshaft transmits the same amount of power by moving faster at its outer edge but being subject to less force... A thinner driveshaft moves slower at its outer edge but is subject to more force. However my hope is that by having the wall thickness so much greater it may be strong enough.

I guess I will go ahead and use it: I just installed a part time case and am getting ready to install locking hubs (I am installing locking hubs so that if I damage a front axle shaft or front driveshaft I can disengage the hubs and continue in 2wd while being less likely to have something banging around and causing more damage).
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95 Jeep ZJ V8

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