What's the difference in slip vs fixed yoke?

[81Ramchargerman]

I was just searching the forums about all kinds of crap and when I searched for my np 208, there seemed to be lots of talk about fixed and slip yoke. Which is better and why. Is that why the splines are worn on the slip yoke/driveshaft on my truck? Because it slips instead of being fixed?

 

[RockMonkey]

With a slip yoke the driveshaft is a fixed length, and when the axle moves up and down (changing the distance between the transfer case and the axle) the yoke at the transfer cases slips in and out (hence the name). With a fixed yoke the yoke at the t-case is fixed in place (hence the name) and the driveshaft gets longer or shorter as the axle moves up and down. There are a couple advantages to a fixed yoke. First, the output on the transfer case is normally shorter with a fixed yoke, allowing you to have a longer driveshaft, and improving your ujoint operating angles. Second, your driveshaft can fall out of the slip yoke if your axle drops too much, a driveshaft can be made with much more travel than a slip-yoke has. Third, if you break a driveshaft, most slip-yoke transfer cases will leak fluid after the yoke is removed, so you can't just remove the driveshaft and drive out in front wheel drive. Ummm... There's prolly more reasons, but my fingers are sore, so I'm quitting.

 

[Caleb]

So what Rockmonkey is saying in short is Slip Yoke sucks and Fixed Yoke is good

 

[81Ramchargerman]

Thanks rockmonkey for takin the time to explain that to me in detail...

 

[RockMonkey]

Thanks rockmonkey for takin the time to explain that to me in detail...

Werd.

 

[crimsonride]

Also, with slip yoke, when the axle pulls the driveline out and power is applied the combination of harder u-joint angles and torque can cause the driveshaft to pop out and in worse cases break the tailshaft housing.

 

[H-K]

For me, the biggest advantage was increased driveshaft length and thus, decreased driveshaft angles. My vehicle has a very short wheelbase and after lifting it, the driveshaft angle became too severe at maximum extension of the suspension. Going with a SYE on the NP231 allowed me to have a longer driveshaft. I also opted for a CV shaft instead of a conventional one for extra strength (reduces angles on u-joints).

However, if you're inquiring about SYE for a transfer case on a long-wheelbase vehicle, a few inches of driveshaft length might not benefit you so you'll have to look at the other benefits to see if they are of value to you and your particular situation.

Maybe somebody else can chime in on this, but I'd guess that longer driveshafts actually travel less distance on the t-case output of a slip shaft. I mean, a long driveshaft does not move as much in the coupling as a short one would. If this is the case, are problems such as dropping the driveline or shortening the spline contact area less of an issue/probability?

Disclaimer: I'm not pretending to be an expert -- this is just what I've gathered from research and discussions with experts...

 

[crimsonride]

You're right, a longer driveshaft moves less in the slip yoke, driveline angles suck for road driving. Less contact area on the splines sucks for offroad. Less contact means less strength. Of course you can run into this same problem in your driveshaft.
If wear is all you've ran into with your current setup I would just have the driveshaft lengthened if need be and have a new yoke put on. That'll give you more spline contact.