Drive Shaft Length

[Weebz]

So while doing the break down of the jeep I have it at “full droop” and this is what my front drive shaft looks like.   There is 4.5” on the exposed male side and 5.5” on the receiving female side.   Now I say it’s full droop but either the upper arms have this bound at the joint which is what I think because shocks are disconnected and it won’t go down any more and I have a good 3-4” before the DS hits the cross member with the crossover pipe removed.   
 

im having the drive shafts both rebuilt so my question is should I have this lengthened?    
 

 

[Jdofmemi]

If you unbolt the yoke and pull it apart, then you can see how much spline is still engaged. 

Before you do, jack the axle up to full bump, and get that measurement as well. 

 

It looks to me like it may be shorter than ideal, but having pics and measurements at both extremes of travel will show the story. 

[KevinG]

If you are changing everything I would think that you’d probably want to wait till you have it set to check it at full bump too. Probably need both measurements to know if you need more length. 

[Weebz]

43 minutes ago, Jdofmemi said:

If you unbolt the yoke and pull it apart, then you can see how much spline is still engaged. 

Before you do, jack the axle up to full bump, and get that measurement as well. 

 

It looks to me like it may be shorter than ideal, but having pics and measurements at both extremes of travel will show the story. 

There is no putting this at full bump right now.   Way too unstable until the back e d is back together and I can move stands around.  It’ll wait

[JKBrick]

Your ds will be longer at full bump than full droop, our local place wanted both measurements. 

[Nice Little Jeep]

 Those are some serious jackstands I’m now embarrassed I sent you my little ones

[AJK]

You probably have a inch left on the spline from what it looks like. I think there is like 5 inches of blue before the spline ends. 

Those are nice stands, I love mine.

[MIOffroadCustoms]

On 1/16/2022 at 11:36 AM, Jdofmemi said:

If you unbolt the yoke and pull it apart, then you can see how much spline is still engaged. 

Before you do, jack the axle up to full bump, and get that measurement as well. 

 

It looks to me like it may be shorter than ideal, but having pics and measurements at both extremes of travel will show the story. 

This is the best way to tell

[Redline]

If you have a good driveshaft guy, all you should have to do is give him 3 measurements of each front and rear suspension. Full bump, ride height, and full compression, from there they will give you optimal length driveshafts. We generally set everything up in the racing world is so at the shafts’ shortest length in the vehicle there is still 1/2” of plunge left. Some vehicles have very bad angles though and plunge a lot so obviously that should be accounted for if needed. But never less than an extra 1/4” plunge allowed outside of max suspension travel capability because it pump all the lubrication out and end up seizing quickly.

[Jdofmemi]

1 hour ago, Redline said:

If you have a good driveshaft guy, all you should have to do is give him 3 measurements of each front and rear suspension. Full bump, ride height, and full compression, from there they will give you optimal length driveshafts. We generally set everything up in the racing world is so at the shafts’ shortest length in the vehicle there is still 1/2” of plunge left. Some vehicles have very bad angles though and plunge a lot so obviously that should be accounted for if needed. But never less than an extra 1/4” plunge allowed outside of max suspension travel capability because it pump all the lubrication out and end up seizing quickly.

Personally, I like a little bit extra at full plunge, to account for things that may go wrong at speed, like bushing deflection. 

It's less of an issue with the way Jeep suspension swings, as the shaft stretches on compression of the suspension. 

On leaf springs, like my Toyota days, a hard hit could push the shaft through the transfer case. 

 

You know, like hitting a 3' deep washout at 60+, or hitting a rock that breaks the spring pack in half, things like that. 

[Weebz]

1 hour ago, Redline said:

If you have a good driveshaft guy, all you should have to do is give him 3 measurements of each front and rear suspension. Full bump, ride height, and full compression, from there they will give you optimal length driveshafts. We generally set everything up in the racing world is so at the shafts’ shortest length in the vehicle there is still 1/2” of plunge left. Some vehicles have very bad angles though and plunge a lot so obviously that should be accounted for if needed. But never less than an extra 1/4” plunge allowed outside of max suspension travel capability because it pump all the lubrication out and end up seizing quickly.

Good info.   I think based on this I’m still fine but will confirm when I start reassembling this thing.   Got a ways to go before I can check again.  

[BaddestCross]

1 hour ago, Jdofmemi said:

Personally, I like a little bit extra at full plunge, to account for things that may go wrong at speed, like bushing deflection. 

It's less of an issue with the way Jeep suspension swings, as the shaft stretches on compression of the suspension. 

On leaf springs, like my Toyota days, a hard hit could push the shaft through the transfer case. 

 

You know, like hitting a 3' deep washout at 60+, or hitting a rock that breaks the spring pack in half, things like that. 

So Jerry stuff then

[Redline]

1 hour ago, BaddestCross said:

So Jerry stuff then

I am never arguing with Jerry!

Like I said, “in the racing world”. In our race trucks if something causes enough deflection to change plunge that much, there is a MUCH bigger problem going on.