Replacing rear driveshaft on 95, double cardan?

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I have a 95 with 177000 miles. Previous owner had all of the goodies installed, ARB bumpers front and rear, Warn 12k winch, Slee sliders, OME 2.5" lift, 33" Goodyears. I've had it for about 2 years now, fixed many things neglected by the PO and am now working on u joints for the driveshafts. There's a vibe from the transfercase knob when under power, goes away when coasting. The rear driveshaft has loose splines, it clunks when twisting it by hand. I'm looking at replacing it with a Tom Woods but I'm not sure if a double cardan would be helpful or counterproductive. When the suspension components wear out I'll either replace them with another OME 2.5" kit or possibly a 4" lift. Any thoughts on what to do or any other suggestions? Thanks in advance.
 
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A U-joint induces sinusoidal oscillations in the relative position of each side of it. Having 2 of them in phase and at the same angle relative to their flanges makes them cancel out for no vibration. (Of course, you’re still accelerating and decelerating that whole shaft with every revolution, and doing it more at more extreme angles)5

If you have a double cardan on one side (and a DC has an alignment mechanism so each half of it is always at the same angle, so there will be no sinusoidal oscillations from a DC) and have the normal UJ on the other side, then you will get oscillations as the UJ no longer has another to cancel with.

The exception to this is if the axle flange is perpendicular to the the driveshaft so it does not induce any sinusoidal position variance.

That’s in an ideal world, realistically you’re somewhere, and the angle changes as ride height changes, etc.

You can get a little .1 degree resolution angle finder from harbor freight and measure your TC flange angle and axle flange angle. They’re probably no longer parallel because of the lift, remember how far off they are. Now unbolt your driveshaft at the TC flange, and put it on a jack stand in about the same position it would be if it had a DC joint at the TC flange. Now measure the axle flange to the shaft angle and see how far off it is from 90 degrees. Whichever number (difference from 90 for the DC or difference between the flanges for a normal shaft) is smaller will be smoother.

I reckon you could reinforce your lower rear links and fix your axle flange angle while you’re at it, and it would be the smoothest without even replacing the shaft. When I took mine to the shop for new Ujoints and slip joint because I thought it was worn, they said don’t worry about the slip joint because the splines self center when there is even just the tiniest bit of torque acting on them. (Which in hindsight, duh, that’s why we use involute splines for everything. They self center so fit isn’t critical)
 
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Check your angles to see if a DC shaft is applicable for your truck. Doesn’t quite sound like it’s an angle issue (ujoints not properly canceling each other), given your description, but who knows. Could simply be worn ujoints, you’ll just have to check.

Mine is at 4” with caster plates up front. I need a DC front shaft (joint is angled at TC, but no angle at front axle) while my rear is close enough to keep using the stock shaft. So like jfz80 said, at 2.5” you shouldn’t need to go DC in the rear. I’d second the suggestion to lock the center diff & drive with rear shaft removed to see if the vibration goes away. This was part of how I confirmed it for my front shaft, before I measured angles.
 
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A U-joint induces sinusoidal oscillations in the relative position of each side of it. Having 2 of them in phase and at the same angle relative to their flanges makes them cancel out for no vibration. (Of course, you’re still accelerating and decelerating that whole shaft with every revolution, and doing it more at more extreme angles)5

If you have a double cardan on one side (and a DC has an alignment mechanism so each half of it is always at the same angle, so there will be no sinusoidal oscillations from a DC) and have the normal UJ on the other side, then you will get oscillations as the UJ no longer has another to cancel with.

The exception to this is if the axle flange is perpendicular to the the driveshaft so it does not induce any sinusoidal position variance.

That’s in an ideal world, realistically you’re somewhere, and the angle changes as ride height changes, etc.

You can get a little .1 degree resolution angle finder from harbor freight and measure your TC flange angle and axle flange angle. They’re probably no longer parallel because of the lift, remember how far off they are. Now unbolt your driveshaft at the TC flange, and put it on a jack stand in about the same position it would be if it had a DC joint at the TC flange. Now measure the axle flange to the shaft angle and see how far off it is from 90 degrees. Whichever number (difference from 90 for the DC or difference between the flanges for a normal shaft) is smaller will be smoother.

I reckon you could reinforce your lower rear links and fix your axle flange angle while you’re at it, and it would be the smoothest without even replacing the shaft. When I took mine to the shop for new Ujoints and slip joint because I thought it was worn, they said don’t worry about the slip joint because the splines self center when there is even just the tiniest bit of torque acting on them. (Which in hindsight, duh, that’s why we use involute splines for everything. They self center so fit isn’t critical)
Good to know, I'll replace both u joints and put it back in. I can't see the movement but can feel/ hear it, it's not sloppy. I just assumed it would need to be a really close fit.
 
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Check your angles to see if a DC shaft is applicable for your truck. Doesn’t necessarily sound like it’s an angle issue (ujoints not properly canceling each other), given your description, but who knows. Could simply be worn ujoints, you’ll just have to check.

Mine is at 4” with caster plates up front. I need a DC front shaft (joint is angled at TC, but no angle at front axle) while my rear is close enough to keep using the stock shaft. So like jfz80 said, at 2.5” it’s not likely you need to go DC in the rear. I’d second the suggestion to lock the center diff & drive with rear shaft removed to see if the vibration goes away. This was part of how I confirmed it for my front shaft, before I measured angles.
Will do, I'm going to put the front one back in once the joints are swapped and see if it goes away. Then I'll just put the rear one back in with new joints and fresh grease on the splines and see what happens. It's more likely that they never got greased by the PO than an angle issue.
 
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Good to know, I'll replace both u joints and put it back in. I can't see the movement but can feel/ hear it, it's not sloppy. I just assumed it would need to be a really close fit.
Holding the longer side still and wiggling the shorter piece I had between 1/32” and 1/16” of play in the slipjoint. New UJs and and it’s perfectly smooth again. (But I am at stock height so my flange angles are good)
 

LandLocked93

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+1 replace u/js on rear shaft or get a new rear shaft and re-eval.
Are you familiar with phase and orientation? Or strictly speaking, do you recall the phase and orientation they were in before removal?
Not replaced in the same way they were removed can sound like you left a box-end on a flange bolt.
 
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+1 replace u/js on rear shaft or get a new rear shaft and re-eval.
Are you familiar with phase and orientation? Or strictly speaking, do you recall the phase and orientation they were in before removal?
Not replaced in the same way they were removed can sound like you left a box-end on a flange bolt.
Both shafts were the correct phase, according to the service manual, when I removed them
 
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Just buy a new complete rear DS from Toyota. It comes with new u-joints and only like $350.

You definitely do NOT need a double cardan shaft on the rear of that truck.

DC shaft is most common on a front and only when 4"+ lift is used.
Good to know, I remember reading somewhere that they were no longer available. I already have the U-Joints so I'll swap them and see what happens but I'll definitely go that route if it needs replaced.
 
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Good to know, I remember reading somewhere that they were no longer available. I already have the U-Joints so I'll swap them and see what happens but I'll definitely go that route if it needs replaced.
I recently bought mine from:

They are definitely still available.
 

smritte

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