FJ62 SOA Rear Driveshaft Question

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julianramirez1005

julianramirez1005

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Jun 12, 2025
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Location
Eureka, California
Im getting lots of vibration at higher speeds under load. I watched Tom Woods Driveshaft video and read through this SOA Tech article and feeling like a double cardan is the only solution. 89 FJ62 SOA

I'm a big visual learner so i made this quick schematic of what I got going on. Any thoughts from people with experience with double cardan setups?

I have a 1.5" spline diameter, 16 spline driveshaft thats missing a female slip yoke. more info in my build thread
1774652498271.webp

Thanks for reading
 
Unfortunately that tech article is incorrect. Traditional u-joint shafts absolutely require the pinion and output flange to be parallel (same angle) with each other to remain vibration free. That is the only configuration in which the phasing of the u-joints cancels out. The FJ60 is no exception. Some people are less sensitive to driveline vibrations than others, and some vehicle configurations can tolerate more misalignment before the vibrations become too noticeable. Regardless, the differential and transfer case output flange must be parallel to be correct.

When using a double cardan or CV style shaft, it's important your pinion angle matches your driveshaft angle. Also keep in mind that those CV joints don't really enjoy operating at extreme angles either, and can vibrate a little bit at high speed (especially when operating at high angles)
 
I'll add a little to this. When using a dc drive shafts the dc adds to the overall angle because the physical dimensions are longer from having two universal joints and the cervical ball or whatever the dang thing is. Hopefully someone is understanding what im trying to say without me having to draw a picture lol
 
I have a soa fj62 and a dc shaft in the rear. Never had any vibration issues. The angles in your illustration are pretty severe. If that’s what you actually have you need to correct your pinion angle. My pinion flange angle and my t case flange angle have never been parallel. My pinion was probably around 5 degrees up. Just installed another rear axle and using an angle finder I set it to 1 degree lower (pointing down) than the t case flange. I did this because I actually have the angle finder now, just eyeballed it before. So you want the flanges to be as close to parallel as possible. One degree under so when loaded the axle rotates up and the flanges are closer to parallel. I’ll still be running the dc flange in the rear just haven’t got it back yet.
 
Thanks for all the info everyone. What I’m gathering is I need to correct my pinion flange angle with some shims under the leaf springs.

As far as getting the ds angle less severe I’m a bit confused. I would have to raise the axle up a considerable amount no?
 
klip said:
I have a soa fj62 and a dc shaft in the rear. Never had any vibration issues. The angles in your illustration are pretty severe. If that’s what you actually have you need to correct your pinion angle. My pinion flange angle and my t case flange angle have never been parallel. My pinion was probably around 5 degrees up. Just installed another rear axle and using an angle finder I set it to 1 degree lower (pointing down) than the t case flange. I did this because I actually have the angle finder now, just eyeballed it before. So you want the flanges to be as close to parallel as possible. One degree under so when loaded the axle rotates up and the flanges are closer to parallel. I’ll still be running the dc flange in the rear just haven’t got it back yet.
Click to expand...
Couple of questions: What springs and shocks are you running? What angle is your DS in relation to your t case output shaft? How many inches over stock ride height did you end up with
 
klip said:
I have a soa fj62 and a dc shaft in the rear. Never had any vibration issues. The angles in your illustration are pretty severe. If that’s what you actually have you need to correct your pinion angle. My pinion flange angle and my t case flange angle have never been parallel. My pinion was probably around 5 degrees up. Just installed another rear axle and using an angle finder I set it to 1 degree lower (pointing down) than the t case flange. I did this because I actually have the angle finder now, just eyeballed it before. So you want the flanges to be as close to parallel as possible. One degree under so when loaded the axle rotates up and the flanges are closer to parallel. I’ll still be running the dc flange in the rear just haven’t got it back yet.
Click to expand...
Reading your build thread atm.
 
stock springs. On a spring over set up you set your pinion angle when you weld the spring perches on the axle housing. I’m not 100% sure of the numbers on my old setup. But currently my t case flange is 4.5 degrees and my pinion is 3.5. Pointed downward 1 degree from t case angle. Although I have not ran it like this yet because I’m still doing some work to the front, I’m not expecting any problems🤞 I have just a spring over set up, stock springs.
 
Last edited:
julianramirez1005 said:
Thanks for all the info everyone. What I’m gathering is I need to correct my pinion flange angle with some shims under the leaf springs.

As far as getting the ds angle less severe I’m a bit confused. I would have to raise the axle up a considerable amount no?
Click to expand...
If you have a single u-joint at either end of the driveshaft, your t-case flange and pinion flange must be parallel, generally when the vehicle is moving. So people will usually set the pinion flange maybe 2-3 degrees low, so the torque of driving will nose the pinion up. This is fiddly, as it entirely depends torque being applied to the axle.

If you have a double-cardan CV joint up at the t-case, your pinion angle needs to be the same as your driveshaft angle when under load. You basically want the u-joint to be almost doing nothing. The pinion needs to point directly at the yoke coming off the cv joint.

The bigger issue is that your driveshaft angle of 16° relative to the transfer case. With a CV shaft, you're going to be around 8 degrees per joint, which is going to harm u-joint life (looks like Spicer says anything over 3° will result in reduced life).

In the Jeep world, people will start using low-profile transmission mounts, or cross-member spacers to pull the whole drivetrain at a downward angle to reduce rear u-joint operating angle. You just have to be careful, because you can inadvertently increase the front operating angles doing that. Less of an issue though, because the front driveshaft probably isn't going to be spinning at highway speeds.
 
update New
Update. When I measured it the car was not on flat ground and I think that influenced the driveshaft angle reading. rookie move I guess... still learning and this is the first time Ive ever done this.

So I zero out on the output flange
Output Shaft 0°
Driveshaft is 12°
Pinion Flange 8°

--[ 0° + ]------[ 12° + ]-- 8°

So clearly my pinion flange is way off. The pinion flange needs to move towards the ground I do not feel good about cutting the mounts off the axle and re doing it.

I'm thinking the x member spacer is the best option for me and retaining the stock driveshaft and get it lengthened or a longslip yoke. Seems simple enough. Does the spacer need to be angled like a < or can it be flat - ?

  1. Unbolt x member and drop til my angle finder reads 1 degree up from pinion flange
  2. measure the space in between the x member and frame brackets
  3. head to the scrap pile at the shop and hopefully find something that can fill that gap
  4. sand blast and paint
  5. Install and hope for the best

Big thank you to @Lead Head & @klip for the help and please let me know if theres anything else I should be considering in this equation.
 
Shims, 8 degree to match the tcase flange

4xshaft.com

Axle Shims (pair)

Axle Shims Steel shims to go between your leaf springs and your spring perch. These are used on leaf spring vehicles in order to adjust pinion angles and achieve proper drive line geometry. Our shims are 2.5" wide and 4" long, machined from steel, and include a new set of 3/8" diameter center...
4xshaft.com 4xshaft.com

Or similar
 
BurntToast said:
Shims, 8 degree to match the tcase flange

4xshaft.com

Axle Shims (pair)

Axle Shims Steel shims to go between your leaf springs and your spring perch. These are used on leaf spring vehicles in order to adjust pinion angles and achieve proper drive line geometry. Our shims are 2.5" wide and 4" long, machined from steel, and include a new set of 3/8" diameter center...
4xshaft.com 4xshaft.com

Or similar
Click to expand...
Ok yeah I'm overthinking it. Good Idea
 
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