Double Cardan Angle no bueno - Page 2 - JeepForum.com
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post #16 of 62 Old 05-01-2021, 07:44 AM
fishadventure
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Yes on MML.

The clearance at the top is more than sufficient. It might just be the angle of the photo I can fit my entire fist over it and between the tub

Does anyone know if aftermarket transmission mounts are lower profile at all?
I meant the sections of the top joint hitting
Ahh ... it does appear that way and I'm trying to figure why the heck it would be.

Like I said I did drive it around my underground car park, but 30 km/h is the highest I could get it. It felt ok.

I'll go down with a flash light to make sure there is no contact, but even if there isn't any, it appears I have NO margin for any droop at all.

What the heck happened here? I'm not in a position to modify my current transmission mount and am curious if there is a lower profile option out there.
I see what you mean BUT flat skid or not, the factory skid elimination I did makes it SO nice to work on stuff. You ‘could’ theoretically do same and keep the shovel. It just solves so many issues to have a crossmember instead of the skid-dependent mount
Fish... usually you are on point, you're missing the issue here lol

An independent cross member in my current predicament would exacerbate this particular issue. Maybe I should start a thread. This would go on for a few more messages and do not want to muddy up the WDYDTY YJ thread.

Re-direct: https://www.jeepforum.com/forum/f12/#/topics/4431765
The way I suggsted should gain you 1.25”? Because a 3/8 plate is shorter than the trans mount.


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post #17 of 62 Old 05-01-2021, 07:50 AM
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Ill run mine down in a few minutes so it sets at ride hight. I was looking at mine the other day and it looked close but I'm not getting any binding even at full flex. This has me thinking the cv angles wont change much over the full range of suspension travel. If so and your not binding now you shouldn't bind when your out and about.[IMG class=inlineimg]/forum/images/JeepForum_2016/smilies/tango_face_grin.png[/IMG]
I dont know man, the dairy queen parking lots around here have some pretty scary curbs and potholes.
Every DQ is like that man. It’s all I can do to get my Jeep into the one on North Ave.
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post #18 of 62 Old 05-01-2021, 07:52 AM Thread Starter
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maybe i haven't had enough espresso this morning.

The 3/8 plate profile im understanding but, as it stands the "connection" point for my transmission - the point of contact with my skid plate - is sitting rough 1" below the frame rails. I dont question the profile of the plate, i question the height it would be sitting at.

It eliminates the giant albatross of an OE transmission mount for sure, but wouldn't it still theoretically be "connected" at a higher point?

again, keep in mind i have an auto transmission

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post #19 of 62 Old 05-01-2021, 08:17 AM
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that is sitting on the ground and close to bind. But how is it at full droop? if it goes past bind at droop it can be catastrophic. the main issue like any U joint is its working angle. once you get past that they wear rather fast, more so on a street jeep.

i would have that jeep setting on stands at full droop NO drive shaft. then see if it can reach the pinion and still not bind. reaches it works when it has to cycle that far.

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post #20 of 62 Old 05-01-2021, 08:24 AM Thread Starter
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that is sitting on the ground and close to bind. But how is it at full droop? if it goes past bind at droop it can be catastrophic. the main issue like any U joint is its working angle. once you get past that they wear rather fast, more so on a street jeep.

i would have that jeep setting on stands at full droop NO drive shaft. then see if it can reach the pinion and still not bind. reaches it works when it has to cycle that far.
I'll be finding that out shortly. I'll post back.

Thanks y'all

Just really never ever saw this being an issue anywhere else.

Special thanks to @fishadventure for the conceptualization of utilizing the XJ shaft in this configuration and the limitation and compromises of repurposing a front shaft from an XJ shaft as my rear end in crazily modified terrain.

The double cardan joint itself is the limitation because of its construction.

I am sure this thread would actually be valuable to someone down the line going the same route (which is a fairly common route). Teaches us the things we dont really think about. Theoretically, we dont conceptualize the nuances of a setup of a double cardan shaft. Well not the regular duder like me. And there are plenty of Me's in this game.
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post #21 of 62 Old 05-01-2021, 09:43 AM
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I'm late to the party but that is a crazy steep angle for ride height especially with a SS SYE. With an 8.8, the easiest way for me to test rear driveshaft is to unbolt the 4 flange bolts and lower it. Just remember that the double cardan joint binds at one angle but not necessarily the other. I was blown away by how little the double cardan joint actually flexes. I know I got a few extra degrees by grinding mine but I still ended up running a diff limiting strap because I have a lot of droop.

Aren't the stock transmission mounts really tall? I'm guessing that's the big problem because I didn't think you were running crazy lift height. My driveshaft is almost on the tub with a 1" BL and a flat skid. I am stretched 2" in the rear but also have the standard length SYE so probably similar distance between axle and xfer case output.


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post #22 of 62 Old 05-01-2021, 09:58 AM
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^^^^ oh yeah, right. I have the 1” mounts, too.

But his issue is the angle that binds

Is your jeep level at the door sill? Probably

What is the angle of the valve rocker cover? 3* or so from the angle of the door sill I hope.

That’s an interesting thought

Then you can measure the driveshaft slope angle. You can also measure from the flats of the tcase yoke and subtract the driveshaft angle to see the variation.

The door sill to engine rocker cover may tell things, however.
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post #23 of 62 Old 05-01-2021, 10:51 AM Thread Starter
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You're right. And I'm on 3.5" springs (still true).

I had the same thought when I had it all together and took that snap shot. I saw the picture and it just looked crazy for the angle at ride height. I cannot put my finger on it.

Anyways. I jacked it to full droop... thing is I'm not even sure now if the double cardan joint is limiting droop. Both wheels were off the ground and fully and easily spinnable.

Driveshaft didnt spin, wheels fully turned without issue In Drive gear.

I have some new photos, close ups of clearances. It looks better than the initial photo when up close, so I know I'm ok for moderate trail riding and on road. Which is a positive.

I suppose I can run it this way as I have no intention of wheeling this season. If I can keep it to light camping trails and the street, I should be able to get by for the year. But, I thought it was an interesting observation regardless.

My plan is to take the angle grinder to the rubber of the OEM mount, chop off .5 to .75" of rubber and cut the bolts down accordingly so they don't stick out. That should be able to get me within a comfortable peace of mind state which will do for 2021 - hopefully.

I took it out of the underground and illegally drove it around the block. I should note I still have no rear shocks from the outboard project so really bouncy in back which fir this experiment actually helps when staying on pavement. It was smooth. Actually... smoothest I've experienced in this jeep. No rumble, no grind. Had no issue gunning it from a stop sign. But yes, I need to be weary of droop considering how it appears at ride height.

Below is my method of lift. Really handy bumper. And a close up of the outer joint in the double cardan at full droop (considering the droop I have now... it passes through and everything is close but there is no grinding Mark's on the metal at all). I have no way of telling if the surfaces are contracting internally where I cant see... I assume they are.

What is a good test to find out if any contact is limiting droop now? Because I'm fairly certain a bind up is hampering the droop. Here are the rear shackle angles at what I could reach at my current full droop. I would think it should be a little more forward. Is the lack of drive shaft spin while spinning the wheels (which move freely) at this position in drive indicative that the joint is bound? I did get to jack the hi'lift up a good amount of steps...didnt keep track unfortunately.
Like I said, this is a street prowler for 2021 until I get things setup as finalized in 2022, so I'm okay knowing I'm fine on moderate dirt trails and water crossings here in Ontario. I'm mid-stage. Just thought it was an interesting enough topic to start a thread.

The last photo are at ride height.
Attached Thumbnails
20210501_113756_1619885059615.jpg   20210501_113529_1619885316487.jpg   20210501_114648_1619885880177.jpg   20210501_113544_1619886324552.jpg   20210501_113811_1619886766132.jpg  

20210501_112430_1619887051249.jpg  

~YJOTM MAY '16, JULY '19~


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post #24 of 62 Old 05-01-2021, 10:53 AM Thread Starter
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Good thought.

Gotta hockey game matinee to watch now which takes precedence... but I will take and post those measurements of the sill and valve cover later on!

~YJOTM MAY '16, JULY '19~


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post #25 of 62 Old 05-01-2021, 12:06 PM
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I usually7 put the trans in 2wd and neutral to spin the driveshaft. If it's in gear, I'm not sure the driveshaft will move.

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post #26 of 62 Old 05-01-2021, 12:07 PM
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Tcase in 2WD. Trans in neutral. Rotate the driveshaft. It’s the folding-together yoke edges with centering ball yoke that will hit in 2 places (four if you add the front of the centering yoke180* apart on either end) for probably 20-25* of rotation.

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post #27 of 62 Old 05-01-2021, 12:19 PM
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Tcase in 2WD. Trans in neutral. Rotate the driveshaft. It’s the folding-together yoke edges with centering ball yoke that will hit in 2 places (four if you add the front of the centering yoke180* apart on either end) for probably 20-25* of rotation.
Haha we're on the same wave today...even though I didn't mean to hit the submit button on my phone earlier.

Based on the pictures, it looks like the driveshaft is in almost the worst position but it's hard to know for sure if it's bound up or not. When you spin the driveshaft by hand and it feels lumpy or you can't rotate it easily past a certain point, then you know that it's binding. Luckily leaf springs don't have crazy droop under their own weight and flexing one tire will drastically make the driveline angles better. That said, even when running harder trails, you'd basically have to turtle to get to the point where both tires are nearly off the ground.


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post #28 of 62 Old 05-01-2021, 03:04 PM
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If you want to know for sure if its binding before you jack it up pull the drive shaft off the 8.8 then let the axle relax all the way down. When its down bring the drive shaft down like you're going to reinstall it and spin the drive shaft with it centered on the axle flange. I you feel any binding as you spin the shaft you have contact somewhere and if you don't and it spins free you all set. If you cant get the shaft down to reinstall because of binding you know you got some issues. Also with the drive shaft off the axle you can play with the angles and see how the CV is acting with the movement.
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post #29 of 62 Old 05-01-2021, 05:25 PM
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OK... I'll ask..

What are the actual numbers?

Have to done the math to see how much you need to correct?

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post #30 of 62 Old 05-01-2021, 05:29 PM
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OWhat are the actual numbers??
This thing. I have four or five (not this brand, and magnetic).
Invaluable for so many stupid things.
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[size=“3”]Shackles & D-rings are different things.
Cranking IS turning over
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