Jump to content

SOA pinion angle question


Recommended Posts

I am currently in the middle of doing a D35 to C8.25 SOA swap on my 88 long bed MJ 4.0L PukeGoat 231. The DS is the stock one piece. FYI I got a s.y.e. because I plan on going up about ~6.5" or whatever.

 

My question is what do I set my pinion angle at with my DS setup?

 

I know WITHOUT a s.y.e. you want the pinion/output shaft to be parallel with each other and a good rule is to set the pinion about 2* lower for take off.

 

But what do I do with a s.y.e. setup or is it the same as without a s.y.e.?

 

Help I confused? :???: :dunno:

 

TIA

:cheers:

 

Oh yeah, I did search this really did not find direct info for the s.y.e. angle setup

Link to comment
Share on other sites

The pinion should be pointing up towards the center of the output shaft less 2-3 degrees downward to make the alignment closer under acceleration. This is accomplished of course either by rotating the spring perches or axle shims. Since you have a long bed and the driveshaft is longer, that helps out with with the t-case u-joint operating angle.

Link to comment
Share on other sites

If I remember my physics and math (especially geometry) correctly, the pinion should be pointing directly at the SYE flange (actually a little behind it, where the centre of the double cardan joint would be) if you use a drive shaft with a double cardan CV joint (like the stock front ds).

 

For a drive shaft with just a single U joint at each end, the pinion shaft needs to be parallel to the t-case output shaft to minimize vibration caused by the slip joint oscillating under normal driving conditions, even on perfectly flat roads. This all stems from the fact that a U joint actually lengthens and shortens twice during each rotation if they are at any angle other than straight. With the two shafts parallel, the joints run at equal, but opposing angles, causing the change in the one to be counteracted by the other one. Now the entire shaft evenly shifts back and forth without the slip joint having to move (unless the suspension moves from a bump or whatever).

 

To go back to the first paragraph: the double cardan cancels itself out, and you want to other u joint to be straight under normal driving conditions, so it stays even.

 

If you'd run a double cardan joint on each end, it would not matter where anything pointed. This would be ideal, if not for the fact that double cardan joint can not turn as steep an angle as a regular single u-joint

Link to comment
Share on other sites

The pinion should be pointing up towards the center of the output shaft less 2-3 degrees downward to make the alignment closer under acceleration. This is accomplished of course either by rotating the spring perches or axle shims. Since you have a long bed and the drive-shaft is longer, that helps out with with the t-case u-joint operating angle.

 

This is correct FOR LEAF SPRUNG SUSPENTIONS. Like our trucks have.

As the suspension loads up, it lifts the pumpkin into alignment and off you go. The SYE is only going to allow more articulation with out binding. to tell you the truth, is not going to have much effect on/with the long drive shafts in our trucks. BUT It is STRONGER than the slip yoke, so that a good thing.

 

BTW, You only point the pumpkin directly at the out put for COIL SPRUNG SUSPENTIONS.

 

CW

Link to comment
Share on other sites

The pinion should be pointing up towards the center of the output shaft less 2-3 degrees downward to make the alignment closer under acceleration.
That is the long & short of it. I have always gone with 2 degrees low on the ones I have done. :cheers:
Link to comment
Share on other sites

You should never use a SYE with a 1 piece d-shaft. The SYE eliminates the slipping on the output shaft on the TC. As your suspension cycles you angle from the TC output and the flange on your rear axle changes, thus the length of the driveshaft will change. If you go with a SYE and a 1 peice driveshaft and you flex at all you'll most likely bend your d-shaft, break your pinon flange, or destroy your t-case.

Link to comment
Share on other sites

You should never use a SYE with a 1 piece d-shaft. The SYE eliminates the slipping on the output shaft on the TC. As your suspension cycles you angle from the TC output and the flange on your rear axle changes, thus the length of the driveshaft will change. If you go with a SYE and a 1 peice driveshaft and you flex at all you'll most likely bend your d-shaft, break your pinon flange, or destroy your t-case.

 

Very good info. Of all the SYE threads I've read I have never heard this before. So you would want to use a drive shaft that has the compression thing(like a shock) in the driveshaft itself rather than a slip yoke?

Link to comment
Share on other sites

Where you point the pinion depends on the type of drive shaft, not on the suspension type.

 

The above statement is not true.

 

Leaf springs flex with engine torque. That's the reason for a slightly downward alignment at static. Also something to ponder, traction bars are made for leaf springs NOT coil springs. that because most coil sprung suspensions use control or trailing arms and there is little to no movement because of engine torque.

 

I think the cardan joint is getting you confused as when your using one it will change the alignment. BUT most of the time its at the output shaft of the tranny or Tcase not at the axle/pumpkin end. So having one or not doesn't change anything at the pumpkin end of the axle.

 

You should never use a SYE with a 1 piece d-shaft. The SYE eliminates the slipping on the output shaft on the TC. As your suspension cycles you angle from the TC output and the flange on your rear axle changes, thus the length of the drive-shaft will change. If you go with a SYE and a 1 piece drive-shaft and you flex at all you'll most likely bend your d-shaft, break your pinon flange, or destroy your t-case.

 

 

YES very true!!

 

CW

Link to comment
Share on other sites

Anybody know if I could swap a CV DS off of a XJ or ZJ front or any thing else that will work?

 

you can have that front shaft retubed to the proper length. my shortbed auto comanche with dana 44 rear, SYE, and a double cardan shaft has a center to center measurement of 46.5" (your measurement will be longer) from center of the yoke on the transfercase to the center of the yoke on the axle. this is of course with the slip-shaft at mid-slip.

 

 

I highly suggest having them use ONLY the cardan from an xj front shaft, then finding a larger diameter rear slip-shaft from some other vehicle which and having them get the proper parts to mate the two together.

 

for $40 I got the rear slip-shaft from a 77 ford (i don't know anything else but that) and the cardan from a 94 cherokee, and all told with a complete rebuild with greasable joints, the new part to put the cardan on the shaft, and retubing it all cost me $200 plus the $40 to buy the shaft (he retubed it anyways so he could mate the parts together properly...and I'm not complaining at all.

 

suggest that you get your transfercase built then installed first, and have it lifted, THEN install the rear axle. otherwise it is IMPOSSIBLE to set the rear pinion angle properly.

 

the rear shaft I used was measured and installed before we ever set pinion angle. the pinion angle is set at -2 degrees to the straight part of the rear shaft, to allow for lift under acceleration.

Link to comment
Share on other sites

Where you point the pinion depends on the type of drive shaft, not on the suspension type.

 

The above statement is not true.

 

Leaf springs flex with engine torque. That's the reason for a slightly downward alignment at static. Also something to ponder, traction bars are made for leaf springs NOT coil springs. that because most coil sprung suspensions use control or trailing arms and there is little to no movement because of engine torque.

 

I think the cardan joint is getting you confused as when your using one it will change the alignment. BUT most of the time its at the output shaft of the tranny or Tcase not at the axle/pumpkin end. So having one or not doesn't change anything at the pumpkin end of the axle.

 

Nope not getting confused. Ask a drive train/suspension professional and see what they say.

 

They have always told me parallel with single u-joints, pointing straight at the centre of the double cardan joint (which is supposed to be opposite the axle end, like you state) if using a double cardan ds.

 

If you want to adjust by 2-3 degrees to make up for axle wrap, that does not change the basic theory. If everything is balanced properly, and working properly, you shouldn't get vibration as long as the angles are close to what they need to be. The only times I had vibes was either because of a bad u-joint, or a bent shaft from hitting/setting the truck down on a boulder.

Link to comment
Share on other sites

Anybody know if I could swap a CV DS off of a XJ or ZJ front or any thing else that will work?

 

You know, it I were you, I would give it a go before shelling out coin for the expensive SYE kit. Since you have a long bed, do your lift, slap on an extended length slip yoke on the front of your driveshaft (like the one linked to Ebay below), then use axle shims to get your u-joint operating angles right (front & rear = parallel less 2* down on the diff pinion), and try it out. This way you're only out the cost of the yoke and the shims. I know a couple of guys down here who have 5"-6" of lift on their longbed MJs and get no vibes.

 

http://tinyurl.com/5hg7r6

Link to comment
Share on other sites

FYI,

I am also at about 6.5 of lift running the STOCK shaft with no altercations. I swapped in the 44 so that made up the difference in length. it was close, but I didn't even need to touch the DS. (Short of new joints. ;0 )

 

SYE is nice for the extra strength it affords, but it ain't necessary for the MJ's.

 

CW

Link to comment
Share on other sites

FYI,

I am also at about 6.5 of lift running the STOCK shaft with no altercations. I swapped in the 44 so that made up the difference in length. it was close, but I didn't even need to touch the DS. (Short of new joints. ;0 )

 

SYE is nice for the extra strength it affords, but it ain't necessary for the MJ's.

 

CW

 

agreed.

 

i kinda had one fall into my lap (hard to pass up a complete case with SYE for $250) and so I installed it...it cost me MORE money than running the other one, BUT i only have 1500 into a pretty much rust-free 4.0 auto shortbed with 6.5" of lift, and half the parts are new...

 

play your budget and find out what you're capable of, and build within your budget. if the SYE is in your budget, I would probably go for it simply for the added strength, and being able to wreck your rear shaft and drive home still with no leaks (front wheel drive)

Link to comment
Share on other sites

Wow.. all this discusion on a SYE. The main advantage of using on is the ability to pull your rear shaft WHEN it gets damaged by a rock. That being said... If you carry spare DS not an issue. As for what shafts to use.. Look at full size fords of the late 70's and some of the early 80's. Most of them had a Double cardan style shaft.

Link to comment
Share on other sites

Wow.. all this discusion on a SYE. The main advantage of using on is the ability to pull your rear shaft WHEN it gets damaged by a rock. That being said... If you carry spare DS not an issue. As for what shafts to use.. Look at full size fords of the late 70's and some of the early 80's. Most of them had a Double cardan style shaft.

 

Does a full size ford DS bolt right in? Or what do you have to do to make it work right?

 

I am trying to spend the least amount of coin on this?

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...