ok thanks Ed, I've been doing a bit of internet research & most of the opinions out there are against multiple cardans,i think I will just stick to a double at the yoke end & a single at the diff.

I still think my custom shaft I had made here is a dud, the double cardan seems a bit stiff to me & it has too much run out for my liking.

cheers I'll let you know how it all goes

Yea. It finally started coming back to me on the way home last night.

There are three different configurations for drive shafts. Two u-joints - one on each end, Cardan and u-joint - one on each end, and a Cardan on each end.

Level of potential for vibration/vibration follows that order with the first being the least likely and the last being the most likely. If at all possible, you ALWAYS want to use the first, followed by the second if the 2 u-joint setup won't work, followed by the last if NOTHING else works.

And, never use a double-Cardan joint setup for high-speed highway use. Such as in a NP242 AWD setup.

As explained to me, the u-joint and drive shaft stabilize the Cardan joint. That's what makes this setup work on the highway at high RPM. Its like having a rotating solid shaft attached to the end of the Cardan joint. It minimizes potential vibration through the pinion/u-joint/drive shaft and stabilizes the Cardan joint.



Hmmm. Don't know there. I think all your worrying about run-out is for nothing. The tech that works on my Sports at the dealership built his drive shafts at home for his Truggy. He swears he can run it at 60 down the highway and there's not a hit of vibration. I'm pretty sure the 'run-out' on his shafts isn't down to specs you were quoting.

If it were me, I'd bite the bullet and align the front diff correctly. If I put that much work into something and then had to live with an unnecessary vibration, I'd go nuts.

Edward

i'll see how Toms shaft goes first.

I think this shaft is well & truly F A R K E D.

I have been hiding the front vibes by running the vehicle in 2wd with the front axles disconnected via the vacuum system.

This has allowed me to get around daily without vibes until I can get a new shaft built.

Well today I went on a long drive 70k & back to town & the vibes were really bad. So I stopped off at the local tool shop & bought the spanners I needed to take the front shaft off. I'm getting good at taking it off now!. Took it off & what do you know , vibes gone.

So I reckon the unis may be stuffed which is not very good considering its all supposed to be NEW. So it may be a case of dodgy parts rather than anything else.

Anyway , hope Tom can come good for me with a new shaft.

Hey ed, looks like I spoke too soon on the driveshaft problem. The shaft Tom made for me has certainly improved the problem but I still have a vibe (annoying vibe) between 85-95 kph. Its more noticeable on deceleration or coasting & produces a hum as well. I didnt notice it before as I hadnt really taken it for a long run only a short one.

So now I am back to chasing the problem. Can you elaborate on your suggestion above to rotate the front diff. When you say 2.3 degrees I am assuming you mean rotate the diff upwards 2.3 degrees. How did you come to that figure?

I am now wondering if I have something out of alignment in the front end, maybe bad bearing or cv??

My plan would be to swap over the entire front end with one in my spare car that I know is good. It has to be the entire front end as you cant mix & match cv shafts between 97 & 99 as they had different lengths. Plus I need to redo the ball joints as well as all the bushes as I have a bad squeek & groan from the left side. If I have everything out , I can move the diff upwards & re weld the brackets, but need more info on this, thanks

Dang. Sorry to hear that Ian. I was hoping from your last post that the new DS had taken care of that.






I took your numbers for pinion angle on the front diff, drive shaft and so on and did the math to figure out how much you'd have to rotate the front differential to get the pinion to point directly inline with the drive shaft.



But, now I can't figure out how I came up with that number either!

A perfectly horizontal pinion is 0 degrees. Rotated down would be negative and rotated up from 0 would be positive.

The 8.9 degree operating angle doesn't make any difference if you're running a CV at the t-case. And that's where you want the CV, BTW.

The front drive shaft is at -3.4 degrees. As I pointed out before, the CV/U-joint drive shaft needs the pinion-u-joint-drive shaft in line. The diff would have to rotate the pinion enough to make that happen.

I don't know what the front differential pinion angle is now, but it you assume it is 0 degrees, you'd need to rotate the pinion up 3.4 degrees to get it in line with the drive shaft.

If the pinion is +1 degree, then you'd need to rotate it +2.4 degrees - the difference between 3.4 degrees and 1 degree.

+2.4 = 3.4 - 1

Now, this is just the static math. Usually there is a degree 'off-set' figured in, to take into account torque rotation under power. When you apply force to a differential it tries to rotate one direction or the other depending on whether the gear box is in forward or reverse which changes pinion angle.

There isn't a hard and fast rule here for how much (in degrees, or fractions of a degree) you add or subtract because it totally depends on how much stuff rotates when the vehicle is in motion. For instance, I get a lot of pinion shift in the back axle because I have a heavy vehicle and run leaf springs with big tires and a LOT of gearing. The amount of pinion shift would be much less with a link suspension where differential rotation is strictly controled. So, you can't just say, "Do the math and add 1 degree and you're good."

Obviously, you don't have front housing rotation because that's IFS. You DO, however, have engine/transmission/t-case rotation. This is kind of a sucky configuration from a math standpoint because normally the differential would rotate up when the t-case rotated up as gas was applied and things would kind of stay in the same line, but you have one moving point and one static point.

I know how to calculate this, but I don't know how to get the data. What you need to know is how much the DS angle increases when the vehicle is under steady state cruise, with the vehicle at its average loaded weight and the tire pressure set where you normally run it (with the tires you normally run). On mine that would be, say, 115 KPH. About 70 MPH. That's where mine spends 95% of its time on the highway and where the most gas pedal is applied to maintain that speed.

So, if the t-cases rotates up and increases the DS angle from -3.4 degrees to -4 degrees, again assuming the pinion is at +1 degrees already ....

+3 = 4 - 1

The front differential would have to be rotated +3 degrees.

The techs can't guess this accurately, and they have a LOT more experience than I do so I'm not even gonna try giving you a number. I drive a M/T so I COULD measure the rotation using the M/T gear shift lever, figure the distance from the drive train center line to the top of the gear shift, measure DS center line to the center line of the t-case output and get the front DS angle increase that way. Being that we run the same DS assembly the static math would be relatively accurate - but all this depends on how much flex and opposing force is involved and that would be where the math totally falls apart.

We're talking about very small numbers so if the drive train is pretty stable and you don't have much movement of the t-case, you MAY well be able to do the simple math - line the DS and pinion straight up - and call it a day. Maybe.

I think if I were doing this I'd put your vehicle on a pad, put a jack under the output end of the t-case and jack it up 1". Simulate t-case rotation. Measure the front DS angle. I would guess that the DS angle @ 1" would be what you'd want to use as your DS angle for the math to figure out how much the differential needs to be rotated. But, if you think the t-case shifs up more than 1" - say, 1.5" - then jack it up that far. You have a one piece drive shaft and that's pretty long so the change in DS angle shouldn't be that much (in degrees).



Maybe. I wouldn't rule it out, but what you've described sounds like drive line. You could pull the front DS and try it again, but the last time you said that when you did that the vibration went away.

Edward

thanks Ed,

having another look at the angles

Drive angles

it would appear that 2.3 degree up tilt of the front diff would bring the diff onto the same aligment of the shaft, so maybe thats how you calulated it/

But using that theorey , then shouldnt my rear shaft be vibrating as well as it has a difference of 1.8 degrees alignemnt. the rear shaft does not vibrate.

maybe there is some problem in the front end after all.

Ed,

Ive been thinking hard about this. The pinion points up at 1.1 degrees & the driveshaft then goes up 3.4 degrees from that.

You said rotate the pinio up by 23. degrees , but dont forget that as the pinion goes up then the shaft angle also decreases as they are joined together. So I reckon I only need to rotate the pinion up by 1.1 degrees , so that the pinion goes up to 2.2 & the shaft comes down to 2.3 (nearly identical).

How does that sound?

Correct. Right now its close to horizontal - +1.1 as you have noted below.



Correct. For a CV/u-joint drive shaft setup, the pinion is inline with the drive shaft. In other words, you'd be able to draw a straight line along the center line of the drive shaft and pinion, straight through both.



You're putting to much into the math. I am trying to keep this REALLY basic for the sake if illustration. That 2.3 degree number isn't accurate. If you really need to figure the rotation mathematically, you need ...

1) The length of the "pinion". This is the distance measured from the center line of the axle shafts to the exact center of the u-joint along the center line of the pinion.

2) The distance from the axle shaft center line to the "pinion" center line and whether the measurement is from above the axle center line or below (+/-).

3) You need the length of the drive shaft measured from the center of the pinion u-joint to the center of the Double Cardan u-joint connected to the drive shaft.

And then you need to do a lot more math than I've shown. And it the answer still wont' be exact. I don't know what any of these measurements are so I can't begin to give you an exact number of degrees.

This is one of those things where figuring out all the math ahead of time takes more work than fixing the issue.

Edward

Ed,
well after a lot of trial & error I finally got it balanced by myself.

The first thing I did was take apart the slip joint & moved the splines to 4 different spots at 90 degrees apart until I felt the least vibration. Funny but the least vibes were not in the original position but rather 90 degrees off.

Next step was to strap on a 35 gram weight to the front in 4 different spots until the vibes improved. they did at one spot but still some there.

So I strapped on a 35 gram weight at the transfer case end in 4 different spots but didnt get any joy from that. Then finally as a last resort I machined up a 50gram weight & strapped that on at one spot. Voila ! No more vibes, I couldnt believe it after all the mucking around. So I fine tuned it a bit by moving it a couple of centrimetres either way of that spot , & finally settled on one spot .


SO thats it , although I am sure that the shaft was balanced 'on the lathe' once it was fitted it vibrated , so now I have 2 hose clamps on both ends with weights under them.

I now need to make up new weights with the weight of the clamp screw added which was 14 grams. & then weld them on.

I cant believe I fluked this finally. I guess there are some inbalances in either the transfer case or front diff ,but I finally got it!