Driveline angles

ok need some help with this.

Here is my main objective

1. to correct the driveline angles after raising my rig about 3". Time to get the geometry right.
2. My truck is a tiny bit higher in the front than the rear. I want to get that rake back to it where its slightly taller in the rear than the front.

Here is a measurement that might help.
When sitting on a flat surface, the truck sits at 38 1/8" ground to fender flair at rear tire.
and at the front we are at 38 1/4" not a huge difference but enough to be seen.

Also the inclinometer also says the truck has a rake of .19 degree or .2% of rake front to back.

By adding axle shims to my suspension, I'm thinking a 1/4" or 3/8" shim will correct some driveline angles and at the same time, raise the rear up some to be at least level and I'd actually like to be bit higher on the front.

A 4 degree axle shim measures around 3/8" inches think it its thickest end.

Have a look at the drawing for where my current driveling angle are.
All help is appreciated

 

Gotta ask. You can see 1/8 of an inch difference???

G.

 

well here is the thing,
The truck is naturally supposed to sit slightly higher in the rear than the front. This is for fuel mileage and aerodynamics, etc etc.
Normally it would sit 1/2" higher in the rear of so and I generally like that look.
So yes, seeing the difference between it being 1/2" high in the rear vs 1/8" low in the rear is a 5/8" and yes that can be seen

 

Those are slope measurements; you haven't calculated working angles?

Do you have a carrier drop?

 

Seems complicated. If you’re worried about vibes and want to raise the rear get an AAL and a one piece drive shaft.

 

No I dont use a camper top, any suggestions?

 

explain more.
To me it doesn't seem that complicated, if I raise the rear by way of some small wedge shims under the springs and I raise them 3/8" with some 4 degree shims, it seems like this raises the rear some, but also improves the driveline angle by raising the nose of the differential a little bit and reducing and straitening out the angle of the rear drive shaft vs the differential yoke angle.

The rear differential is sitting at an angle of 4.74. By raising it up by 4 degrees, it will be at 8.84 degrees. The rear drive shaft is at 8.83 degrees, that seems like a better match up to me but I'm not an expert at this.

 

Just seen a lot of guys chase driveline angles.

 

Who said anything about about a camper top? I'm asking you if the measurements in your diagram are the slopes.

Is 4.4 degrees the slope of your output shaft? Is 4.74 degrees the slope of your pinion shaft?
If yes, your 'working angles' are:
1st: 7.59-4.4=3.19*
2nd: 8.83-7.59=1.24
3rd: 8.83-4.74=4.09

*3.19 is also the slope of your first shaft if you were to use the output shaft as a zero. This seems like a lot, and why I asked if you have a carrier bearing spacer drop.

With all due respect, I can tell by your response to cfagan14, you have no clue how a 2-piece drive shaft with 3 single u-joints is supposed to be setup.
You're trying to set it up like a 1-piece driveshaft with a double cardan(CV) in the front and a single u-joint in the rear.

 

Yes correct, these are the slopes, I thought the graphic I provided made that fairly clear to extrapolate but to your points.
If it sees like a "lot" to you, then I'm interested in your thoughts on that and why that might be.
I do not have the carrier bearing spaced down, its in the stock position.
And you are very correct in saying I do not know much about the 2 piece vs 3 piece and its proper geometry. This is the reason I posted the question on the forums, in hopes that someone with experience could guide me in correcting it.
Not because I already understood it. In fact, If I already understood it fully, Id be able to come up with my own answers.
Thanks though for some of the info you have provided, its helpful

 

No, it wasn't fairly clear; 4.4 and 4.74 could be working angles for all I know.

How are you measuring those two slopes?
Inclinometer on the yoke flat or machinist square on the mounting flanges.
The proper way is to measure on the flat of the cross journal but that requires a special tool. Next best, is using the machinist square on the mounting flanges.
I'm asking because, as I said, the first working angle is a lot at 3.19 degrees. It should be more like 0-1 degree. This makes me suspect your measuring method might be off.

It takes 2 single u-joints at the same working angle to cancel each other. Since our driveshafts have 3 single u-joints, one of them needs to be zeroed. The proper way on a 2-piece/3 single u-joint shaft is to zero the 1st working angle and equalize the 2nd and 3rd. Some choose to zero the 2nd and equalize the 1st and 3rd. If your measuring is correct, you are actually closer to the latter method.

 

Gotcha, thanks,
As far the measurement,
Yes I used a square to be sure I was getting it right, then used the square to seat the inclinometer to making sure the measurement was taken with everything as square and plum as possible.
I do know that when my lift kit was installed, they did a drop up front of some amount that came with the kit but no drop or spacers were used under the carrier bearing.
I know they must have done the shimming up front because now when I take off my skid plate to change the oil, there are spacers of about 1/2-3/4" under the skid plate where it has been shimmed down also.

 

Do you currently have a rear lift? What kind?

Well, like I said, you're really close to the alternate method of correcting angles...
1st: 3.19
2nd: 1.24
3rd: 4.09

If you use a carrier drop; that would increase the 1st angle, lessen the 2nd angle and lessen the 3rd slightly.

Doesn't help with the lift you want, though.
Have you considered spring sag in the rear over time? If you have stock leafsprings, you might want to consider more lift and re-examine angles after.

 

For a while, I had about a 1/2" spacer under the carrier bearing. The truck felt fine but when coming to a stop and braking, there was a vibration.
I took out the spacer and vibration is gone.
There is NO vibration now in the drive line and it feels great but, I'm just trying to be proactive in being sure its reasonably within acceptable specs AND if there is any way to bump up the rear some, that is my goal to make it look a little nicer.
I do have a lift yes, as I recall it was a 3" lift all the way around but its a cheap kit with rear blocks and the spacers over the front coils

 

This is a really good idea, the spring sag is a rear thing. If I added an extra leaf, I can pick up maybe a 1/2" or so and also reduce the idea of spring sag some, good idea, who makes an extra leaf like this?

 

Most add-a-leafs are 1.5".
Blocks or a custom leaf from a local shop are about your only options. You can source blocks with the angles built in, but it's a guess what you would need...or need it at all.

 

If i were to use a small shim to change the rear drive shaft angle by 4 degrees, does that hurt or help my sitation?

 

Hurt...
These are your working angles:
1st: 3.19
2nd: 1.24
3rd: 4.09

You can either do;
1st-0
2nd-equal
3rd-equal
or,
1st-equal
2nd-0
3rd-equal

Your'e closer to the latter. A slight drop in the carrier bearing would get you close. Maybe a 0.5 degree shim in the rear; depending how much axle wrap changes your pinion angle under acceleration/cruise.

A 4 degree shim would get you approximately;
1st-3.19
2nd-1.24
3rd-0.09 or less while under load from acceleration/cruise

Do you have driveshaft vibes?

 

I dont have any vibration at all sir.
Well, you know what i have to work with and where im at now and my two objectives are
1. Raise the rear of the truck slightly.
2. While doing so, make any improvements i can to driveline angles.

Please tell me what you would do then and thanks

 

Get the lift you want in the rear. If you get vibes, then worry about angles.