Drive Shaft Vibrations Solved Step-by-Step

Is there a best out of the 4 or are all 4 equally good? Does the guide I’ve read about no angles > 3* apply to all 4?
Thanks!

 

Yes.
A=0
B=C

The others are:
C=0
A=B

B=0
A=C

A+B+C=0

The majority of folks are closer to A+B+C=0

A=t. case u-joint
B=center u-joint
C=pinion u-joint

But like I said, I'm 99% sure you have a double cardan center joint...it's a different animal.

You want A=C. Don't worry about B.
From your diagram, A=1.6 and C=10
If this is the case, you would benefit from a CB drop and angled shims. The CB would increase A and decrease C. The shims would further reduce C.

 

The 3 degree rule isn't a hard rule.
U-joint longevity is measured with the assumption working angles are 3 degrees or less. Working angles greater than 3 degrees have a shortened lifespan. They don't necessarily induce vibration, as long as they are cancelled.

 

awesome -- thx. I intercepted the post a few threads back by @Islandtruck -- he has the 99 (double cardan) so he should be focusing on the cb drop to even out the A and C angles and shim to get them as close as possible.

I have an '05. Angles A = 4.0 down, B = 1.5 down, C = 4.7 up leaving the pinion 0.8 up. In my case it looks like I could slightly lower the CB to get the B angle < 1 and my A and C would be roughly 4.5 if the stars align. Hopefully that addresses the shudder on accelerate (only place I notice it) and I'll just do this knowing I'm reducing the life of the U-joints. The alternative is to get A to 0 but that would require rasing the CB and probably shimming the pinion 2 degrees or so. I think I'll try the drop first and see where that take me. THANKS!

 

My apologies.
I had you two confused.

 

Thanks for the help @splitbolt and @dk_crew! Mine is a ‘97 actually, used to have a 99. So not sure about the double cardan gonna go check today. So basically I am going to try and bring down the CB to even out that 1.6-10* change and that will bring the pinion down a bit too? and if the pinion is still up from TCase then I will shim it to bring it down. In my case this means fat side of shins forward I guess? The weird thing is when I took the old rusty stock springs off they had shims on them but I couldn’t tell if they were fat side or skinny side forward.

 

Driveshaft angle out of TCase on double cab is already at 4 degrees so never made make sense to me to drop carrier bearing any further, if anything, flip it upside down to reduce the angle on first UJoint then rotate differential up to reduce angles on joints 2 and 3 and ideally to be equal. Depending on amount of lift you use, there Will be a different answer as witnessed by the 900 plus opinions already in this thread And mine is now the 947th one.

 

Should be fat side to the rear, rotating the pinion up, decreasing the working angle.

 

Definitely, a lot of variables...
I've yet to see anyone make an attempt at measuring the true compound working angles.

I prefer the method you describe as well. Unfortunately most are closer to the A+B+C=0 method...having to juggle everything around.

 

Just my two cents...
When breaking, the pinon will want to wrap down (pinion pointing to the ground) and when accelerating the pinion will want to wrap up (pointing to the sky). Blocks will increase the wrap on stock leafs regardless of shims so finding a good "working range" for the pinion would need to be considered when adding shims... or getting an AAL (progressive 3) or full new leaf pack.

I have the Icon "1.5 add a leaf and originally left the original overload leaf (OL) out and put in a 2.5 deg shim (pointing the pinion up, fat side to the rear). Vibes were better but added weight to the back and threw a cut down OL in and it is as good as it gets unless you want to go torsion bar or full 4 link. Make sure the drive shaft is straight by lining up the zerks with a string or something. Make sure your carrier bearing is not crap and that the u-joints are OK. My numbers are not perfect for any of the cases presented but it works (for now). No carrier bearing (CB) drop after extensive f***ery and no benefit. This does not mean a CB drop will not benefit others and it is the cheapest, easiest, first thing to try. No Diff drop because that does nothing except tilt the front diff and that is not advisable. I may feel the pulsation of my needle bearing *possibly* but that's to be expected since it is a piece of garbage design. It will be replaced once it gets too annoying (or fails). Just adding my two cents... it seems that every truck has it's own demons.

Good Luck

 

Over simplified to avoid having to write out trig equations but basically the first UJoint at TCase adds vibration that increases with angle, UJoint at 2nd joint will subtract some of that vibration and 3rd joint will add more vibration back in. Thus what you want to do is set ujoint at one end to 1 degree and make other two joints to be equal angles so they cancel each other out. Doesn’t matter if you set ujoint at TCase to near zero by flipping carrier bearing or add shims to differential to point the nose to be in line to carrier bearing as long as Ujoint in middle angle is same as one of other two and remaining 3rd joint is less than 1 degree. Due to the trig functions, it does not need to be opposite angles as long as equal. Other option is to play with shims at carrier bearing and differential to get angle joint 1 plus angle joint 3 minus angle joint 2 to sum to zero. This is good for small angles but to do this correctly you need the Ujoint equation since it is really the sum of sine/cosine of the angles and not a straight addition.

 

This one?
cos(a) + cos(b) = 1/2 x (cos(a-b) + cos(a+b))

All Greek to me...

 

Ok so went and got a bunch of washers today. And yes my truck does have the double cardan joint @splitbolt

after adding in about 5/8” of washers I checked my angles again-
tcase - 0
1st shaft- 1.4 ( don’t know how this is less angled)
2nd shaft- 7

I did get some longer bolts but not enough washers to keep going.

I guess my question is how far can you shim the CB? At this rate I am going to have to go 2” or more is that safe?

 

Don’t have the time to endlessly mess w this and am looking very close at Tom Woods driveshaft... however if it doesn’t work it gets to be an expensive experiment when you have to ship stuff back and forth from Hawaii

 

I got a good stack of spacers going under my carrier bearing. After putting in a 3* shims to adjust the pinion angle, I've got like 4 spacers each side crammed in there. Need time to play around more. Vibes are almost gone except slightly around 20mph.

I want to see someone else with a Tom Wood's driveshaft on a 3rd gen before putting down the money.

 

What's the pinion angle?

 

Just went nuts on the spacers.. I think I probably have 2” in there. Just test drove the truck and it feels great! Probably not perfect but it is so much better than it was I can’t even tell.

Angles were- 0, 5.6, 6.7, .4 up

unless I am missing something (is this bad for my u joints??) I am probably just gonna leave it and be happy.

 

Fix your vibes?

 

Yep! Pretty much completely gone from what I can tell... and if I ca't tell good enough for me!