The 8.25 4.56 gear swap... vibration issue.

My humble apologies....you're right, I had it backwards. Your diagram cleared it up. I've been over thinking this way to much. 2 degree shims would be the answer in this case.

I guess my theory would work for a MJ though :)
 
Sean, let me know what happens as I am having the same issue and I want to eliminate my vibrations - mine start at about 60 and get worse as I speed up. Also, what did you do about the pin/leaf bolts to make them go through the shim?

Any thoughts anyone on this:

I have 4.5" RE lift with SYE, 33" and 4.56's. I am asking in another thread where I can order steel shims, and I was going to just go with 4 degree. I put an angle finder on my driveshaft and it is at about 19 - 20 degrees. I did the best I could do with the angle finder on the diff/pinion and I came up with about 13 degrees. So I figure about 6-7 degrees difference , if I bring the axle up 4 then I should still be down 2-3 degrees and that should be perfect, provided I read my pinion angle correct. How do you put the angle finder on it, just line it up with what looks like the seam?

Sorry, I don't mean to hijack the tread, but I think we have the same issue, and possible the same resolution.
 
You can get shims from rubiconexpress.com as well as numerous other places.

There are two spots on the rear of the axle (where the housing meets each tube) that are machined flat. They each have a hole in the center of them. Use that flat spot to mount the angle finder. The pinion is 90* to that spot. To measure the driveshaft, just put the angle finder on top of the shaft.

Note that a 4* shim should probably be good. The driveshaft and the pinion length are different so when you move the pinion up 4* you are also moving the driveshaft up 1-2* at the same time.
 
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Shims really aren't what I would consider a permanent soloution. Cutting off the spring perches and rewelding them when the axle is in the proper position is always best.
 
I can't see where you are talking about, I dont have any holes. It is an 8 1/4. Could it be possible that the surface that the cover mounts to is exactly 90 from the pinion?
 
Just talked to a guy from Rubicon Express, gave him my spring P/N (they are RE springs) and my shackle length and he advised 4 degree. The pins come free!!

He started by suggesting 6 degree, but I told him about Seans situation and said I didn't want to go over, that's when he asked about my shackle length and then when I told him 5" he said that 4 degree would be better for me. Weirdo was right!! So maybe when Sean adds the longer shackles his problem will be solved.
 
98GhostXJ said:
I can't see where you are talking about, I dont have any holes. It is an 8 1/4. Could it be possible that the surface that the cover mounts to is exactly 90 from the pinion?
Click to expand...

Yes, the cover surface is also 90* to the pinion. These are the pads I was talking about (see red squares, this is a D44 but should be same as C8.25):
d44axle.jpg


If you use the pads, you don't have to drain the oil.

We fixed Columbus' vibes tonight (so says a short test drive). We added longer shackles and removed the 4* shims which were too much for him. With his shorter shackles, he needed 2* shims. With longer shackles, he didn't need shims (or could possibly use another 1/2* of shim.).
 
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In my experience, having the pinion near zero* shouldn't give you vibes at the higher steady speeds when there is min torque loading the driveline. Having the pinion lower 1-2 degrees is optimal for accelerating and to lube the u-joints.

IMHO, keep the pinion angle for now. Your statement about vibes on decel leads me to believe you don't want to lower the pinion further ...at least for now.

From what you describe, I would start with removing the DS and check the u-joints thoughly even removing the u-joint caps if you're willing and check the slip splines for wear. Second is to spend 40 bucks and get the DS balanced so you know for sure it's good.

BTW, you do have a CV driveshaft, right?
 
Yeah, its a cv shaft.

We pulled the shims tonight and added RE shackles that are 3/4 inch longer. The angle is now just a hair below 0.

I went for a short test drive, and it felt good, but when I was driving home, I verified with Josh's GPS that the vibes start up again at 65 mph, and get worse. It feels fantastic until 63 mph. (So it is better than with out the shackles, and with the shims.)

At this point, I'm going to check the shaft. 2 years ago when rebuilding the shaft, I knock one of the weights off. We re-welded it in the exact same spot, but I have a feeling the tiny bit of weld we added might have thrown it off. Im going to grind the weld down, and at least see if it helps for now.

Cali-gold- Please let me know of a place that will balance a shaft for 40 bucks. all the places around here suck... I got quoted 125 bucks. :(
 
So we went down to Hollister, and I beat up the rear shaft good.

I was getting vibe right at 65, but after Hollister the vibes start at 50.

Josh had a spare shaft, so we swapped it out, and it didn't help, or change the problem. Vibes are still nasty.

Looks like we need to machine my 4 degree shims down to 2 degrees. I have to go home in 5 days. Fail.
 
Oh man, sorry to hear about the drive line issues.

I have to second getting all the angles first for everything, that should help with getting things mapped out. (and good information for the rest of us!)
 
we will further SNAFU his rig tonight. :explosion
stop by if you get bored & laugh at us while we toil away on his P.O.S.
 
I got a meeting with the Thailand factory from 6PM-7PM. Might be able to make it over to the Fun Factory after that.
 
srmitchell said:
Thats not cool, my sister calls it a POS.

Touchy subject yo.
Click to expand...

she calls it a precision offroad system too?
nice!
as Borat would say...high 5! :gee:
 
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