SOA vibration (1 Viewer)

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Sep 22, 2005
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After completing SOA on my '82 fj40 using the springs from man-o-fre a few weeks ago, I been chasing a problem and figured I'd better stop and ask for directions. By not using the original springs it gave me nearly 2 in extra lift and figured I'd turn the axle and point the pinion to relieve stress on bottom u-joint. I've since shimmed it back (thinking it may have produced a harmonic issue) and cut the angle in half and it still hasn't solved the problem which is this. A test drive produced a bad vibration and found there was slight binding in the shaft knuckle and it had to be taken back out and fixed. After reinstalled, another test gave way to a similar problem. Check and replaced side and spider gears and pin not making a difference. Pulled it in garage, jacked up one rear wheel with dif cover off let it run in gear at idle speed. Shaft appears to have no vibration. One of the symptoms are with one wheel touching the ground appears it wants to lock in producing a rocking motion side to side in the rear end. Its got me puzzled, my wife says burn the beast. :mad: Any suggestions unlike hers?
 

woody

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holy run on sentence.... ;)

did you cut-turn the housing for the SOA?
is the vibration in 2wd or 4wd, and what speeds?
what is your current caster angle?
 

Trollhole

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If you didn't do a cut and turn you cannot trun your diff up towards the transfer case. It will throw your vehicle into a negative camber issue which is probably where you are getting your vibration from. +14 +-1 is about normal if you cut that in half you are still at -7. . Put it back to stock and do a cut and turn.
 
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Addditionally, you can't turn the pinion up unless you use a double carden at the transfe case end of the shaft.

If you use Ujoints at both ends you have to keep the angles very close. Within about 3-4 degrees. Otherwise you will have vibration. Did you check to ensure that you ujoints were in phase. Easiest mistake to make and the cause of more unexplained vibration than anything else.

Same goes for the rear axle/driveshaft.


Mark...
 

Trollhole

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Mark. It's been my experience that you don't need a CV on the front unless you plan on running at high speeds with the hub locked. LIke over 30 mph. Generally I don't do more than 5mph in 4wd with the hubs locked.
 

dgangle

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When I installed my 4" SUA springs from BTB I had terrible front and rear driveshaft vibration. I solved this by installing a double cardan driveshaft (DC DS) on the rear and tilting the pinion up to nearly eliminate any difference in angle at the pinion flange and the DS. Up front another DC DS with a C&T was the solution. Now no vibration at all in either 2WD or 4WD @ +70MPH. I did have to have the FJ60 donor DS's lengths altered at a local DS shop to get the lengths correct.

If a DC DS is not an option for you I would recommend making the rear pinion mounting flange angle match the DS mounting surface on the parking brake drum. Different angles on these two surfaces will cause different amounts of travel in the U Joints which will = vibration. Phase is also important as others have mentioned but my post assumes this to be correct.
 
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I don't mean this harshly 'cause I know that some of you guys only use your rigs on short, slow speed, highly technical trails. But in my world a rig really isn't right if you can't run 4wd at road speeds. Even off road I occasionally need to be able to use 4wd at speeds up to 25mph or so (a trap line that called for me to run 80 miles every night up a frozen river a few years back comes to mind.. that one saw 45-50mph routinely). Between long distance trails and all weather use I can't make those kind of compromises.

The final test of every rig I do an SOA on is a 65mph run with the front hubs locked. Any vibration and it's back in the shop for adjustments/corrections.


Mark...
 

nuclearlemon

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i also think that if you build a mildly modified rig, it should be roadworthy...i drove my soa 40 to moab at 70+ mph with the front hubs locked since it was snowing...never did have to use the 4wd, but previous around town experience tells me it shouldn't have been a problem. i didn't to c & t...when i did my soa years ago, it wasn't such a big deal...the two others that helped me also didn't do c & t and they don't have any probs either. we made sure the ujoint angles matched at each ends of the front shaft, rear is a toy runner front shaft with dc.
 
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Thanks for all the responses! For the record, I haven't even put the ds in the front end yet...gotta get passed the rear first. I may reverse the soa just to see if the vibration goes away for sanity sake and go from there. But from the replies it sounds like if I'm gonna point the pinion up I need a cv joint on the upper end. pics to come!
 
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Make sure your drive line ujoints are in sync. Out of sync u joints can cause nice vibration at speed. Sync means they are aligned properly.
 

nuclearlemon

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if we're just talking rear, are you running a cv shaft (toy 4runner /pickup front shaft, early to mid 85's works well)? do you angles at each end of the shaft match?
 
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I tried rotating the ds 90 degrees at the spline to see if it increased or decreased the vibration and it became worse. The angle ends do not match since the soa and from what I've read, it seems that is where my problem is located, so it looks like I'm headed for a cv joint. A 4-runner front ds will work well? The perches are already set angling the pinion to the xfer case hoping to lessen the stress on the u-joint. Can't wait to get to the front end. Thx again for your help.
 

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