Death vibration in the rear :(

[littlejackass]

I am getting motivation to work on the samurai again. I lost interest at the beginning of the school semester when I got crazy vibration in the rear. (Only have front driveshaft, and 4 shock mounts to be finished :( ) Well the semester is almost done, so I am back at the drawing board again. This vibration starts at like 5 mph and gets worse the faster I go. My 1st thought it was the ujoints, but they are all good. Then I thought it was the driveshaft being too long, (no play in the shaft when I installed it) so I got it shortened, still nothing and added an extra 1.5" in wheelbase. I was told my diff angle was too much, so I repositioned the diff, so the driveshaft was pointing straight up. (the output of the third member is straight with the driveshaft)

Here is my setup in the rear:
85 rear toy diff
3" cj front leaves, with a droplink,
the pin holes on the perches and ubolt mounts pushed forward 1.5" (to gain an 1.5" of wheelbase)
85 toyota front cv driveshaft shortened by 2"
85 sj413 t-case with the drum e-brake

The only I can think of it might be is that the rear length hasn't been stretched enough to compensate with for the center diff. Does anyone else have any ideas? They would be greatly appreciated.

Chris

[littlejackass]

I think I am going to remove the rear ebrake drum, I think there might be something there that is causing problems.

[xtrmtoy]

Is the driveshaft phased properly?
If so the next thing I'd check is the mounting at the tcase. How does the driveshaft center itself on the tcase? I hope it's not just the bolts.
Can you put the rear diff on jack stands and check the runout on the various flanges and the driveshaft with a dial indicator?

If that all checks out, Have you checked the cv. Is it in good shape?

Just a few thoughts.

[KAC]

is yer rear shaft pointed directly at yer t-case?

[Big-block-Sami]

Here is my setup in the rear:
85 rear toy diff
3" cj front leaves, with a droplink,
the pin holes on the perches and ubolt mounts pushed forward 1.5" (to gain an 1.5" of wheelbase)
85 toyota front cv driveshaft shortened by 2"
85 sj413 t-case with the drum e-brake

The only I can think of it might be is that the rear length hasn't been stretched enough to compensate with for the center diff. Does anyone else have any ideas? They would be greatly appreciated.

Chris[/QUOTE]

Xtrmtoy has given you some very good advise, let us know what you find out.
Just by the dates on your forum you must be very busy, or frustrated with it or both !:( :(
So you say you have front leaves in the back? Okay, so you may be getting some good flex there and rear axel wined up.
Do as Xtrmtoy said check your driveshaft to ensure the u-joints are in phase ( both yokes are the same, not out by 90 degrees)I have seen them come back from the remanufactures 90 deg out(UAP),believe it or not!
And then put the rear axel up on jack stands( not a jack, stands!), first with the wheels and tires on.Have your buddy run the truck SLOWLY checking for any signs of vibs.Show us some pics of your set up.
You may have a bet axle or rim that's wobbling
watch you driveshaft, it mat be bent
you have a cv in your rear shaft up at the x-case,right? well that means that the diff should still be angled down slightly a couple of degees in relation to the rear driveshaft angle (this is so whe there is torque put the rear axle the diff will torque upwards slightly and then be in line with the driveshaft.)the only time you wouldn't do this is if you rear axel was held firmly be a four link set up.
How long is your rear shaft? You said you relocated the spring prch FORWARD 1.5 inches, I assume you ment BACK 1.5". Anyhow, if you have a big lift and a shoft d-shaft your CV may not be flexy enough and require some clearencing( grinding) stock CV's are not as flexy as some people may think, I've known guys who have has to remove them because of this reason.
Good luck
BBS

[littlejackass]

Ya it has been a long while.
I wasnt able to check it this weekend :(, Ill check it out this weekend. Ill see if I can get my hands on a dial indicator.

Thanks for the help Xtrm and big-block

U-Joints are all good.

I did lift it on jackstands before, and there was no vibrations. Vibrations only came when there stress or resistence on the rear. (I applied the brakes when it was on the jackstands) Noise is coming from the cv/tcase area.

The rims are brand spanking new, so they arent bent.

Yokes are phased properly.

I am using the '85 front driveshaft, which are supposed to have alot more clearance then most. (flexes twice as much as an IFS style front shaft) It is also about 4" longer then the pre 84 driveshafts.

Ya the cv is at the t-case.

no the hole is 1.5" forward from the center of the spring perch, which pushes the the rear end 1.5" back. Id say the rear is push back maybe 3.5" from stock. I would like to push it out another 2-3" but i would need to change my suspension setup for that.

There really isnt that much lift on my truck, i did alot of fendertrimming to fit the tires i have. I actually had more lift when i was running 35s and stock axels.

[littlejackass]

is yer rear shaft pointed directly at yer t-case?

My drive shaft is pointed straight at the t-case but the diff is center.

[Grumpy]

Chris, all the joints in the rear d-shaft are tight? I could see a problem if you didn't have a CV there, but you do so it should cycle without a problem. Perhaps the rear output bearing in the T-case is screwed? Or for that matter maybe a problem in the t-case itself? Glad to hear you're back at her.....maybe some year we'll see ya at Suzican :rant:

grumpy

[Mudslug]

What is the vibration like? Do you feel it in the steering wheel or through the seat? At super low speed is it still there? I would look at the third if you have ensured your d shaft is balanced and phased.....remember there is a little divot on the shaft and yolk that need to be lined up.

[MuddMachine]

I'd check is the mounting at the tcase. How does the driveshaft center itself on the tcase? I hope it's not just the bolts.
.

:flame: :flame: :flame:

TCASE- YES!

Whats the angle like at the front shaft where it meets the tcase?

[twistedzuki]

i also have an acelleration vibe,i am running a cv shaft and my pinion is also pointing up the shaft.but i am also running a tracker axl which means i also have a combo angle,down and centered!!! niagara drive terrian said i should b running a dual cv shaft to cure any vibes,but its not a dd so i dont care!!! maybe you should have a look at yours and see if its the same???should be.:)

[Depot]

Check how much slop u got in ur d-shaft splines! Personally, i dont believe in the cv theories as I have always run 2 simple u-joints with a centered rear diff. All my vibes went away when i pu in brand new shafts and came back the split second i torched off the coating on the splines that took up all the slop (only cause it seized full of mudd).

try packin ur d-shaft full of greae to help absorb some of the slop.

gl

D

[Fullload]

I had the same prob with my set up.

The guy at the driveline shop wanted to charge me 300 plus to rebuild shorten and balance my shaft so i said just cut it and leave it. He schooled me on his reasoning on why it needed a re-build.

here it is. He said if the u-joints/CV will not hold it's own weight it needs to be done. So if you hold your shaft straight up and down and slowly bring it horozontal it should be able to stay straight, without the u-joints moving.

Thats what he told me anyhow. But thats where i put my money as well.

[Big-block-Sami]

[QUOTE=littlejackass]I)

Here is my setup in the rear:
85 rear toy diff
3" cj front leaves, with a droplink,
the pin holes on the perches and ubolt mounts pushed forward 1.5" (to gain an 1.5" of wheelbase)
85 toyota front cv driveshaft shortened by 2"
85 sj413 t-case with the drum e-brake



Wow, I know this is a bit late but it just hit me.....
you have the toy rear end with a offset sj413 t-case...right?

You have a compound angle on rear driveshaft... you can't use the cv shaft in the case because the pinion on the diff. MUST point directly at the t-case's output.Your cv shaft would work perfect if you had a centre output on your t-case (but you don't). your only option is to loose the cv joint and lower your pinion angle so the diff pinion is parallel to (not pointing at) the the t-case.
Hope this isn't too late.
BBS