Front drive shaft vibes

So I have a buddy with 6.5 or 7 on a shortarm setup he's got jks uca and lca 4.5 rusty's coils and acos's he just had a sye installed and and rebuilt his front shaft .We put his front drive shaft in today and it vibes around 25 to 40 then its gone ? He pulled the drive shaft out 6 months ago because the cardon joint was toast and more lift and now this .What do you do when you get front drive shaft vibes ,cut and reweld all the spring seats and brackets? Or put in a disco any help would rock

Thanx :banghead:

Are his control arms adjustable? Hows the pinion angle?

Which D30 is this? disco or solid?

Not sure how you get 6.5-7" of lift with 4.5" springs (but the height doesn't really matter much anyway).

Anything over 4.5" of lift in the front is going to be a compromise between castor and front drive line vibes (not an issue on a disco axle because it isn't spinning out of 4x4).

Basically you need to adjust the to get as much as possible without driveline vibes. If you end up with not enough castor (tire vibrations, steering not wanting to go strait, not returning to center, etc) then you have to live with the vibe you end up with with as much castor as you need to make it drive able.

The reality is that short or long armes don't make any difference here, it is all about the alignment and making the angles work as best as possible given the geometry.

If you can't get rid of the vibes with enough castor then you either need to lower the front end, stretch the front end out (longer wheel base) or ?

Michael

The rest of the lift would be from the Acos (basically adj coil spacers)

It definently needs adjusted but unless he has adj upper and lower control arms I don't see how its gonna adj enough to fix it. There just isn't enough adjustment in the stock parts to compensate for 7" of lift.

Also IMO at that height he should really be running control arm drop brackets or long arms,it must ride like crap

He's got uca and lca made by JKS very adjustable also mnkyboy acos is where the extra 2.5 to 3 come from. Could we adjust it forward more to staighten out his coils and fix pinion angle ? Pinion angle look ok I was told by Jason at better off road to make the pinion angle happy we want to try and keep the diff cover parallel.And he has a disco to put in but he will need to reGear the rear axle(3.07) to 4.11 disco :wierd:

muddypunk said:

He's got uca and lca made by JKS very adjustable also mnkyboy acos is where the extra 2.5 to 3 come from. Could we adjust it forward more to staighten out his coils and fix pinion angle ? Pinion angle look ok I was told by Jason at better off road to make the pinion angle happy we want to try and keep the diff cover parallel.And he has a disco to put in but he will need to reGear the rear axle(3.07) to 4.11 disco :wierd:

Click to expand...

It sounds like you really need to read though the basics to doing an alignment. do a search.

Basically:
1. Adjust the wheel base to where it should be or where you want it (I would stretch an inch or two based on tires fiting in the wheel well)
2. Adjust the castor angle to get as much as stock (or a reasonable compromise) This is not eye balled like you mentioned above, it is checked on both sides of the axle as accurately as possible (this is a critical adjustment on these lifted trucks).
3. Center steering

Not sure what the disco and rear axle gearing has to do with it? Most people don't add the disco, most remove it? When I say Disco, I am talking about the front D30 and if has an axle disconnect on the passenger side or not. (Vacume disconnect).

It used to be "normal" to run a 6-8" lift on short arms. It may not ride as nice as a long arm but it is entirely possible to make it work fine. But why does he need that much lift to start with?

Michael

Putting the disco in would stop the drive shaft from binding but it has 4.11 gears he has 3.07 gears thats what it has to do with it and his wheel base is 100' 5/16' angle looks good good tires are centered We have done that I just wanted to see if I could get some advice but it seems He just needs to take to a shop and have them move the the brackets around to get the issue fixed
Thanx :greensmok
Also I do Alignment all the time Pretty much after every wheeling trip also on all my buddies rigs too Its simple and Ive been working on Jeeps for 6 or 7 years now I just never go that high so I thought maybe other have and I could get some help

muddypunk said:

Putting the disco in would stop the drive shaft from binding but it has 4.11 gears he has 3.07 gears thats what it has to do with it and his wheel base is 100' 5/16' angle looks good good tires are centered We have done that I just wanted to see if I could get some advice but it seems He just needs to take to a shop and have them move the the brackets around to get the issue fixed
Thanx :greensmok
Also I do Alignment all the time Pretty much after every wheeling trip also on all my buddies rigs too Its simple and Ive been working on Jeeps for 6 or 7 years now I just never go that high so I thought maybe other have and I could get some help

Click to expand...

Lets back up here a little bit.
He has 6.5 - 7 inches of lift, with 3.07 gears, and a 35" or larger tire (I am making this assumption because the only reason to need that much lift is with at least a 35" tire.

Now. The general consensus is that the disco axle is not as strong at the non disco. It is also much more difficult to make trail repairs with. What shafts does he have in each of these axles?

100" is WAY short on the wheelbase.
You don't need to move any brackets around to change the wheelbase or the alignment.
5/16" angle? don't have a clue what you are talking about here?

Michael

could the front driveline be too short or was that corrected with the lift

So we moved the uca and lca around got it dialed in and no more vibes

muddypunk said:

So we moved the uca and lca around got it dialed in and no more vibes

Click to expand...

There you go. Congrats!

Michael