Topic: Weird vibration on 94 Xtra cab

[deadicatedweim]

I have a 1994 xtracab short bed that has a vibration that I cant figure out.  It starts at about 50mph but is bearable, once you hit 60 its terrible you can barely accelerate.  If you can get to 72mph it immeditaly goes away and stays smooth to at least 90 plus mph. 

I have tried putting stock tires and rims on and it doesn't change the vibration so that rules out the wheels. 
I have tried 2 different cv 1 piece drive lines on the rear and no change but I have wondered if I should try a 2 piece similar to the stock design? 
I have had the rear 3rd member rebuilt due to a broken tooth so I assume its good as new.
I have switched the diffs front to back with no success. 
I don't feel any play in the drive line u-joints and I don't feel any play in the transfer case output flange or the 3rd members flange. There is a slight leak from the t-case rear output seal that has been there since purchase but has never been bad enough to change.
I haven't noticed jerking in the steering wheel.
I drove the truck in front wheel drive with the rear drive line off and the vibration was barely noticable.  So I'm thinking it has to be associated with the rear power train.

Is it possible the rear part of the dual cases could have something wrong?  I built a 93 xtracab in 2003 and that was when I first purchased the dual cases and 3rd members. I have always had issues with this vibration. I was hoping when I built the 94 something would change and  I would loose the vibration, but its still there. I reused the dual cases, front axle and rear 3rd from the 93 but everything else was new to the 94.   

Sorry for the long rant any help would be appreaciated. Below are the specs on my truck if needed. 

Much Thanks Conner


Specs on my truck... I have the 3.0 v6 manual trans backed with mc dual cases the rear case is 4.7.  I have a 1 piece drive lines with cv's front and back.  Both diffs have arb lockers and 529 gears.  The front axle has the bobby long 30 splines the rear is stock. I put 4 degree shims on the rear axle to correct the pinion angle issue.  My 3rd members are from 4cyl trucks but I have the v6 rear axle  I have mc 5 inch springs with a 5 inch shackle.  I run 37' mtrs.  I have the mc heavy duty skidplate/tcase holder.

[Phazertwo]

I have the same problem with my 92 xtra cab.  Thing was smooth like butter when I first did the SA, than when I did my duals, things went to hell.  My vib never went away (unless I was below 15-20mph).  Turns out that the x-member that I made for the cases lifted the cases to far, and threw off the drive line angles BAD!

I had never really had to deal with drive line angles since than so I started talking to a buddy of mine who is a drive line wiz.  We came to the conclusion that I needed to move my carrier bearing (I stayed with the 2 piece shaft), and change my pinion angle with new spring perches.  I am in the process of doing that now.

When you install dual cases it moves the drive line back, which throws off the drive line angles, which can be made up for a few different ways, a new x-member, a new CV rear shaft, and changing the pinion angle.  If you have a carrier bearing, it makes things a little more complex, since you now have twice as many angles to look out for.  To change the angle from the t-case to the carrier bearing you will need to change your x-member, or move you carrier bearing.  Anyone one of these may fix the problem, but in my case I will have to change the pinion angle and move my carrier bearing

Search drive line angles, and school yourself on how it works, and how to set them up, it will help allot!

Also, since you took out the carrier bearing and have a one piece shaft, you have to worry about the shaft "jump roping". When you make a drive shaft longer, you have to make the walls thicker so that it can stand up to the extra force.

Hope this helps!  You can read my build to keep up with what I am doing to take care of my vibes, just check my sig!
PZ

[deadicatedweim [OP]]

I'm going to try to dropping the marlin transfer case skid plate down an inch to 1.5 to see how that helps.  Do you think its worth putting a HP third member in to help out the drive line angle?  I have a 4cyl arb third already with 5.29 gears how much of that stuff can I reuse on a HP third member?

[boggerunner]

sounds like it might be a loose rear flange on the t-case, expecially if its leaking.
could even be a bad bearing from running an unbalanced driveline.

[deadicatedweim [OP]]

to change the bearing do i have to split the case or can I access it through the tear drop shaped cover on the back?

[Phazertwo]

I'm going to try to dropping the marlin transfer case skid plate down an inch to 1.5 to see how that helps.  Do you think its worth putting a HP third member in to help out the drive line angle?  I have a 4cyl arb third already with 5.29 gears how much of that stuff can I reuse on a HP third member?

Try lowering the skid.  If that helps, than you have an idea of whats going on. You cannot safely run a high pinion thrid in the rear. You would be driving on the coast side of the gears... no good.  As for the ARB, it depends on what model it is to fit in a HP.  If you have the newer RD132, than it fits the 4 and 6 banger, and HP diffs.  The old RD01 (like I have) only fits in a 4 banger diff.

A big help to us would be pics of the drive line. Take a side view pic of the pinion, and of the t-case.

 Similar to this, but try to focus on the drive shaft where it connects to the diff, and the t-case.

(FYI this is a not so good drive line angle)

PZ

[deadicatedweim [OP]]

That's good info to know about the hp diffs. thanks

[deadicatedweim [OP]]

I will post some pics as soon as I get enough posts.

[Phazertwo]

ah, I forgot about that rule. If you e-mail me the pics I will post them. PM me for my e-mail.

[deadicatedweim [OP]]

I talked to a local tranny shop today and he told me that if the transfer case output main bearing was going out it would make lots of noise and vibrate at any speed.  So he doesnt think that is my issue since my vibs are betweeen 60-72 and then smooth after the 72.  Does the guys theory make sense?  I will get pics loaded up today and Is there a rebuild kit that replaces all the bearings and wear items in the tcase or do i have to order the parts seperate?

[Phazertwo]

http://www.marlincrawler.com/transfer-case/parts-upgrade/transfer-case-rebuild-kits


However, I really don't think that the t-case is your issue.

PZ

[Snowtoy]

I talked to a local tranny shop today and he told me that if the transfer case output main bearing was going out it would make lots of noise and vibrate at any speed.  So he doesnt think that is my issue since my vibs are betweeen 60-72 and then smooth after the 72.  Does the guys theory make sense?  I will get pics loaded up today and Is there a rebuild kit that replaces all the bearings and wear items in the tcase or do i have to order the parts seperate?

Generally speaking out of balance tires/separations will cause vibrations that come and go at different speeds.  You should have one of the sets tires balanced and checked, then run them and see if that changes your vibrations.

Drivetrain issues that vibrations shouldn't ever really go away, and are usually felt through the seats.  Worn u-joints caused by wear/poor driveline angles/out of balance drive shaft are usually felt when acceleration/holding constant, but then go away when coasting.