nasty driveline vibration. need help

[zachary g]

Hello everyone, i have a 1974 fj40 with a four speed transmission. i have a pretty big vibration at around 25 MPH and then it stops temp. till i get to about 40 mph where i get another smaller vibration which then it seems to increase with speed. i do not hear any noise when i do this. it is not just at the top of 2nd gear but at the same speed in 3rd.i have taken out the rear driveshaft and driven with only my front axle and the vib. was not there. i do not believe it is the driveshaft because i have switch it with the front driveshaft that is good it makes no vib. things to consider are that the rear axle was rebuilt and this problem immeditly started, when i put the axle in i lowed the car becuz i changed leaf springs, and the output on the t-case is a little loose. I am stupmt and could really use some help. thank you, zac.

 

[RLMS]

Did you fix the t-case output problem?

If so, I would assume the rear end did not get rebuilt properly



Justin

 

[vk7ybi]

Welcome. Slop in TC output can cause DS to go off centre and vibrate.. Not keeping pinion flange and TC drum brake parallel and DS joints in correct phase can cause vibrations also.

 

[zachary g]

I wasnt really aware that i had a problem with my t case till today. but i find it odd that it would have magically come loose when i had rear end rebuilt, and there a simple way to get rid of the slop in t-case output? thanks, zac

 

[zachary g]

Another thing is that that driveshaft's u-jionts dont line up correctly no matter how i try to put it in. but the front drive shaft does and i did try that and didnt notice much of a difference, it seemed that the vibration ever so slightly lessened but not sure but eitherway it was 100% still there. this vibration by the way is pretty severe, and rattles the entire truck. thanks for anyones reply I am really stumped and NEED this resolved, zac

 

[John Smith]

Another thing is that that driveshaft's u-jionts dont line up correctly no matter how i try to put it in. but the front drive shaft does and i did try that and didnt notice much of a difference, it seemed that the vibration ever so slightly lessened but not sure but eitherway it was 100% still there. this vibration by the way is pretty severe, and rattles the entire truck. thanks for anyones reply I am really stumped and NEED this resolved, zac

Based on this it sounds like your rear drive shaft is out of phase. That would account for the vibrations. Check out this link and look at the section on "phase". Pirate4x4.Com - Extreme Four Wheel Drive

 

[zachary g]

i have just measured the drive shaft at its shortest point and that was just under 25' and the distance is just about the same lenght. could this be my problem too long of a driveshaft? i measured the front and that is a little more then 25 and a 1/2 inches. would that be why it doesnt vibrate while i have power only going to the front wheels? thanks alot, zac

 

[John Smith]

i have just measured the drive shaft at its shortest point and that was just under 25' and the distance is just about the same lenght. could this be my problem too long of a driveshaft? i measured the front and that is a little more then 25 and a 1/2 inches. would that be why it doesnt vibrate while i have power only going to the front wheels? thanks alot, zac

Your issue is that your driveshaft is not in phase. I provided you a link above explaining what phase is. Remove the rear drive shaft, separate it, and align the splines so your ujoints are in phase and your vibration issue should disappear.

In your first post you mention the output on the transfer case is loose. By this, do you mean the nut that holds the flange is loose? If so, did you tighten to spec and re-stake the nut?

 

[zachary g]

no matter which angle i put the drive shaft together it will not be in phase. i check your link and altough you are corrrect it is not in phase when i drove it in the front it made no vibration.

i did tighten the e-brake nut to spec and it tightend up well with no play.
I belive now that my driveshaft is too long and needs to be cut. i am going to do this and it will also line the DS up correctly so that it will be in phase and it wil have room to move in and out.
do you belive this vibration could be caused by the DS being too long and putting pressure an both flanges and therefor pushing the DS out from center? thank you very much for your help. zac

 

[K2KK]

Zac, I had alot of vibration a while back and it turned out to be the nut on the pinion flange in the rear diff was loose. Since I have a solid crush sleeve I just tightened it down and that fixed the problem. Are your universals in good order?

 

[zachary g]

my u-jionts are have no bad signs what so ever. Although i greatly appretiate your help i dont belive that the pinion nut is loose. I am going to check it right now. if i dont post a follow up, assume it was tight.thank you, zac

 

[Degnol]

no matter which angle i put the drive shaft together it will not be in phase.

zac

Yes, it can be aligned correctly. Don't ignore good advice.

And how in the hell did you run a rear driveshaft on the front?

 

[dargreg]

When you lowered the rig it made your DS shorter so its probably binding like you say.You have to fix the phase problem so get them to shorten it ,that has to be done anyway.

 

[zachary g]

"Yes, it can be aligned correctly. Don't ignore good advice."
I am sorry but it does NOT align. this shaft was not made right.

"And how in the **** did you run a rear driveshaft on the front?"
my front and rear are identical in everyway, might have something to do with the nimrod that put them together, zac

 

[K2KK]

Not that this is relevant in Zac's case but my front and rear dl's are within 1/4"-3/8" in length difference so I can if the situation occurs swap them. When my po did the sbc conversion it just worked out that way. Intentionally or not. It is a good thing.

 

[Mark W]

Unless you have had the DS shortened or lengthened and it was done wrong. It WILL go together correctly. This is your problem. your joints are out of phase. Debate will not change this. This IS the problem.


Mark...

 

[zachary g]

I sure hope you are right. i will have the driveshaft back today and you can bet it is going striat on, in phase . i will put an update asap.

 

[zachary g]

I have another question. how come the driveshaft worked before? And why would it start happening? I checked it several times and I hope everyone can belive me when i say they would NEVER lined up,perfectly they were always a little off. can anyone clearify to me how is possible? thank you, zac

 

[Degnol]

I have another question. how come the driveshaft worked before? And why would it start happening? I checked it several times and I hope everyone can belive me when i say they would NEVER lined up,perfectly they were always a little off. can anyone clearify to me how is possible? thank you, zac

Because the drive shaft was removed (at least partially) when you had the rear end rebuilt, the slip joint came undone and it was not put back together in phase

 

[zachary g]

but no mater which way i put the ds together it would never be in phase.