front drive shaft break? why would this happen???

[72k5junky]

the 4 bolts that hold the drive shaft to the cv joint (which then conects to the trans case) sheared off. it is a corporate 10 bolt with automatic locking hubs (setup is out of 86 suburban but now is in 71 k5). i was backing up in a cement parking lot with the wheels at full turn when snap the 4 bolts let go, breaking in half.
-my question is: i wasnt in 4wheel drive, so there shouldnt have been any power goin to the front wheels so why would the bolts snap?

-does the t-case still send some kind of power to the front diff even when in 2wheel high?

-i am lost in trying to gigure out what made this happen and how i can fix it so it wont happen again...any input would be great thanx

 

[big83chevy4x4]

is the tcase have the flange type front output? if so most likely the bolts were not tight. also the auto locking hubs, when they have some miles on them, do what they want whenever they want. so it may have been locked in.

 

[blazerpro79]

if the bolts were lose, driving creates vibration, and overtime it can shear the bolts off...

when you drive, the front shaft does spin though, just no power is transfers to them.

 

[blazin_blazer]

what????

if the bolts were lose, driving creates vibration, and overtime it can shear the bolts off...

when you drive, the front shaft does spin though, just no power is transfers to them.

when in 2wd and front hubs are unlocked the front drive shaft shouldn't turn!

 

[Roz]

mine in 2wd and hubs not locked i can spin free by hand- should not be engaged at either end


i vote for the auto lock screwy.

 

[ntsqd]

when in 2wd and front hubs are unlocked the front drive shaft shouldn't turn!

It can though if there's enough drag in the locking hubs. Usually doesn't turn at wheel speed, but it will turn slowly.

I had those same bolts work loose. I put longer G8's in and ran nylox down on the back side of the flange.

 

[nvrenuf]

The front shaft can indeed turn even while in 2wd with the hubs unlocked. It wont turn at the same rate as the rear but it will turn, I believe fluid current in the t-case is the reason.

is the tcase have the flange type front output? if so most likely the bolts were not tight. also the auto locking hubs, when they have some miles on them, do what they want whenever they want. so it may have been locked in.

I agree with big83; loose bolts + auto hubs = who knows what can/will happen.

I would get some 8 grade replacements for the driveshaft, manual locking hubs and not worry about it anymore.

 

[Roz]

it wont turn unless with force- unless u are in need of a serious lube job or lockers messed up

 

[Pookster]

mine doesnt turn at all. Heck, for a few weeks, I had it hanging there with some wire when I had to get my exhaust redone

 

[az-k5]

it wont turn unless with force- unless u are in need of a serious lube job or lockers messed up

Force from parastatic drag induced by circulating fluid. If everything is in good working order the swirling fluid in the t-case is enough to spin the shaft. It won't go much past idle speeds, but it will spin.

 

[blazin_blazer]

it will spin but...

not with enuff force to break 4 bolts and if auto lockers did lock up due to failure it should still just free wheel at transfercase...and by the way if ur using a bolt that has a shear facter(sideways force on bolt) to it as in this case it is best to use grade 5 bolts when the bolt is used for clamping two pieces together(pressure straight between head and nut) then use grade 8....this because the 5 is more mallable and the 8 is so hard in shear preasure is applied it will snap where thea grade 5 will strech awile before braking and before you ask or make smart remarks...yes i am a mech engineer

 

[az-k5]

and by the way if ur using a bolt that has a shear facter(sideways force on bolt) to it as in this case it is best to use grade 5 bolts when the bolt is used for clamping two pieces together(pressure straight between head and nut) then use grade 8....this because the 5 is more mallable and the 8 is so hard in shear preasure is applied it will snap where thea grade 5 will strech awile before braking and before you ask or make smart remarks...yes i am a mech engineer

Did your old wife say that?? Cause that is what it is, and old wives tale.

I am studying to be a mechanical engineer, and fasteners is a pet project of mine. This has been argued many times over, a grade 5 will completely fail, shear, snap, break, bend, explode, long before the grade 8 gets to its failure point. It is true that sometimes that the grade 5 will bend and let you know it is failed without breaking, but that is long before a grade 8 would even flinch. Look on PBB, there are some long threads with some actual test info from multiple sources.

 

[blazin_blazer]

times a changing

when i got my degree sum 12 yrs ago that was a law to live by....as rockwell hardness goes up so does its shear strength go down..proportionally..the 8 is definitly stronger but that is what we were taught...they've changed this now? what is pbb i would like to read these threads if i'm wrong i'm not the type to argue a point to try and seem right...i would rather sum1 correct me and tell me why i am wrong...i call it learning thanx but tell me what this place is i can read about the factors and specs..you know they just proved that 1 of our known laws of physics is wrong also! so i'm open to knowledge always..oh the law all of our physics is based upon light being a constant, and they just learned recently that it is not so, that light does indeed slow down after a certain distance and continues to decelerate after it starts slowing...i wonder if it ever completly stops like run out of energy and cease to be anything?

 

[3rdshiftdesign]

Proof.

 

[Roz]

oop, i ment it wont turn with any force behind it if unlocked. it should be easily stopped

 

[az-k5]

oop, i ment it wont turn with any force behind it if unlocked. it should be easily stopped

Very true, I agree.