Broken pinion shaft

[MolallaCruiser]

Went out wheeling yesterday and snapped my rear pinion shaft in half at the front splines. I was articulating a bit with the rear (approx 1') and going up a steep short climb to a bypass started to spin, backed about 2 feet took another run at it and then POP. Fairly certain I was just to heavy on the right pedal but was curious if anyone had other ideas for other things that might have caused it? I was kind of thinking axle wrap binding a u joint but i guess that would have broke something on transfer case side not axle side. Curious if there is something else I should address after I swap the third member. My rig setup is currently 383 SBC 4 speed 3.73 gears 32" all terrains SOA. I know its quite a bit more power than it came with but with 32's and stock gears didn't think I'd break there.

 

[Spike Strip]

"383 SBC" --- 'nuf said.

 

[MolallaCruiser]

Well did a bit more searching and axle wrap seems the likely culprit. Looks like a ladder bar setup is in my future.

 

[Dynosoar]

SOA with out an anti wrap bar is the culprit.


Dynosoar

 

[vipergrhd]

Pics?

I'm curious on how it breaks,do you mean the shaft and not the gears? I've never seen the shaft breaks on any diff yet,pics please.

 

[weak-link]

SOA with out an anti wrap bar is the culprit.
Dynosoar

X2 SOA+anti-anti wrap=two piece pinion

I'm curious on how it breaks,do you mean the shaft and not the gears? I've never seen the shaft breaks on any diff yet,pics please.

Really? A snapped pinion is like in the top 5 of trail fix's in a land cruiser, Just below a birfield.
The shaft snaps at the splines of the pinion. The land cruiser's achilles is the pinion. Rear's snap more then fronts but they both bring the suck.

 

[Mace]

. Rear's snap more then fronts but they both bring the suck.

Side note, the rear snaps more than the front because of traction as opposed to any design differences between the two diffs. The front and rear pinions are identical (unless something is screwed up).

 

[Radd Cruisers]

U-joint bind due to axle wrap is the #1 killer of pinion shafts.

If you did this to your front end, I would bet that you have not done a (proper) C&T.

~John

 

[Bret]

Looks like this I bet??? Same deal 383 with a little skinny pedal but with 4"SUA in a 40, doing a wrap bar now.

 

[MolallaCruiser]

Sorry no pics till saturday rigs 45 minutes away. Little different than brets, virtually no damage to the splines themselves more of a clean cut. Research paid off again as I figured out I can pull the pinion shaft next time and not have to drag my car dolly down a trail I have one free 4.11 third member so probably just going to change to a couple of those until I have enough $$ to re-gear. Anyone know through what year I can swap out a rear from the newer cruisers? Also for the older 40 series, 78+ should be fine spline and swap right in correct? Last question, is there anything that can be done to prevent the front from snapping? Thanks for the info

 

[Poser]

I have one free 4.11 third member so probably just going to change to a couple of those until I have enough $$ to re-gear. Anyone know through what year I can swap out a rear from the newer cruisers? Also for the older 40 series, 78+ should be fine spline and swap right in correct?

You do not indicate what year your truck is.

Newer Cruisers?

62 series front and rear would be 4.10/1. 80 series REAR non electrical locking differential would also be 4.10 and compatible with your rear axle. 1978 was the only year that the 40/55 series had a fine spline pinion with 4.11 gears. In 1979, they switched to 3.70.

08/84 and later companion flanges used the larger bolt pattern and would need to be re-drilled or swapped to be compatible with the 01/74-07/84 companion flange bolt pattern. You could swap the flange or source the female part of the slip and stub on the drive shaft for the other pattern, and then flip the drive shafts end for end if this is an issue.

Last question, is there anything that can be done to prevent the front from snapping? Thanks for the info

Control axle wrap. If you do not do that, you will twist off any pinion; Dana 60/70/80, 14-bolt, 9” does not matter. Bind up the joint at the diff and you will destroy the pinion every time, without fail.

 

[MolallaCruiser]

Thanks for the info poser, sorry its an 81 fj60. I better double check the third member I have is 4.11 not 3.70. Its fine spline and pulled from a stock fj40 but not sure of the year. I understand I need to control the axle wrap so installing ladder bar in rear, but was curious if there is anything that needs to be done so that I don't snap the pinion on the front aswell. Good info one the flange bolt pattern being different, I'll make sure and keep the one I have now.

 

[Kurtis]

What type of driveshaft are you running? I've got a 5.7 auto SOA 35s no anti rap bar but I do run a high angle long travel cv driveshaft front and rear. I've wheeled it pretty hard without trouble. I'll probably still run a rap bar someday but the pinion can rotate a long long way before ever coming close to binding. I want to say its a 45 degree shaft. You might want flex out your truck and see how close the driveshaft you have is coming to binding without axle rap.

If you used the stock shaft that is probably not very far making a trac bar extra important. You may want to clearance the shaft a little as well.