lobukbuild

do you or have you run a locker in an ifs? ive never broke at the diff just at the outer cv both sides almost at the same time. this happened twice after about an hour of moderate with small obsticles kind of trail riding. (two sets of axles) i believe ive got it narrowed down to a steering problem (wheel turning to far exceeding cv limit) i made a bunch of changes on my truck at once. one idea turned into another and so on. a diff diff, 488s, locker, bj spacers, diff drop, etc. once i started breaking cvs i didnt know where to look first and started prematurly blaming the locker.

MudHippy

Who me? Hell no. I ain't that dumb.

I did weld my front diff once upon a time. That lasted a grand total of one half-ass wheeling trip. One of the least fun wheeling trips ever. Ummm...no good. This is no good AT ALL! WTF?! Where's all this extra traction I'm supposed to have? And why the hell is my steering wheel refusing to turn for me? What stupid ass retarded thing have I went and done now? Grrr. I'm going home and undoing this nonsense ASAP!!!

But hey, if you can put up with that. And it still seems like fun to you. Go for it.

And, yes. It's mostly the steering thing breaking the CVs. Plain and simple. Or you'd be snapping that stub shaft first. Like I keep saying.

lobukbuild

welded front is a little tuff, an actual locker is more forgiving but not as much as a limited slip. i thru this locker in just cuz i had it around in the parts bin and said wth ill give it try since i was changing the diff out any way. thats when i noticed a lot of wobble on the stub. fixed that. then found a set of bj spacers while looking for the locker and thru them in then built a diff drop etc etc classic case of snowballing.anyway ive been snapping cvs ever since. seems that the issue might be a broken steering stop on the lower control arm.all other angle appear to be within its limits.

RJR

Well, here's some fun with numbers. No new conclusions here, just some engineering backup to what we already know.
- The 3vz makes 180 ft-lbs of torque. Multiply that by a 45:1 crawl ratio and you have about 8000 ft-lbs available at the axles.
- Pulling some formulas from the ASME handbook and doing some digging on the shear strength of axle steels, it looks like the 1.1" diameter Toyoto front drive axle is good for about 2500 ft-lbs of torque before failure. If they used absolutely top of the line steel, that could go up to 3500 ft-lbs, but that's not likely. Either way, there's plenty of engine torque to twist off an axle.

- Fortunately, tire traction limits how much torque gets applied before the wheel starts spinning and saves the hardware. If we assume dry rock or pavement, with a fairly high coefficient of friction of .7, 31-inch tires, 2500 lb front-end weight evenly distributed on both wheels, and an open diff, one of the front wheels will start spinning when torque hits about 1100 ft-lbs, well within the axle capability. Put in a locker and put all the weight on one wheel, and now the torque goes to 2200 ft-lbs before slippage occurs. Bump up to 37 inch tires and you reach 2700 ft-lbs, a definite danger zone.

- That doesn't mean that anytime you lift a front wheel on bare rock that you're going to snap an axle. Generally, unless you're chained to a stump, the vehicle will start moving long before you reach those torque levels. Most of the time our trails don't give us that much traction, and if you're going up a steep hill, the weight over the front wheels is less, causing them to slip sooner. So, a lot of factors can work in our favor. But, wedge a wheel between two rocks where it has to climb straight up, and pour on the power, and it's probably going to pop.

None of this addresses the other weaknesses of either the CV joints when turned sharply, or the stub shaft that MudHippy has pointed out. Those are limitations that further reduce strength, but are beyond my information resources to be able to calculate any numbers.

Changing the subject slightly, my experience with my Aussie locker on trails has been very positive. Steering issues are almost unnoticeable, and turning radius on switchbacks is relatively unaffected. It's been much more civilized than I was prepared to expect. These are gravel/dirt trails, with plenty of opportunity for wheel slippage. I suspect that driving on dry slick-rock might be quite a bit more difficult. I'm seriously considering twin-sticking the transfer case so I can drop out of 4wd but maintain low range when necessary.

lobukbuild

thanks, kinda makes you look at things in a different way when you bring the math out. would of preferred to lock the rear n leave frt open but i used what i had on hand. not sure if i can even get a locker to fit the rear that im using. its a special app factory diff with factory 4.88s, the rear carrier is almost a solid case with 6 internal gears (spider) with enough drag that it acts slightly like a lsd.

MudHippy

3.83(1st gear R150F) x 2.56(VF1A 4 Low) x 4.88(Differential) = ~47.85:1 x 180 ft.lbs. = ~8613 ft.lbs.(closer to 9000 ft.lbs. than 8000 ft.lbs.)
1. Sure you can. Not a problem.
2. Because that's a standard V6/Turbo diff. with 4-pinions(spider) and 2 side gears(not spider).
3. No, not quite. Very much still an open diff. Not even close to enough drag to make any noticeable traction difference compared to any other open diff.

One more thing. You didn't extend the upper control arm bumpstops to accomodate for the BJSs? Then there's part of the problem too. Wanting extra suspension travel from installing ball joint spacers? Not a good plan(even with a diff drop). They are really only good for one of two things. Lifting while keeping the torsion bars at their original setting. Or relaxing the torsion bars while leaving the ride height at its original setting.

RJR

I based my calculations on a 4.56 rear-end. I should have stated that. The ability to over stress the axles goes up with higher ratios, for sure.

lobukbuild

1, can i still use the same carrier with a locker? (lunch box type) 2.yes thats the diff i used but with factory 4.88s (towing package and 31" tire package v6 non turbo is the trk it came from) 3. maybe not intended to act like a lsd but it spins both rear tires alot more than my old diff did. i figured more spiders and moving parts was possibly the reason. ya maybe compsring to a lsd was a reach but you get my drift. i do realize it is an open diff and is usless once you fift one tire but on the flat stuff its pretty impressive.

Gevo

I know, I know epic old post revival. I couldn't help myself though. I had to show my appreciation of RJRs math approach. The engineer in me had a gigantic smile through this read.

Was just doing some research before I install my locker in the ifs diff when I came across this thread.