Another reason to re-gear

[Albuquerque Jim]

Most of us re-gear as a way to bring our gearing back to stock or better than stock when going to larger tires.

When I started wheeling in 2003 and went to larger tires I chose not to regear my diffs as I figured 4.30's we plenty low for what I could handle.

Over time, I modded my truck, I got more brave, I burnt a few clutches, and I decided 4.30's were not low enough for the trails I was running but they seemed like a nice compromise of fuel economy and power for the street so I added an Ultimate Crawler. I had the best of both worlds, fuel economy on the street and low-low gearing for the trail.

Well, that all sounds well and good...

October 2006, while wheeling in Moab, UT I broke 5 teeth off of my rear ring gear and destroyed the pinion (approx. 100k miles on the diff). I u-hauled home and fixed my truck with a used rear diff from a junkyard (approx. 100k miles on the diff). I actually broke the front ring and pinion too, but that's a different story.

March 2007, while wheeling in Farmington, NM I broke 3 teeth off of my ring gear. I limped home in front wheel drive (rear drive shaft removed).

http://pics.montypics.com/albuquerque_jim/2007-04-23/1177389196_p4220025.jpg

I can't figure out why I am breaking diffs...I have to build a stronger one. I am curious about Cryo-treatment. Steve at Sonoran Steel informed me that Bobby Long will Cryo gears. I call Bobby and explain the situation. He tells me that he thinks I am breaking parts due to the extreme power from the crawler and the deflection of the gears since I am running diffs with a lot of miles on them. I trust an industry legend like Bobby Long to diagnose the issue.

Long story short....if you have re-geared you have probably avoided this issue since your diff has been re-set. If you don't re-gear at least have your side bearings tightened and check your back lash to reduce the deflection caused when things wear naturally over time.

My solution

Short Term: I bought a new OEM diff, it's in and running smooth.

http://pics.montypics.com/albuquerque_jim/2007-04-23/1177389280_p4220021.jpg

Long Term: I have a set of gears a Bobby Longs getting Cryo'd. I will build a bullet proof rear diff and keep the new OEM for a spare. I am not going to miss a day of wheeling due to a broken rear diff again. :D

[AxleIke]

I think your differentials just hate you...dang man...3 diffs in six months.

Perhaps you can talk a little more about the cryo stuff. Internet buzz has been that cryo helps with shock load, but can expereience trouble with long term wear. Of course, that is the net...What did you find out from bobby?

[olharleyman]

I asked my friend (a Machinist) about cryo and he told me that unless your going to do serious wheeling its not worth it but if you do hard core then getting all the air pockets out(cryo rearranges the moliques forcing the air out of the metal there for strengthening the metal as much as 4 times what it when you get them from suppler drop the part into a vat to like -320 and then slowly brings it back to normal temp thus forcing all air out of metal and hardens metal) is very worth it.

[AxleIke]

Jim does serious wheeling, and wheels his junk really hard...not to mention the torque multiplication from his crawler alone behind the 3.4, thats enough to kill gears on a dirt road.

I think the cryo is an excellent way to go for what he's doing, i'm just asking about long term wear, since he spoke to people who actually do cryo, and all i have to go from is the idiot internet hype.

[Albuquerque Jim]

Bobby Long suggested to just cryo the rear gears. This will align the molecules and make them stronger.

For a front application he recommends cryo then heat treating. The heat treating will soften them a bit and make the gears handle shock loads better. This is not suggested for a DD in the rear because it may cause the gears to wear faster.

[00Runner]

Here is some relevant info I was given by a reputable shop that installed my front ARB. This is in regards to a front IFS diff, though.

They said that they see a number of busted gears in the front IFS diffs of Toyotas that are locked. They said the cause is the diff housing. It isn't strong enough to keep the gears from deflecting under the added torque from being locked up. The front diff lacks any cast ribs that add strength like the rear v6 diffs have. With such a flexible housing, under torque the gears deflect putting the stress on the thinner outside surface of the teeth in the ring and pinion resulting in breakage.

[Albuquerque Jim]

I support that perspective. It's basically the same concept as what has happened to my rear diffs, but a different cause. This could have been the actual cause of my front ring and pinion failure as well. I wonder if there is any way to beef up the front housing?

[AxleIke]

ahh, hadn't thought about that, though not really something i ever need to worry about.

you guys with the 3.4s and gearing i can see the housing flexing easy. I'm sure there is a way to beef it up, but it would require a pretty good knowledge of where the housing actually flexes, and them some careful welds so that the integrity of the metal isn't jeapordized. Could be a very cool mod though.

[Albuquerque Jim]

I would bet the shallow half flexes the most due to less mass of steel. I will have to look at my front diff and see if there is a way to gusset it.

[AxleIke]

I also forgot that you guys have the clamshell type. I was trying to figure out what you were talking about until i realized we have totally different diffs. My bad. I understand now.

[SteveO]

Wow, that sucks.

Before I put gears into my front diff (during the SAS), I sent my gears off Bobby to have my cryoed as well. They have been doing great thus far.

[MTL_4runner]

I asked my friend (a Machinist) about cryo and he told me that unless your going to do serious wheeling its not worth it but if you do hard core then getting all the air pockets out(cryo rearranges the moliques forcing the air out of the metal there for strengthening the metal as much as 4 times what it when you get them from suppler drop the part into a vat to like -320 and then slowly brings it back to normal temp thus forcing all air out of metal and hardens metal) is very worth it.


Just to be clear, there aren't really any air spaces in the metal instead there are micro voids (on an atomic level.....so small one molecule of air could not even fit in) which when too large, may weaken the steel (this is why iron is brittle and steel is tough.....the carbon atoms present in the steel structure lock each other in place). What cryogenic treating does is to transform the steel structure itself by nearly eliminating the atomic voids thereby eliminating the weaker points in the structure. These voids actually cause areas of high stress (ie failure points) so by removing most of the voids you lower the internal stresses of the part and the likelyhood it will fail in use. The removal of the voids essentially locks the crystaline struture of the steel together and makes it more uniform. The cooling of the parts down to near absolute zero actually slows down the molecules themselves and allows them to move closer together thereby having the effect of organizing the crystal structure (locking mechanism) of the steel. The harder the steel is on the surface, the more critical it is to retain toughness internally. In the case of something like gears where you need both (surface hardness for wear longevity and part toughness for resiliency and resistance to torque loading), this can make a dramatic difference in when failures might occur.

Here's some good articles on the subject:
http://lennon.csufresno.edu/~rlk16/cryo.html
http://www.gocryo.fr/technicals.php?page=3