BigCountry96

1. Does anyone know the approx. break-in milage for a set of used 3.55 gears in a new wear pattern, with all new bearings in the rear end, it's a chrysler 8.25, not sure that makes any difference but just thought I'd let everyone know so people don't ask.

2. Ok so theres a story behind why I had to rebuild my rear end that I will tell before I ask the second question. So my friend and I are driving down the road in my 96 XJ, we hear a faint clunk followed by my MPH reducing, thinking its nothing more than the trans hic-upping, I give it a little more gas and it picks back up to speed. There is already snow pack in the wheels so there was a slight vibration in the steering, but about 2 miles farther down the road it gets really bad, and a guy pulls up next to us(4 lane divided highway) and says, "Hey man your trucks on fire!" so I quickly pull over to the side of the road and shut it off, not knowing if its the fuel lines or what! We started throwing hand fulls of snow towards the flames and eventually it went out with lots of hissing, we can tell it's not the fuel, but something is wrong, so we get back in and limp it up the shoulder doing 10mph for 3 miles to his brothers house, to let it sit till we can get a trailer to drag it back to my place and look at it. So the problem was the pinion seal went bad and lots of dirt and what not got up in the outer pinion bearing and ruined that, causing my pinion to bend at about a 20 degree angle. It was spewing gear lube everywhere when we were driving and the muffler being covered in it decided to light itself up. But it's all back together now, and running good so far!(knock on simulated wood grain dash!) Now here comes the question, all input will be appreciated, My buddy, who is pretty handy with vehicles, his older brother, and their dad who was a ford mechanic for over 12 years, seem to think that the pinion bent from drive-train stress from me using 4Full-Time(I have the NP242) too much! They say driving around in 4Full-Time on dry pavement and what not is too hard on it! I have read up on that t-case before i bought the jeep, and have been told by others, the 4Full-Time function on the NP242 is just like having a vehicle with all wheel drive, that it is safe to drive in, in any conditions, even up to speeds of 75+(if your jeep can get that high, lol, I don't know if mine can anymore) and you should never have a problem! Now I don't go cruising around all summer long in 4Full-Time, but as soon as the first snow fall hits here i put it in and leave it in till i think the roads are decent enough. I would like your thoughts on this, did driving around in 4Full-Time too often put too much stress on my rear end and cause it to go out? I remind you that my 1996 XJ had 161,XXXmiles on it and those were the stock gears bearings and seal in it before they went out.
All opinions greatly appreciated!

a1racer

where you using awd or 4 hi if it was 4 high that was probably what did you in i thought the 242 or what ever it was only had awd then 4high and 4low. and i can take approx 500 to 1000 miles to break in gears.

BigCountry96

no the NP249 is the one that is 4awd then 4Low, which i believe is only in a select year range of some grands, like 97 - 01 or something

i have the NP242 and i have 2WD, 4Part-Time, which is said to be more for driving in really snowy conditions, 4Full-Time which from what i read is supposed to be just like AWD cus the t-case doesnt lock in all the way, its kinda like an open rear end, when the rear starts to slip and lose traction it transfers a portion of the power to the front to help pull, like if you were in snow or on ice or something, then i have my good 'ol 4Low that everyone can say has saved their butts a few times, lol

the NP231 is the standard kinda t-case that most vehicles have with its 2WD, 4High, 4Low

whowey

Wow... another Ford mechanic that knows nothing about Jeeps.... Remember these are the people that tried to tell us that push-button 4wd was better....

The 242 can safely be used in 4wd full-time on dry pavement. You do not want to use either of the part time settings on dry pavement. The center axle differential allows for the needed 'slippage' to allow safe operation on the highway.

I used my 242 the same way you do. When the roads are mixed conditions, just put it in and go... It was great for my wife... no more calls about when to use the 4wd...

I don't know how long it would take a used set of gears to wear into a new pattern.

finneys98xj

Wrong uncle has that transfer case in his 94 GC.

BigCountry96

i said or something like that

and thank you whowey

mike37

now way any of that was from driving in full time 4x4
it was the lack of lubrication from the bad pinion seal that caused it all

BigCountry96

well i guess i should state we don't know for sure that the seal was junk, that is just what we assumed happened, we had to cut the pinion with a torch to get it out of the housing and in the process cooked the bearing like KFC, so there was no way to tell if the bearing was bad, but before we started cutting it did spin in the housing fairly freely, it only got hung up on one spot where the pinion yoke was rubbing against the axle housing because the pinion was bent, so we really dont know which came first, did a bad seal and bearing cause the pinion to bend under load, or did the pinion some how bend and crush the bearing and seal?

mike37

well the pinion was not bent when you were driving cus it would have
vibrated you off the road
and being in 4x4 did not cause any of this
the thing that can cause a fire heat and combustible/oil

my bet is at some point you wrecked the pinion seal
oil started to leak out
at some point the oil was to low to lubricate the pinion
that caused heat then fire

BigCountry96

Thank you for your opinion!

and I thought 5000 miles was about right, but someone told me it could be as much as 30,000, for breaking in the rear end.

knobturner75

There's probably no way to tell for sure now since there was a nice cleansing fire, but I know someone that had a similar situation. I don't know if there was a fire or not, but they had to replace the bearing and seal in their rear end. What happened was, the owner was driving her Chevy truck down the road. A Wal-Mart sack blew across the road in front of her. She drove over it like most people would. When she did, the sack attached it self to the spinning drive shaft. It then worked itself into the seal area frying the seal and bearing. All over a piece of trash blowing around.

XJ?2010

I use my full time just like you i have never had a problem

SeattleCrwlr

I have also heard of contaminants in the oil breaking it down will cause exessive heat which will break down the seal as well(water especially), might want to check breather!!

just a thought.