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New 4.56s... Break in time?

B

btfury

NAXJA Forum User
Location
AR
My Jeep is currently in the shop getting some new Precision 4.56s installed, and I've got a couple questions about the break in time on them.

I've heard that you're supposed to drive 15-20 miles and then let the axles cool completely, and then drive normally and change the diff fluid after 500 miles...

Well unfortunately the timing of this didn't work out too well, and I'll get the Jeep back on Tuesday and then have to head back to school on Thursday. The drive is about 445 miles, so I'm guessing by the time I get there the new gears will have over 500 miles on them. I'll definitely drive it the fifteen or 20 miles when I get it back from the shop and then let them cool completely...

If I change the fluid when I get there is this going to be a big deal? Will I be ok on the highway even though the gears are so new? Any advice would be appreciated...
 
Then you should be fine. If you drive them around the 15-20 miles after you get the jeep back. Let it sit for as long as you can, then drive it to school and change the diff fluid there, if that is an option.
 
Why don't you record your miles, and then pull over at a rest stop or a car parts place on the way and change the fluid then at 500 miles to be safe.
 
Begster said:
Why don't you record your miles, and then pull over at a rest stop or a car parts place on the way and change the fluid then at 500 miles to be safe.
Click to expand...

That's a good idea. Now the only issue with that is how long am I supposed to wait to let the RTV seal before driving again?
 
That's a good idea. Now the only issue with that is how long am I supposed to wait to let the RTV seal before driving again?
===================================================
Read the tube.
Almost 0. dried spit will hold back 90W.
 
Empty the diff, clean it, seal it , tighten the bolts, get something to eat, fill with 90w and hit the road!

No lubelockers needed.
 
Is 50-100 miles really going to make that big of a difference? I mean, is it that necessary to do it on the road?
 
It's better safe than sorry, I'd pull over.

reelbigdundy87 said:
No lubelockers needed.
Click to expand...

While I've never ACTUALLY used them, from everyone I've heard they're that much easier to use(read = no mess and reusable and they can't be pinched out) and they were glad they paid the 30 bucks for front/rear together. I plan on getting them as it seems a good enough theory for me.

Sure they're not necessary but a cheap convenience to me...

Back on topic!
 
Last edited:
gaskets with silicone beads on them (vs "normal" fiber-only gaskets)

If you could drive back from the shop, cool it down, then do one more bit of local driving 15-20 or so, cool it down again (then drain & refill before the trip) that would work best...

I think as long as you give it one or two heat cycles before the trip, you should be fine... drain/change when you get to school. Just don't forget to do it!
 
I wait 15 minuts after siting the cover back on before I put in the oil and usuley wait a little while longer to drive. I also do other things to the jeep while chainging the dif fluids. and they are the first to be worked on and last to be finished up.

I had a simular situation where I got the gears done then had to make a 560 mile drive while towing and I did not run into any problems. Just take it easy and when you stop for gas it would not hurt to let the gears cool for a while.
 
woody said:
gaskets with silicone beads on them (vs "normal" fiber-only gaskets)

If you could drive back from the shop, cool it down, then do one more bit of local driving 15-20 or so, cool it down again (then drain & refill before the trip) that would work best...

I think as long as you give it one or two heat cycles before the trip, you should be fine... drain/change when you get to school. Just don't forget to do it!
Click to expand...


Yeah that's definitely doable... How long does it take the gears to completely cool? And When you say drain and refill, I'm assuming you mean refill with new gear oil... right?
 
If it's hot outside, they'll be a long time to get cool... Overnight even?

When I broke my gears in, I filled it with regular gear oil, ran it for 15-20 min up on stands twice, with maybe an hour cooldown (warm to touch was all I'd get at 90* day outside) after each run. Then tossed the wheels on and went for a 25 mile +- ride...varying between coast and load and not going more than 45-50.

Then after it cooled from that, I drained the dino-juice out and refilled with Mobil-1 synthetic gear oil... done & done. The original oil was very shiny - lots of metallic particles in suspension... glad i got it out of there.
 
Do car manufacturers break in the diff fluids on all new axles before installing them into new cars, cause if not, one can argue........(not trying to start an argument, just food for thought).
 
btfury said:
And When you say drain and refill, I'm assuming you mean refill with new gear oil... right?
Click to expand...

yep, deffinitely do new gear oil on the refill. the purpose is to remove pieces of metel that becomes suspended in the oil. its the fine pieces that rub off durring the break in process.

i have seen a set of bearings on an axle where it didnt look like the gear oil had ever been changed in its life. the bearing races were shot- deeply pitted and grooved. the rollers were not much better.
 
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