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Overfilled X-Case & Friction Modifier

Island XJ

NAXJA Forum User
Two quick questions. My searches yielded nothing. I want to know, is there any danger in overfilling your transfer case? My manual says 1.2 litres, but since my driveway is so steep and the fluid settles when the jeep is parked, i can actually get 1.5 litres in the case. Is there a contraindication to doing this? (ie might it screw something up?). I would think extra fluid is extra lubricant and extra cooling and therefore is a good thing.. am i wrong here?

And the other question, my front diff does not have a limited slip but my rear does, will it harm my front diff if i use friction modifier in the gear oil? I have a large bucket of synthetic gear oil that has friction modifier premixed into it. I know i can use it in the rear diff with my limited slip, but how about the front?

Thanks in advance,
Island XJ
 
First off don't add too much to the t-case fill it on a level surface and remember the factory specs were made for a reason. Overfilling can lead to foaming and thats not good. Secondaly yes you can use gear lube with friction modifier in a non-limited slip diff so it is safe to use all around.
 
jeepguy97 said:
First off don't add too much to the t-case fill it on a level surface and remember the factory specs were made for a reason. Overfilling can lead to foaming and thats not good. Secondaly yes you can use gear lube with friction modifier in a non-limited slip diff so it is safe to use all around.

Good to know I can use FM in my diffs.

Foaming isn't good, that is right, but it seems to me that in order to produce foam i would need to add considerably more than another 300mls, which is all the extra I can get into the case right now. I know factory specs are made for a reason, but i have enough engineering experience to know that what is printed is not necessarily what is best for a component, specs can be set up for a number of reasons other than because it is best for a component. What i want to know specifically is, are there any contraindications to adding another 300mls? (Other than foaming?)
 
Ok I'll try to make it simple my 4.0 can probably hold 7 quarts of oil but it only calls for six, only needs six, and will probably overflow if over filled, why would you want to add more than necessary.
 
I routinely overfill my 231 since it leaks a bit past the rear output seal... Not a ton extra, just 3-4 pumps on the dispenser and some of that escapes before I can thread in the plug.

A little extra isn't ALWAYS a bad thing.
 
Well, seeing as how the instructions to refill the TC do not incude 'attach the trailer hitch to an engine hoist and raise the rear bumper to waist height' I think I would fill it on a level surface in which case you need quick hands to get that plug in before the overfill runs out :D . The TC does have a pump in it, the fluid does not just lay in there and splash lube the components. I think that if you overfilled it too much it might come out the breather valve on the firewall or could cause over pressue in the TC and force a leak past the seals. Never really thought about it before. I probably get a bit more than is called for in mine, depends on which way I parked in the driveway, I also tend to overfill it a bit because I have the underbody lube option that seeps enough fluid out the rear output that I get no rust under that area and generally keep things well lubed in that area. :D
 
where do the breathers come out at? i can see where the axle end is, but other than that...??
 
Island XJ said:
Thanks guys, I didn't think it was going to adversely affect it simply by adding 8 1/3% more fluid. Although I guess i should lower my hi-lift before i fill it. :)

0.3 / 1.2 is 25%, not 8-1/3%
 
small pederson said:
where do the breathers come out at? i can see where the axle end is, but other than that...??

Look on the firewall, passenger side on my 98, little white doohicky behind the valve cover kinda. :D
 
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