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Unread 03-30-2015, 10:37 AM   #1
niero
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1997 ZJ 
 
Join Date: Jun 2012
Location: Minneapolis, MN
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Diff Oil Change, Open Diff/Limited Slip

I'm getting ready to change the diff oil, starting w/ the rear. I've been reading through the loads of threads on it, but I'm seeing conflicting info, and wanted to clarify. Current plan is for 75.90 in front, 75.140 in rear.
1997 Jeep GC Laredo Tsi, inline 6, fulltime 4WD, NP242


Friction Modifier
Will adding an FMA to an open diff hurt anything, or cause slippage?

I'm still working on figuring out for certain whether I have an open or limited slip. The current rear end was from a salvage yard, had 110K on it when I bought it. It was installed about 2.5 years ago. It's been working great, but I want to change fluid since I can't remember if I've done it since getting the new axle/diff.


Oil Weight
Will 75-140 hurt anything if in a diff that doesn't see heavy tow/offroad use?
I'd like some extra protection to make this rear end go as far as I can. It already had 110K on it when purchased.

I've heard only 75-90 unless you tow or do off road, then 75-140, and I've read the opposite. I drive a lot of 1-2 mile trips in city stop&go, dry pavement, with occasional hwy miles.
I only use 2wd and Full Time 4WD.
FT4 a lot in winter, but will also run it on dry pavement in summer (if it was rainy and I forget to switch to 2D) sometimes FT4 in a ditch or farm field.
I had a ton of issues w/ the diff grinding when I bought the Jeep, replaced the rear end, all has been great for 2+ years. I figure 75-140 would give extra protection and extend this diff for as long as I can.


Tire Effect
Do the tires play into heavier or lighter wear on a diff? I run winter tires year round. Does the softer/grippier rubber change the stress dynamics on the gearing, esp. w/ the 1-2 mile stop/go/stop/go on dry pave?


Cleaning
Should I spray brake cleaner on the gears to clean them?


Still need jack stands, wheel blocks, and another pump before I can do it.
Thanks in advance if you're able to respond.

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1997 Jeep GC Laredo Tsi / 4.0 I6 / 182K miles on engine, 221,320K on Jeep / d. oil 10w30 + MMO
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Unread 03-30-2015, 10:46 AM   #2
PolkaPower
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Adding FM will not hurt it but it's better to have more oil instead of the FM taking up space. It's only function is to keep the track lock from making a bunch of noise by letting the clutches slip more in normal driving.
You will know if you have a limited slip or not when you open up the diff. It's painfully obvious. The open carrier is rounded and the track lock is more square.
You can use the brake cleaner but spraying off the gears isn't necessary unless you find a bunch of material inside. I'd just lightly spray inside and wipe out with a rag.

Larger tire = more stress
More torque =more stress
screen-shot-2015-03-30-6.43.25-pm.jpg  
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Unread 03-30-2015, 11:08 AM   #3
niero
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Awesome, thanks PolkaPower. Had no idea the diffs were different shapes.

Oh, and for the gasket, should I be using this stuff?
http://www.amazon.com/Permatex-81182...x+RTV+silicone

Thanks.
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Unread 03-30-2015, 04:03 PM   #4
PolkaPower
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The diffs are the same shape. It's the insides that look different. with a LSD and open. Once you get the cover plate off it will be obvious.

I never used RTV from the tube. It's a pain and takes time. If you use RRV use the squirt can and let it sit for about 15-20 minutes before you bolt it back. You don't have to but it's better if you have time. Permatex is good stuff.

I always just squirted it on and bolted it up. Never had any leaks. SScraping the gasket is kind of a pain or meditation lol.
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Unread 03-31-2015, 07:44 AM   #5
niero
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Thanks, guys. A lot of the videos on youtube show a blue gasket seal that you draw around the holes. Does that type of gasket just come off w/ a plastic scraper, like the vids, or is a serious pita?

Thanks.
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Unread 03-31-2015, 07:50 AM   #6
niero
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Quote:
Originally Posted by PolkaPower View Post
If you use RRV use the squirt can ...
I always just squirted it on and bolted it up. Never had any leaks. SScraping the gasket is kind of a pain or meditation lol.
Is RRV something else, or did you mean RTV?
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Unread 03-31-2015, 08:03 AM   #7
PolkaPower
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Quote:
Originally Posted by niero View Post
Is RRV something else, or did you mean RTV?
I meant RTV. Just any oil resistant RTV/gasket maker will do. Doesn't matter the color. TRV comes off with a scraper. Sometimes it's a pain sometimes it's not. Kind of messy either way.

You can also get re usable gaskets.

Try not to over think this, it's very basic. Should take about 20 minutes, longer if you let the RTV set.
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Unread 03-31-2015, 08:27 AM   #8
niero
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Okay, cool. I think I'll stick w/ RTV since I'm familiar with it vs. other methods.

I agree about not over thinking. Just started working on Jeep on my own and want to avoid stupid mistakes


A little off topic, but I'd like to throw a couple things in back just to have in case of emergency. Ruptured hose, brake line leak, or etc.

Is there anything you keep in your Jeeps for an "oh sh&*" moment?
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Unread 03-31-2015, 08:36 AM   #9
PolkaPower
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Yea, AAA card, a set of tools. If you have known leaks then keep a bottle of whatever is leaking handy.
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Unread 03-31-2015, 09:10 AM   #10
niero
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AAA is always good backup. I know I have a minor brake leak somewhere. Shop said it's very small. Any DOT 3 or is it DOT 4?

In addition to some Gorilla Tape, I'm thinking some kind of hi temp silicone sealant would be good. I'm sure almost anything would do, like these:
http://www.amazon.com/s?ie=UTF8&page...rtv%20silicone

Is there anything like that you would say NOT to use?
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Unread 03-31-2015, 09:21 AM   #11
PolkaPower
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I always used Right Stuff or Ultra Black in the squirt tube. The squeeze tubes are a pain.
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Unread 03-31-2015, 09:47 AM   #12
niero
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Cool, thanks. I'll keep an eye for them.
Thanks for your help
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Unread 03-31-2015, 02:53 PM   #13
XJ93
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75-140 is meant for towing package vehicles, 75-90 is for everything else. I have always used 75-140 with a friction modifier as even the Valvoline with friction modifier isn't enough for Chrysler specs. Use DOT 3 brake fluid and do not mix your fluids. If you want to use DOT 4 you should flush the brake system.
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Unread 03-31-2015, 06:41 PM   #14
zwoobah
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Quote:
Originally Posted by niero View Post
I know I have a minor brake leak somewhere. Shop said it's very small. Any DOT 3 or is it DOT 4?
There's very few places that your brake system can leak without it being major. Most of the time if it is leaking, you are in danger of losing your brakes. Brake fluid is also corrosive, and not something you want leaking or spraying onto any rubber or painted parts. I'd fix that before you drive it, especially if you plan to go on the highway.
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Unread 03-31-2015, 06:48 PM   #15
MurdaJs
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Quote:
Originally Posted by XJ93 View Post
75-140 is meant for towing package vehicles, 75-90 is for everything else. I have always used 75-140 with a friction modifier as even the Valvoline with friction modifier isn't enough for Chrysler specs. Use DOT 3 brake fluid and do not mix your fluids. If you want to use DOT 4 you should flush the brake system.
Dot 3 and 4 is mixable

Valvoline has a bottle that literally says dot 3 and 4 on it lol

4 just has a higher boiling point.

It's dot 5 that you don't want to mix. You don't really want to use it at all actially
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differential , limited slip , modifier , open diff

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