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98 ZJ Grand Cherokee Factory Engine/Diff/Transmission...Are They Really That Bad?

1K views 16 replies 9 participants last post by  Candymancan 
#1 ·
Hey Everybody.

I've read a lot of posts on a lot of websites over the past 4 years since I bought my 98 Grand Cherokee, and I read one thing more often then any other. That the factory parts on a 98 Grand Cherokee are prone to fail.

In relation to the Diffs, 42RE transmission and transfer case...I have read terms like "horribly unreliable", "poorly designed" and "weak" over and over and over again.

I live in Australia and it is difficult to find parts to replace or upgrade for my ZG, so I have had to mainly buy rebuild kits to rebuild the factory components of my Jeep. I have rebuilt the transmission, replaced the VC in my transfer case amongst other sensors here and there and replacing the front end steering and suspension components. It drives well and it is a nice reward for all the work and money that I have put in.

But here in Australia there are many places that I would like to take it off road...but in the back on my mind are all the opinions and quotes that I have read over the years...that they are weak, and break easily off road, the transmission is ineffective for off road use, the transfer case it poor and the diffs are weak.

Now I do not intend to do extreme off roading or rock crawling...mainly just bumpy trails, sandy deserts ect. Probably some hill climbs and things like this.

Just keen to hear some opinions here on the reliability of the factory I6 engine, 42RE tranny, NP249 Transfer case and diffs.

Maybe I just got some bad luck and found mainly negative threads on the web? :p

Thanks in advance.

Take care.
 
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#2 ·
If you're trying to bolt 35's to the stock drivetrain and then go beat the piss out of it, yes, the stock vehicle is woefully inadequate.

If you have a brain and aren't overdoing it then you'll be fine. The stock components are perfectly strong for the stock jeep, and you can modify things a little past that. Overall the ZJ was designed to be reasonable offroad and pretty good onroad, but it was never intended to do the rock crawling that a lot of us put it through, so we find ourselves needing to upgrade axles, t-case, trans.

The d35 is your weakest point right now, the t-case isn't going to give you issues unless you run mismatched tires, and if you've got a good rebuild on the 42re you'll be fine.

Hunter (texasZJ1) wheeled stock axles, stock trans, and a big V8 on 35's quite effectively, but his wheeling style is slow and smart, not a lot of skinny pedal mashing.
 
#3 ·
Can't testify to the 4W capabilities as kg can. But a little perspective won't hurt. I got mine 2nd hand, it had been moderately neglected and the main thing at the time pretty old, approaching the big 200;000 in miles. First thing to go was the d35 but I aided it by incorrectly replacing a seal. So I rebuilt it and replaced the suspension. Then the steering box, so I rebuilt it and replaced pump and hoses and the front suspension, steering.
Then the head gasket,so I pulled the head, had it totally reworked, replaced the valve train, timing components,new injectors, new exhaust manifold. Presently, I'm gearing up to rebuild the transmission. Do I feel shorted, or like I got a lemon, or a poorly designed vehicle? Nope. It is a perfect representation of 1998. AND at least I can do the work myself without involving a dealer. I beat on this thing fairly hard as I am not a patient driver. So simple upgrades in braking, suspension ect. pay off even in a non 4W frame of mind. If I could figure out a cloaking device it would come in handy:smile2:. I maintain it to the point of obsession. The 250,000 plus motor is showing its age in the bottom end, but it doesn't burn oil and when I stomp on it moves along quite nicely. You bought a older vehicle, stuff is gonna break, and stuff is most likely worn out. Work through it, fix what needs to be fixed, treat it well somewhat, and you will enjoy it. The electronics are a pain sometimes, but there is some excellent support here for that.
 
#4 ·
Thanks guys for your replies. Sounds like I have to pay some attention to the D35. Definitely will not be doing extreme off roading. I need to get new tyres soon too, I think they have 28's or 29's on them at the moment...would you recommend staying this size on the stock axel or can you go an inch or two bigger?

Thanks again.
 
#5 ·
I believe the common wisdom is that you can put 31" tires on the ZJ without any modifications. Once you go bigger, the angles on driveshaft and the stock steering/suspension parts gets too far out of spec, and you will probably have to modify your wheel wells. I only went a bit larger than stock, at 235/75/15, on my 4.0L 4x4. Admittedly, I have the worst low-end gearing of the bunch at 3.55. If you have 3.73's in yours, you'll do better than I could with the larger tires. Good luck.
 
#6 ·
30" is the max that makes sense on stock suspension, if you run 31's you'll have no travel.

31's on a BB is very capable and isn't overloading the stock components.
 
#7 ·
Hunter had a super dana 35 kit. Much stronger than a stock 35. Still a teeny weeny ring gear though.

I'd say for the D35c you could get away with 33's unlocked if you don't beat on it. By that time you'd want to regear because it would suck with 33's and stock gearing so you might as well ditch the 35 for something stronger.
Just don't drop off any ledges or put the pedal to the metal.
Make sure you add a transmission cooler unless you want to kill it.
 
#8 ·
I didn't want to start a new thread for this, but I have been doing some research on the 4.0l Inline 6. An Inline 6 has been proven to have more torque than a v8. We may not see the difference in our zjs, but the gross torque in an Inline 6 is much more than the gross torque of a v8. If you research it, an Inline 6 is used wherever you want torque, tractors have Inline 6s. 90% of semis are Inline 6.

I didn't want to start anything, just wanting to share this. I was talking to one of my friends (who designed engines for GM) about putting a 5.2L in my ZJ, and that is basically what he told me. I have a lot of data on this if anyone wants it.
 
#14 ·
Can easily tell that AMC 4.0 I6 tone from a mile away. I do landscaping and when im outside at a customers house every now and then ill hear that exhaust and think.. ahh a jeep.. turn around and its a wrangler or grand cherokee lol
 
#15 ·
I do enjoy the sound of the I6 even on my stock exhaust. I have been debating putting a CAT back exhaust on but I have a few more things to do before that...though the CAT is 18 years old and is probably blocked. Speaking of engines though, I have noticed over the past 4 years that my number 1 cylinder plug wears much faster than the other plugs.

I do look after the engine. I change the oil every 4000 - 5000kms (3000 miles) along with the oil filter. Plugs are done once every year along with the air filter. Regular coolant checks etc. I have owned it for 4 years and have only put 20,000kms (12,000 miles) on it myself...though the engine overall has 285,000kms or 177,000 miles. Is it normal behaviour for the number 1 cylinder plug to wear much faster?
 
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