Firstly, hello ;D

Secondly, I bought a 98 Cherokee about a month ago and so far, it's been surprisingly pleasant to drive, comfy, fast (ish) and easy to work on, but I have one big question. The front diff hums like an underground train in 4WD, it feels like it's grabbing more at the front and steers very strangley at anywhere near full lock. I thought it was a knackered diff, but read somewhere else that a tyre mismatch might result in similar symptoms. The previous owner put 215/75/15 on the front and 225/70/15 on the rear, totally different brands too, the fronts being Wranglers and the rear being Cheung Fa Wong Whale Brand Export Quality or somesuch. 4x Grabber AT2 are going on at the weekend, but I just wondered if I should dare to hope that the tyre mismatch is the cause of my Jeepy's woes.

I've changed the diff oil, it was a bit grubby and there was fine sludge stuck to the magnetic plug. The diff was pretty damned warm last time it did a few miles in 4WD.

Any thoughts?

 

Mis-sized tires aren't going to help, but these things all do horrible things when used in 4wd on dry pavement. Also, even in dirt at full lock you'l usually get some clunking and bouncing. Long term abuse like that is bad for the transfer case.

 

I don't think its a good idea to run that set up in 4WD.


Tire Size Results

Specification Sidewall Radius Diameter Circumference Revolutions Speedometer Odometer Difference
215/75-15 6.3" 13.8" 27.7" 87.0" 728/mi 60MPH 10000mi N/A
225/70-15 6.2" 13.7" 27.4" 86.1" 736/mi 61MPH 10108mi -1.1%

 

agreed the sizes need to match in 4x4

 

tires all same size and no 4x4 on hard pavement

 

Have you got it in 4wd full time or 4wd part time?

Sounds like you may have it in 4wd part time chum...

Mine sticks like **** in 4wd part time, take a bit of rocking and gear changing for it to go to full time and then to 2wd. It might be that too...

In reality the difference in tyre sizes you mention is pretty insignificant, would doubt it'd cause such a reaction (overall diameter different by under 8mm) between the two tyres

 

Fantastic, thanks to all of you! especially freegdr. I never got an owners manual with the Jeep so it's a case of picking things up as I go along and hoping nothing explodes.

I love the removable rear seat though, and the fact that it has a bottle AND a can holder for the driver .

 

2WD now, it'll stay like that till it snows now. Surely even only 8mm multiplied by many many rotations is going to wind up the transmission something awful. To get from 4WD back to 2WD I just select neutral on the main box, neutral on the 4WD selector thing, rev it a bit then back into 2WD on the little gearstick and back into drive with the main auto box.

 

if you searh you can find free on line repair manuals to down load in pdf

 

I run míne in full time 4wd all the time with no problems. The issue at full lock could be worn UJ's.

 

running i 4 all the time will put more stress on your front end components and will ultimately cause things to wear faster than just running it in 2.

 

Well, I have recently replaced hubs, uj's and ball joints. Doesn't it balance out with less wear on the rear though?

 

your front end has to incorporate all the movements that the rear does, but it also has to compensate for when wheels are turned. this is when the wear factor comes in more. the rear is far more basic and less expensive than the front. and besides, its a jeep, it will take it just fine!!

 

Well, I put the Grabber AT2's on and everything appears to be good now. I only took it for a spin on some gravel in 4WD, but it's a totally different beast now, especially at full lock. I'm pretty happy with the Grabbers too, except for the aggravation of getting the bead seated, I ended up using the brake cleaner and a blowtorch trick, good fun but you need to commit to a good amount of accelerant otherwise all you achieve is a small wheel fire. Probably lost about half an mpg over the Wrangler MT/Chiang Fong Wa or whatever they were, setup. We'll see how they deal with the few inches of snow that will inevitably bring the UK to a grinding halt in the next few months.