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My 1998 Grand Cherokee has an automatic 4WD system - no locking hubs or controls to select for 4WD - not clear to me what system it is or how it is implemented. In snow, for example, if the rear wheels start to slip, the front wheels automatically receive torque and pull the car.

A worsening problem I have with it seems to occur when negotiating tight turns (e.g. parking) after driving some distance at highway speeds. The wheels hop - seems as though all the differentials are allowing little to no slip. The car has about 167,000 km on it and I've had all the recommended service performed.

I have been told that the solution is to replace the oil in the differentials. Is this the solution? Could I have missed this as a regular service item? If it is a fix, what is the explanation for old oil as the problem and fresh oil as the remedy?

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  • id advise you seek out a jeep specific forum.(google) There a lot of very knowledgable jeep fans out there who will know about specific issues with specific models.
    – agentp
    May 2, 2017 at 12:22

3 Answers 3

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Has a JEEP mechanic looked at it, rather than a shade-tree mechanic? (note: I'm more the latter than the former!)

It sounds like you have torque-bind. Given that you have automatic 4WD, I'd lean towards the viscous coupler being the cause rather than a transfer solenoid (cos you don't have a 4WD switch on the dash)

Changing the fluid sometimes works, but once the coupler has actually locked solid, I'd be looking for a new one.

Searching for Jeep Viscous Coupler will give you lots of information. It's a common problem on some transfer cases, but not on others.

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  • The thing is, that once it has been parked for several hours, things return to normal - until the next stretch of highway driving. It is as if there is some amount of heat build-up which induces the problem, and a cool down resolves it. Also, I've been told that my Grand Cherokee doesn't use viscous couplings. I know earlier model years did, and at some point, they switched from viscous couplings to gerotor clutches; it's unclear to me if that happened before or after my car was built - I used to think it was after, until a mechanic said my car doesn't have viscous couplings, now I don't know.
    – Anthony X
    Apr 30, 2017 at 1:21
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Replacing the oil is good advice, it may never have been done. As it gets older the properties change / fail so the parts are not getting the protection / lubrication they should. Also, are the tyres all the same size / dimension and inflated correctly?

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  • Tires are all of the same make/model/dimensional spec, difficult to keep them all properly inflated, but usually not more than 2psi between any two.
    – Anthony X
    Apr 30, 2017 at 23:37
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The hop is normal in 4wd mode when making tight turns. In that scenario the differential is not in play. All 4 wheels are driven at the same speed. The tires in the inside of the turn need to be going much slower than the outside tires. On dry smooth surface the tires will skip as they try to speed up to match the outside tires.

The more salient question would be why 4wd isn't disengaging. It shouldn't be in play at highway speeds. And should only be engaging while going slower if tires are slipping. Something is making your system think tires are slipping and you are getting 4WD functionality when it is unsafe

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  • When would hop be normal? Except when the car has had a good high speed run (seems to be about 20 min or more above about 110 kph / 65 mph) I can maneuver the car lock-to-lock with no hop on any surface - differentials seem to be free - what I expect for ordinary driving. Only after high speed driving does something seem to go weird with the 4WD and I get the wheel hop.
    – Anthony X
    May 1, 2017 at 2:48
  • Hop is not normal! it can also be bad for the transfer case (TC). You have indicated you don't know which TC you have. Knowing that is the first step in figuring out what is causing your failure. After a bit of checking I found that the TC isn't coded into your VIN. That means the way to find out is a Round Tag on the upper middle of the rear of the case. You may need to take an old toothbrush and some parts cleaner with you to clean it up. If you take some pictures at oblique angles you may be able to generate a picture that lets you see worn numbers based on texture differences.
    – Rowan Hawkins
    May 1, 2017 at 5:26
  • As has been mentioned a few times before, changing the oil is a good place to start. Of course knowing what tc you have could indicate a specific gear oil to be used. As true with every mechanical vehicle issue, waiting wont make it better, but it could make things worse/more expensive to repair.
    – Rowan Hawkins
    May 1, 2017 at 5:32
  • I think this car has the Quadra-Trac 4WD system, which should have no differential lock when the transfer case is in high gear. So there should be no hop. (en.wikipedia.org/wiki/Jeep_four-wheel-drive_systems#Quadra-Trac)
    – Hobbes
    May 1, 2017 at 9:12
  • @Hobbes There were 2 versions of Quadra-trac. One used a viscious coupling and the other used Gerotor pumps to determine if the axels were slipping.
    – Rowan Hawkins
    May 1, 2017 at 12:07

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