Your Jeep Tech Questions Answered
Pleeease Diagnose My Noise!
I have an ’04 Grand Cherokee Overland with Quadra-Drive and a 4.7 V-8 HO with 84,000 miles on it. I had synthetic fluid put in the differentials approximately two years ago at 73,000 miles. Previously I had changed the fluid with synthetic fluid in the diffs and transfer case at 29,000 miles. I have had a bad grinding or binding sound when I back out of the driveway or make a sharp turn out of a parking lot for the past year or more.
First, I’d start by checking the boots on your CV-style front axleshafts. If these are broken and grease has leaked out of the joint, you may hear sounds coming from the front axleshafts. But they usually make a clicking or a popping noise rather than a grinding noise when they are bad.
Next, I’d check the fluid in the front and rear axles and transfer case. If the fluids are low ,fill the part with the correct fluid. The NV247 transfer case (found in WJs with Quadra-Drive) uses Mopar Transfer Case Lubricant PN 05016796 (gold colored), while the NV242 transfer case (WJs with Selec-Trac) uses ATF-4 (red colored). If all are full, then you may have more of a problem. Sounds like this is very difficult to diagnose long distance, but here is what I would bet my money on if I were a betting man. If you only heard the grinding sound when turning, then it could be coming from one of your differentials. In that case, I’d say that one of your differentials had some damage. Your differentials allow differences in speed from the two axleshafts as the Jeep goes around corners. This is because the inside tires actually travel a shorter distance than the outside tires. But since you also have this grinding when you back out of the driveway, I’d bet that the sound is most likely coming from the transfer case. Since your Grand has full-time four-wheel drive when you go around a corner, the differential or viscous coupler in your transfer case has to compensate for differences in speed between the front and rear axles, much like the differentials in your axles do on a turn. Again, here the front axle is actually traveling a slightly larger distance than the rear axle that is following it. Because of this difference, the front driveshaft will turn a little bit more than the rear driveshaft. To allow this, your NV247 transfer case has a part like a differential called a viscous coupler. It sounds to me like this viscous coupler needs to be replaced. Also, as you back up the weight of the vehicle transfers forward and would cause slight speed differences between the front axle and rear, causing the grinding in the transfer case viscous coupler.
You can check this by chocking the front tires and jacking up the rear axle with the Jeep in park so that both rear tires are off the ground. Then turn one of the rear tires by hand. If you hear grinding coming from your rear differential, there is your problem. If not, lower the Jeep and with the front tires still chocked, shift the transmission into Neutral. Then jack up only one of the rear tires and rotate it by hand. If you hear grinding coming from the transfer case, you have located the problem. If not, put the Jeep back in park and chock the rear tires. Then jack up the front axle so both tires are off the ground and repeat the first test you performed on the rear axle. You should hear the grinding coming from your front axle’s differential if that’s where the failure is.
I have been reading Jp for a number of years now, and I always trust you guys for Jeep advice. I was hoping to get an update on the Shrink Ray TJ. Unless I missed something, I don’t think we have heard from you since Part 2, when you shrunk the rear. How is it working? Have you made any other upgrades? Would you do anything differently? Would you do it again? Can we expect to see a Shrink Ray Ray TJ: Part 3?
I am going to buy a TJ soon for my next project, but I am not sure whether to get a four-cylinder or the six. I like the concept of the Shrink Ray TJ, and want to use it as inspiration for my next project, but I just wanted to get an idea of how it is working out before I pull the trigger on a four-cylinder because most people would steer you away from it.
This is what I am looking to do: buy a stock, manual, early TJ and build it on a budget as a daily driver/ weekend warrior. My limited cash will force me to keep most of the original drivetrain, but I will add a mild lift to clear 33-inch tires. I will slap on upgrades as funds allow such as armor, lockers, winch, and so on until I have a decently capable Jeep that maintains good road manners. The question is should I get the 4.0L for power and build it heavy, or should I get the little four-banger and chop it down light? Any advice would be much appreciated. Keep up the great work over there at Jp!
The Shrink Ray TJ is doing well. I have been wheeling it pretty hard over the past year or so, and it’s about to go under the knife for a little more work and repair. I’ll get to that in a minute. First let me catch everyone up on what I have done with it since Shrink Ray Part 2. Keen readers will have seen the little TJ in “Clearance Clarence,” (Mar. ’13) where I installed a T&T Customs high-clearance center skidplate/T-case crossmember. At that time, the little TJ that can also got a cable shifter and slip-yoke eliminator kit from Advance Adapters. That required some Brown Dog 1-inch-lift motor mounts and a Tom Wood’s Custom driveshaft.
Since then I have added a set of old forged aluminum 5-on-51⁄2-inch 15x8 Weld wheels that I had been toting around the country for several years. These wheels were modified with lightweight OMF Beadlocks and wrapped in a set of 35x12.50R15 Explorer Pro Comp MT2s (“Tight as a Tick,” June ’13). I made the wheels fit the stock Dana 30 and 2WD V-6 Toyota Tacoma 8.25 bolt patterns by adding a pair of adapter/spacers from SpiderTrax and an old and well-used Dana 30 Warn locking hub conversion with Chromoly shafts and CTM U-joints from my pal, Trent McGee. I also added a junkyard fresh set of ZJ front coils (“Super Cheap,” Oct. ’13) to replace the sagged and beaten stock TJ front coils that were on Shrinky.
Since Part 2 appeared in the magazine, I have wheeled the little TJ all over Moab, a few trails and dunes out in Johnson Valley, and all over southern Arizona. With the addition of the larger tires, the combination of gearing of the AX5, NP231J and 4.88 axle gears is not quite low enough. I will be swapping the light duty AX5 for an old-school granny-geared manual, but I am not gonna give away which one just yet. Also the Jeep needs new lower front control arms, a timing chain, and some general loving. It’s next on the docket to spend time in the garage getting this trans and loving as soon as I can get some space cleared.
With the lighter weight and proper axle gears, this TJ feels pretty peppy despite the four-cylinder. If I had it to do over again, I might have held out for an ’03-or-newer TJ with the 2.4L, but in general I am pretty happy with the Jeep. Honestly, it works better than I expected. You could do a similar conversion with a 4.0L-powered TJ, only without moving the grille and radiator and you’d have a nice lightweight Jeep with some realistic horsepower. Of course you won’t get the same approach angle (which is definitely zero with the 35s) as I did with Shrinky, but you’d have more usable power. All in all, if you want to build it slowly and keep the Jeep ultra-light as I did, I would probably suggest a four-cylinder Jeep. Right out of the box with factory 4.10s in the axle, they crawl pretty well and are cheap. If you know your TJ is gonna end up heavy, go right for the 4.0L—unless you think you may swap engines some day, in which case the added cost of the 4.0L will be wasted.
If I have any regrets, it revolves around the grille and hood. I had and almost swapped on an old beat up M38A1 grille. I could have matched this with an M38A1 hood. I think that would have taken this build over the top. Can I go back and swap on a vintage grille and hood? Yeah, sure, but I probably won’t. It would be lots of work and undo lots of stuff I already did, and did well (if I do say so myself).