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Q&A: YJ and TJ Wrangler Routine and Miscellaneous Service 

     Enjoy the many detailed, traditional 'Q&A' exchanges in these article columns...'Q & A' has now moved to open, interactive forum discussions. Visit the forums, you'll want to join—for free!

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Is the TJ Wrangler's Oil Pressure Gauge "Real"?

Hi, Norm…Nice to get your note…The ’04 gauge reads actual pressure.  This is an ohms-sensitive sender and gauge arrangement.   

 

I have attached the “official” description of your oil pressure gauge’s operation. If you need troubleshooting guidelines, I’m available! 

 

Best, 

 

Moses  

 

From: Norman F.

Sent: Saturday, April 16, 2011 6:47 PM
To:
 4WD Mechanix Magazine

Subject: Oil Pressure gage. 

 

Moses, 

 

I have a 2004 Jeep Rubicon.   Is the oil pressure gage a true gage or just connected to a oil pressure switch to show pressure or not (aka “Idiot light”)? 

 

Norm

Keeping a Desert Crawling TJ Wrangler Alive!

 

From: Jack F.

Sent: Sunday, April 10, 2011 11:15 AM
To: 4WD Mechanix Magazine

Subject: 1999 Jeep Wrangler Question  

 

Hi, Moses,

  

I have been following your web site for a while after I learned of it through the Carson Valley Sierra Stompers 4X4 Club emails. 

  

I have a 1999 Jeep Wrangler Sport, 4.0 engine, auto trans in stock condition.  It has 132,000 miles on it and it runs great.  I plan to keep it as it is perfect for what I do in the Mojave Desert and Death Valley areas. 

  

But as the miles continue to climb I am wondering what I should start looking at in the way of major service or replacement of parts that could start to fail.  And when I am out in Saline Valley, I would have rather done preventive service than follow the wait till it breaks way of doing things. 

  

I recently had the transmission checked at Carson Valley transmission in Gardnerville and they report that the trans is in great condition.  So is there anything else I should start replacing, like U-joints, for example? 

  

Many thanks for any suggestions you may have! 

  

Jack F. 

 

Hi, Jack…As you can tell from the website/magazine, I use a ’99 XJ that now has the same miles as your Wrangler. It has a lift kit, tires, ARB Air Lockers front and rear and new ring-and-pinion gearsets with bearings and a new rear/CV driveshaft. (Work down is visible around the website/magazine.) As for items that have “needed attention”, this vehicle receives regular service, I serviced the AW-4 as you have your 32RH, the front hubs and rear driveline have been renewed, and brakes have been serviced.  The engine receives regular tuning and routine service as prescribed in the owners and shop manuals. Like yours, this XJ is central to our safe four-wheeling, so it receives regular service, including air and oil filters, fluid changes, belts and hoses as necessary.

 

As for what to consider on your Jeep, I would check all U-joints, both the drivelines and the front axle shafts. Also check the rear axle bearings, front wheel hubs and the brakes. The ignition needs a distributor cap, rotor, plug wires and spark plugs at normal intervals, and the cooling system must be in good shape.  I would install a new water pump, hoses and thermostat if there is the slightest sign of wear, coolant seepage or cooling issues.  (I will be doing an upgrade on the ’99 XJ’s cooling system shortly and plan to share details in an article at the website.)

 

Note that there is no fuel filter on the ’99 Wrangler, the pump has a sock pickup screen and a pressure regulator attached above the pump. That’s why I suggested checking the fuel pressure and volume, which can be readily done at the rail test port on the engine’s MPI/EFI system.

 

Also, you mentioned that Carson Valley Transmission did a service. The 32RH does have band adjustment needs. Check your invoice to see whether the bands were adjusted. If not, on your next fluid/filter change, have the bands adjusted. This is routine and keeps the transmission functioning well. 

 

The battery must be in good condition, as well as the starter motor and alternator. You can have the fuel pressure checked for telltale signs of fuel pump wear, the pump is key to backcountry survival on an EFI system…Any signs of wear should be met with preventive care/service.  If you drive the desert much, you likely will need a quality shock absorber upgrade. 

 

As a whole, you hear stories of XJs and TJs that run to 250K miles or more.  This is true.  However, for Death Valley or the Mojave, preventive care is the best insurance for keeping your 4x4 safe enough for remote travel. 

 

I’m available for further questions, Jack… 

 

Happy trails! 

 

Moses 

 

Checklist: A TJ Rubicon’s Latest Modifications

 

Hi, Moses! The local shop just installed a variety of components on our ’04 TJ Wrangler Rubicon. I’d like to share the list and see if you would add or modify any of the items…

 

Full-Traction 6" Long Arm Performance Suspension Complete Exhaust System, cat-back

CV Driveshafts

HD Engine Skid Plate

Steering Stabilizer

3-Way Adjustable Rear Sway Bar

“M Force” Shocks

Skyjacker Transfer Case Relocation Bracket

Warn – Front Rock Crawler Bumper

Warn - Rear Rock Crawler Bumper

Warn - Tire Carrier

Warn - Fuel Tank Skid Plate

Warn - Differential Skid Plates

Warn – 2” Receiver Shackle

B&M - Short Throw Shifter

Mickey Thompson Classic II 16”x8” Wheels

Toyo Open Country M/T LT315/75R16 (same as the 35”x12.5Rx16” size)

Thanks for evaluating our Rubicon’s modifications. We’re headed for Moab!—Joe M.

 

Joe, this sounds like a thorough list for putting 35” diameter tires on a TJ Rubicon chassis. You have probably added an issue that I talk about often at my Camp Jeep workshops: the impact on gearing created by the increase in tire diameter from 31” (OEM) tires to 35” aftermarket tires. Any increase in tire diameter will create an “overdrive” effect. The Rubicon’s stock 4.10 factory axle ratios work very well with 31” tires. Now, though, your change to 35” diameter tires requires 4.88:1 gearing (front and rear axles) to restore the vehicle’s original driving characteristics. Even lower (numerically higher) gearing than stock is of value when you add the weight of rugged bumpers, a winch and extra skid plates. Some builders use 4.88:1 gears even with 33” tires; however, 4.56:1 will actually correct and slightly improve performance over stock when running 33” tires on a TJ Rubicon. (This is a good formula—as long as the transmission has an overdrive gear—for any TJ, YJ or XJ Cherokee.)

 

Let’s evaluate a TJ Rubicon’s direct 1:1 ratio 4th gear (an NV3550 five-speed application), using various axle ratio and tire diameter combinations. For simplicity, let’s use 60 mph as a benchmark for clocking engine rpm:

 

1) Stock Rubicon 4.10:1 axle ratios with 31” OEM tire diameter = 2667 crankshaft rpm.

2) Stock Rubicon 4.10:1 axle ratios with 33” tire diameter = 2506 crankshaft rpm.

3) Retrofit 4.56:1 gears with 33” aftermarket tire diameter = 2787 crankshaft rpm.

4) Retrofit 4.88:1 gears and 33” aftermarket tires = 2982 crankshaft rpm.

5) Retrofit 4.88:1 gears and 35” aftermarket tires equal 2812 crankshaft rpm.

 

Note that the closest ratio for preserving stock-like performance with 33” diameter tires is 4.56:1. (The slightly higher engine rpm indicates a gearing advantage that offsets the added weight of hefty accessories.) 4.88:1 gearing would raise crankshaft rpm even further and provides better performance in terms of acceleration, the ability to stay in a higher gear without lugging the engine, possibly better fuel efficiency and an improvement in compression braking. 35” diameter tires also gain slightly from 4.88:1 gearing…

Joe M.'s modified Rubicon TJ Jeep, photo supplied by Joe

Given the real-world cost for labor and parts to install 4.56:1 or 4.88:1 axle gearing, I always advise owners to be prudent. If you find that the 4.10:1 gearsets work okay with 33” tires and your driving conditions, it might be smart to adjust for the speedometer error and call it good. (4.56:1 or 4.88:1 gears, or any other choice, may require a slight speedometer correction.) The taller gearing effect with 33” or 35” tires and stock 4.10s does place a greater load on the clutch and reduces the compression braking effect, so adjust your driving accordingly if you stay with 4.10s...

  Note: For those puzzling over why there is not a “perfect” axle ratio to compensate for, say, a 33” tire retrofit, the answer is very simple: Axle ratios available for Dana 44 axles would be 4.10, 4.27, 4.56, 4.88, 5.13 and 5.38s. The 4.27:1 gearsets make for 2610 crankshaft rpm at 60 mph in 4th/direct gear of the NV3550 transmission with 33” diameter tires. This is still slightly overdriving when compared to 4.10s with stock 31” diameter tires. Since there is no gain, and 4.27:1 ring and pinion gearsets are scarce, running slightly lower (numerically higher) gearing of 4.56:1 makes better sense…Because overdrive transmissions use various 5th or 6th gear ratios, I like to use a 1:1 4th gear ratio for illustrating rpm. For the curious, the NV3550 has a 22% overdriving 5th gear ratio, rated as a 0.78:1.

 

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