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Need some help with some basic questions

doclouie

NAXJA Forum User
Location
Logan, Utah
Hey everybody I am new to this forum and new to anything relating to the drivetrain of my XJ. I have totally rebuilt the engine and beefed it up and did all the work myself but I have some quick questions about the drivetrain. Don't laugh cause I know some of these questions will be basic.

What is a disco front end?

When you say you have a 3.55 rear end what exactly does it that mean? I know it is a ratio but is 4.07 better than a 3.55?

What is this talk of a solid front axle? What years were these sold?

Are lockers easy to install?

I will be going to Moab this year and am looking to maybe change out the dana 30 for a dana 44 and adding front and rear lockers.

Thanks in advance for your help.
 
doclouie said:
What is a disco front end?

"Disco" is short for "disconnect." The XJs with the 231 (Command-Trac) transfer case prior to 1991 had a vacuum-operated slip spline on the right front axle so the right side would freewheel in 2WD. That allowed the differential to not rotate, which reduced drag and theoretically improved gas mileage. The savings were negligable, and DaimlerChrysler stopped using the disconnect in 1991.

When you say you have a 3.55 rear end what exactly does it that mean? I know it is a ratio but is 4.07 better than a 3.55?

What's "better" mean? Better for what? With standard size (stock) tires and for street and light wheeling, 3.55 gears are about optimum -- at highway speeds the engine is turning at around 2200 to 2500 RPM, which is where the torque peak happens to fall. That's ideal for economy, and at 2500 RPM you're certainly not over-revving the engine.

However, when you start going to larger tires, they reduce the effective gear ratio. Serious rock crawling requires slow speeds, and the 3.55 gearing may not provide a slow enough crawl ratio. If you plan to run larger tires, eventually you'll want/need more gear.

What is this talk of a solid front axle? What years were these sold?

All XJs of all years have solid front axles. It refers to an axle that has straight axle tubes pressed into the differential housing. The opposite is independent front suspension (IFS), in which the differential is attached to the engine or chassis and the axles have some sort of u-joint or CV joint to allow them to articulate relative to the differential.

Are lockers easy to install?

Some are, and some are not. The class of lockers referred to as "lunchbox" or "drop-in" lockers do not replace the carrier, they replace only the guts within the carrier. That means the very delicate adjustment of the ring gear and pinion remains unchanged during installation. The Lockrite is an example of this type of locker.

Other lockers completely replace the carrier. In this case, the adjustment of the ring gear to the pinion is lost, so the gears must be "set up" again. This requires special equipment, and/or experience in "reading" the pattern made by the gear teeth as they mesh. The Detroit Locker and the ARB air locker are full carrier lockers.

However, if you are changing the gear ratio at the same time as installing a locker, the ring and pinion have to be set up anyway, so at that point the only advantage to a drop-in locker is lower cost. The disadvantage is that the stock carroer generally isn't as strong as the carrier of a full carrier locker like a Detroit.
 
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