Your Tech Questions Answered
35s and 4.10s
Being no stranger to serious gearing, I read Firing Order (July ’12) with great interest. My first Jeep build (in 1975) utilized an M38-A1 frame and running gear with a fiberglass body. The M38-A1 body was pretty well trashed. Advance Adapters helped me mate an SM465 with the military transfer case and Warn overdrive giving me 16 forward and 4 reverse gears. I eventually sold that Jeep to buy a house. Yes, those were the good old days.
I currently have an ’04 TJ Rubicon with an automatic (I’m getting older). As you pointed out, low ratios can be great and sometimes necessary, but the 4:1 Rubicon transfer case is too low for many trails. You didn’t mention, but I am considering, the Advance Adapters Rubi-Crawler. In theory, it should be the answer to every Rubicon owner’s dreams. It would be cheaper than a three-speed transfer case swap, provide 2.72:1 or 4:1 low range plus provide crawler gears to boot. Have you had any feedback or experience with this product?
I am also going to 35-inch tires. With the Rubi-Crawler, do you think I can get away with keeping the stock 4.10 gears? I do little highway driving.
Your insight is appreciated and I enjoy your magazine and your great articles.
Lake Forest, CA
The Advance Adapters (www.advanceadapters.com) Rubi-Crawler is a great addition to any ’03-’11 Wrangler with the factory four-speed automatic transmission. As you note it is especially helpful on the Rubicon models with the 4:1 T-case. It gives you a wider range of gears that make your Jeep more versatile and better suited for different types of terrain.
As for the axle gears, while not ideal I think you can run 4.10 gears with 35s and the auto tranny. But if you frequent roads with any kind of elevation changes you will be extremely disappointed with the performance. The factory auto transmission will be constantly hunting for the correct gear and never really find it. Ideally you would switch to 4.88 gears. But if you don’t use it on the road much or don’t care about on-road performance the 4.10s can be made to work. The 4.10 gears will be just fine off-road, especially when combined with the factory 4:1 T-case and the 2.72 low range of the Rubi-Crawler.
I recently read the July ’02 issue about gearing and different ratios. I have a few questions. I have a ’73 Chevy short box Stepside 4x4 with an 8-inch BDS lift, Daystar greaseable front shackles, 3-inch rear lift blocks, and 1-inch ORD bodylift. It’s running the original four-bolt main 350 V-8, and SM465 transmission, and an NP205 T-case. It sits on a 14-bolt rear axle and a Dana 60 front axle on 44-inch Super Swamper Bogger tires. I would like to eventually swap in the 454 big-block I got from an ’86 1-ton. As I don’t have the money or access to a 32-spline NP203 to build a doubler, what axle gear ratio would work best for this mud-only toy? More importantly, what would work best for the 454 when I eventually swap it in? If it helps at all, the rear diff has 3.73 gears and a Detroit Locker. The front has 3.55 gears at the moment. I was thinking of going with 4.88 gears, but I want to be able to spin those big tires in the mud.
Baldonnel, British Columbia
If it’s a mud-use-only off-road only rig I bet you’ll be able to get by with the 3.73 gears when you shift the T-case into low range. If you prefer to run in high range or you drive it on the street at all I think you should look into some 5.13 or 5.38 axle gears.
I have an ’88 Nissan Pickup, Z24 four-cylinder, two-wheel drive (unfortunately) that I bought for $1,300. I recently changed the ignition wires and it started missing a lot. Now I have replaced the distributor cap, button, spark plugs, and fuel filter, and it still does not want to stay running. I can get it to fire up, and as long as I keep my foot on the gas it will stay running, but when I let off it dies. Would you have any ideas to how to fix this? Keeping in mind I’m on an extremely low budget.
It sounds like a vacuum leak. Is it possible you may have either knocked loose or maybe broke a crumbling old vacuum line when installing the plug wires? Start there first. Also, in the past I’ve often found that some cheap parts-store plug wires and ignition parts don’t work so great on the import trucks, even though the manufacturer claims they fit. My advice would be to hit the Nissan dealer and get the factory plugs, wires, cap, and rotor. Don’t forget to properly gap the new plugs.