November 2012 Techline Tech QuestionsPosted in How To: Tech Qa on November 1, 2012 Comment (0)
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.
I’m thinking I want to put 40-inch Boggers on my 1¼-ton CUCV truck. So that means I pretty much need 15s or 16.5s since that’s all the wheel sizes that tire is available in. If I go with 15s I have to run steel wheels so they will fit over the calipers (once I grind them). I’m leaning toward MRW (www.mrt-wheels.com) because I like the thick beadlock rings and the ability to get them in 15x10 or even bigger with almost any offset.
The other option is recentered 16.5-inch military Humvee wheels. However I’m worried that at 9.75 inches wide I just won’t get the look I want. I know you ran them on your Dodge Ramcharger for a long time with 42-inch Super Swampers. Did you hate your recentered Humvee wheels? Are they easy to mount tires on? Are they heavy? Other input?
Editor, Four Wheeler
I tried to put 15s on my Ramcharger to avoid the 16.5s. You’ll be really surprised at how much you actually have to grind out of the Dana 60 caliper even when using wheels with 2 inches of backspacing.
On the Humvee wheels, they assemble comically easy. You just have to make sure you don’t get too aggressive with the impact gun when tightening them and spin the ½-inch studs. Still, they’re made to be assembled with air tools in the field, so I don’t know why I worried. Oh, and lube the O-ring. I don’t know about Vaseline, but there’s a lube made for pool filter O-rings. I’ve discovered that’ll work really well. You can buy it at any Leslie’s Pool Supply, but when I did mine I just used Windex to lube them and I never had a leak. I bet you can just spit on ’em and they’ll be fine forever.
I kept the magnesium runflats full-height in my wheels, but some guys trim them down to avoid pinching a tire at lower pressures. Because of the runflats, I never really aired down past 10 psi because I was worried about pinching. You can trim most of the runflat down if you have access to a bandsaw. That’ll let you air down to like 3 or 5 psi, which is really where you’d want to be for some terrains and thick-wall bias-ply tires.
I had no problems with my wheels other than the weight. Remember, Humvee wheels have 7 inches of backspacing, so you really have to recenter them unless you’re running dualie axles. Back when I did mine, I couldn’t find anybody who would recenter them with dished centers. Jason at Twisted Customs (www.twistedcustoms.biz) did mine with 3⁄8-inch-thick, cold-rolled centers. They were strong and didn’t bend, but they were crazy heavy. Today you can have Stazworks (www.stazworks.com) recenter them with normal-gauge dished centers that will resist flexing and bending without chucking hillbilly amounts of steel at the centers, that’d be the way to go.
Or you could just pick a different tire and use some 17-inch beadlocks and make your life easy.
Editor, Jp Magazine
I have been reading your magazine and off-roading since I was in diapers. I have a decent amount of technical knowledge and wheeling experience, but when it came to regearing my Chevy C1500 Prerunner I am stuck between a rollcage and a hard place. I read the July ’12 issue which discusses gearing several times and I am still stumped.
To set the scene: my truck is a 2WD ’08 Chevy Silverado 1500 with the 4.8L V-8, 4L60E, and GM 10-bolt rearend with 3.27 gears. This truck is my daily driver and it sees a lot of trips from Camp Pendleton in Oceanside, California, to Phoenix, Arizona. But it is also set up for high-speed desert use with a Camburg Mid Travel kit and 33-inch Hankook’s. However, the truck originally came with a 28-inch tire. I have lost all torque. I want a gear ratio that will keep the trucks great highway manners (low cruising rpms and 15 mpg) but give me more torque for the desert and better mpg around town.
I have been told a 4.11:1 ratio would be best but wonder if that would be too much for highway use? I guess to make a long story short, I wanted your opinion as I know you really know your stuff when it comes to gearing. Being an active-duty Marine I only have the money to do this once. I really appreciate any help you can give me.
With the stock 28-inch tires and 3.27 gears your engine would run at about 2,000 rpm at 75 mph. With the 33-inch tires and 3.27 gears the engine should be running at about 1,700 rpm at 75 mph, which is really too slow. To correct this you would ideally run a 3.83 gearset. But there isn’t a 3.83 available for your axle, the closest gears are 3.73 and 4.10. So if you find that you spend most of your time on the highway at speed and you want the best economy possible, you might want to go with 3.73 gears. With the 3.73 gears and 33-inch tires the engine will spin at about 2,000 rpm at 75 mph, which is what it did stock.
For more torque off-road and slightly less top-speed highway work the 4.10 gears would be a good choice. Me? I would go with the 4.10 gears which would up the highway cruising-speed rpm and fuel consumption, but it would also make the truck peppier around town. With the 4.10 gears and 33-inch tires your engine will spin at about 2,200 rpm at 75 mph.
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