Q I have an '85 Chevy army truck with a 6.2L diesel and a TH400 transmission. My problem is the truck is screaming to reach 50 mph. would I get better speed by swapping in an NV4500 five-speed? Or must I change my axle gearing? If so, what would you suggest?
A I had an '86 Chevy army truck that was stolen a year ago, Bryan. Man, I miss that truck. (To the scumbags that stole it: Hope we never find you!) I put an NV4500 in my truck and would not recommend it. The price and time needed to swap the 4500 isn't worth the effort, and the 6.2L doesn't have the power to pull the odd gear spreads of that manual transmission. Plus, the NV4500 requires special oil, resulting in $100 of lube to fill it!
These military trucks are perfect with the TH400; they just need taller tires. If you upgrade to 37s you'll be just fine for most highway jaunts. The axles are plenty strong, the rear has a Detroit Locker already, and by adding a front locker and a winch you'll be hard-pressed to come home walking. I added the Banks turbo for some more power, but the stock 6.2L isn't that bad. Well, OK, it is bad, but you can deal with it.
I miss my truck. Please keep your eye out for it. It had camo seats, a winch hidden under the front bumper, and steel rock sliders welded to the frame.
More Deadly Wobble
Q I have been helping a friend build a YJ. The stock axles have been swapped with a Dana 44 up front and a Ford 9-inch rear. Ever since the axle swap, when driving down the road at approximately 40 mph the Jeep starts to shake terribly up front! It feels almost like the front wheels are wobbling. The only way to make it stop is to slam on the brakes. The YJ hasn't been aligned since the axle swap, so I guess that could be some of the problem. However, the wheels seem to be sitting level and straight ahead. We did use a tape measure to try and make it close.
I am pretty sure the front gear ratio is 5.89 and the rear is 5.83. That may not be exact, but it is very close to what they are if it isn't. I know the ratio should be the same front to back, but the guy who installed the gears said being that close shouldn't hurt anything as long as the front hubs aren't locked in on dry pavement. I don't know if that could be causing this shake. I wouldn't think so because it's in two-wheel drive when it acts up.
Also, the tie rod bar (from tie rod end to tie rod end) is slightly bent. You know how gentle rocks are! I guess that could cause it as well.
The next upgrade is in the works: flat-top knuckles and high steer setup. We were wondering what your thoughts were as to whether these modifications would correct the shaking problem. Any input you can give us would be awesome!
A You are experiencing the elusive death wobble, Anthony, and trust me, you're not alone. I get questions like this every month. It is a phenomenon when one wheel starts to act on the opposite wheel via the tie rod, and the next thing you know there is a deadly front shake.
To start with, you need to get an alignment. Make sure the tires have the proper air pressure, check all steering and axle joints for slop or wear, and try swapping the tires front to rear because they may be unevenly worn up front. Proper toe, caster, and camber are important, and this can all be fixed with the alignment.
Fixing the tie rod would be helpful as well after you go to the high steer. Some folks use a steering stabilizer to help control death wobble, but this doesn't always eliminate the problem.
Q I'm 17 and recently bought an '02 GMC Sierra 1500 4x4. It has a five-speed manual transmission and a limited-slip differential. I'm just getting into off-roading. The only thing I don't like about my truck is its engine, a 4.3L. I can't afford to do an engine swap. So I was wondering what would be an affordable way to get more power.
A I have a truck that runs 39-inch-tall tires with a 2.7L four-cylinder engine. I can rockcrawl, play in the mud, and still run down the road. The trick is gearing. Your truck has an overdrive transmission, and the 4.3L is a hearty little engine, maybe not as powerful as a V-8, but a good start nonetheless. If you could get lower gearing in your transfer case or, better yet, your axles, you'd be surprised at how much better the engine pushes your truck around. Gearing isn't inexpensive, but it's cheaper than an engine swap.
Q Do you know of someone marketing heavy-duty steering parts for a GMC HD2500? My truck has 170,000 miles, and it is requiring new idler arms and tie rod ends for the fourth time. I have been useing original parts. The truck is used mainly for pulling a horse trailer, so any play in the steering is noticed, since it is primarily on the highway.
A Cognito Motorsports (866.426.4648 www.cognitomotorsports.com) has heavy-duty tie rods and idler pivot systems for your truck. Otherwise, some auto parts stores offer products with a lifetime warranty, but that doesn't solve the problem, just makes it more affordable.
Q I'm hoping that you might settle an argument between a dad and his son. This last hunting trip I chose to air down my tires. I have an '00 Jeep TJ with 35-12.50x15s. The disagreement ensued after my father told me that I need to be careful airing my tires down. I have always gotten to where I need to go with my tires fully inflated but due to lack of tread I wanted a larger footprint.
Is there a rule of thumb when airing down tires? I know that tires have different sidewall thicknesses and compositions. Is the tire size versus wheel size a consideration also? It seems to me that with a thicker sidewall and possibly a smaller sidewall area, you would be less likely to roll a tire off its bead.
A First, your dad is always right. He's your elder so he must know more.
Second, don't tell your dad we said so, but you're right. Airing down your tires is a good idea for any off-road use, as it improves traction and ride quality.
I recently spent time in Russia, and the guys who set up the trucks we were driving had aired the tires up to 40 psi for what he thought was more protection against puncture. I aired them down to 20 psi, and all of a sudden the trucks rode much better and didn't seem to skitter all over the gravel roads. I think a rule of thumb is don't air below 12-15 psi if you don't have beadlocks. Also, if you are using 161/2-inch wheels, stay above 15 psi unless you have beadlocks, as these wheels/tires have less of a safety bead inside the wheel.
A smaller sidewall does pose a problem when airing down. We like to stick to the rule of half: Your wheel should be no more than half your tire diameter for off-roading.
Airing up is great for on-road use, as it increases safety, reduces rolling resistance, increase fuel economy, reduces heat within the tire, eases steering, and helps the longevity of tires.
Q I have a '77 Ford Bronco that has a 5-inch lift on 35s that I just got roadworthy after four years of restoration. I was wondering what gears I should run to make it drive like it has stock tires. It is going to mostly see pavement, but after four years and a lot of money I don't want it trashed. I am in college, so money is a little tight at the moment to be rebuilding everything all the time. I go to the Silver Lake Sand Dunes a few times a year, so I don't really need superlow gears, just something that will make it drive like stock and turn the tires over easier than they do now. Thank you.
A Your Bronco probably came with either 3.50 or 4.10 axle gears. A good formula for gearing is the new tire size multiplied by the old axle gear ratio divided by the old tire size, and then go one ratio lower.
Say you now have 35s and 3.50 gears. Multiply those and divide by 30 for the stock tire size, and you get 4.08 (35 x 3.50 ÷ 30). That's roughly 4.10. Then, to make up for the larger mass and rolling resistance, go to the next lower (numerically higher) ratio. I'd say 4.56 is your perfect option.
If you have 4.10 gears now, then you'll likely want 4.88 gears.
Look on your front axlehousing for a small tag attached to the diff cover bolts that will list the gear ratio.
Bored, Need Help
Q I have 30-plus years of your magazine in boxes all over my garage, attic, and o ffice. I am looking for a tech article that detailed how to put 35-spline axles into a 31-spline Dana 60 (rear) housing. I remember it required a cutting tool to bore out a portion of the inner diameter of the axlehousing. Can you please direct me to that article/issue?
A I am not sure the exact article you are referring to, but you will need a spindle boring tool (PN YT H31) from Randy's Ring & Pinion (888.905.5021, www.ringpinion.com). This attaches to your spindle and allows you to bore it out so the 35-spline axleshaft will fit in. Then just add the 35-spline differential of your choice and larger axleshafts.
Nuts, I'm Confused
Safety first Q I believe that safety is the number one priority when out on the trail. I have had a disagreement on what I think is a safety issue. On occasion when off-roading I have become stuck and had to use my Warn winch to extricate myself. I use the cable weight bag to slow the cable down in case of a failure. The disagreement comes when my wife wants to exit the vehicle until the winch is no longer in use. She is afraid that if the cable breaks it could come through the windshield and harm her and the kids. I have told her that the safest place to be is inside the vehicle. This way she is using the body of the vehicle as protection for her and the young ones should a failure occur. My concern is that if she's outside the vehicle and the cable does break, there could still be potentially lethal projectiles such as a busted clevis (D-ring) or rocks.
The second part of my question is on the securing of cargo. I have put all my recovery gear inside plastic storage totes in the back of the 4Runner and secured the totes to the 4Runner. My concern is that during a rollover the plastic totes may become compromised from all the weight of the recovery gear and I will end up having unsecured recovery gear while the storage totes would still be secured.
A Two great questions, Don, and for them you've won this month's Nuts, I'm Confused prize, a gift certificate to 4Wheel Parts.
Safety around winching is very important, and I would say both you and your wife are correct. If you get your family out of the vehicle while winching it reduces the weight and makes for an easier recovery. Plus, it could be best to have the vehicle unloaded of majority occupants should the cable snap and the vehicle roll away. Another option is to simply raise the hood of the vehicle onto its support strut. Should the cable snap, this will block the ricochet of the cable from coming into the vehicle.
If they do exit the vehicle, have them stand a fair distance away behind a tree, a boulder, or another vehicle.
As for the totes in the back of the vehicle, I would recommend a cargo barrier such as those that hold pets in the back. We installed one from Slee Off Road a few years back that was a great way to separate passengers from gear.
We are sending you a 4Wheel Parts gift certificate good for all sorts of upgrades for your 4x4. Whether you are looking for tires, winches, or more recovery gear, 4Wheel Parts has it all. For more information check out the company's ad in this issue or the website www.4wheelparts.com.
Confused? Email your questions about trucks, 4x4s, and off-roading tech using "Nuts, I'm confused" as the subject and include a picture (if it's applicable). Digital photos must measure no less than 1600 x 1200 pixels (or two megapixels) and be saved as a TIFF, an EPS, or a maximum-quality JPEG file. Also, I'll be checking the forums on our website (www.4wheeloffroad.com), and if I see a question that I think more of you might want to have answered, I'll print that as well. Otherwise drop it old-school style with the envelope addressed to the address below. Letters published in this magazine reflect the opinions of the writers, and we reserve the right to edit letters for clarity, brevity, or other purposes.
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