4x4 AnswerMan - Your Truck and SUV Questions Answered

Jun. 27, 2013 By Jaime Hernandez
Ford F-150 SVT Raptor built by RHD USA. This unique right-hand drive truck is built to turn heads in the USA and roam freely in the Australian and African outback. Look for a future story on this cool truck.

Have a truck or SUV question for the 4x4 AnswerMan? Send your questions to editor@off-road.com. Please include your name and location, and be as detailed as possible about your questions.

More 4x4 AnswerMan Columns
May 2013

April 2013

March 2013


4x4 AnswerMan,
Read your very informative article on Toyota ADD. I acquired a high mileage (min or zero off-road history) 1999 4R for rehab V6, Limited mod, push button on 4WD control lever, has separately actuated via instrument panel switch, rear locker, uses a 4WD ECU for overall system control and protection.
The 4WD system is dysfunctional, initial look and instrument panel lights suggests it’s in some in between mode. I believe the ADD is engaged however the T/case is not. Runs on the highway without coughs or growls.  No Toyota experience, but can troubleshoot and diagnose if I know functionally what is supposed to mechanically happen in the various modes.
(a) what happens h2 to h4 via p/button on shift lever
(b) what happens h2/h4 to h4L via shift lever movement
(c) what happens  h4L to L4L via shift lever
(d) What does the "L" in the shift mode infer
Thanks, Pat Hickey
Fredericton, NB, Canada

Hello Pat,
The Automatic Disconnecting Differential System (ADD) basically controls the front differential from engaging and disengaging during the use of 4WD with the aid of a sleeve. This sleeve allows the front axles to turn with power from the transfer case. When not in 4WD, the sleeve is disengaged. This type of system is very common on 4x4 vehicles that don’t use manual locking hubs.

As for function in each transfer case setting, all modes leading any 4WD power will engage the ADD, which is vacuum activated. Shifting your transfer case into 4HI, 4LO is all done manually with the transfer case lever.  Internally the transfer case uses a fork to move into each gear (2HI, 4HI, 4LO). If the front axle sleeve is not engaging in any of these, which is what you have stated, you can try and manually lock with forced vacuum. If this work-around proves to work, then the problem is going to be somewhere in the ADD system. 

Check the vacuum lines, wiring, and solenoids located on the passenger side of the engine compartment. The vacuum hoses are almost 15 years old, so even a small hole can decrease the required vacuum pressure needed to engage the front differential. It might be worth replacing them.

For further information and trouble shooting the Toyota 4WD ADD System, please reference this tech article on Off-Road.com

The Automatic Disconnecting Differential System

Good luck



4x4 AnswerMan,
Hi I'm new to the whole 4x4 thing I was wondering what bigger axels I can put on my truck. Just trying to build me a weekend toy, picked the Dakota up cheap and need to know what axels would fit. Thanks.

Aaron T

Hi Aaron,
Welcome and get ready to have some fun. If your truck is a runner, I would suggest you put some off-road-worthy tires on there and just have fun with it in the dirt so you get your whistle wet. This will give you some time to figure out what parts you need to build up your weekend warrior. You might find the IFS with a mild lift is all you need. For the hardcore crowd, a popular axle swap is Dana 44 up front with Ford 9-inch in the rear. This combination will make a great rock crawler or mud truck.

Here’s a build thread from our sister site Pirate4x4.com that should help.

Dodge Dakota Axle Swap



Hi 4x4 AnswerMan,
I have a question. Will the 2004 Colorado rims fit my ‘97 Chevy K1500 Z71?

Hi Bryan,
The lug pattern on a 2004 Chevy Colorado 4x4 is 6x139.7, which is the same from 1967-present for all 4x4 1/2 ton GM Trucks.  Both of these vehicles’ wheels are centered using the lugs, not the hub.  You’ll be fine as long as the center bore is larger than 78mm, most Colorado wheels are 100mm.  Where you may run into problems is with the backspacing.  If possible, test them out to make sure they will not rub on the fender or when turning.


4x4 AnswerMan,

I have a 2008 Toyota Tundra 4X4 SR5. The truck is level. However, I want to lift the truck 2-3" and I need additional support in the rear. I carry tools and haul frequently. What are some quality and reasonably priced products or combination of products?
Dick Todd
Tallulah, LA

Hi Dick,

When you lift your truck 2 or 3 inches, typically the rear is lifted with a block. You might be able to get away with the current rear leaf suspension setup if it’s not sagging too bad when loaded. If you only tow/haul on occasion, suspension air helper springs (a.k.a. air bags) are great. They are there when you need them to carry extra weight, yet they can be aired down to provide a smoother ride when not in use. If you don’t want to deal with air bags, there are some extended rubber bump stops that help with loads, but these may get in the way of articulation off-road.

If you find yourself with a constant load all the time, heavy-duty leaf springs may be your best choice. You can either have some custom ones made by adding more leafs to your factory pack. The other option would be to look for heavy-duty rear leaf springs designed for off-road and also carrying heavy loads. ARB’s Old Man Emu suspension makes such a part for your truck. More info at http://arbusa.com/




4x4 AnswerMan,
I also have an ‘07 mega with the Core fox combo. How do you know what bag to order or is it one size fits all?

Letter sparked by Project Dodge Mega Cab: Air Helper Springs

Hi Mark,
Firestone makes vehicle specific kits, which come with hardware and brackets designed to work with your make and model truck. Our 3rd Gen. Dodge Ram 2500/3500 Mega Cab called for the Firestone Ride-Rite Air Helper Spring Kit #2299. The Firestone Air Bag included is part #6401.

We’ve had it on the truck almost four years and have not had any issues or tears.  It flexes with our KORE rear leafs and works great in tow/haul.

Here is a link to the Firestone Ride-Rite application guide, which should help: http://www.firestoneip.com/site-resources/ride-rite/pdf/2012_APPGUIDE_WEBSITE.pdf



4x4 AnswerMan,
I need a load sensing valve for a 86 Nissan D21 Hardbody.  I just need to know the after market part for it.

Robert Brown

Hi Robert,
We spent some time looking for your specific year, make, model but couldn't find a factory or aftermarket replacement Load Sensing Proportioning Valve for your Nissan 4WD. Since there is little aftermarket support for these vintage trucks in the US, you may be able to find something overseas.

I’m not familiar with your specific vehicle, but the Load Sensing Proportioning Valve may still be good. All it may need is adjustment. It’s very possible it is out of adjustment, considering the truck has been on the road for over 27 years.    Here’s a link to a pretty handy repair/installation guide for the Nissan Hardbody D21 that shows how to adjust the Load Sensing Proportioning Valve.

If you are still having a hard time finding one, you may need to pick up a used one on Ebay or a wrecking yard. You could also delete the factory proportioning valve altogether, or replace it with a universal proportioning valve, available at Summit Racing http://www.summitracing.com/ .

Good luck.


DURAMAX Diesel Engine built by Banks Engineering.

4x4 AnswerMan,
I am looking for an off road programmer for a 2011 Duramax.
Keith Weigart

Hi Keith,
You’re in luck because there are plenty of options for your truck.  Each manufacturer and tuner has their specific application. Some are mapped to increase MPG, while others are for towing/hauling. Some will uncork your engine, providing an additional 100hp, with a push of a button.

For the hardcore diesel racers, there are custom tuning modules that allow the user to dial in their aftermarket injectors, turbos, intakes, exhaust, propane and water injection for crazy horsepower and torque.

We've had good experiences with some of the more popular ones like Banks, Edge, Superchips, Bully Dog and Jet over the years for semi-stock applications. I would suggest starting with those.

One thing we like about the Superchips power programmers is the feature to set your tire diameter, which comes in handy for vehicles running larger tires. It not only re-calibrates the speedometer, but it also factors in with shift points on the transmission.

You can read more about it in our review of the Superchips Flashpaq

Good luck.



4x4 AnswerMan,

Great looking rig. I am looking for the same steel wheels now for my ‘94 TLC. I currently have 285/75 R16 on 16x8 factory rims. Will these tires be okay on a 16x7 inch rim?

Letter sparked by
Shop Build: Slee Off-Road Toyota 80 Series Land Cruiser

Hi Bernard,
Thanks for resurrecting this story. This is a great build by Slee Off-Road.  As for tire-and-wheel-size compatibility, you should be able to run the 285/75 R16 on Toyota 16x7 steel wheels with no problems. There is a slight chance you may need to use wheel spacers if there are any clearance issues.

Darryl, owner of this fine 80 Series Land Cruiser, is running a skinny 35x10.5 R16 Super Swamper Radial TSL. Even then, I believe he did have to run a wheel spacer.

Enjoy your Cruiser.




4x4 AnswerMan,
I've heard from a guy in Washington of a modified suspension that would make my ‘76 GMC heavy-half ton 4X4 ride better. I was going to add dual shocks up front.  Ron Butler

Hi Ron,
It’s possible to make your GMC 4x4 ride smoother than stock. This can be achieved by using a progressive rate leaf spring for both the front and rear. Most truck springs are linear, meaning they have a constant spring rate. The progressive spring, on the other hand, will ride smoother and get stiffer as it is compressed more (typically under load). We run progressive springs on our diesel Dodge truck and it rides much smoother than it did with the linear springs. 

You can either talk to some of the large spring manufacturers, like Deaver or National Spring, to see if they can make you a set. There might even be a local spring and suspension shop in your area that can build you a custom set. Just make sure to let them know what you’re looking for, like a smooth riding suspension, any lift, etc. Custom usually cost more, so get ready to pay some good dough. Look at other options as well, like the Superlift Softride springs, which are also progressive but much cheaper than custom springs.

As for the dual shocks up front, if you want it to ride smooth you need to make sure they are valved correctly. In other words, if you plan to run two shocks instead of one, the valving needs to be split between both shocks so they share the workload. If they are not, there is a chance the front suspension will ride very rough since you will be running a total of four shocks designed/valved to control the front suspension with only two.



4x4 AnswerMan,
What plug for 2008 Sport Trac with 4.6L?
Larry Roberts

Letter sparked by Innovative Champion One-Piece High-Thread Spark Plug Solves Tuning Challenges on Ford 4.6L, 5.4L and 6.8L Engines

Hi Larry,

Thanks for bringing up these specially designed Champion Spark Plugs for the Ford 4.6L, 5.4L and 6.8L engines. According to Champion, the spark plug number for your vehicle is CHA7989.

What’s nice about the one-piece design from Champion is that it reduces failure or headaches down the road. When servicing the engines, sometimes the factory two-piece plugs can separate during removal, potentially leaving the base trapped within the engine’s cylinder head. The Champion Double Platinum Power spark plug utilizes a one-piece “high-thread” design that replaces two-piece original equipment and/or aftermarket plugs utilized in these engines.

For additional information regarding Champion Spark Plugs please contact your automotive parts and service provider or visit http://www.championsparkplugs.com/



Hi there 4x4 AnswerMan,
I'm a girl so I've got what is probably considered a "stupid girl" question by some but here it goes. I just purchased a 2010 Chevy Silverado LT 1500 4x4 and I would like to put 32" or 33" BFG All Terrains on it. Will they fit without needing any lifts, spacers, etc?

Thank you for any advice you can offer.


Hi Andrea,

First off, there are no stupid questions when it comes to learning more about your truck. The tire size you mentioned should fit on your 2010 Silverado with no lift.  If you would like to give the front tires a little more room, and also level the truck suspension in the process, you can get away with only doing a front leveling kit. It will look good, retain the factory ride and not break the bank.

Enjoy your truck and please feel free to send us more questions anytime. We like girls and trucks.



Dear 4x4 AnswerMan,
I have a problem of leaving my 2004 Jeep Grand Cherokee Laredo 4x4 in "Full-time 4-wheel drive." It snows a lot in Alaska and I always switch back and forth depending on what street I happen to be driving on. With gas prices so high I cannot afford to keep buying gas so quickly because of my lack of awareness. I understand it is also bad on the drivetrain.
The first setting after park is "Part time 4-wheel drive" and has an indicator light. Since I never or hardly ever use the "Part time 4-wheel drive" I do not want or need the indicator light to turn on. Is it possible I can unwire that "part time" indicator lamp and make the lamp only light up when I shift to "Full time"? Can you please describe the procedure to do this if it is possible?
I feel that once I have an idiot light constantly reminding me, I will switch back to 2-wheel drive sooner rather than later. Thanks for any help you may be able to give.
Daniel Sanchez
Anchorage, Alaska

Hi Daniel,

Thanks for your letter.  We leaned on our Off-Road.com Jeep expert Jim Brightly on this one. This is what he had to say:

Sorry, Daniel, you can’t just change some wires around to light a full-time 4WD indicator. It takes a micro switch on the transfer case shifter, the mounting of which would have to be fabricated (you’d need a good transmission or 4x4 shop for that). You could rig a toggle switch and light to remind you to shift out of full-time, though.
Good Luck Jim Brightly, KF7SCT aka “Jeep Creep”

Get more Jeep answers in our monthly Jeep Creep column  


Dear 4x4 AnswerMan,
Are 16-inch wheels available in black that will increase the outside offset to lower the center-of-gravity on a 2008 Toyota FJ Cruiser?
Fred McCoy Houston Texas

Hi Fred,
There are many options for your FJ Cruiser that will achieve what you’re looking to do. You could also black out your factory Toyota wheels and add some Spidertrax wheel spacers (
http://www.spidertrax.com/) if the main purpose of your modification is to increase stability. If it’s to change the look of your FJ, then custom wheels with a positive offset will be your best bet. Discount Tires has a pretty wide selection of wheels on their website that may help you narrow down a brand and design.

If you need specifics on what wheel sizes and offsets are being successfully used on FJ Cruisers by real people both on and off the trail, we suggest you also check out our sister site http://www.fjcruiserforums.com/.  They have an FJ Cruiser Wheel Application Guide that will come in handy http://www.fjcruiserforums.com/forums/wheels-tires/139195-fj-cruiser-specific-16-17-wheel-tire-fitment-guide.html

Good luck.

Have a truck or SUV question for the 4x4 AnswerMan? Send your questions to editor@off-road.com. Please include your name and location, and be as detailed as possible about your questions.

Off-Road.com Newsletter
Join our Weekly Newsletter to get the latest off-road news, reviews, events, and alerts!