Click for Coverage
Exclusive Content
Original Shows, Motorsports and Live Events
Try it free for 14 days
Due to the EU’s Global Data Protection Regulation, our website is currently unavailable to visitors from most European countries. We apologize for this inconvenience and encourage you to visit for the latest on new cars, car reviews and news, concept cars and auto show coverage, awards and much more.MOTORTREND.COM
  • JP Magazine
  • Dirt Sports + Off-Road
  • 4-Wheel & Off-Road
  • Four Wheeler

Nuts & Bolts - July 2014

Posted in How To: Tech Qa on May 29, 2014
Share this

Swapped Axles = Check Engine
Q I have an ’04 Ford F-150 with axles I swapped in from an ’05 F-350 Super Duty. I have always strived to drive a truck that no one else has, but now I feel I am ahead of the times and have had a miserable time with the computer system in this truck. Every time I go over 40 mph, the check engine light on the dash comes on. If I cycle the key it goes out, but again at 40 mph the check engine light returns.

It has a generic trouble code stating that the throttle body has been put in a safe mode. The axles have been regeared with 4.88s and I run 37-inch Goodyear tires. It’s possible that the ABS computer thinks the truck is going one speed while the VSS is telling the PCM something different. I thought I could outsmart it by cutting a new tone ring for the rear diff back to the tooth count of 108, which is the same as the stock F-150 rearend. But then I realized that with 4.88 gears in the axles, the 108 tooth-count still is not right because with 3.73 revs of driveshaft would be 108 tone pulses. Now with 4.88 gears it should be 141-ish. Am I even on the right track?

I’m just a backwoods Alaskan who’s been building trucks for 14 years but this one has me stumped. Has anyone out there done this or run into this problem? I’ve had countless phone conversations and spent hours online looking for fixes, but I haven’t found one yet. Help!

Keep up the good work on the magazine.
Brian McManus

A Cool truck! While modern vehicles have lots of really cool features, it’s stuff like this that has a lot of us wishing for the old days. I was just as stumped as you were, so I consulted with a company that specializes in doing 4-wheel drive conversions on late-model Ford vans to see if they had any insights. While they didn’t really have any firm solutions due to differences between Ford trucks and vans (there are more than you might think), they did have suggestions that might help point you in the right direction.

I agree with you that the culprit likely has something to do with the PCM receiving info that conflicts with the VSS and ABS system, as the ABS sensors are also often used for things such as vehicle speed, transmission shift points, and so on. You also didn’t directly state that the speedometer is working, but based on your question we’re going to assume that it is at least reading even if it isn’t accurate. If the speedo functions then the computer is getting some sort of speed signal, and this signal is in conflict with information that the computer is gathering elsewhere.

You didn’t specify whether you used the wheel sensors from the Super Duty axles or adapted the F-150 sensors to the donor axles. One of the things that the conversion company mentioned was that the distance of the sensor in relation to the tone ring is really important, and that if the depth is even just a little bit off (like thousandths of an inch), it can cause problems. So if you adapted the F-150 sensors to the Super Duty axles, that might be one place to look. Compare those between the stock applications and adjust as necessary. Depending on which route you took for the swap, you can also try splicing the Super Duty sensors into the F-150 wiring, or vice versa.

Regarding your tone ring question, I’m not sure that’s the right track because people regear Super Duty trucks and F-150s all the time without issue. Sure, the speedometer (and other speed-related functions) may be off without a programmer, but regearing by itself doesn’t typically throw codes in either an F-150 or a Super Duty. Although your math appears to be right, the number of teeth and related pulses is more about system accuracy than whether or not the system works at all. If you have the tools and equipment to machine a new tone ring to mimic the factory configuration, I say go for it, but that’s probably not going to solve your problem. In the best case scenario it might help you avoid needing a programmer to make the speedo accurate, but at worst it will just cause more problems. That said, it wouldn’t be a bad idea to inspect the rear axle tone ring carefully, as they are easy to damage during a gear swap.

Since the check engine light comes on over a certain vehicle speed, it could be that the signal needs to be sped up or slowed down. In other words, the computer could be thinking that you’re going over 100 mph when you’re only doing 40. Our contact mentioned that some of their conversions require a little box that alters the speed signal (slows it down) so that it matches what else the computer is seeing.

The truth is, however, all of this is really nothing more than spit-balling for a solution. Although this probably isn’t what you want to hear, what you really need to do is take the truck somewhere that has a high-powered scan tool that can log data and show you what’s going on in real time. This is the only definitive way to know for certain what the problem is and then come up with a solution. Even though you’d think that these systems are the same across all of Ford’s truck platforms, unfortunately that’s just not the case when it comes to these kinds of problems. These days, F-150s are very different from Super Duty trucks and even vans, and there’s not as much interchangeability as there once was.

I welcome readers to chime in with any potential fixes. Definitely let us know if you get to the bottom of it, as I’m sure you’re not the only one out there trying to do this swap. Good luck!

Pre–OBD-II Touchscreen
Q I’m still in the planning/prep stage of an engine swap for my ’78 Wagoneer and could use some help with instrumentation. My motives are better mileage, towing, and reliability than the current tired 401 under the hood. I have a GM 6.2L diesel that is going in and a new Banks Sidewinder turbo staring at me in the garage. The engine rebuild is almost complete, but I haven’t put any sensors on it yet. Since this Jeep has been in the family since new and is my daily driver, I want to keep the interior (and dash) looking stock.

I’d love to hide a Banks IQ system in the glovebox instead of hacking up the dash for a tach, pyrometer, and a few other gauges I need to add. The Banks IQ allows you to customize your on-screen gauges, use it as a nav system, add a backup camera, and if hooked up to an amplifier it could even be a stereo with Bluetooth phone integration. The only problem is that this system and all the others I’ve seen require an OBD-II interface.

Since my 6.2L has the older, pre–OBD-II, mechanical injection pump I can’t just grab an old harness and sensors from a ’90s-era truck. I asked Banks a while back and they said that their system will not work on older rigs that don’t use OBD-II. Does anyone make a setup like this that can interface with older, analog sensors? If not, are there any cars or trucks that I can harvest a computer and harness from to handle the IQ-to-sensor translation? It seems crazy to add a bunch of hack-job wiring and electronics just to translate oil pressure and temperature. It seems like a thousand guys with hot rods and resto-mod trucks would have tackled this problem by now.

A While what you have in mind sounds pretty cool and appears to be quite simple on the surface, it is actually more difficult than it seems because you’re trying to apply newer digital technology to an older analog platform. If we’re understanding you correctly, your ideal would be a touchscreen that you could clip to the dash, mount in the glovebox, or put on the seat next to you, but in a second stash the screen under the seat or in the glovebox for a totally unmolested, stock-looking interior, right? Unfortunately, that’s going to be a tough one to pull off.

Your choice of a Chevy 6.2L diesel is an interesting one and probably not the first choice for some people, but it’s outside the box, different, and should be easy enough to pull off in the Wagoneer’s cavernous area under the hood. Plus, as you mentioned, the 6.2L is going to be all mechanical, so it’s going to be very simple to make the thing run. Unfortunately, that mechanical stuff does not translate well to systems like the Banks IQ, which relies on later OBD-II technology to obtain its information. With OBD-II systems, pretty much everything you would need to run gauges plus a bunch of other information is all delivered electronically to the vehicle’s computer, other vehicle systems, and the OBD-II port under the dash with a few wires. It sounds simple, but it takes a lot of technology to make that happen, and unfortunately it’s not like you can wire in an electric oil pressure sender to the system and expect it to work. Or worse, attempt to adapt the OBD-II harness from a different vehicle just to try and make something like what you want work. Sorry, but I just don’t see it happening.

All is not lost, however. Auto Meter ( has recently released a compact and fully configurable LCD dash display. Designed mostly around racing but with a nod to the street rod crowd, I’d be willing to bet this would get you very close to what you’re looking for even if it does not have a touchscreen. How so? If I were in your shoes, I would take advantage of the unusual position of the glovebox on your Wagoneer, which is right in the middle of the dash. This Auto Meter Dash Display is compact enough that with some simple fab work you could mount the display just inside the glovebox door. Open the glovebox when you need to see the gauges, but when you get where you’re going, simply close the glovebox and you have an unmolested factory dash and interior. Since the Auto Meter unit is totally configurable, you can have it display whatever (the pyrometer may be a tall order, but check with Auto Meter) and however you want. Keep in mind that you should be able to run the sensors for the Auto Meter dash and the factory dash in tandem so the Jeep’s water, speedometer, and oil pressure gauges will still function, yet you can choose to display these gauges on the LCD screen as well. If this doesn’t fit your needs, then keep scouring the street rod scene for some whiz-bang product that’s closer to what you’re looking for, but this is the best solution I found.

Clunky Rear
Q I bought a used ’03 Chevy Silverado Z-71 in 2012. I also purchased an extended two-year warranty that runs out this July. The truck has a clunk in the rearend at certain times, so I took it to the dealership. They removed the driveshaft and checked it out, but they said everything is OK and that it’s just backlash. I read somewhere that backlash is play in the ring gear, and that the pinion and ring gears are not meshing properly. It had 97,000 miles on it when I bought it and it has 104,000 miles on it now, and I haven’t abused it at all during this time. Can you help? If it needs to be fixed, what do I tell the dealership to make them fix it? All of the fluids are good and I only play mildly in the mud. I’m told the rearend is a 10-bolt with a G80 differential. Thank you very much.
Dennis M.

A Backlash is a specification that measures the amount of free play, or “slack,” between the teeth of the ring gear and the pinion in a differential. A small amount of backlash is necessary to ensure proper lubrication of the ring and pinion gears. That said, one of the first telltale signs that a rearend is worn out is when backlash is outside recommended specifications.

According to Randy’s Ring & Pinion (, the backlash specification for your rear axle is 0.006-0.010 inch. This specification is measured by pulling the rear differential cover and using a dial indicator to measure how much movement back and forth the ring gear has before it engages the pinion (the pinion must be immobilized while measurements are being made). If the ring gear consistently measures greater than 0.010 inch of movement, the backlash is out of specification. Considering the mileage of the vehicle, a couple thousandths of an inch outside that spec is probably OK, but too much outside is indicative of worn bearings or an excessively worn ring-and-pinion. While you’re there, grab the pinion yoke and see if it has any movement in or out, or side-to-side. If there is, new pinion bearings are in order.

If you don’t have the tools and experience to measure backlash yourself, then take the truck back to the dealer and ask them to show you the backlash measurement of your truck’s rearend. This will, in theory at least, make them actually measure it. Also be sure to read the fine print of your warranty contract; many extended warranty contracts allow them to install used parts or a complete used rearend as part of a warranty claim. If the clunk is slight and only happens every once in a while (which isn’t all that uncommon, especially with a G80 differential), sometimes a slight known inconvenience is better than swapping in parts with a completely unknown history.

Missed the Brakes
Q Your answer about flat towing (“Towing Flat,” Nuts & Bolts, Apr. ’14) neglected to mention any provision for applying the brakes in the towed vehicle when the driver hits the brake pedal in the towing vehicle. Not only is this required by law in most states, but it’s also a pretty good idea. There are various systems available to make this work.
G. Blair

A Well, I guess I really stepped in it this time, because it turns out you are correct. Though not required in every single state, most states do have some sort of law that requires towed vehicles of any kind (trailer or otherwise) over a certain weight to have a brake system that will apply the brakes on at least one axle of the towed vehicle when the towing vehicle’s brakes are applied. The requirements vary quite a bit from state to state: California requires brakes on anything over 1,500 pounds, while Texas doesn’t require brakes on any trailer under 4,500 pounds. Still others have braking requirements for trailers (cargo) while specifically excluding towed vehicles like a car or truck. The majority of the states require brakes on anything being towed over 3,000 pounds, and since most of our 4x4s are over that, just about anyone reading this should have a brake system on his or her 4x4 when flat-towing it. It has been my experience and that of many others that these laws are not enforced, but even so, flat-towing without brakes in a state that requires them opens you up to some serious liability in the event of an accident, even if the accident is not your fault.

But your last point is the best one: It’s not just the law; it’s a good idea. Not only do these brake systems enable you to stop more quickly, but they’re just safer in general. Most systems even have a breakaway function that applies the brakes on the towed vehicle in the event it comes loose on the road. We’ve all heard horror stories about that.

A variety of electric, hydraulic, and vacuum-assisted systems on the market can be temporarily or permanently mounted in a flat-towed vehicle. Pick up an RV magazine or visit any store that caters to RV clientele for more information on a system that works for your needs and budget.

Nuts, I’m Confused
Older Jeep, Better Ride
Q I have a ’75 CJ-6 that I special-ordered and bought new in April 1975. It has a 360, 3:73 gears, and the old narrow springs. It sat for years while we raised four kids, but now it’s my time! I am not a rockcrawler or heavy mountain climber, but dirt roads and tackling some hills is great. I want a decent ride and better handling on the road while maintaining good off-road manners, and I would like to update the Jeep with a new spring setup. I understand that coils and a four-link are the way to go, but I would prefer to keep it on leaf springs. Should I use Wrangler springs or do you have a better idea? It’s my understanding they ride better and have a more progressive spring rate.
Wayne C.

A I’m sure many of our readers wish they had hung on to a 4x4 from their past, so congrats to you for keeping your somewhat unusual Jeep all these years. CJ-6s make great trail rigs due to their longer wheelbase, and the production numbers were low enough that you don’t see very many of them on the trails these days.

A four-link suspension with coil springs has its advantages, especially in the ride and handling department, but that’s probably not the best option for your needs and uses. First, it would take a whole lot of custom fabrication work to pull off a four-link on one end, let alone both ends, of your Jeep. Aside from the extensive fabrication involved, you will quickly find that the narrow frame under your Jeep (among a few other things) doesn’t lend itself to packaging a properly designed link suspension without basically throwing everything away but the body and drivetrain, and then starting over. Second, setting up any type of four-link correctly takes a lot of knowledge; there are only a few ways to do it right and a whole lot of ways to do it wrong. But the third and most important point in my eyes is you just don’t need to go through all that work. Not only would you be taking away from the cool vintage aspect of your Jeep, but you can easily work with a leaf-spring suspension to deliver the comfortable ride you want while maintaining off-road capability.

Lots of people with early CJs like yours have had great success using 21⁄2-inch-wide springs from ’87-’95 YJ Wranglers. The wider springs, combined with the newer designs and technology that go into them, generally yield vast improvements in both on-road ride and off-road flex. You didn’t mention your desired lift height or tire size, but there are excellent YJ springs available from several suspension manufacturers in a variety of lift heights, so you have a lot of options.

To do the conversion, you are going to need new, wider spring hangers for the frame, wider spring perches for the axles, and wider U-bolt plates with new U-bolts. Both the hangers and the perches can be purchased from shops that supply suspension builder parts and brackets, such as Rusty’s Off-Road ( or Bluetorch Fabworks ( You can also make your own with some time, knowledge, and plate steel. Attaching these components to the frame and axles will require welding and possibly some light fabrication, but nothing like a four-link suspension. Unless you plan on going with some really tall tires, resist the urge to do a spring-over conversion, as this would open up a whole different realm of things that need to be addressed. If fabbing up new mounts is more work than you want to do, you can always consult with a custom spring manufacturer such as Alcan Spring ( about having a set of springs built to your specifications.

Submission Information
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 (, 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. Write to: Nuts & Bolts, 4-Wheel & Off-Road, 831 S. Douglas St., El Segundo, CA 90245 fax to: 818.566.8501 Email to:

Connect With Us

Newsletter Sign Up

Subscribe to the Magazine

Browse Articles By Vehicle

See Results