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Your top 4x4 and off-road tech questions answered here

Posted in How To: Tech Qa on June 5, 2017
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Spacy Blazer

My ‘88 K5 Blazer rear axle is a GM 10-bolt. It is approximately 3 inches narrower than the front 10-bolt axle. I'm running 35-inch tires and I don't plan to upgrade the axles yet. However, I would like the track width of the front and rear axles to be the same. Is there any downside to running rear wheel spacers to make up the width difference? I know GM built them this way for a reason, maybe for improved tracking when going down the road or a tighter turning radius. What do you think? Also, what brand of wheel spacers do you recommend?
@kvarady77
Via Instagram @cappaworks

The width difference between the front and rear axles on the solid-axle GM 4x4 has always been a hotly debated topic. Some believe the width difference allows the rear axle to track through a slightly different path than the front, which helps keep the vehicle from getting stuck in deep snow or mud. Others believe it improves the turning radius or provides driver confidence that if the front fits through a tight section, the rear will fit for sure.

All else being equal, widening the front track width of a vehicle will typically cause more oversteer (dials-out understeer), while widening the rear track width will increase understeer. So it’s possible that the GM K-Series Blazers and trucks originally had an understeer problem. Perhaps the front and rear track width difference was done to combat this problem. Only the engineers at the time would know for sure.

If the width difference bothers you, you can certainly run the wheel spacers in the rear to match the front and rear track widths. In theory, you will be increasing understeer, however you will likely not notice any significant adverse handling issues. Because it is a fullsize truck, I’d recommend some quality 6061 T6 aluminum wheel spacers rather than going with a generic spacer made from who knows what. Companies such as Spidertrax (spidertrax.com) offer quality wheel spacers for many different lug patterns as well as adapters that can be used to fit wheels with a different lug pattern. Be sure to use thread-locking compound on the wheel studs that retain the spacers. Properly torque all of the lug nuts to ensure that they don’t come loose while driving down the road.

No 4x4

I have a ‘95 Jeep Wrangler YJ and the 4x4 doesn't work. I installed a 4x4 Posi-Lok thinking the vacuum lines were cracked and leaking, but this didn't fix the problem. I changed the differential fluid too, but this didn't fix the problem either. Could the issue be coming from the transfer case? I have the AX-5 transmission. I know the transfer case shift lever works because when I put it in 4-Low, the Jeep creeps along slowly. Sometimes the Posi-Lok will get stuck on and it is hard to disengage.
@m4tt1020
Via Instagram @cappaworks

The factory axle-disconnect system found on the Jeep YJ Wrangler and some other 4x4s can be problematic, especially as the vacuum hoses and other components age and wear out. The 4x4 Posi-Lok (4x4posi-lok.com) is an excellent upgrade for the vacuum 4x4 disconnect components, which are replaced with a mechanical shift linkage.

It’s possible that something could be screwy inside the transfer case, but it's unlikely. You might want to change the fluid in the transfer case anyway and look for metal bits just to be safe. If there is a lot of metal in the oil, you might need to dig deeper. Although, I think the real problem is in the front axle somewhere.

Were there metal bits in the differential oil when you changed it? Did everything look OK inside the axle? Is the front driveshaft still intact? It’s possible that you may have a broken axleshaft, broken shift collar in the axle, or maybe some broken differential gears. Are you are sure you installed the 4x4 Posi-Lok properly? It should not be sticking. Did the shift collar in the axle look OK and slide freely prior to installing the 4x4 Posi-Lok? Did you match up the shift fork on the 4x4 Posi-Lok with the groove in the shift collar? I think you might want to start your inspection at the 4x4 Posi-Lok shift fork, axle collar engagement, and shifting. Pull the 4x4 Posi-Lok off of the axle housing and make sure everything is clean and functioning properly, then reinstall the 4x4 Posi-Lok and check the engagement and disengagement.

Narrowing Dana 60

I have a Dana 60 rear axle out of a ‘99 Ford van. It has 3.5-inch axle tubes. It also has a differential which is offset to the passenger side. If I wanted to narrow the whole thing so that both axle shafts are the same length, would I just measure the shorter axleshaft, subtract from the longer one, remove that amount from the long side axle tube, and then order another short axleshaft? Or is there another factor involving the differential? What do I measure from point to point on the axle housing to get the correct axleshaft length?
@az_mikes_willys
Via Instagram @cappaworks

There are several ways to measure and narrow a Dana 60 axle assembly. Most custom-length axleshaft manufacturers such as Currie Enterprises (currieenterprises.com), Moser Engineering (moserengineering.com), RCV Performance Products (rcvperformance.com), and others offer printable online spec sheets that show what axleshaft measurements are needed.

Yes, your proposed method would absolutely work, but remember that the pinion will still be slightly offset to one side, even if the axleshafts are the same length. When a Dana 60 rear axlehousing is cut to allow for equal-length axleshafts, the pinion will be offset a 1/2-inch to the right. Of course, this small amount of offset will generally not be a problem, especially on a longer wheelbase vehicle. Also, it’s not unusual for the engine, transmission, and transfer case of a 4x4 to be slightly offset a few inches to one side of the frame. The problems you could encounter will depend on the vehicle you are working with. Your biggest concern could be rear driveshaft clearance around a longitudinal fuel tank that rests between the framerails.

Diesel Jeep Wrangler

I’m looking to replace the minivan engine in my Jeep Wrangler with a diesel. Does anyone have a complete or partial kit to make the swap?
@30sauce
Via Instagram @cappaworks

Making a diesel engine swap into any 4x4 is quite a labor commitment and financial investment. If you’re making the swap in hopes of paying for the conversion with the increase in fuel economy that a diesel provides, I’m afraid it will be a wasted effort. With normal use of 12,000-15,000 miles a year, a diesel conversion could take 10 or more years to pay for itself at the pump.

If the fuel savings is only a small part of your reasoning for making the conversion, then a diesel swap can make sense for you and you have a few options. The most turnkey option would be to drop the Jeep off at a shop that specializes in diesel Jeep conversions. There are several to choose from such as Bruiser Conversions (bruiserconversions.com), which can sling a four-cylinder Cummins 4BT under the hood and back it up with a 4L80E automatic transmission or an NV4500 manual transmission. Jeff Daniels Jeeps (jdjeeps.com) also specializes in swapping the Cummins 4BT into Jeeps with several different transmission choices including the GM TH400, 700R4, and 4L60E, or Ford AOD for those that desire an automatic or the AX-15, NV4500, or the NSG370 if you prefer a manual. Coty Built (cotybuilt.com) can mate a VW TDI diesel engine to your factory Jeep XJ, YJ, TJ, or JK transmission. All three companies also offer individual parts and kits to help you make the swap at home.

Cummins (cumminsengines.com) has been working on a crate diesel engine program that will start with the R2.8 turbodiesel and expand to other popular Cummins diesel engines. The company plans to have all the wiring, emissions, and paperwork figured out for the shop or at-home swapper. However, you’ll still need to figure out engine mounts and other conversion parts once the Cummins engine kit is available.

Considering the cost of a diesel swap as well as the vehicle downtime encountered when making a swap like this, you might think about waiting for the new ’18 Jeep Wrangler JL to come out. It’s believed that the ’18 or ’19 model will be available with a 3.0L turbodiesel backed up to an eight-speed automatic transmission. Waiting for this Jeep to hit dealer lots is likely the most cost-effective and prudent option.

Clunky Cat

I have a ‘89 Jeep Cherokee XJ with the inline-six. There is a rattling coming from the catalytic converter area. It comes and goes, but mostly stays there. I can really hear it at idle and just as I start to accelerate it gets louder, then the sound of the exhaust and wind noise drown the rattling sound out. It almost sounds like a bolt in a vibrating metal tub. Is there supposed to be an insulator between the exhaust pipe and the cross member? I don't think the catalytic converter has ever been replaced in the last 27 years. Ironically, I just had a new muffler welded on last summer and it’s welded right onto the cat. I'll try to unbolt the cat from the downpipe to see if that makes the sound go away. If not, hacksaw here I come.
@liamlikeneeson
Via Instagram @cappaworks

Exhaust systems can be easily bent when they make contact with off-road obstacles. Sometimes an exhaust hanger can break too. Once bent or allowed to move more than intended, the system may make contact in places it didn’t before, creating new noises. You can check for clearance around the catalytic converter and if it's making contact anywhere, but I think you have a different issue.

It sounds like the monolith inside the catalytic converter is damaged and loose inside the chamber. Catalytic converters can be damaged from impact and they eventually simply wear out. A misfire condition or oil blow-by from worn cylinders and piston rings does significant damage to a catalytic converter too. Oil in the exhaust, unburnt fuel, and running leaded race fuel will cause the insides of a catalytic converter to overheat and melt. The monolith can then break apart. The pieces will tumble around inside and plug the exhaust, significantly decreasing engine performance. A plugged catalytic converter makes it difficult for the engine to rev up and it feels like the power is really choked down. The rattling inside the converter is a tell-tale sign. You may not have any performance issues yet, but they typically follow a rattling catalytic converter. Your Jeep is likely due for a new catalytic converter soon.

Fab 9-inch

I'd be interested in hearing your opinion on using a RuffStuff Specialties fabricated Ford 9-inch housing as a Toyota front axle and utilizing Jeep JK Dana 44 end forgings, knuckles, and so on. What is the overall strength compared to a Dana 44, Dana 60 and the cost/benefit ratio? I don't want or need 1-ton axles the size of a Dana 60 with eight lugs on my wife’s daily driver.
Steven Hoffmeier
Via facebook.com/JohnCappa4x4

The 1-ton knuckle and wheel end parts are expensive and overkill for a lot of smaller and lighter 4x4s like your Toyota. There are many advantages to keeping a lightweight axle assembly under your 4x4 and the Jeep Wrangler JK has tons of aftermarket support, so your idea is a sound one. However, the plan to use a RuffStuff Specialties (ruffstuffspecialties.com) fabricated Ford 9-inch housing does have a few hurdles that need to be overcome. You’ll probably want to start by adding heavy-duty JK end forgings, like those available from aftermarket companies like Dynatrac (dynatrac.com). They are much stronger than the factory end forgings. From there on out to the axle ends you could use factory Jeep Wrangler JK parts. The problem is that I don’t know of any 6-lug JK unit bearing kits and you can’t easily redrill the unit bearings for the Toyota 6-lug pattern because of overlapping holes. However, Adaptit USA (adaptitusa.com) offers a bolt-on wheel spacer adapter that can be used to mate the factory Jeep JK unit bearing with a 5-on-5 lug pattern to your Toyota 6-on-5.5 lug pattern. The Wrangler JK brake rotors will need to be drilled to match the 6-lug spacers and your wheels. If you choose to, you can compensate for the added width from the wheel spacers and decrease the scrub radius by using wheels with more backspacing.

The other issue will be with the axleshafts. Of course a factory JK outer stub axle can be utilized, but the inner axleshafts will have to be custom made to match the 31- or 35-spline Ford 9-inch differential you choose. Companies such as Currie Enterprises (currieenterprises.com), Moser Engineering (moserengineering.com), RCV Performance Products (rcvperformance.com), and others can machine custom axleshafts for this and many other custom applications.

Ultimately, this is just another way to build a light-weight heavy-duty axle assembly. The unsprung weight of a 1-ton axle is fine for slow-speed crawling, but it’s a huge detriment to handling and suspension performance at speed both on- and off-road. The 9-inch center section will be significantly stronger than a Dana 44, but not quite the strength of a Dana 60. It fits in between the two axles. The downside is the low-hanging pinion of the Ford 9-inch, which could cause driveshaft angularity and ground clearance problems depending on the application. If driveshaft angles are a concern, you could go with a True Hi 9 (truehi9.com) high-pinion Ford 9-inch third member.

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