Converting to manual locking front hubs

[1stDeuce]

Confused a bit. First - what is CAD (assume its not Computer/cardboard aided design)? Second, what is hydro coupling?

If only both wheels spin when unlocked and there is no axle movement, I would think that the reduction in moving parts would reduce wear, produce lighter steering and better braking and possibly add a little better gas mileage.

In my friend's truck's case and in watching many videos, it appears only the wheels spin when unlocked and that neither of the ujoints spin either.

Not trying to be argumentative - just trying to learn a bit.

Thanks

Seems nobody answered your questions...

CAD is Center Axle Disconnect. GM and Dodge/Ram trucks use it instead of any sort of "locking hub" to disconnect most of the front driveline, or more precisely, the most power robbing parts of the front driveline... CAD uses a sliding splined coupler on the pass side axle shaft. It disconnects the passenger side axle shaft into two parts that can spin independently. The part of the shafts that you can see on both sides are still connected directly to the tires. The inner part of the pass side shaft becomes disconnected from the outer shaft when the splined coupler is slid to one side by the CAD actuator.

If we consider moving forward, the outer part of the driver side shaft is still connected to the diff and rotates forward with the tire. Inside the differential, the carrier ideally stays still. (More on this in a bit...) The carrier being still keeps the driveshaft from spinning, which would then spin the chain in the transfer case. Both the transfer case chain and the front differential case are partially submerged in oil, so there is definitely some reduction in drag from keeping them still. Meshing gears and bearings fo the differential are also in oil and would cause drag if they spun. All this drag is eliminated by CAD, and adds up to somewhere between 0.1 and 0.5 mpg by most accounts.

Back to the differential side and pinion gears... So the carrier is still, which means the driver's side axle spin results in spinning the side gear of the differential that it is splined to. That side gear meshes with the two pinion gears, which also mesh with the other side gear. The result is that the disconnected stub shaft (splined to it's side gear) spins backwards at road speed. While that sounds awful, none of those parts have any load on them to speak of, and all of the bearings or moving parts involved have some oil film distributed to them at all times. Is there drag associated? Yes, but not likely enough to make a detectable improvement in mileage if you eliminate it...

I mentioned that earlier trucks than yours had no CAD. Everything spun all the time. Stopping ALL of that stuff from spinning with a hub conversion did reduce rotating mass significantly, and would also reduce the drag from spinning all those parts in oil, hence there was a measureable mileage improvement. I find it odd that steering and braking improvements would be detectable at all. I would attribute most of that "improvement" as being due to the seat-of-the-pants-ometer, which has generally proven to be highly influenced by a significant lightening of the wallet...

Back to the diff, which is holding "still"... It turns out that spinning the side gears and pinion gears of the differential with an oil film between them and the case causes SOME drag. This drag can very slowly rotate the differential and driveshaft. This is generally called hydro coupling. While there is certainly some drag and hence mileage loss from hydro coupling, I would guess that the slow spinning of the driveshaft from hydro coupling adds up to qute a bit less drag than your mirrors produce at road speed. Ie, the majority of parasitic drag that would come from the spinning the entire front driveline is eliminated by the CAD. SOME amount is still present in the shafts and side gears, but not much, and likely not enough to measure as an improvement in MPG...

Before you "worry" about all the spinning side gears and CAD parts wearing out, realize that my 310k mile truck has had zero issues with any of those parts, nor with the CV shafts or boots. All of those parts have 310k miles on them too. Ford and Dodge trucks both seem to need infrequent axle U-joint replacement as they seize up. This happens with or without them spinning...

So the big improvement of these kits is eliminating the unit bearings in favor of serviceable tapered bearings. My truck went 220k on the stock front bearings before I replaced them because I thought one was possibly getting noisy. Turns out it was a well cupped tire and the bearings were fine... I have 90k on the new bearings with no issues. My truck is a CC Duramax with a winch bumper and a Warn 8274 with steel cable. I'm probably right at my front axle GAWR, and the "weak" unit bearings seem to be doing fine with it... I would head for Tierra Del Fuego with this truck tomorrow if the opportunity presented itself...

If you do frequent deep water crossings, it is likely to end your unit bearings sooner than if you don't. It is also (from my experience with old school hubs on my '78 Chevy) going to mean you will need to re-pack the bearings in your aftermarket hub conversion more frequently, as they can also be contaminated by water. How many sets of unit bearings will you not have to replace by spending 3x more on a hub conversion? In my case, probably not enough to recover my money, and I plan to keep my truck forever...

I'm not going to say you should or should not spend money to go to aftermarket hubs. I think the pro's and con's are obvious at this time and since it is your truck and your $$ it is certainly your decision.

I will ask that if you do it, please take some photos and do a little write-up with your thoughts.

 

[broncobowsher]

The drag in the axle is from the preloaded bearings on the pinion and the carrier. They are preloaded to maintain accurate alignment during operation. The CAD removes that drag. The spider and side gears spin around, but they are fairly small and have minimal windmilling losses in the oil There is no preload on the spider and side gears, they just float around inside the carrier.

The axle disconnect is generally considered the same economy gains as manual hubs.

If this is an act for fuel economy, you will never see the payback. Any gains just won't add up to cover the cost of the kit.
Servicability? That is a stretch as well. If you actually go through unibearings on a regular basis, maybe. How much is a unibearing? How many do you go through for the cost of the conversion kit? Now add in the time and cost to service the bearings yourself. How much are the seals? How much is the grease? How many times do you need to service these bearings over the life of a sealed and forget about it unibearing?

 

[ramblinChet]

There is a whole lot more to it than serviceability.

A unit bearing on a superduty that rarely seem to last more than 75k, when it goes bad, is downright dangerous.

Point being, and the primary reason I went to traditional taper bearings is that they are more reliable and SAFER.

What is the danger you are talking about?

 

[IdaSHO]

What is the danger you are talking about?

I've already spoken of the danger.
It has everything to do with the plastic bearing cages on OEM unit bearings.
When they go bad, they can go real bad real quick.
So... from stranded in the back country or on the side of the road to put you in the ditch, on your lid, or worse...

I havnt even mentioned all the other hard parts that could be damaged during a nasty failure....

Side by side with the Dynatrac freespin kit that uses proper Timken taper bearings.

Anything else, this motortrend article should help.

4x4 Wheel Hub Upgrade - 1999 Ford F550 - Diesel Power Magazine

Read about Dynatrac Hub conversion kit installation for this 1999 Ford F550, only on dieselpowermag.com, the official website of Diesel Power magazine.

www.motortrend.com

This Turtle Expedition page is a good read as well

Turtle Expedition » The Bearing Thing

www.turtleexpedition.com

 

[ramblinChet]

I've already spoken of the danger.
It has everything to do with the plastic bearing cages on OEM unit bearings.
When they go bad, they can go real bad real quick.
So... from stranded in the back country or on the side of the road to put you in the ditch, on your lid, or worse...

I havnt even mentioned all the other hard parts that could be damaged during a nasty failure....

Side by side with the Dynatrac freespin kit that uses proper Timken taper bearings.

Actually, all of your information points to one single source, Gary Wescott, where according to him, a single unit-bearing failed. A sample size of one is hardly representative of the entire population. What Gary reports, if accurate and true, is a statistical anomaly. If he was unable to identify progressive bearing failure it would logically be reasonable to question his ability to diagnose the root cause of the failure. The failure he describes happens so infrequently it has no relevance. If, on the other hand, this was a common and deadly as you suggest, I am sure we would have heard about it long ago.

Unit-bearing assemblies have been used successfully in the automotive industry for a half-century or more. And no, when unit-bearing assemblies go bad they do not fail without warning nor do they fail catastrophically. Like most bearing failures, they happen gradually over an extended period of time and they provide multiple indications that they are not well. When failing bearings begin to fail they first signal you with a lower frequency that can be felt in the floorboards or pedals. As the failure progresses, the frequency increases and the bearings begin to ring or squeal. If this progressive failure is ignored the frequency shifts much higher with harmonics of the fundamental frequency becoming very high. The temperature of the bearing grows very high, very quickly, at this point and begins to degrade the bearing and other assemblies in close contact.

And unit-bearings are quite easy to replace. I have replaced many over the years and if it takes more than an hour to swap it's usually because the vehicle is a decade old, has 150k miles, and rust is preventing these machined parts from easily separating. I have even removed them on the trail when a fellow adventurer snapped a front axle shaft. We reassembled and kept the stub shaft in the hub assembly and all was well.

You make is sound like it's a big deal, it's not.

 

[IdaSHO]

For most, this isnt a big deal.
But most people change cars/trucks like they change their underwear.
Considering your signature, Id bet you are one of them.
And Ive got a friend that "loves" his Rams, but cannot seem to keep them longer than 80k
Guess what, he hasnt seen a wheel bearing failure either.

The rest of us, that roll heavy and/or with oversized tires, intend to keep our trucks for the long haul and acknowledge the shortcomings in both serviceability and safety, look for a permanent fix.
So we fix it. Its really that simple.

FYI, going rate in parts & labor with OEM is anywhere between $600 and $1000 per side.
Dynatrac is about $2500 So assuming you are already in need of bearings the cost difference is minimal.
If you are already looking at buying new locking hubs or upgrading auto-hubs to manuals, its a wash.

Believe what you want, but these bearings do go bad fast.
Mine went from a slight noise to a wobbling tire in less than 100 miles.

The big difference is context.

Is it momma going across town for groceries and hears a noise?
Or is it a full time RVer blasting down I-80 at 70+MPH?

And I do find your comments interesting, considering your comments in my Dynatrac thread from last march...

Although this is interesting I am curious as to what the numbers are.

First, how many miles do we expect to own the truck? 100k, 250k 500k+?

The next most important question is how often do the unit bearings fail and how much do they cost?

And finally, how much does the Dynatrac kit cost, how much maintenance is required and how many miles will it last?

I am all for performing valuable modifications or upgrades but the numbers tell the truth and I am curious to see some. That way, if my unit bearings fail at some point in the future Dynatracs might or might not be a consideration for me. Your thoughts?

Dynatrac Free-Spin kits (getting rid of unit bearings)

ive had them for years, on the dodge Yukon and Synergy make the conversion kits as well. Might be worth a look.

expeditionportal.com

 

[craig333]

I had one fail with absolutely no noise or feel. I had it in the shop for other service when they found the unit bearing completely gone. I'm not a mechanic but the shops always told me they need special tools to replace a unit bearing (at least one my truck). At least if I have an issue now I can probably repair with the tools I carry.

 

[Metcalf]

I had one fail with absolutely no noise or feel. I had it in the shop for other service when they found the unit bearing completely gone. I'm not a mechanic but the shops always told me they need special tools to replace a unit bearing (at least one my truck). At least if I have an issue now I can probably repair with the tools I carry.

I'd argue that changing normal wheel bearings requires more specialized tools ( and knowledge ) than changing a unit bearing.

To change a 'normal' bearing set on a front ( or rear floating) axle you will need a special spindle nut socket and something to remove and press the bearing races in place. You can do this with a hammer and drift, but it doesn't really mean you should. Then you have to setup the new wheel bearing end-play and make sure the spindle nut is locked into place correctly. Not to mention you have to properly pack the wheel bearings with grease and continue to adjust the end play over the life of the bearings.

In contrast, a unit-bearing is all self contained and ready to go. All the guts are sealed also for easy and clean field installs. Other than perhaps a larger than normal socket for the axle nut ( depending on style ), it is a pretty straight forward process.

 

[IdaSHO]

Well thats just it. Unit bearings can fail quick and to the point of undriveable.

Not so for traditional bearings. Even if they are making noise they wont leave you stranded.

And back to my point (perhaps in the other thread) rarely do traditional bearings were to the point of legitimate roller or race damage. And even then, a shot of grease to both bearings and adjusting end play is an easy “fix” to get you home without it getting much worse.

 

[Metcalf]

Fwiw,
Unit bearing change wont go well if rusted on.
Even in equipped workshops, they can be pita to change.
Maybe something a legitimate ExPo Guy to prepare their existing hubs for if they forsee needing to change them roadside.

If traditional taper bearing setup is too rusted to come apart, it was not in rolling condition to begin with.

When a conventional front wheel bearing goes, it will generally take the spindle with it. I've seen just as many failures with traditional vs unit-bearing setups on the road and the trail. One often overlooked issue with these 'conversion' systems is that they use custom made parts that are not easy to replace on the road. You can always convert back to a unit bearing in the autozone parking lot to get you home. I've also seen a fair number of front axle shaft failures take out the spindle in traditional setups.

A rusted on spindle is going to be bad either way. Moot point. Assemble either with a smear of anti-seize and plan ahead.

I like serviceable parts like wheel bearings just as much as anyone, but this thread is stretching things in a lot of different directions trying to make a case one way or the other.

 

[Metcalf]

Well thats just it. Unit bearings can fail quick and to the point of undriveable.

Not so for traditional bearings. Even if they are making noise they wont leave you stranded.

And back to my point (perhaps in the other thread) rarely do traditional bearings were to the point of legitimate roller or race damage. And even then, a shot of grease to both bearings and adjusting end play is an easy “fix” to get you home without it getting much worse.

I think it really depends on what kind of unit bearing setup we are talking about. There are millions upon millions of unit bearing setups on the road that make it hundreds of thousands of miles without any issues. If we are talking about a 1/2 ton truck doing 1-ton work with oversized tires, we might see more failures. It's a stretch in general. If you're worried about failure, throw a spare unit bearing in the parts bag if that is what you vehicle came with.

Personally, I would be much more worried about bolting on a bunch of custom aftermarket parts that will be very difficult to replace on the road. While the wheel bearings might be fairly common and fairly easy to replace, you better pray any kind of failure doesn't go any deeper to the spindle or bearing hub if something does go wrong.

 

[billiebob]

Greetings

A number of people I know have replaced the unit bearing assemblies in the front and replaced them with one of the several brands of hub conversions. They report a slight mpg advantage, lighter steering and better braking.

Sorry but this is snake oil spin. Modern trucks do this automatically but even stepping back 50 years the mpg difference was pure spin. I had a 1979 F250 4x4 Crewcab..... I regularly had an 850 mile commute. In the winter I mostly locked the hubs in November and rarely disengaged them. I disengaged them because my peers said "Bill disconnect and save gas"....... so I did. But 850 miles 6 times a year thru the mountains I never saw any change in MPG, hubs in or hubs out.....

If you are SPENDING $$$ to convert to manual hubs you will NEVER see daylight. The payback even if you read the most optimistic reviews will take 100 years to actually MAYBE save a few pennies..

There are reasons to switch to manual hubs but none of them involve braking/steering performance or SAVING $$$$.

 

[ramblinChet]

For most, this isnt a big deal.
But most people change cars/trucks like they change their underwear.
Considering your signature, Id bet you are one of them.
And Ive got a friend that "loves" his Rams, but cannot seem to keep them longer than 80k
Guess what, he hasnt seen a wheel bearing failure either.

The rest of us, that roll heavy and/or with oversized tires, intend to keep our trucks for the long haul and acknowledge the shortcomings in both serviceability and safety, look for a permanent fix.
So we fix it. Its really that simple.

FYI, going rate in parts & labor with OEM is anywhere between $600 and $1000 per side.
Dynatrac is about $2500 So assuming you are already in need of bearings the cost difference is minimal.
If you are already looking at buying new locking hubs or upgrading auto-hubs to manuals, its a wash.

Believe what you want, but these bearings do go bad fast.
Mine went from a slight noise to a wobbling tire in less than 100 miles.

The big difference is context.

Is it momma going across town for groceries and hears a noise?
Or is it a full time RVer blasting down I-80 at 70+MPH?

And I do find your comments interesting, considering your comments in my Dynatrac thread from last march...

Dynatrac Free-Spin kits (getting rid of unit bearings)

ive had them for years, on the dodge Yukon and Synergy make the conversion kits as well. Might be worth a look.

expeditionportal.com

Not sure what you intended regarding the underwear reference - I don't wear them

My main point was that your post read like it was intended to scare people. If a unit-bearing goes you will end up on the side of the highway upside down, blah, blah, blah. My goal was to correct this and say that is not true in most all cases. It is a slow and progressive failure.

And to compare apples-to-apples: you are correct, the Dynatrac kit costs around $2,500 and personally, I think it is pretty cool. On the other hand, the OEM replacement hub assemblies go for $484 per side and can easily be found for $350. Let's say labor is a wash even though we both know installing and setting up the Dynatrac will take a bit more. So not we are down to parts, $700-1,000 for OEM or $2,500 for Dynatrac? In my opinion, that is not worth it.

The questions I asked in my post from long ago were asking the very question I just answered above. Is it worth it or not?

For some it is and I respect that - I have no problem with you doing what you think is best for your rig. But for me, the stud who wears no underwear and goes through girlfriends like you go through tanks of gas...Dynatrac are no bueno señor

 

[toddz69]

I ultimately did the tradeoff that @Metcalf mentions with my '01 SD, which of course has locking hubs but also has unit bearings. I bought the truck with 14K on it 20 years ago and now have 232K on it. I had the unit bearings changed at some point in the past few years as a preventative measure while I was having them do the balljoints. I really like the Dynatrac kit (and I've serviced that type of bearing assembly zillions of times on my EB) but in the end, I figured it didn't make much sense for me to pay for the conversion when a unit bearing assembly will last 150-200K for me (one tire size larger than stock).

Todd Z.

 

[IdaSHO]

Nope, not everyone will see the benefit. And thats fine.
In all of my years driving, likely more than a million miles at this point, 600k + logged commercially, Ive never experienced or even seen a traditional wheel bearing failure.

In just the past few years of owning a unit bearing truck, Ive already seen a failure. So by my math, the conversion adds up, and is just one less thing to worry about on the road.

And to be clear, my intention was never to scare people about unit bearings. But their design and nature if failure is real. Real enough for Dodge to push a recall just a year or two ago…. Just more food for thought.

Dodge Ram Wheel Bearing Recalls: A Full Explanation - VehicleHistory

Worried your Dodge Ram might have a wheel bearing recall? Great news, Vehicle History has your back. Here’s everything you need to know.

www.vehiclehistory.com

https://static.nhtsa.gov/odi/rcl/2007/RCONL-07V038-6323.pdf

And word for word….

The front wheel bearings on your truck (VIN: xxxxxxxxxxxxxxxxx) may have been manufactured with an insufficient amount of grease and could fail. This can lead to wheel separation and result in a crash without prior warning.

So ask yourself…. whats the difference between a bearing with not enough grease and a bearing that is at the end of its service life? And have you ever seen a traditional taper bearing setup fail to the point of the wheel coming off of the vehicle?