13 replies to this topic

[philos65]

On another WTW forum on truck carrying capacities someone mentioned that the majority of 1/2 ton pickups and recent 3/4 ton trucks have rear axle bearings that ride on the axle shaft.  He mentioned he'd replaced 8 or more axle shafts over the years from bearing wearing into the shaft causing pitting and metal loss on the shaft where the bearing rides. 

 

He recommended adapting a full floating axle and 14 bolt differential.  Curious, I checked online prices and they were anywhere from $300 on up plus shipping.  These were pre-1999 chevy 3/4 and one ton rear ends.  

 

Is this a common problem with 1/2 ton pickups carrying pop-up slide in campers and gear?  I'd not heard of this issue before and wonder how closely I need to monitor axle bearings and shafts...

 

Jeff...

 

 

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Edited by philos65, 23 December 2017 - 08:28 PM.

[Mighty Dodge Ram]

Most, if not all, 1/2-ton trucks have semi-float rear axles. I do not know of a 3/4-ton or heavier that does not have full float axles. While it’s true that full floaters are designed to carry more weight, there are plenty of semi-floats out there carrying leightweight campers...Tacomas, Tundras, Rams, Rangers, etc. Assuming you’re not exceeding your GVW with the camper (or close to it) I believe “mechanical sympathy” plays a much larger role in whether your axles hold up or not. My 21 year old, 300k+ miles Dodge Ram 1/2-ton has carried it’s 6400# GVW (and more) over some very rough territory and the rear axle assembly has held up just fine. YMMV. Decide on a camper and then choose a truck that has the appropriate payload rating. Treat your ride with care and it will repay you in adventures!

[Wandering Sagebrush]

<snip>
Treat your ride with care and it will repay you in adventures!

Well said!

[ardvark]

I agree completely with Mighty Dodge Ram and also want to point out the illogical reasoning in the initial axle statement because I often heard statements like that when I worked on RVs.

 

If all or nearly all or the vast majority of anything is market dominate it will naturally follow that if something in that category fails, it will be a member of the category is more widely sold. So if all half-ton trucks have semi-floating rear axles, if any axles in half ton trucks fail, it will be a semi-floating axle and so on. Watch for statements of this nature on the Internet whenever folks make comparisons. To make a valid comparison, you would need a number of examples of each type of axle in the same model truck carrying the same load under the same conditions. If you do not have that there are so many confounding variables, in my opinion, you can't make a valid statement about component reliability.

[Malamute]

I agree completely with Mighty Dodge Ram and also want to point out the illogical reasoning in the initial axle statement because I often heard statements like that when I worked on RVs.

 

If all or nearly all or the vast majority of anything is market dominate it will naturally follow that if something in that category fails, it will be a member of the category is more widely sold. So if all half-ton trucks have semi-floating rear axles, if any axles in half ton trucks fail, it will be a semi-floating axle and so on. Watch for statements of this nature on the Internet whenever folks make comparisons. To make a valid comparison, you would need a number of examples of each type of axle in the same model truck carrying the same load under the same conditions. If you do not have that there are so many confounding variables, in my opinion, you can't make a valid statement about component reliability.

 

 What part of the statement you refer to seems illogical, and how does it relate to work on RVs?

[JaSAn]

 . . . He mentioned he'd replaced 8 or more axle shafts over the years from bearing wearing into the shaft causing pitting and metal loss on the shaft where the bearing rides . . . 

 

I wonder if the original poster knew that the inner race of the bearing is replaceable?  I've had to replace them before.  The inner race might look like part of the shaft but it comes off (must know naughty words in at least 6 languages to remove it).  The only time i ever saw a semi-floating axle shaft damaged is when the bearing froze and the idiot kept driving.

 

jim

[ntsqd]

Not all semi-float rear axles have an inner race. Those in older GM 12 bolt trucks don't to the best of my knowledge and I know for a fact that the semi-floater in our old FJ60 didn't have an inner race. (Nor do the GM pass. car semi-floaters from the days of RWD pass. cars.)

However the Ford 9" does have an inner race. I believe that Dana 44's do as well. The semi-rare semi-float Dana 60 probably does too.

 

I'm not a fan of semi-float axles. I rather dislike them somewhat passionately. That said, I need a real reason to bother with installing full-floater to replace an perfectly functioning semi-floater. Usually there are a whole bunch of collateral effects of such a swap that increase the cost.

 

Those semi-float axles that don't have an inner race tend to be those that use a "C-Clip" to hold the axle shaft in the housing. That is one of the parts that I really dislike about the design. The other is that the axle shaft much be surface hardened in an area where it also flexes. Not a great idea, but if you look at how many miles semi-float, C-Clip axles have collectively accumulated it's pretty hard to condemn the design.

If you have one of the these axles I would suggest annual maintenance and lube replacement. I would also suggest that a quality synthetic lube or a SWEPCO product lube be used. I post this knowing that I'm behind the curve on a GM 12 bolt.....

Edited by ntsqd, 13 January 2018 - 01:58 AM.

[Vic Harder]

Not all semi-float rear axles have an inner race. Those in older GM 12 bolt trucks don't to the best of my knowledge and I know for a fact that the semi-floater in our old FJ60 didn't have an inner race. (Nor do the GM pass. car semi-floaters from the days of RWD pass. cars.)

However the Ford 9" does have an inner race. I believe that Dana 44's do as well. The semi-rare semi-float Dana 60 probably does too.

 

I'm not a fan of semi-float axles. I rather dislike them somewhat passionately. That said, I need a real reason to bother with installing full-floater to replace an perfectly functioning semi-floater. Usually there are a whole bunch of collateral effects of such a swap that increase the cost.

 

Those semi-float axles that don't have an inner race tend to be those that use a "C-Clip" to hold the axle shaft in the housing. That is one of the parts that I really dislike about the design. The other is that the axle shaft much be surface hardened in an area where it also flexes. Not a great idea, but if you look at how many miles semi-float, C-Clip axles have collectively accumulated it's pretty hard to condemn the design.

If you have one of the these axles I would suggest annual maintenance and lube replacement. I would also suggest that a quality synthetic lube or a SWEPCO product lube be used. I post this knowing that I'm behind the curve on a GM 12 bolt.....

Huh, I thought I was in the clear with my GM 3/4 ton... looking at some exploded parts diagrams makes me think that it is a "semi-float" without an inner race.  Can you confirm?  2002 GMC 2500HD is the truck.  Can you also clarify what you recommend for the annual maintenance?  I already change our most fluids and filters every year... 

[JaSAn]

My parts book gives both inner and outer wheel bearings for a 2001 - 2010 GMC 2500HD: Timken QU50399 inner and QU50411 outer.  That would make it a full floater.  Your rear axle should have a large flange with multiple bolts not simply a center bolt in the center of the wheel (see diagram in post #1).

 

All semi-floaters I have ever worked on the wheel bearings are lubed by differential gear lube.  To get to the wheel bearing you must pull the axle out, so no regular maintenance.

 

I stand corrected on integral inner race on the axle; stupid design.

 

jim

[Vic Harder]

My parts book gives both inner and outer wheel bearings for a 2001 - 2010 GMC 2500HD: Timken QU50399 inner and QU50411 outer.  That would make it a full floater.  Your rear axle should have a large flange with multiple bolts not simply a center bolt in the center of the wheel (see diagram in post #1).

 

All semi-floaters I have ever worked on the wheel bearings are lubed by differential gear lube.  To get to the wheel bearing you must pull the axle out, so no regular maintenance.

 

I stand corrected on integral inner race on the axle; stupid design.

 

jim

Thanks Jim, yes, that does look like my truck's axel.  And thanks for the part numbers.  The rear seals on both axels were replaced 30K Km ago (truck has 217K km on it) but the bearings themselves have never been replaced.  Most of those KM were highway miles hauling a 5th wheel.  Would you redo them, just because?