Broken Axle?

[FishAR]

How do you know if you have a broken axle? I got stuck on my lot, buried down one side. Turned out the reason is the park brake was rusted to the drum on that side. While gently rocking it under the supervision of the tow truck driver who winched me forward we heard a loud pop.

The passenger side wheels were just dragging in the sand. 

I've got a knowledgeable guy here who got the brake unstuck, he used to be a big truck mechanic. I asked him about the pop. He said he hoped it wasn't the u joint. Motorhome moved under it's own power after he unstuck the brake, we only moved it a foot. He found the driveshaft strap off and thought we had big problems, but it turns out it was left off from my tow almost 3 years ago. He said I was very fortunate. He's left to get new straps.

I asked about the axle, he doesn't seem too concerned about it. He said the only way to tell is to pull it apart. He says the other side will drive the motorhome therefore not being able to tell.

 

Asking what you guys think, if anyone has ever broken an axle, or if anyone thinks it's even a remote possibility. It's just something that worries me, hopefully without merit.

[DavidL]

Highly doubtful the axle snapped...and if it did, and if the rear end is "open" (which most all are), then it would not drive forward if one of the axles spins free due to being snapped.

https://www.differentials.com/wp-content/uploads/2018/04/Differential-and-Axle-Exploded-View-Diagrams.pdf

[Dr4Film]

There were some recent postings about rusted drums and not to attempt to move it without first freeing up the rusted drum.

One person posted that it cost him big bucks having to rebuild the rear end.

Here is the thread.

 

[vito.a]

David is correct.  Your differential will turn the side that turns with least resistance.  If an axle was broken, then the motorhome would not move under it's own power.  It would just spin that side internally.  

[Tom Cherry]

OK….DUMB OLD ME.  I used to get “stuck” sometimes….should NOT have been where I was…W/O 4WD.  Also had buddies that specialized in “Wedding Pranks”.

On a NORMAL auto or SUV the poor man’s Posi-Axle is to, when one wheel is spinning, gently apply the parking brake.  That then slows down the wheel with NO TRACTION….it eventually then transfers enough torque to the OTHER WHEEL and you get traction….how much….obviously depends on the terrain and surface.  But I have personally walked a few vehicles out when they got a rear wheel embedded in mud, but had hard ground on the other side.  The Posi-Axle has clutches and mechanically did that….modern ATS systems monitor the individual wheel revs and apply the brakes via the “computer”.

My “friends” would place a bottle jack under the Groom’s ride…one side.  FUNNY ….up to a point.  The solution….rev up the mill and apply, gently, the parking brake.  BINGO pops right off the bottle jack.

OK….MY DUMB TEST…

Block the front (BOTH)  and ONE side of the drive. Jack up one side….maybe an inch.  Have an assistant.  Wear heavy leather gloves.  Have the assistant drop the tranny into gear….do NOT accelerate…while you hold your gloved hands on the outside of the jacked up wheel…tight, but not so much, you’d “SPIN”.  If it doesn’t turn or you can sort of hold it…have the assistant increase the RPM.  A speaker phone is nice for communicating…

NOW…reverse and do the other side.  ODDS ARE…you’re fine.  The POP was the drum with rust breaking free….

As Vito said…you would or should know or hear “mess”.  But, he just like me, agrees….and my “OK! I’m super worried” test above will ally your fears….OR show that the Differential or an Axle (broken?)…has done been “hurt”.

LET us know what you do and find out…

[Dr4Film]

When your coach needs to be towed, the road tech will either remove the drive shaft at the universals or remove one side of the drive axle. I have seen it done both ways.

[Ivan K]

I have broken more than one axle in the day and even though it was a locked axle, there was a definite scary pull to the broken side. No way you could move the rig with only one good axle on our open rear ends. Either way, it is easy to pull and inspect an axle to check the splines if damage was suspected.

[FishAR]

Thanks everyone, I believe you have allayed my fears.

I probably just misunderstood him, he was talking about something called a power divider and said it was like atc. He was talking over my head.

He crawled back under and greased my u joints and that got me to thinking again. Not only did the guy 3 years ago not put the driveshaft saddle back, apparently no one doing my service has ever greased the u joints. If they had I'd think they would have noticed that saddle just hanging there. I guess it's called a saddle, not sure, he changed both of them. Gave me the old one as a souvenir as it had a half moon worn in it from the driveshaft. He said God had really been looking after me.

[Ivan K]

Just a terminology but a 'saddle' is machined into the yoke and 'straps' are what keeps the ujoint in them. By 'power divider', he had to reference the actual diffential unit with spider gears, inside the pumpkin, and if they were damaged, you should hear and obvious crunching sound. Big motor rigs typically do not use straps and the ujoints are pressed in, making axle removal an easier option. Yes, you were lucky not dropping the front of driveshaft into the ground.

[Benjamin]

If the U joint saddle or strap was missing, you wouldn't get far.  Even one bolt missing out of a U joint and it would fail under the first hard acceleration.  I would think the saddle and strap were a safety hanger for the driveshaft, but I've never seen one on a DP driveshaft that's what, 12" long?  A power divider is the differential between two powered axles on a tandem drive. If you don't have tandem drive, he was bamboozling you with five dollar words, or he was making a comparison and you missed the comparison part. 

It is possible that you broke something inside the differential yet it still goes forward. I'd jack each side up and turn it to feel for a clunk. Or, clean the magnet on the fill plug and check it again at 50,100, 200, 500 and every 1,000 until you're comfortable. 

Edited May 17 by Benjamin

[96 EVO]

8 minutes ago, Benjamin said:

  A power divider is the differential between two powered axles on a tandem drive.  

Ya.... None of us have 'tandem drive'!

[Tom Cherry]

WOW….getting mixed terms and so forth.

I’m going to declare my alligence to Ivan and Vito

Lets stay on the same page.  A standard differential, whether on a lawn tractor or an OTR rig, not “tandem” has been around since Henry Ford.  The gears and such inside allow one wheel to turn faster than the other….otherwise…it would be a solid axle.

https://www.hrparts.com/blog/post/what-is-differential-diagram-how-works

Suggest folks not familiar, or those “quasi familiar” go here.. 5 minute read….with pictures.

We have an OPEN differential…. PURE and simple…. Matters not on a Motor Home or a John Deere tractor or whatever.  If it has a pure or open differential….it works the same…. Just a matter of scale….like comparing a “8 OZ hammer to a 10 pound sledge”….a hammer, generically speaking…is a hammer…same for a differential.

OK…wild terms and confusion.  Technically, the standard or open differential is a “power dividing mechanism.  When one turns sharp…most of the power, as in the inner axle is “transferred” from the drive shaft to the inner axle.  Almost…if you like….LOCKED or a direct gear drive.  The Outer one is just floating along and the movement of the carrier or the “innards” allow the outer to MOVE FASTER….otherwise….mega tire wear.

NOW…back to my example…  when one axle (wheel) is allowed to turn faster and the other one is barely moving or NOT moving, the antiquated design will allow all the torque to go to the axle with less drag or resistance.  SO…one wheel on pavement snd one in the mud….bingo, the one in the mud spins like a whirligig in a hurricane.  The one on the pavement is content to rest….thus…one is incapacitated and stuck.

Hot Rodders and Hunters and off road enthusiasts KNOW that one can mire up and get even a 4WD stuck.  Seen it many times.  Both sides in the mud and the other sides on harder or surfaces with more coefficient of friction….YOU ARE STUCK….

Thus, the design on the inside was modified.  A set of clutches was installed….on each side.  When one axle is spinning its Wheel….the clutches work interactively (memory)….and then the hey, isn’t this fun spinning axle gets “cut off” as in all the driveshaft torque is transmitted to the other one.  Bingo…that wheel begins to dig in and the wheel has traction and the vehicle moves forward…but when that wheel gets stuck….then the clutches swap back and the other wheel starts to PULL.  Drag racers may have a locked or solid axle…since the ain’t making turns.  Folks like me then using a Positive Traction (Posi”) axle, with expertise and throttle control, can “walk” out a stuck vehicle.  Tricky…but if you happen to have a Posi in the front…even my DW could do it…  WE DO NOT HAVE A POSI….BUT UNDERSTAND THE PRINCIPLE.

My example still stands.  Modern Day ATS systems apply, precisely, enough braking so the free wheeling or spinning axle slowed down….and more torque is applied to the non moving side.  And the old fashioned “learned in the mud” method of gradually applying the parking brake slows both down….but the power will be shifted to the one not turning enough….get it moving and also get a little traction….and you “walk” the beast out.

Hope the link helps and this keeps things back on track.

Based on understanding how ours works and the voices of experience and also, been there….done that…the advice to block and jack and test is appropriate.

Otherwise, find a good OTR shop or a HD truck shop that specializes in repair of differentials involved.  Otherwise test and drive on.

ODDS ARE…things are fine.  We have an over engineered or poerhaps a robust rear drive train… 

Just be aware.  A Frozen drum brake is a potential for issues.  It MIGHT be better to pay a mobile “mechanical” tech from a heqvy duty truck garage to come put and break loose the rusted bond,  ORDINARILY….backing up and then pulling forward….not rapid shifting, will break the bond. But if try to pop into drive….rev it up and then punch R…at anything other than idle…is gonna hurt the rear end and the Allison and the driveshaft and you may spend 10 times what a mobile tech would have cost….  

Experential Docent

[Dr4Film]

Some coaches come with the ATC option. My Windsor has it along with my Dynasty. I had to use the ATC when I got the Windsor stuck in my back alley way in the soft sand. It is a momentary switch, hold it on and the drive axles are now turning together. The coach walked right out of the soft sand it had been stuck in.

[Tom Cherry]

1 hour ago, Dr4Film said:

Some coaches come with the ATC option. My Windsor has it along with my Dynasty. I had to use the ATC when I got the Windsor stuck in my back alley way in the soft sand. It is a momentary switch, hold it on and the drive axles are now turning together. The coach walked right out of the soft sand it had been stuck in.

Yes,

BUT, it is a bit different.  As I explained....the old fashioned application of the parking brake worked in a car. BUT, the Posi-Axle was more effective and was far superior.

If you read the Owner's manual explanation of the ABS/ATC , there are subtle nuances.  YES, the braking or individual wheel braking is used.  BUT, also the ECM (ECU) is over ridden, so the engine sort of "perks up" and allows MORE torque at a lower RPM.  Frank McElroy might clarify my simplification...but you get MORE torque.

Then the individual spinning wheel is "throttled back" as in slowed down. The normal operation of the Differential takes over...and it, internally, kicks up the torque to the wheel with traction.  OK...a Posi-axle on a FWD is quicker...but eventually, the controlled braking took over.  My old International Scout with the Dana transfer case was a BEAST of a FWD system....and it came with a Pos-Axle.  IT only got stuck once...and I worked hard at accomplishing that.

I don't think....other may know...exactly HOW much or what percentage increase the ATC switch does....compared to what one is used to on a FWD...the old or the new ATC controlled braking.

SO, if it works... GREAT.  OPPS...if the brake DRUMS ARE RUSTED AND FROZEN....the ATC ain't gonna work...

Good comment....

2009 Camelot Owner Manual....ATC activation and explanation.pdf

[Benjamin]

That wouldn't be Automatic Traction Control if it was a momentary switch, would it.  Maybe you turned the ATC OFF to let the engine give more power?  I don't have ATC, just assuming it works similar to cars and is on by default, the switch if for turning it off in soft conditions when the programming won't let it use enough power to get out.  Traction control seems to work better than I can do on paved slippery surfaces and all the snow I've encountered, just not programmed for off road, though maybe that's fixed on newer 4wd.  In any case, ATC would not enable a broken axle shaft or differential to move like a differential lock or posi does, and I've never heard of posi on a motorhome.  

I'd like to see a pic of the saddle and strap you're talking about.  And also which side was locked up?  I'd think the one that was free would spin and bury itself, while the stuck one would stay on top of the ground. 

Stuck brakes can usually be freed with gentle pressure.  If that doesn't work, then tapping the pads loose is not hard, just dangerous if you don't block the wheels, or can't fit.  The parking brakes have to be released, hence the danger. 

 

[Tom Cherry]

1 minute ago, Benjamin said:

That wouldn't be Automatic Traction Control if it was a momentary switch, would it.  Maybe you turned the ATC OFF to let the engine give more power?  I don't have ATC, just assuming it works similar to cars and is on by default, the switch if for turning it off in soft conditions when the programming won't let it use enough power to get out.  Traction control seems to work better than I can do on paved slippery surfaces and all the snow I've encountered, just not programmed for off road, though maybe that's fixed on newer 4wd.  In any case, ATC would not enable a broken axle shaft or differential to move like a differential lock or posi does, and I've never heard of posi on a motorhome.  

I'd like to see a pic of the saddle and strap you're talking about.  And also which side was locked up?  I'd think the one that was free would spin and bury itself, while the stuck one would stay on top of the ground. 

Stuck brakes can usually be freed with gentle pressure.  If that doesn't work, then tapping the pads loose is not hard, just dangerous if you don't block the wheels, or can't fit.  The parking brakes have to be released, hence the danger. 

 

read the excerpt from my manual.  You can download any 2006 or on up manual or at least Camelot on up.  The ABS/ATC is a fully active...FULL TIME SYSTEM.  It gives you braking and traction control during events like rain and such.  That is what Bendix designed it for.  SO....note the ALWAYS ACTIVE note. I didn't feel it was necessary to print the previous page as it went into the tech side of it.

BUT, if you read this.  You get an ATC BOOST... (and If I used ATS...my bad)...that is what a lot of automotive companies call it.

The Momentary Contact ATC switch is like a Turbo Boost for a system that is full time.  SO, technically, it overrides the conventional....just rolling down the highway system....that is ALWAYS ON.

Next, it, per the page, does two things.

SO, depending on your point of view or the semantics...

WE ALWAYS have a certain amount of ABS....which is really the MOST important and critical. BUT, if you need immediate help...like you made an UH OH, then when you push and it is NOT locked in....MOMENTARY...the ATC control...you get the TWO step boost...as explained.

That's how it work...and how it is explained.

[Benjamin]

Traction control limits torque, and applies brakes to limit speeds at low speeds. I'm not so sure of what that manual is saying.  To me the "ATC switch" paragraph sound just like it's turning the system OFF, like has always been available with ATC, but explained in a more salemanlike wording.  It could also be limiting the limit on engine power, while still applying some braking?  Or it could be a power boost over stock settings?  The way the paragraph starts and ends with garbage sentences, I have a hard time putting any credibility in the rest of the paragraph. 

so the three possibilities I see

1. the switch turns off the system

2. the switch reduces the hp limit on the system and still provides some braking

3. the switch provides a hp boost over stock

Edited May 18 by Benjamin

[Tom Cherry]

12 minutes ago, Benjamin said:

Traction control limits torque, and applies brakes to limit speeds at low speeds. I'm not so sure of what that manual is saying.  To me the "ATC switch" paragraph sound just like it's turning the system OFF, like has always been available with ATC, but explained in a more salemanlike wording.  It could also be limiting the limit on engine power, while still applying some braking?  Or it could be a power boost over stock settings?  The way the paragraph starts and ends with garbage sentences, I have a hard time putting any credibility in the rest of the paragraph. 

so the three possibilities I see

1. the switch turns off the system

2. the switch reduces the hp limit on the system and still provides some braking

3. the switch provides a hp boost over stock

Well, that is what Bendix says and how it was designed...

My take...

The ABS/ATC works, full time and is always ACTIVE so you are safer...especially in a panic braking situation.  BTW...I attended a 3 day Corvette Performance (and defensive driving) school.  The first thing they taught us and took us out onto a wet skid pad....  DO NOT BABY THE ABS.  HIT IT WITH BOTH FEET.  It is designed for a PANIC stop.  YES, use the controlled or pulsating or feathering braking techniques you were taught.  Their major gripe...that Drivers Ed teachers gloss over or don't really understand ABS.

When you say OMG...I GOTTA STOP...hit the pedal hard (on the Vette)...same for the ABS.  You have to "wake it up" and put it in the panic mode to control the stopping and IT will keep the wheels from totally locking up....

OK...next up...the infamous switch.

It says  "THIS IS A BOOST" You are NOT supposed to drive with this switch on...that is why it is MOMENTARY CONTACT"

Past that. 

The NORMAL ABS/ATC SYSTEM is now OFF...NADA...KAPUT....as in there is a BOOST NEEDED...as in you are in trouble....and potentially stuck.

The ECM is now being put into a HOT ROD MODE...as in the Torque is being kicked up...more torque to the wheels to try to extricate you from your stupidity.

The ATC Braking now is focused on the REAR WHEELS....forget the front...they ain't gonna pull you out.  SO, the ATC acts like my old Posi-Axle and the wheel spin is reduced or controlled and the natural or designed action of the Open Differential takes over or is allowed MORE FREEDOM.  Thus the illfated spinning wheel gets shut down.  That kicks MORE Torque to the wheel with traction and the Engine is deliverig MORE fUEL but the RPM are being controlled.

That's my take and understanding.  Download the Bendix manual...

OK>>>BOGO...here it is... Happen to have my PDF on another screen...

 

 

Bendix ABS_ATC Manual.pdf

[Dr4Film]

Here is another thread which discusses the use of the ATC Switch.

 

[Benjamin]

Where does it say "this is a boost"?  maybe that would help explain it.  I still can't find anything that indicates the ATC ever applies more fuel or more hp than without the ATC.  I can't believe there is a "hot rod mode" in the ECU, the EPA would love that. 

From the Bendix manual, it's possible the switch turns on the "smart ATC" or more likely the "optional off road ATC mode".  Those both allow GREATER wheel slip than the standard ATC mode, that is, they reduce the ATC's reduction to engine power, not provide additional power over the base mode.  

In my opinion, the switch should be used on soft surfaces, and it "dials down" the ATC settings.  On ice or snow on hard surfaces, the standard mode seems to work. 

Another thing ATC does is protect the driveline from operator abuse.  It is in the manufacturers interests to keep it on, and turned up to limit wheel slip as much as possible as long as possible. 

[FishAR]

9 hours ago, Benjamin said:

That wouldn't be Automatic Traction Control if it was a momentary switch, would it.  Maybe you turned the ATC OFF to let the engine give more power?  I don't have ATC, just assuming it works similar to cars and is on by default, the switch if for turning it off in soft conditions when the programming won't let it use enough power to get out.  Traction control seems to work better than I can do on paved slippery surfaces and all the snow I've encountered, just not programmed for off road, though maybe that's fixed on newer 4wd.  In any case, ATC would not enable a broken axle shaft or differential to move like a differential lock or posi does, and I've never heard of posi on a motorhome.  

I'd like to see a pic of the saddle and strap you're talking about.  And also which side was locked up?  I'd think the one that was free would spin and bury itself, while the stuck one would stay on top of the ground. 

Stuck brakes can usually be freed with gentle pressure.  If that doesn't work, then tapping the pads loose is not hard, just dangerous if you don't block the wheels, or can't fit.  The parking brakes have to be released, hence the danger. 

 

There were 2.Front one hanging by one bolt.T

Edited May 18 by FishAR

[Benjamin]

I was wrong, that looks exactly like Ivan described, the U joint strap.  Even if you had to remove and replace the yoke from the differential, that is about the cheapest and easiest place to break, if something is going to break. 

[Tom Cherry]

10 hours ago, Benjamin said:

Where does it say "this is a boost"?  maybe that would help explain it.  I still can't find anything that indicates the ATC ever applies more fuel or more hp than without the ATC.  I can't believe there is a "hot rod mode" in the ECU, the EPA would love that. 

From the Bendix manual, it's possible the switch turns on the "smart ATC" or more likely the "optional off road ATC mode".  Those both allow GREATER wheel slip than the standard ATC mode, that is, they reduce the ATC's reduction to engine power, not provide additional power over the base mode.  

In my opinion, the switch should be used on soft surfaces, and it "dials down" the ATC settings.  On ice or snow on hard surfaces, the standard mode seems to work. 

Another thing ATC does is protect the driveline from operator abuse.  It is in the manufacturers interests to keep it on, and turned up to limit wheel slip as much as possible as long as possible. 

Benjamin,

Seems like this was covered in detail in the post that Richard shared from August 2023.

If you don't like the semantics of my term BOOST....then we shall have to agree to disagree.  It was NOT a technical term but my interpretation or description. Basically, if you read on....  The NORMAL mode covers NORMAL driving.  When you get into a situation that is NOT NORMAL and you need ADDITIONAL TRACTION (like being stuck or almost stuck), the MANUAL ON MODE is used.  If you don't like BOOST....then fine.  That was my layman's term to describe it....

But in answer to your post(s?) in August 23, which were also copied here.....

The ATC is a MOMENTARY CONTACT SWITCH to provide additional traction in special situations... (read the manual text).

The ABS/ATC system is always active and in use as you drive, providing there are no faults or warnings.  It is designed to give you the combination of reduced stopping (as in applying the brakes individually to each wheel to prevent lockup and skidding) as well as to give you increased traction if you hit a slick spot in rain or inclement weather. This is exactly how modern day cars work....so the concept matches the "FMVSS" regulations/specifications or intent.

The Momentary switch is like an AUTO/ON switch.  The switch is an "INTERRUPT" function.  I have NOT pulled the wiring, but the switch is there to disengage the normal (see the information of the ABS/ATC being full time and activated during normal operation) function.  Thus Pressing it and HOLDING IT takes the ABS/ATC out of AUTO.

Holding down the switch to the ON mode, as I defined it.....that function or mode change then changes the software in the ABS/ATC Module.  Call it on OVERRIDE or a MODE CHANGE. The two functional Mode Changes are in the manual and spelled out....as posted.

Thus...after the event is over, and you RELEASE the Momentary Contact switch....which is to provide you with the needed additional traction, the ABS/ATC system reverts back to FULL AUTO.

YES...for the sake of discussion...  When you PRESS and HOLD the ATC Switch....the NORMAL, Full Time Auto functions or operating parameters are now OFF...  BUT...you have NOT DISENGAGED or turned off the ABS/ATC System.  You have selected a different mode.  One that matches you need for additional traction. The ON mode is controlled by the driver.  You MUST hold in the momentary contact switch to have the different features or software parameters.  

Thus the ABS/ATC has two discreet functions....NORMAL DRIVING...and SEVERE OR UH OH (I prefer BOOST).

There is NO MANUAL WAY (probably is...but we don't need to go there) to TOTALLY TURN OFF the ABS/ATC system....only change functions or modes.  

Hope this clarifies how it works. Lets move on as this was a "morphed sideroad" of the original post.  

Thanks...

[Benjamin]

Sure, I was thinking the "switch" turned off the ATC like it did on earlier ATC systems, when this is a newer system that has an "off road mode" that is activated by the momentary switch (as far as I can tell from the bendix info).  Similar to the newer SUV traction control systems with different off road modes.  The disagreement comes from labeling this a "boost" when it is closer to turning the system OFF, than turning it "UP".  The off road mode allows MORE wheel slip, it does not "lock the wheels up". That's why it's on a momentary switch, so you can't leave it on, then pull out of an uphill gravel driveway, and spin the tires then snap something when the spinning tire grabs pavement.  If you're trying to get through a long soft muddy driveway, then there's less danger of "grabbing pavement" but you'd still want to release the button before hitting pavement.  That's why it's good to understand what the system is doing.  There is no additional traction in the sense of tire grip, only more power and more spin, and therefore more risk of damage, or digging deeper faster, but also the possibility of pulling out of soft conditions that standard mode ATC won't allow enough power for. 

This relates to the broken axle, because that's how most axles are broken.  I'm still curious which brake was locked up and which wheel dug in.  Not sure how ATC could have been used in that situation. 

[Larry Laursen]

The ATC on the Monaco coaches as explained by a Bendix representative at a 419 Maintenace session uses the ABS system.  That is when the ATC button is pressed the ABS senses the difference in RPM between the drive wheels.  It than applies the brake to the spinning wheel transferring the power to slow side.  It is only active at low speeds.  I am not sure what speed it disengages at but around 10 mph.  The differential has no locking feature and thus if an axle breaks it won't move.  That's why the tow truck can remove one axle and tow.