Axle Fundamentals - Explanation of the Inter-axle Differential

This video aims to demonstrate the speed change that happens with an open interaxle power divider as well as the speed difference in an open axle carrier. The use of a locker is demonstrated as well showing that the front and rear axle will need to turn at the same speed due to the dog tooth lock system used in the inter-axle differential.
This video was made for training of technicians using cutaway photos, training aids or shop space of The Southern Alberta Institute of Technology. This video is made to be an open resource for the instruction of the Heavy Equipment Industry and can be used for said purpose and may not be duplicated for commercial distribution or retail.

[@marcnicholson2426]

Thanks for this great video! I’m glad I found it. I have been trying to explain how the Meritor RT-160 tandem axle drives work to our fire department. We have drivers that constantly disagree with me that they operate like this. I’ve needed this video for the last 20 years!

[@THET1916]

Glad this could be helpful

[@taurus600]

Amazing, I've been wondering how exactly these things work and, I had a decent idea but really needed this visual. Great video

[@dmajumdar2059]

best video on interaxle diffs

[@edwinlipton]

Excellent demo

[@paulcashier2926]

This is really helpful

[@FerminDelgado]

Great video! very clear explanation.

[@billybobs841]

You a good teacher man thank you

[@chrispinmitambo3746]

Well explained.

[@brentsmith5647]

Brilliant video thank u

[@dsprojects8580]

Great video thanks 👍

[@harlemlambatin8347]

Nice explanation sir 👍👍

[@duanefischer1721]

It’s amazing how many people don’t know how a differential works. Throw it in as an inter-axle and people lose their minds. Great explanation though!

[@MrSami2023]

Any max speed recommendations on inter lock.some ppl keep it locked at all speeds

[@remarmechanic132]

I love this tutorial hi I'm your new friend I watching full video ❤️ with big thumbs up boss

[@THET1916]

Thanks for watching, glad it could help you out

[@Mechanicaltricks]

Wow, amazing.

[@THET1916]

Thanks!!

[@JuanCruz-xy4pn]

I have a semi that when I put in gear it won’t move till I put in the power divider then it’ll move but just the rear not the front rears will turn. When the power divider is on the drive shaft will just spin from the transmission. Any help?

[@johnysilver1853]

I have problem with my truck I think axle differential won't engage. It just keeps spinning one wheel on rear axle on right passenger side and thats it. What can be the problem?

[@happymann839]

Ausgezeichnet 👍👍👍👍👍

[@vishalpatil1717]

Sir I have confusion that is in normal condition means without switching inter axle lock , is the power transmit to all 4wheels or only last two wheels?

[@laurenfingerson6040]

Power to all, all the time locked or not. Locked just makes all have equal output even during slip.

[@jamesblackwell703]

Would that require a 1 to 2 planetary gear input on the output ?

[@brianb-p6586]

No. When nothing is slipping, both axles of the tandem set turn at the same speed.

[@arthanza112]

Basically all wheels are driving/floating until you hit the diff lock.

[@rev9fan1]

Can the inter axle lock be engaged at any speed as long as the tires are losing traction?

[@THET1916]

The inter axle should only be engaged with no speed or no speed differential from front to rear drive axle and depending on the model, limited to the max travel speed while engaged. Any turning done in better traction with the inter axle locked will result in damage to the inter axle.

[@billybobs841]

No don't do it you will be taken it apart if you

[@mustang4928]

Hi. My truck is a 10 speed manual (Eaton) the gears stock was on high range (I was told that this was a minor issue) But The mechanic told me it's a big damage, they need to rebuild it for $ 3500 without labor!!!. I agreed. Then I found out, that he replaced it with another one, that one doesn't have a cooler (my transmission had one) tell me please if what the mechanic did is right/okay?. Should I accept this transmission ( the new one without the cooler)? He's working on the truck now, haven't finished yet.. I still have time... should I accept what he did or not?? Please reply 🙏

[@robertnagtegaal4355]

Hi Mustang, There are too many variables to speak to your situation. That being said, make sure that the expectations of the job are clear before work proceeds or continues. If you are quoted a rebuild, then swapping for another unit is a change in scope. The mechanic may be trying to save you money in finding a good used one. With swaps, the question is warranty, have a conversation about what you can expect. As for the cooler, most can have a cooler added by simply removing the plugs and connecting the existing cooler to the transmission. If you are getting a rebuild due to a failure though, the cooler should be replaced or you will have another contamination related failure. Whatever you do, you should talk to the mechanic, don’t try and hold the payment for the work after it’s done. If you don’t want what they are doing, talk to them.

[@THET1916]

I agree with Robert ;) I think communication is key. Clarify the budget, clarify the work, clarify the warranty expectations. Don’t hold work you approve from payment after the fact. If you have not approved the work, then the shop shouldn’t be doing it until they get approval. If you clarify all the above and they deliver something different or don’t deliver, then don’t pay until it is done as agreed.

[@mustang4928]

@@robertnagtegaal4355 Thank you so much 💓 💗

[@mustang4928]

@@THET1916 Thank you for the advice 🙏

[@mustang4928]

@@robertnagtegaal4355 Thank you Robert and Heavy equipment for the help i appreciate it. Just for clarification; i don't get to see the work while they're doing it. In my opinion i think they're trying to swap transmissions so they don't lose time... Yes, i was quoted in advance for a rebuild in my transmission, but by chance i discovered that he swapped it instead of doing the actual rebuild. When i returned today to see the truck i asked why did he install the one without the cooler, he replied" you don't need a cooler for the transmission, and your pipes for the anti freeze are rusty and i don't wanna mess eith it... " is it true that the transmission could run without a cooler or was he making excuses? Also couldn't he have just changed the pipes? Thank you very much.

[@Javid-bc3mc]

If we removed the drive shaft between two differential truck still able to move ?

[@potatoboy792]

Yes but you'll have to activate interaxle lock

[@Javid-bc3mc]

@ulrichpatterson61 If don't locked the power divider is not able to move right ?

[@ubu3393]

My question is stupid, but I will ask ..if I drive 100 .Iles with the differential lock on. Will it damage anything..driving at 65mph

[@DDDquick]

If you drive in a straight line on a perfectly flat road, it might be ok but the chances are it will cause transmission wind up.

[@THET1916]

Yes you will likely cause damage. The comment from 3d quick about a straight line is a valid point. The problem is that the tires likely have different wear, tire pressure and this causes the wheels to want to turn at a different speed as well as roads are rarely perfectly straight. When the diff is locked, they cannot turn at different speeds left to right. That causes wear at the axle shafts with increased torsion. It also puts the bearings supporting the axle shafts under additional load and puts stress on the lock itself. There is also a likely situation that you will cause tire scrub which will wear the tires more which will result in more stress and more damage. It isn’t uncommon in commercial vehicles to come across broken axle shafts. All this stress and wear creates more heat which breaks down the oils ability lubricate which in turn creates more stress and wear. There should be a theme emerging, follow the manufacturers usage guideline to reduce the chance of damage. Keep in mind I am responding from a commercial environment. In light duty vehicle they often have limited slip diffs and they handle the situation differently but are not often selectable.

[@TravNewton]

I put buzzer/flasher combo warning systems on all of my trucks for axle and diff lock functions if you don't they will get left in and destroyed by the drivers!

[@dineshkovalan3904]

Sir my doubt is, during a normal driving condition, all the four wheels of two axles take power or the frist drive axle of two wheels take power, the second rear axle is in dead condition.

[@THET1916]

I encourage you to watch again. The torque on an open interaxle is split between the front and back drive axle equally and then split again on an open axle carrier to the left and right wheels of each axle. It is a myth that one axle is unloaded and is not driving when unlocked and is not true. Any additional wear to any one of the two axles has to do with axle alignment or wheel wear or vehicle misloading

[@DDDquick]

In normal conditions the engine is driving both the front and rear axle but because the centre differential is open, it will send power in the path of least resistance to either the front or rear axle so typically in slippery conditions the wheel out of the 4 with the least traction will get all the power and spin while the others remain static. Locking the centre differential power divider ensures one wheel on both axles receives power. For all 4 wheels to get power then the front and rear differentials need to be locked too. Not all trucks have that as standard though. Really in 2022 thise setup is archaic and there should be an automatic locking system like a Torsen device that senses traction loss and locks the diffs before the driver even realises.

[@brianb-p6586]

​@Heavy Equipment Tech Training (HETT) both axles are always driven in this case because there is an interaxle differential. Some trucks have an always-driven leading axle and a trailing axle which is driven only when engaged; I don't know if this is common enough to bother with, but perhaps you could show that in a separate video.

[@Mohamedseddek]

♥️👍

[@vikrantsangawar8265]

Sir, do the interaxle differential, and differential in the tandom boogie operate at the same time when the vehicle is turning.

[@THET1916]

Yes, the bevel gear of each axle will go the average speed of its wheel assemblies while the unlocked interaxle will have its differential cross shaft rotating at the average speed of the two drive pinions as the cross shaft is connected to the interaxle input

[@Igotshot9x8390]

So many driver believe that u only send power to the back when its not locked. They drive around locked all the time thinking they are wearing tires more evenly and they are doing the truck a favor

[@undergroundagentpresents]

Seriously? I've never heard of that before... I don't doubt you one bit! The only time I lock in is when there's potential for slip. I.e. a hairpin with gravel up a steep grade or when going from dry pavement to dirt... or when slip happens on ice and I've managed to stop and lock safely. ... I know better than to shift diff when wheel is spinning.... that being said... I somehow broke an output shaft the other day while in first gear on flat ground not loaded! It was like a laser cut the shaft! (Believe it was a factory defect) ((since the Eaton inter diff was almost exactly a year since a slip seat blew up both diffs!)) What a fluke!

[@quarry1030]

The thing I'm really questioning is why do you need variable speed on both axles why not just have the whole thing a solid mechanism

[@THET1916]

It’s a concept called Ackerman’s principle. As the vehicle turns a corner each wheel assembly will take a different path with different sized radius. This will cause each wheel to turn at a different speed. If the diff is locked this difference of speed will be limited causing axle shaft, bearing stress and wear. It will also cause tire scuffing and excess tire wear.

[@guacamoleweiner69]

Weld your differential and try to turn. You'll see why

[@G55STEYR]

How about the triple axle?

[@THET1916]

The doubling that happens from the front to mid would double again from mid to the rear. Spinning Wheels on Tridem is a costly practice for tire wear.

[@G55STEYR]

@@THET1916 The first interaxle should be 33-67% then. Yes one wheel spinning is gonna have 6x speed

[@THET1916]

@@G55STEYR not 6, 8x... I have been working in making a video showing htis using a tridem. It would be a collab with another instructor, I hope to get it going soon.

[@brianb-p6586]

@@THET1916 If the first interaxle differential has the 33:67 distribution suggested by G55STEYR, it would only be 6X, because the forward axle's splitter would only multiply the rearward output speed by a factor of 1.5 (not 2). At least recent Meritor tridem sets (e.g. MZ-610, P600, ProTec 5000) have this configuration.

[@LegarioMosaso]

Ok

[@vroor32]

Question to channel trainer: I have 2 trucks. Volvo with Eaton 3.90 rear, and Freightliner with Meritor 3.73 rear. The Meritor 3.73 loses traction very easily on uneven ground, so I have to engage diff lock to keep moving WHEREAS the Eaton can creep up without effort. Is this due to the minor rear end ratio? 🤔 Also I checked the fluid level of the Meritor thru finger port and immediately upon unscrewing the plug, darker fluid came out but had an obvious shiny glittery dusty metal look to it. I got the fluid drained and the "metal dusty" effect was not there. I change the fluids annually, so I'm at a loss of what's going on. Both trucks just hit 1M miles on original diffs, unopened diffs. Looking forward to some insights. Thx

[@THET1916]

Thanks for the questions. Simple one first, for the silvery oil, install a mag plug and it will catch/attract large metal particles and you can swap them for inspection without changing the oil. As for 1M miles, while others may get longer and will chime in I’m sure, most manufacturers warranty to 750K so a clean 1M record is great. Just a bit of advice, a rebuild before failure is hugely cheaper than one after. What I recommend is find a good shop on some quiet time and get them rebearing and reseated and the cost should be a lot less than after failure. Just get a shop that does these often as they will have to set the pattern back to the old pattern to reuse the gears. As for the crawling, like the small ratio difference is making a difference. Another thing to consider on open diffs is tire pressure, tire wear and tire brand for traction on the ground. All this equal and the ratio will make a difference to what can be made, the tires determine if the torque can actually be delivered. Torque is only as good as the traction of the tires. To explain the ratio impact I’ll use some real numbers Assuming a 2000ftlbs clutch maxed out with a transmission in first with a ratio of 14.6:1 for both trucks. With the 3.90 ratio it can max generate 113880ftlbs of torque with the 3.73 it will make 109500ftlbs making a 4380ftlbs difference in generated torque. Hope this helps.

[@papitruck]

Prefiero MACK

[@bruzote]

IF the purpose of this video is to teach fundamentals rather than show exposed features only, it is rather deficient IMO. First, dedicating yourself to this particular teaching hardware involves highly limited visibility of key mechanical features and cause-and-effect relations. It would be better to use some other toy model that gives one a full view. This is the biggest limitation IMO, but not the only one. I feel like the instruction is "teaching to the answer" for a test, not teaching for comprehension. Quite frankly, this is often seen in practical, trade, or OJT teaching since the purpose of training is to quickly and cheaply get the trainees to answer a question with the right words or take the right action, regardless of true understanding. People who have learned from this teaching method often apply to all situations, when it is not appropriate to do so at times. Second deficiency, the instruction uses jargon ("splined", etc) with implied understanding of what the jargon means. However, this is worse than you might think. Even if one understands the jargon, the instruction expects implied understanding of how the jargon-specified features are related to the mechanics. That is far from certain for most viewers of this video. To understand the implications, one would either need to have an existing understanding of this hardware (so why even watch the video) or one would need to see it (which one can't, since the model is solid metal and key parts are hidden). If you are teaching based on implied understanding, you have to first teach about the features and reasons you expect to be understood as well. Perhaps this video accompanies live classroom demos that are more comprehensive? If not, I do believe it represents a lot of lost opportunity to pass along knowledge.

[@THET1916]

Thank you for your feedback.

[@brianb-p6586]

"Splined" is not a problem. Some degree of prerequisite knowledge is necessary; for instance, the video is in English so the audience must understand English. Terms such as "gear" and "shaft" must be understood... and "spline" falls in the same category of basic knowledge.

[@badgerpa9]

I would think if you read the title you would catch what it is about, it is not titled Axle Parts names 101. He has 20 some videos on this subject. Expecting every video to start at level one would make videos days long. Start at the level you are; do not expect every video to start at the level you are.