Is it possible for one wheel assembly on a double drive bogie to lock up (frozen brake) and drive down the road with only three wheels turning freely? No interaxle or diff locks engaged and the vehicle making both left and right turns.
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Yes, perfectly possible, but not very good for the tyre which is not rotating as it should.
If you find yourself in that situation again, and you can’t wait for it to thaw out, then if you engage both the interacted and cross locks and drive along slowly in a straight line, it will force the reluctant wheel to turn, and may be enough to free it off.
Interaxle.
B------d predictive text!!!
Thanks for that, It wasn’t me driving, but yes you’re right, it doesn’t do the tyres any good at all, in fact it completely destroys them. The phone call from my driver telling me he had a double blow out is how I was made aware of the phenomenon. The really confusing part was that it happened during a journey, not at the beginning, he stopped at a set of lights, felt it dragging a bit when he pulled away, checked the trailer wheels were turning in the mirrors and then heard the bang.
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I can’t get me head round what speed the wheels still turning (the pair opposite the locked wheel) would be doing, would it be road speed (same as the other pair still driving normally) or would they be turning faster than actual speed.
Forgive me if its a daft question.
Juddian:
I can’t get me head round what speed the wheels still turning (the pair opposite the locked wheel) would be doing, would it be road speed (same as the other pair still driving normally) or would they be turning faster than actual speed.Forgive me if its a daft question.
It can only go the same speed.
It confused me too, hence the question. I’m still puzzled as to how it’s possible, surely drive would have been sent to that wheel during a turn?
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AF1:
Juddian:
I can’t get me head round what speed the wheels still turning (the pair opposite the locked wheel) would be doing, would it be road speed (same as the other pair still driving normally) or would they be turning faster than actual speed.Forgive me if its a daft question.
It can only go the same speed.
I’ll take your word for it, but still can’t get me head round it.
Prop going a set speed, one wheel can’t turn, locked brake, so all the drive goes to the other, for some reason i’m expecting the wheel spinning to spin at twice its previous rate.
It must be me, been a hard week and i’m knackered 
, that’s the only mitigating excuse i can come up with.
Juddian:
I can’t get me head round what speed the wheels still turning (the pair opposite the locked wheel) would be doing, would it be road speed (same as the other pair still driving normally) or would they be turning faster than actual speed.Forgive me if its a daft question.
Not a daft question at all. In fact, on a single driving axle arrangement, ie 6x2/4x2 or whatever, the wheel which is free to turn will in fact rotate at twice the normal speed. Why? I don’t know, but it does. I have asked qualified motor/mechanical engineers about the phenomenon, and no one has been able accurately to tell me.
However, in the case described by newmercman, the vehicle was a 6x4, and I think, but I may be proved wrong, that the third diff (interaxle) would permit differentiation between the front and rear axles, (which is why it is there) and the vehicle would proceed normally, except of course that one set of wheels on one or other axle is not turning.
If it makes it any easier to understand, you can fit a double drive bogie with two completely different final drive ratios, and as long as you never engage the interaxle lock, the vehicle will drive normally, at a speed determined by the lower of the two diff ratios.
Engage the interaxle lock, however, particularly when moving and you will instantly have a very expensive pile of scrap.
Tonight’s gold star goes to JUDDIAN! !!
newmercman:
It confused me too, hence the question. I’m still puzzled as to how it’s possible, surely drive would have been sent to that wheel during a turn?Sent from my SM-G950W using Tapatalk
My understanding of a diff is power get sent to the wheel with least resistance, which is why it’s that wheel that spins when stuck in mud etc. So I wouldn’t think cornering going round corners would make any difference if one wheel is locked solid.
Does this make sense or have I got it completely wrong?
That’s my understanding of how it works too Muckles, I thought that turning would apply drive to the outer wheel because of that and that would have been enough to break that wheel free, I now know the latter part is wrong though.
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Old John:
Juddian:
I can’t get me head round what speed the wheels still turning (the pair opposite the locked wheel) would be doing, would it be road speed (same as the other pair still driving normally) or would they be turning faster than actual speed.Forgive me if its a daft question.
Not a daft question at all. In fact, on a single driving axle arrangement, ie 6x2/4x2 or whatever, the wheel which is free to turn will in fact rotate at twice the normal speed. Why? I don’t know, but it does. I have asked qualified motor/mechanical engineers about the phenomenon, and no one has been able accurately to tell me.
However, in the case described by newmercman, the vehicle was a 6x4, and I think, but I may be proved wrong, that the third diff (interaxle) would permit differentiation between the front and rear axles, (which is why it is there) and the vehicle would proceed normally, except of course that one set of wheels on one or other axle is not turning.If it makes it any easier to understand, you can fit a double drive bogie with two completely different final drive ratios, and as long as you never engage the interaxle lock, the vehicle will drive normally, at a speed determined by the lower of the two diff ratios.
Engage the interaxle lock, however, particularly when moving and you will instantly have a very expensive pile of scrap.
Tonight’s gold star goes to JUDDIAN! !!
Doh! i completely forgot about the inter axle diff, which is even more unforgiveable when we run two so called full time 4x4’s, both of which have centre diffs, one lockable one on a car being electronic.
Thankyou, your explanation has put it so even a thicko like me can understand.
I was always under the impression that the input to a diff had to go somewhere, in normal operation the input is being divided equally between the two outputs, then on a turn one wheel can go faster than the other, right up to the point if one wheel locks then the free wheel must turn at twice its usual speed for that given transmission input speed.
If you think about it more, if you had a single axle and one wheel locked up, then the wheel still driving is now under direct drive as it were from the propshaft, the diff no longer able to differentiate.
In NMM’s case obviously the inter axle diff did its job in exactly the same was as a normal axle diff would.
Much obliged to me learned friend, no longer confused 
I’ll try and put in a very basic form Juddian
If your going in a straight line ad for example both wheels are doing 100 rpm each ,so that is a combined total of 200rpm.
If you then take a bend then the inside wheel ha to slow down and the outside needs to speed up…So as an example the inside will slow down by 25rpm as it is taking a tighter turn and that 25 rpm will go to the outside wheel …So you still have your combined total of 200rpm.
The transfer of RPM is done through the differential,Thats for another day JUDDIAN lol
Another analogy which ex forces will recognise is when they are marching ,If again going round a bend the man on the inside will then take shorter steps and the outside man takes larger step,if they didn’t it would be a bag of ■■■■…And if the diff didn’t do it’s job it would try and push the vehicle forward
Has that helped lol
norb:
I’ll try and put in a very basic form JuddianIf your going in a straight line ad for example both wheels are doing 100 rpm each ,so that is a combined total of 200rpm.
If you then take a bend then the inside wheel ha to slow down and the outside needs to speed up…So as an example the inside will slow down by 25rpm as it is taking a tighter turn and that 25 rpm will go to the outside wheel …So you still have your combined total of 200rpm.
The transfer of RPM is done through the differential,Thats for another day JUDDIAN lol
Another analogy which ex forces will recognise is when they are marching ,If again going round a bend the man on the inside will then take shorter steps and the outside man takes larger step,if they didn’t it would be a bag of [zb]…And if the diff didn’t do it’s job it would try and push the vehicle forward
Has that helped lol
Sorry - but that “combined total of 200rpm” when the actual rotation speed is 100rpm is nonsense. When travelling in a straight line, both wheels rotate at 100rpm because the whole axle is moving as one. No part of the system is rotating at 200rpm. When the vehicle negotiates a bend, the inner wheel slows a little (e.g. to 90rpm) while the outer wheel goes a little faster by the same amount (e.g. 110rpm).
Roymondo:
norb:
I’ll try and put in a very basic form JuddianIf your going in a straight line ad for example both wheels are doing 100 rpm each ,so that is a combined total of 200rpm.
If you then take a bend then the inside wheel ha to slow down and the outside needs to speed up…So as an example the inside will slow down by 25rpm as it is taking a tighter turn and that 25 rpm will go to the outside wheel …So you still have your combined total of 200rpm.
The transfer of RPM is done through the differential,Thats for another day JUDDIAN lol
Another analogy which ex forces will recognise is when they are marching ,If again going round a bend the man on the inside will then take shorter steps and the outside man takes larger step,if they didn’t it would be a bag of [zb]…And if the diff didn’t do it’s job it would try and push the vehicle forward
Has that helped lol
Sorry - but that “combined total of 200rpm” when the actual rotation speed is 100rpm is nonsense. When travelling in a straight line, both wheels rotate at 100rpm because the whole axle is moving as one. No part of the system is rotating at 200rpm. When the vehicle negotiates a bend, the inner wheel slows a little (e.g. to 90rpm) while the outer wheel goes a little faster by the same amount (e.g. 110rpm).
get agrip i just made the figures up for an example of how it work
Roymondo:
norb:
I’ll try and put in a very basic form JuddianIf your going in a straight line ad for example both wheels are doing 100 rpm each ,so that is a combined total of 200rpm.
If you then take a bend then the inside wheel ha to slow down and the outside needs to speed up…So as an example the inside will slow down by 25rpm as it is taking a tighter turn and that 25 rpm will go to the outside wheel …So you still have your combined total of 200rpm.
The transfer of RPM is done through the differential,Thats for another day JUDDIAN lol
Another analogy which ex forces will recognise is when they are marching ,If again going round a bend the man on the inside will then take shorter steps and the outside man takes larger step,if they didn’t it would be a bag of [zb]…And if the diff didn’t do it’s job it would try and push the vehicle forward
Has that helped lol
Sorry - but that “combined total of 200rpm” when the actual rotation speed is 100rpm is nonsense. When travelling in a straight line, both wheels rotate at 100rpm because the whole axle is moving as one. No part of the system is rotating at 200rpm. When the vehicle negotiates a bend, the inner wheel slows a little (e.g. to 90rpm) while the outer wheel goes a little faster by the same amount (e.g. 110rpm).
get a grip i just made the figures up for an example of how it work .it wasn’t exact figures ,if you read the post it was to keep it simple …But feel free to give the exact figure ,as you obviously know the engine hp ,gearbox ratios, diff ratios , tyre size ,tyre wear,road conditions ,wet /dry .and the exact amount of frition ,speed of the vehicle ,and radius of the bend ,Not everything on the forum has t be worked out to the decimal point ,when you are trying to give a basic understanding
How about this?
Single drive, to make it simpler to start with. One turn of the prop drives the pair of driven wheels 4 turns. As we corner one side goes quicker (outside of the curve) one slower. Extend that picture a bit, one side stops, so the other side must be turning double. So one side is stationary the other side is turning 8 times for each turn of the prop.
If our vehicle is travelling at 10mph in a straight line with both wheels driving, in a tight turn (think fork lift truck) one side stopped the other side doing 20mph.
Now going back to our truck with a locked wheel, (single drive still), the prop will tell the speedo youre doing 10mph. With one wheel locked (and skidding along smoking like crazy) youre actually travelling at 20mph.
So, for what its worth as NewMercMans double drive was going along the speedo would have been 25% out. Hardly his biggest worry I`d agree.
EDIT, I`m open to correction!
Bugger me, just when i’d got me head round it, Franglais chucks a 25% speedo error in.
Juddian:
Bugger me, just when i’d got me head round it, Franglais chucks a 25% speedo error in.
Happy to try to keep you entertained on a Sunday morning mate! 
Keep on thinking about a forklift turning on the spot. Inner wheel stationary outer going twice the straight line speed. Then straighten it out. So thats` a single drive. 50% error. Same principle with the diff between the axles.
I think…
Yeah, i’m quite happy with the concept of the diff working, 100% drive in = 100% out whatever the percentages either side right up to 100% one out side and 0% the other, i’d always thought that to be honest, though it probably better a Norb noted to use rpm instead of percentages.
I’d completely forgotten a double drive having a mid diff though, so i envisaged NMM’s lorry going down the road with 2 wheels driving at say 100rpm, one wheel stationary locked up and its opposite chum trying to spin at 200rpm, as said i’d forgotten that the mid diff would do its job.
The 25% speedo error hand grenade you lobbed in without so much as a by your leave has me completely flummoxed mind
Presumably you’re thinking of that centre diff apportioning more drive to the two wheels driving previously at 100rpm now with drive apportioned equally between three instead of 4 they would all now be turning at 133.3 rpm? so would the speedo error not be 33.3% ? cor this has got complicated.
