Propshaft balancing

[ian thomson]

Clive asks about balancing propshafts.  I think this, and balancing generally, is a poorly understood subject.  I include myself in the ranks of those who don't really understand it but what I do know is that there is more than one type of vibration and it is only too easy to mix them up if you are not aware of the differences.  When we talk of balancing propshafts we are generally talking about minimising the various types of mechanical imbalance which can occur due to too much weight being in the wrong place due to manufacturing intolerances (I think I just made that word up). When we talk about the orientation of the front and rear flanges we are talking about a different type of imbalance altogether.  I'm sure there will be a term for this though I don't know what it is.  Perhaps Eric can enlighten us.   What is happening here is a product of the fact that a Hooke's joint, or a universal joint as it is generally known, is not a constant velocity joint.  This means that in anything but a straight ahead position where everything is lined up the speed of rotation varies slightly over any single revolution.  The design of the joint is such that if the yoke in the middle is offset at all the speed of rotation as felt at the output yoke speeds up and slows down as it turns. Although the time taken for each rotation is the same for the input and output flanges within the rotation there is an acceleration and deceleration which cancel each other out. This increases with the deflection of the joint.  If the two joints at each end of the propshaft are in line then this variation which is induced into the shaft proper by the joint at the gearbox end is removed at the diff end.  If the splined sliding joint is not oriented to do this there will be a vibration felt in the system which it would take a mathematician to explain.  Obviously in any installation the gearbox output and diff input are unlikely to be in a direct line most of the time so a vibration will be felt.  This will increase as the system deflects as the suspension operates.  I hope this makes sense and that I have got it right.  Feel free to put me right though if I have been barking up the wrong tree.

Regards

Ian Thomson

Notre. UK

[Clive Sherriff]

Twas not I that asked, but I did send some explanatory replies. Additional to those :- Props as generally supplied as new are usually well balanced. However they can go out of balance due to physical bending due to accidental damage, through twisting after transmitting too much power ( Dream on !) or even the balance weights actually dropping off !. Also they will be unbalanced as a result of bearing failures allowing the shaft to run out of true. This is most often found resulting from the needle bearing on the Hookes joints wearing and/or failing. The gearbox rear, and diff front bearings will also allow the ends of the prop to run out of true (and hence be unbalanced ) if they fail, but there is more leeway on these usually. Out of balance vibrations can be harmonically linked, as when a road wheel is out of balance only at certain speeds. The same can apply to a slightly out of balanced prop shaft too, producing a vibration only at certain speeds. Clivemn mmmmmmmmmmmmmmmmmmmmm

On Sun, 6 Jan 2019 at 15:52, ian thomson i.thomson@talk21.com [mg-tabc] mg-tabc-noreply@yahoogroups.com> wrote: [u][/u] Clive asks about balancing propshafts. I think this, and balancing generally, is a poorly understood subject. I include myself in the ranks of those who don't really understand it but what I do know is that there is more than one type of vibration and it is only too easy to mix them up if you are not aware of the differences. When we talk of balancing propshafts we are generally talking about minimising the various types of mechanical imbalance which can occur due to too much weight being in the wrong place due to manufacturing intolerances (I think I just made that word up). When we talk about the orientation of the front and rear flanges we are talking about a different type of imbalance altogether. I'm sure there will be a term for this though I don't know what it is. Perhaps Eric can enlighten us. What is happening here is a product of the fact that a Hooke's joint, or a universal joint as it is generally known, is not a constant velocity joint. This means that in anything but a straight ahead position where everything is lined up the speed of rotation varies slightly over any single revolution. The design of the joint is such that if the yoke in the middle is offset at all the speed of rotation as felt at the output yoke speeds up and slows down as it turns. Although the time taken for each rotation is the same for the input and output flanges within the rotation there is an acceleration and deceleration which cancel each other out. This increases with the deflection of the joint. If the two joints at each end of the propshaft are in line then this variation which is induced into the shaft proper by the joint at the gearbox end is removed at the diff end. If the splined sliding joint is not oriented to do this there will be a vibration felt in the system which it would take a mathematician to explain. Obviously in any installation the gearbox output and diff input are unlikely to be in a direct line most of the time so a vibration will be felt. This will increase as the system deflects as the suspension operates. I hope this makes sense and that I have got it right. Feel free to put me right though if I have been barking up the wrong tree. Regards Ian Thomson Notre. UK

[jeffrey townsend]

#ygrps-yiv-1389963362 P {margin-top:0;margin-bottom:0;} Hi Clive and Ian, 'Twas was me that started it a while ago with a question about balancing. It's a slow burner but getting more interesting as it goes on. I remember SHM (simple harmonic motion) from school physics A level (just got it). My question was trying to ascertain if an original shaft in good condition with a balance weight still at each end needs rebalancing after new bearings are fitted. Clive and Ian - you have provided some very helpful replies but in all honesty I'm still not sure so I suppose on that basis I should get it balanced. Thanks for all replies. Regards, Jeff TB OWNERS - CELEBRATE YOUR CARS 80TH BIRTHDAY AT TB80 NEAR OXFORD IN MAY - CONTACT JEFF OR MIKE INGLEHEARN FOR FURTHER DETAILS [b]From:[/b] mg-tabc@yahoogroups.com mg-tabc@yahoogroups.com> on behalf of CLIVE SHERRIFF csherriff99@gmail.com [mg-tabc] mg-tabc-noreply@yahoogroups.com> [b]Sent:[/b] 06 January 2019 16:58 [b]To:[/b] ian thomson [b]Cc:[/b] MG-TABC List [b]Subject:[/b] Re: [mg-tabc] Propshaft balancing    

Twas not I that asked, but I did send some explanatory replies. Additional to those :- Props as generally supplied as new are usually well balanced.  However they can go out of balance due to physical bending due to accidental damage, through twisting after transmitting too much power ( Dream on !) or even the balance weights actually dropping off !. Also they will be unbalanced as a result of bearing failures allowing the shaft to run out of true.  This is most often found resulting from the needle bearing on the Hookes joints wearing and/or failing.  The gearbox rear, and diff front bearings will also allow the ends of the prop to run out of true (and hence be unbalanced ) if they fail, but there is more leeway on these usually.  Out of balance vibrations can be harmonically linked, as when a road wheel is out of balance only at certain speeds.  The same can apply to a slightly out of balanced prop shaft too, producing a vibration only at certain speeds. Clive mn mmmmmmmmmmmmmmmmmmmmm On Sun, 6 Jan 2019 at 15:52, ian thomson i.thomson@talk21.com [mg-tabc] mg-tabc-noreply@yahoogroups.com> wrote:

 

Clive asks about balancing propshafts.  I think this, and balancing generally, is a poorly understood subject.  I include myself in the ranks of those who don't really understand it but what I do know is that there is more than one type of vibration and it is only too easy to mix them up if you are not aware of the differences.  When we talk of balancing propshafts we are generally talking about minimising the various types of mechanical imbalance which can occur due to too much weight being in the wrong place due to manufacturing intolerances (I think I just made that word up). When we talk about the orientation of the front and rear flanges we are talking about a different type of imbalance altogether.  I'm sure there will be a term for this though I don't know what it is.  Perhaps Eric can enlighten us.   What is happening here is a product of the fact that a Hooke's joint, or a universal joint as it is generally known, is not a constant velocity joint.  This means that in anything but a straight ahead position where everything is lined up the speed of rotation varies slightly over any single revolution.  The design of the joint is such that if the yoke in the middle is offset at all the speed of rotation as felt at the output yoke speeds up and slows down as it turns. Although the time taken for each rotation is the same for the input and output flanges within the rotation there is an acceleration and deceleration which cancel each other out. This increases with the deflection of the joint.  If the two joints at each end of the propshaft are in line then this variation which is induced into the shaft proper by the joint at the gearbox end is removed at the diff end.  If the splined sliding joint is not oriented to do this there will be a vibration felt in the system which it would take a mathematician to explain.  Obviously in any installation the gearbox output and diff input are unlikely to be in a direct line most of the time so a vibration will be felt.  This will increase as the system deflects as the suspension operates.  I hope this makes sense and that I have got it right.  Feel free to put me right though if I have been barking up the wrong tree. Regards Ian Thomson Notre. UK

[Bill Hyatt]

More than anyone wants to know about Hooke Joints harmonics. http://www.j-mst.org/on_line/admin/files/24-j2011-1471_2439-2449_.pdfAnd https://www.machineservice.com/technical-101/vibrational-issues/ -Bill HyattTC 4926Sent from my iPhone

On Jan 6, 2019, at 12:16 PM, jeffrey townsend jeff.townsend@hotmail.co.uk [mg-tabc] mg-tabc-noreply@yahoogroups.com> wrote:

  Hi Clive and Ian, 'Twas was me that started it a while ago with a question about balancing. It's a slow burner but getting more interesting as it goes on. I remember SHM (simple harmonic motion) from school physics A level (just got it). My question was trying to ascertain if an original shaft in good condition with a balance weight still at each end needs rebalancing after new bearings are fitted. Clive and Ian - you have provided some very helpful replies but in all honesty I'm still not sure so I suppose on that basis I should get it balanced. Thanks for all replies. Regards, Jeff TB OWNERS - CELEBRATE YOUR CARS 80TH BIRTHDAY AT TB80 NEAR OXFORD IN MAY - CONTACT JEFF OR MIKE INGLEHEARN FOR FURTHER DETAILS [b]From:[/b] mg-tabc@yahoogroups.com mg-tabc@yahoogroups.com> on behalf of CLIVE SHERRIFF csherriff99@gmail.com [mg-tabc] mg-tabc-noreply@yahoogroups.com> [b]Sent:[/b] 06 January 2019 16:58 [b]To:[/b] ian thomson [b]Cc:[/b] MG-TABC List [b]Subject:[/b] Re: [mg-tabc] Propshaft balancing    

Twas not I that asked, but I did send some explanatory replies. Additional to those :- Props as generally supplied as new are usually well balanced.  However they can go out of balance due to physical bending due to accidental damage, through twisting after transmitting too much power ( Dream on !) or even the balance weights actually dropping off !. Also they will be unbalanced as a result of bearing failures allowing the shaft to run out of true.  This is most often found resulting from the needle bearing on the Hookes joints wearing and/or failing.  The gearbox rear, and diff front bearings will also allow the ends of the prop to run out of true (and hence be unbalanced ) if they fail, but there is more leeway on these usually.  Out of balance vibrations can be harmonically linked, as when a road wheel is out of balance only at certain speeds.  The same can apply to a slightly out of balanced prop shaft too, producing a vibration only at certain speeds. Clive mn mmmmmmmmmmmmmmmmmmmmm On Sun, 6 Jan 2019 at 15:52, ian thomson i.thomson@talk21.com [mg-tabc] mg-tabc-noreply@yahoogroups.com> wrote: [u][/u]  

Clive asks about balancing propshafts.  I think this, and balancing generally, is a poorly understood subject.  I include myself in the ranks of those who don't really understand it but what I do know is that there is more than one type of vibration and it is only too easy to mix them up if you are not aware of the differences.  When we talk of balancing propshafts we are generally talking about minimising the various types of mechanical imbalance which can occur due to too much weight being in the wrong place due to manufacturing intolerances (I think I just made that word up). When we talk about the orientation of the front and rear flanges we are talking about a different type of imbalance altogether.  I'm sure there will be a term for this though I don't know what it is.  Perhaps Eric can enlighten us.   What is happening here is a product of the fact that a Hooke's joint, or a universal joint as it is generally known, is not a constant velocity joint.  This means that in anything but a straight ahead position where everything is lined up the speed of rotation varies slightly over any single revolution.  The design of the joint is such that if the yoke in the middle is offset at all the speed of rotation as felt at the output yoke speeds up and slows down as it turns. Although the time taken for each rotation is the same for the input and output flanges within the rotation there is an acceleration and deceleration which cancel each other out. This increases with the deflection of the joint.  If the two joints at each end of the propshaft are in line then this variation which is induced into the shaft proper by the joint at the gearbox end is removed at the diff end.  If the splined sliding joint is not oriented to do this there will be a vibration felt in the system which it would take a mathematician to explain.  Obviously in any installation the gearbox output and diff input are unlikely to be in a direct line most of the time so a vibration will be felt.  This will increase as the system deflects as the suspension operates.  I hope this makes sense and that I have got it right.  Feel free to put me right though if I have been barking up the wrong tree. Regards Ian Thomson Notre. UK

[Duncan]

Bill-That second article explains why the original brass caged R&M double row ball bearing on the (differential) pinion shaft always failed in TC's, forever giving the differential a bad reputation.  A good companion article for this one.http://www.tcmotoringguild.org/techinfo/TClinic-30.pdf DuncanTC9866 [b]From:[/b] "Bill Hyatt usaj24@earthlink.net [mg-tabc]" mg-tabc-noreply@yahoogroups.com> [b]To:[/b] jeffrey townsend jeff.townsend@hotmail.co.uk> [b]Cc:[/b] ian thomson i.thomson@talk21.com>; CLIVE SHERRIFF csherriff99@gmail.com>; MG-TABC List mg-tabc@yahoogroups.com> [b]Sent:[/b] Sunday, January 6, 2019 10:47 AM Subject: Re: [mg-tabc] Propshaft balancing   More than anyone wants to know about Hooke Joints harmonics. http://www.j-mst.org/on_line/admin/files/24-j2011-1471_2439-2449_.pdfAnd https://www.machineservice.com/technical-101/vibrational-issues/ -Bill HyattTC 4926Sent from my iPhone On Jan 6, 2019, at 12:16 PM, jeffrey townsend jeff.townsend@hotmail.co.uk [mg-tabc] mg-tabc-noreply@yahoogroups.com> wrote:

  Hi Clive and Ian, 'Twas was me that started it a while ago with a question about balancing. It's a slow burner but getting more interesting as it goes on. I remember SHM (simple harmonic motion) from school physics A level (just got it). My question was trying to ascertain if an original shaft in good condition with a balance weight still at each end needs rebalancing after new bearings are fitted. Clive and Ian - you have provided some very helpful replies but in all honesty I'm still not sure so I suppose on that basis I should get it balanced. Thanks for all replies. Regards, Jeff TB OWNERS - CELEBRATE YOUR CARS 80TH BIRTHDAY AT TB80 NEAR OXFORD IN MAY - CONTACT JEFF OR MIKE INGLEHEARN FOR FURTHER DETAILS [b]From:[/b] mg-tabc@yahoogroups.com mg-tabc@yahoogroups.com> on behalf of CLIVE SHERRIFF csherriff99@gmail.com [mg-tabc] mg-tabc-noreply@yahoogroups.com> [b]Sent:[/b] 06 January 2019 16:58 [b]To:[/b] ian thomson [b]Cc:[/b] MG-TABC List [b]Subject:[/b] Re: [mg-tabc] Propshaft balancing     Twas not I that asked, but I did send some explanatory replies. Additional to those :- Props as generally supplied as new are usually well balanced.  However they can go out of balance due to physical bending due to accidental damage, through twisting after transmitting too much power ( Dream on !) or even the balance weights actually dropping off !. Also they will be unbalanced as a result of bearing failures allowing the shaft to run out of true.  This is most often found resulting from the needle bearing on the Hookes joints wearing and/or failing.  The gearbox rear, and diff front bearings will also allow the ends of the prop to run out of true (and hence be unbalanced ) if they fail, but there is more leeway on these usually.  Out of balance vibrations can be harmonically linked, as when a road wheel is out of balance only at certain speeds.  The same can apply to a slightly out of balanced prop shaft too, producing a vibration only at certain speeds. Clive mn mmmmmmmmmmmmmmmmmmmmm On Sun, 6 Jan 2019 at 15:52, ian thomson i.thomson@talk21.com [mg-tabc] mg-tabc-noreply@yahoogroups.com> wrote: [u][/u]   Clive asks about balancing propshafts.  I think this, and balancing generally, is a poorly understood subject.  I include myself in the ranks of those who don't really understand it but what I do know is that there is more than one type of vibration and it is only too easy to mix them up if you are not aware of the differences.  When we talk of balancing propshafts we are generally talking about minimising the various types of mechanical imbalance which can occur due to too much weight being in the wrong place due to manufacturing intolerances (I think I just made that word up). When we talk about the orientation of the front and rear flanges we are talking about a different type of imbalance altogether.  I'm sure there will be a term for this though I don't know what it is.  Perhaps Eric can enlighten us.   What is happening here is a product of the fact that a Hooke's joint, or a universal joint as it is generally known, is not a constant velocity joint.  This means that in anything but a straight ahead position where everything is lined up the speed of rotation varies slightly over any single revolution.  The design of the joint is such that if the yoke in the middle is offset at all the speed of rotation as felt at the output yoke speeds up and slows down as it turns. Although the time taken for each rotation is the same for the input and output flanges within the rotation there is an acceleration and deceleration which cancel each other out. This increases with the deflection of the joint.  If the two joints at each end of the propshaft are in line then this variation which is induced into the shaft proper by the joint at the gearbox end is removed at the diff end.  If the splined sliding joint is not oriented to do this there will be a vibration felt in the system which it would take a mathematician to explain.  Obviously in any installation the gearbox output and diff input are unlikely to be in a direct line most of the time so a vibration will be felt.  This will increase as the system deflects as the suspension operates.  I hope this makes sense and that I have got it right.  Feel free to put me right though if I have been barking up the wrong tree. Regards Ian Thomson Notre. UK

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[E.Worpe@surrey.ac.uk]

Just one further thought following Ian's description of a Non-constant velocity joint's need for correct alignment. The cancellation effect between the two universal joints of any modulation in the rotational velocity of the propshaft is also dependent on the axis of the pinion shaft in the diff. being parallel with the axis of the mainshaft in the gearbox. This implies that any rear axle misalignment or failure of the gearbox rear support system could introduce a vibration due to the resultant misalignment of the universal joints. Such a vibration might go undetected against all the other background vibrations, but it's effect would be insidious, especially as far as the double row bearing supporting the flange end of the pinion. Regards, Eric. ________________________________________ From: ian thomson i.thomson@talk21.com What is happening here is a product of the fact that a Hooke's joint, or a universal joint as it is generally known, is not a constant velocity joint. This means that in anything but a straight ahead position where everything is lined up the speed of rotation varies slightly over any single revolution. The design of the joint is such that if the yoke in the middle is offset at all the speed of rotation as felt at the output yoke speeds up and slows down as it turns. Although the time taken for each rotation is the same for the input and output flanges within the rotation there is an acceleration and deceleration which cancel each other out. This increases with the deflection of the joint. If the two joints at each end of the propshaft are in line then this variation which is induced into the shaft proper by the joint at the gearbox end is removed at the diff end. If the splined sliding joint is not oriented to do this there will be a vibration felt in the system which it would take a mathematician to explain. Obviously in any installation the gearbox output and diff input are unlikely to be in a direct line most of the time so a vibration will be felt. This will increase as the system deflects as the suspension operates. I hope this makes sense and that I have got it right. Feel free to put me right though if I have been barking up the wrong tree.

[ian thomson]

Two things occur to me when thinking about this and I hope you will forgive me if I am straying too far from the original point.  Firstly, it strikes me that the tortional vibration will still be present in the shaft itself even though it is removed s far as the world outside of the shaft is concerned by the second joint.  Surely over time this will have an effect on the shaft.  In addition to this it strikes me that though this may be true the fact that this setup is used the vibration must be to small to be noticable.  Would this therefore cause a resonance In the shaft at some critical rotational speed which is presumably well outside the normal operating parameters of the vehicle in question.  This may be something to be born in mind if having a non standard shaft made up however.  Eric's point about the effect being not inconsiderable on the opinion bearing may be a consideration here especially as the system necessarily sounds most of it's time not being in alignment.  That is why the joints are there after all. Secondly modern vehicles tend to use C/V joints, presumably to avoid this problem.  Leaving aside the question of whether such joints really are of constant velocity, they seem to be used on front wheel drive systems, so is this because the effect is amplified by also having to cope with steering input, either because of the greater angles involved or the greater chances of vibration being felt through the steering.  In addition I seem to have an idea that some manufacturers have used a Hooke's joint on the inboard end of the shaft and a C/V joint outboard.  I may stand corrected on this but if it is true what will be the effect? Ian

On Mon, Jan 7, 2019 at 10:55 AM +0000, "e.worpe@surrey.ac.uk" e.worpe@surrey.ac.uk> wrote: Just one further thought following Ian's description of a Non-constant velocity joint's need for correct alignment. The cancellation effect between the two universal joints of any modulation in the rotational velocity of the propshaft is also dependent on the axis of the pinion shaft in the diff. being parallel with the axis of the mainshaft in the gearbox. This implies that any rear axle misalignment or failure of the gearbox rear support system could introduce a vibration due to the resultant misalignment of the universal joints. Such a vibration might go undetected against all the other background vibrations, but it's effect would be insidious, especially as far as the double row bearing supporting the flange end of the pinion. Regards, Eric. ________________________________________ From: ian thomson i.thomson@talk21.com What is happening here is a product of the fact that a Hooke's joint, or a universal joint as it is generally known, is not a constant velocity joint. This means that in anything but a straight ahead position where everything is lined up the speed of rotation varies slightly over any single revolution. The design of the joint is such that if the yoke in the middle is offset at all the speed of rotation as felt at the output yoke speeds up and slows down as it turns. Although the time taken for each rotation is the same for the input and output flanges within the rotation there is an acceleration and deceleration which cancel each other out. This increases with the deflection of the joint. If the two joints at each end of the propshaft are in line then this variation which is induced into the shaft proper by the joint at the gearbox end is removed at the diff end. If the splined sliding joint is not oriented to do this there will be a vibration felt in the system which it would take a mathematician to explain. Obviously in any installation the gearbox output and diff input are unlikely to be in a direct line most of the time so a vibration will be felt. This will increase as the system deflects as the suspension operates. I hope this makes sense and that I have got it right. Feel free to put me right though if I have been barking up the wrong tree.