Half shaft spacers.
05-15-2007, 08:50 PM
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Half shaft spacers.
EDIT: If you're reading this thread for the first time, the good stuff starts around page 8, where we start getting some real facts. Skip ahead to avoid a lot of boring reading and tail chasing. 
End-of-Edit:
I realize that the half shaft spacers have been discussed in other threads, but there are still some unanswered questions. I also want have the real experts examine my understanding to make sure we all actually understand what the spacers accomplish. I've been following the threads for some time, and looking at the way our cars work, trying to figure out some things about the idea. I've talked with XViper about it and had him review my understanding, and I think I've got a handle on it now. I'm hoping that we can produce the definitive spacer thread and sticky it, so I need everyone to help out and make sure my understanding is reasonable.
If you don't know what I'm talking about, do a forum search using "half shaft spacers" and look at some of the old threads. I'm not going to discuss any current theories, but rather just jump into a discussion of how I think things work, and what I think the spacers accomplish, so you guys can pick it apart.
We need to start with an understanding of how the CV joint moves as the suspension goes up and down. You can take the shocks and springs off the car and exercise the suspension throughout it's entire range of movement, and measure things like toe and camber changes, but it's not as straight forward to measure the CV joints movement. However, it is reasonable to believe that the balls do move back and forth in the cup as the suspension moves from full compression to full extension, and it is also reasonable to assume that the joint is designed to accomodate the full movement of the suspension. At no point during the suspension travel will the balls be pulled so far out as to cause problems, and at no point will the balls be pushed so far into the cup as to run out of space. As long as we do not change the total suspension travel the balls remain positioned within the working range of the cup. Note that we are working the suspension throught it's design limits, and that the springs and shocks, and ride height, have nothing to do with what we're seeing.
Although we don't have any measurements, this will be easier for you to visualize if we use some numbers in an example. Let's say that on a stock car the balls travel a total of 40mm as the suspension goes from center to full compression or extension. Let's also say that the joint will accomodate a total movement of 60mm. Further, lets assume that the joint is designed so that there is 10mm to spare on either side of the 40mm used in movement. We know that the joint will be pushed in the most when the a-arms are straight, and will be pulled outward as they move off the center position. We can see that they will be pulled out 40mm more at the top and bottom of the stroke, using 50mm of thte cup length, and having 10mm to spare. Regardless of what we do with the ride hight later when we install the springs, if we install half shaft spacers we move the entire range over which the joint must work, possibly outside it's design range, and certainly outside the range over which Honda intended the joint to work. Given this, we don't want to be adding spacers unless there is some benefit, so let's look at what we might gain.
XViper and others have speculated that perhaps earlier wear patterns, prior to lowering, contribute to CV joint failure. It could be that the cups wear more in the center, becaues that's where they run most of the time when the car is at stock ride height. When the car is lowered, the normal running position changes, moves further out, so now the balls have to travel through an area of greater wear, and there could be some associated vibration and accelerated CV joint failures. IOW, if the spacer puts the balls back in the same spot so the old wear patterns are maintained, it might prevent the joint from failing prematurely.
I am no expert and have nothing but respect for the guys who came up with that theory, but several things don't quite seem to fit. For one thing, none of the claims I've seen for the spacers say anything about wear patterns. For another, getting exactly the same wear pattern would require matching the spacer to the amount of movement caused by the drop. We have different spacing at 1/2", 1", and every other amount of drop, so we can't just use a one-size-fits-all spacer to get the balls centered. I've seen 7mm spacers, and 10mm spacers, but have yet to see any measurements and calculatoins to tell me how far I have to move the balls for each inch of drop. Without that I haven't got a chance of maintaining exactly the same wear patterns, so I remain skeptical.
If you think you are buying insurance against a wear pattern problem and have some assurance that the spacing will be correct for the drop you're running (or "close enough") and you want to install the things, go ahead, but without more information it's a crap shoot for the rest of us.
A better solution seems to be replacing the worn cups, and that only makes sense when and if they fail. I dropped my can an inch at 36,000 miles and am slowly approaching 60,000 miles now, drive the car pretty hard
, and haven't had a single issue with my CV joints. Many others have had the same experience, so it's not even a given that your joints are going to fail when you lower. I've seen spacer ads that tell me that if I drive the car hard my CV joints will fail, but apparently they're talking to people who drive harder than I do (and those of you who know me know how likely that is). If it ain't broke, don't fix it. Lowering does not change the total (designed in) working range of either the suspension or the CV joints. It only changes the most frequent operating position, the normal position. Spacers change both the normal and the range, so at best it's a mixed bag. Unless and until we have more information my advice has to be to leave the joints working over their full design range and just replace them if they fail.
I know some people are probably going to feel a need to defend their purchase decisions, but let's keep this civil and look at it as a Critical Design Review. All I am saying here is that there are some unanswered questions. Any and all answers and theories should be respected and appreciated.
Now, where the heck did I put my Nomex.
End-of-Edit:
I realize that the half shaft spacers have been discussed in other threads, but there are still some unanswered questions. I also want have the real experts examine my understanding to make sure we all actually understand what the spacers accomplish. I've been following the threads for some time, and looking at the way our cars work, trying to figure out some things about the idea. I've talked with XViper about it and had him review my understanding, and I think I've got a handle on it now. I'm hoping that we can produce the definitive spacer thread and sticky it, so I need everyone to help out and make sure my understanding is reasonable.
If you don't know what I'm talking about, do a forum search using "half shaft spacers" and look at some of the old threads. I'm not going to discuss any current theories, but rather just jump into a discussion of how I think things work, and what I think the spacers accomplish, so you guys can pick it apart.
We need to start with an understanding of how the CV joint moves as the suspension goes up and down. You can take the shocks and springs off the car and exercise the suspension throughout it's entire range of movement, and measure things like toe and camber changes, but it's not as straight forward to measure the CV joints movement. However, it is reasonable to believe that the balls do move back and forth in the cup as the suspension moves from full compression to full extension, and it is also reasonable to assume that the joint is designed to accomodate the full movement of the suspension. At no point during the suspension travel will the balls be pulled so far out as to cause problems, and at no point will the balls be pushed so far into the cup as to run out of space. As long as we do not change the total suspension travel the balls remain positioned within the working range of the cup. Note that we are working the suspension throught it's design limits, and that the springs and shocks, and ride height, have nothing to do with what we're seeing.
Although we don't have any measurements, this will be easier for you to visualize if we use some numbers in an example. Let's say that on a stock car the balls travel a total of 40mm as the suspension goes from center to full compression or extension. Let's also say that the joint will accomodate a total movement of 60mm. Further, lets assume that the joint is designed so that there is 10mm to spare on either side of the 40mm used in movement. We know that the joint will be pushed in the most when the a-arms are straight, and will be pulled outward as they move off the center position. We can see that they will be pulled out 40mm more at the top and bottom of the stroke, using 50mm of thte cup length, and having 10mm to spare. Regardless of what we do with the ride hight later when we install the springs, if we install half shaft spacers we move the entire range over which the joint must work, possibly outside it's design range, and certainly outside the range over which Honda intended the joint to work. Given this, we don't want to be adding spacers unless there is some benefit, so let's look at what we might gain.
XViper and others have speculated that perhaps earlier wear patterns, prior to lowering, contribute to CV joint failure. It could be that the cups wear more in the center, becaues that's where they run most of the time when the car is at stock ride height. When the car is lowered, the normal running position changes, moves further out, so now the balls have to travel through an area of greater wear, and there could be some associated vibration and accelerated CV joint failures. IOW, if the spacer puts the balls back in the same spot so the old wear patterns are maintained, it might prevent the joint from failing prematurely.
I am no expert and have nothing but respect for the guys who came up with that theory, but several things don't quite seem to fit. For one thing, none of the claims I've seen for the spacers say anything about wear patterns. For another, getting exactly the same wear pattern would require matching the spacer to the amount of movement caused by the drop. We have different spacing at 1/2", 1", and every other amount of drop, so we can't just use a one-size-fits-all spacer to get the balls centered. I've seen 7mm spacers, and 10mm spacers, but have yet to see any measurements and calculatoins to tell me how far I have to move the balls for each inch of drop. Without that I haven't got a chance of maintaining exactly the same wear patterns, so I remain skeptical.
If you think you are buying insurance against a wear pattern problem and have some assurance that the spacing will be correct for the drop you're running (or "close enough") and you want to install the things, go ahead, but without more information it's a crap shoot for the rest of us.
A better solution seems to be replacing the worn cups, and that only makes sense when and if they fail. I dropped my can an inch at 36,000 miles and am slowly approaching 60,000 miles now, drive the car pretty hard
, and haven't had a single issue with my CV joints. Many others have had the same experience, so it's not even a given that your joints are going to fail when you lower. I've seen spacer ads that tell me that if I drive the car hard my CV joints will fail, but apparently they're talking to people who drive harder than I do (and those of you who know me know how likely that is). If it ain't broke, don't fix it. Lowering does not change the total (designed in) working range of either the suspension or the CV joints. It only changes the most frequent operating position, the normal position. Spacers change both the normal and the range, so at best it's a mixed bag. Unless and until we have more information my advice has to be to leave the joints working over their full design range and just replace them if they fail.I know some people are probably going to feel a need to defend their purchase decisions, but let's keep this civil and look at it as a Critical Design Review. All I am saying here is that there are some unanswered questions. Any and all answers and theories should be respected and appreciated.
Now, where the heck did I put my Nomex.
05-16-2007, 06:16 AM
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Red,
I always assumed that lowering the car pulled the average position of the ball out further toward the outboard end of the cup. This assumes that on stock springs, the normal static ride height has arms horizontal.
I have inferred from earlier posts that if you lowered the car enough, you could reach the limits of travel in the cup. Once the ball moved to the most extreme outboard end (near full compression of a wheel's suspension) that it would hit a shoulder stop on the cup, limiting its travel, while there is still suspension compression travel left before bump stop. This means that extreme suspension compression would cause the axle half shaft to be stretched in tension.
So, in this case, installing half shaft spacers would move the ball back in towards the center of the cup where it didn't run out to the travel stops on the cup during extreme suspension compression travel.
I have not seen even pictures of the cup myself, much less the real item. Is there really a shoulder (travel stop) on the outboard end of the cup that physically captures the ball?
If so, I would think it would be easy enough to check this geometry out by jacking up the car by the A-arm until you hit either the bump stop or this ball travel limit. Maybe someone with aggressive drop coilovers or springs/shocks can try this or add their knowledge.
If there is no travel stop shoulder on the outbard end of the cup, then the stretched half shaft theory is out the window. But I envision this cup as a large socket (not the wrench) layed horizontally. The socket will be strongest at the base (inboard near the diff) and weakest at the open (outboard) end. Maybe just running the ball further outboard than stock is enough to cause yeilding or deformation failures at the weaker (open) end of the cup.
I always assumed that lowering the car pulled the average position of the ball out further toward the outboard end of the cup. This assumes that on stock springs, the normal static ride height has arms horizontal.
I have inferred from earlier posts that if you lowered the car enough, you could reach the limits of travel in the cup. Once the ball moved to the most extreme outboard end (near full compression of a wheel's suspension) that it would hit a shoulder stop on the cup, limiting its travel, while there is still suspension compression travel left before bump stop. This means that extreme suspension compression would cause the axle half shaft to be stretched in tension.
So, in this case, installing half shaft spacers would move the ball back in towards the center of the cup where it didn't run out to the travel stops on the cup during extreme suspension compression travel.
I have not seen even pictures of the cup myself, much less the real item. Is there really a shoulder (travel stop) on the outboard end of the cup that physically captures the ball?
If so, I would think it would be easy enough to check this geometry out by jacking up the car by the A-arm until you hit either the bump stop or this ball travel limit. Maybe someone with aggressive drop coilovers or springs/shocks can try this or add their knowledge.
If there is no travel stop shoulder on the outbard end of the cup, then the stretched half shaft theory is out the window. But I envision this cup as a large socket (not the wrench) layed horizontally. The socket will be strongest at the base (inboard near the diff) and weakest at the open (outboard) end. Maybe just running the ball further outboard than stock is enough to cause yeilding or deformation failures at the weaker (open) end of the cup.
05-16-2007, 07:27 AM
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heres what i know about half shafts. on FWD cars if you take them apart (and i would and am assuming the RWD cars with independent axles use the same type of half shafts) they have, lets think about a cup and inside that cup it has 3 slots that the solid portion of the axle slides into. that has mounted on the ends of it 3 bearings. that bearings allow the sold shaft to articulate inside the cup and in and out. now when installing a hald shaft you have to be careful to not pull the cup end away from the (axle) shaft as it will pull it out of the cup. if you think about it during assembly it would be impossible to assemble a cv shaft with a "stop shoulder" inside the cup as you could never get it together...
at anyrate here is what i have to say on the spacer subject. i never thought about it in this respect prior to this thread but they really dont make sense now that some light has been shined...if you disassemble the tension portion of the rear axle so it can move up and down to the designed limits it should never pull the axle out of the cup. therefore if you lower your car it shouldnt change the way it performs. but as was stated it will ride in a different portion of the cup. the ONLY thing i can think of is that the closer it gets to the end of the cup (the lower the car gets) the weaker it will get and in high horsepower applications or someone who driver spirited like myself this "could" lead to premature failure. obviously the reason for that is the cup is weaker around the edges. i do not now see the benefits of adding a spacer. infact i could actually see that as bottoming out the axle shaft inside the cup itself as you have now added a length to the half shaft. basically like putting the wrong length axle in. i do believe they are designed with a "cusion" obviously honda would not want there to be only 1mm of cusion if someone were to bottom out the suspension (on a stock ride height) as it would potentially bottom the axle in the cup in daily driving. so the theory of 10mm or so inside as a cusion sounds like thats a possiblity. therefor with that adding the spacer would take up the cusion and potentially cause the axle to bottom out.
these are my thought. a little random but i hope they help.
at anyrate here is what i have to say on the spacer subject. i never thought about it in this respect prior to this thread but they really dont make sense now that some light has been shined...if you disassemble the tension portion of the rear axle so it can move up and down to the designed limits it should never pull the axle out of the cup. therefore if you lower your car it shouldnt change the way it performs. but as was stated it will ride in a different portion of the cup. the ONLY thing i can think of is that the closer it gets to the end of the cup (the lower the car gets) the weaker it will get and in high horsepower applications or someone who driver spirited like myself this "could" lead to premature failure. obviously the reason for that is the cup is weaker around the edges. i do not now see the benefits of adding a spacer. infact i could actually see that as bottoming out the axle shaft inside the cup itself as you have now added a length to the half shaft. basically like putting the wrong length axle in. i do believe they are designed with a "cusion" obviously honda would not want there to be only 1mm of cusion if someone were to bottom out the suspension (on a stock ride height) as it would potentially bottom the axle in the cup in daily driving. so the theory of 10mm or so inside as a cusion sounds like thats a possiblity. therefor with that adding the spacer would take up the cusion and potentially cause the axle to bottom out.
these are my thought. a little random but i hope they help.
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05-16-2007, 11:42 AM
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All the spacer does IMO is change the place inside the bucket where the spider bearings are toughing.
It's the angle between axle and bucket that determines the amount of travel or movement of the spider bearings inside the bucket.
The spacer moves the bucket outwards but does not change the angle of the axle in relation to the bucket.
I hope this is all in proper technical English
05-16-2007, 11:56 AM
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Originally Posted by RED MX5,May 16 2007, 12:50 AM
If you think you are buying insurance against a wear pattern problem and have some assurance that the spacing will be correct for the drop you're running (or "close enough") and you want to install the things, go ahead, but without more information it's a crap shoot for the rest of us.