Looking for real information about rear suspension ball joints and bushings
Aug 5, 2012, 04:21 PM
#1
Looking for real information about rear suspension ball joints and bushings
hi guys,
Technical thread started here for the rear suspension.
Recently I posted up about a clunk in the rear suspension coming from the passenger side. Long story short.. after swapping shocks, bushings, top hats etc, the culprit turned out to be the trailing arm ball joint.
There was about 1/16" play in the joint after removal of the arm and inspecting it. I had sourced rear trailing arms and posted up that the dust boots are sourceable from Mitsubishiparts.net.
So the rebuilt parts including ES bushings for the trailing arms are on the car and problem solved.
However I came across some questions while delving into the rear suspension that I would like our resident suspension gurus like Smike or 03whitegsr or other competent suspension guy to look at or answer.
In pulling off arms etc, I noticed something weird about the upper control arms ( "u shaped ones that have a simple bushing on one leg, one bushing with a 2-bolt pivot shaft and finally ball joint on the outside to connect to the hub carrier)
Specifically, that 2 bolt pivot flange shaft appears to be bonded to the bushing. I could not get the shaft to turn at all on either side. Since it is in the same plane as the simple bushing ( one would expect it to be a pivot point) it theoretically should be free to pivot. I could not get either of mine to allow more than a tiny bit of movement. As in just a hint of movement. This was done in a vise with force applied by a long lever
I fully expected these to be able to move to allow the hub carrier to move up and down fairly easily. From the length ratio of those to the lower shock arm, you would gain negative camber under that movement. Clearly in my mind that is what Mitsu intended
IS it possible mine are just seized up? IDK so I did some investigation and searching
I found that Rally Sport Direct sells SuperPro bushings. SuperPro have a replacement for both bushes on the upper control arm. The front inner is a 2 part PU bushing set that comes with the flanged 2 bolt pivot shaft. Clearly that will pivot and allow the arm to move without putting undue force on the upper arm ball joint. The rear inner is a spacer and two part PU bushing to replace the metal shell rubber spacer OEM type
So my question is ..... is this arm supposed to pivot up on that shaft and rear bushing? Would the fact mine wont pivot..then cause wear and tear on the upper ball joint, trailing arm ball joint and toe assist ball joints? Would this situation cause poor travel and compliance for the rear suspension?
Please chime in here...theory and experience , please
BTW For those interested in replacing the non spherical bushings on the rear suspension, SuperPro has both bushings for the upper control arm that I was talking about, the lower control arm ( inner and shock bushing), two kinds of bushing for the toe assist arm( including one with an offset hole in the spacer that allows more adjustment for the toe ) and the trailing arm donut.
Long post I know but it could be very important both for diagnosing non compliance and as being a trouble spot that has been overlooked . If the binding causes undue wear on the ball joints it can get very expensive very quickly. Which affects us all at some point .
I have asked Russell M at MistubishiParts.net to see if the ball joints can be sourced. They are pressed in to the arms and measure up to be the same joint on all three arms in the rear suspension , they even take the exact same dust boot which is sourceable from mitsu BTW
I look forward to some knowledgeable replies
THX
Milburn
Technical thread started here for the rear suspension.
Recently I posted up about a clunk in the rear suspension coming from the passenger side. Long story short.. after swapping shocks, bushings, top hats etc, the culprit turned out to be the trailing arm ball joint.
There was about 1/16" play in the joint after removal of the arm and inspecting it. I had sourced rear trailing arms and posted up that the dust boots are sourceable from Mitsubishiparts.net.
So the rebuilt parts including ES bushings for the trailing arms are on the car and problem solved.
However I came across some questions while delving into the rear suspension that I would like our resident suspension gurus like Smike or 03whitegsr or other competent suspension guy to look at or answer.
In pulling off arms etc, I noticed something weird about the upper control arms ( "u shaped ones that have a simple bushing on one leg, one bushing with a 2-bolt pivot shaft and finally ball joint on the outside to connect to the hub carrier)
Specifically, that 2 bolt pivot flange shaft appears to be bonded to the bushing. I could not get the shaft to turn at all on either side. Since it is in the same plane as the simple bushing ( one would expect it to be a pivot point) it theoretically should be free to pivot. I could not get either of mine to allow more than a tiny bit of movement. As in just a hint of movement. This was done in a vise with force applied by a long lever
I fully expected these to be able to move to allow the hub carrier to move up and down fairly easily. From the length ratio of those to the lower shock arm, you would gain negative camber under that movement. Clearly in my mind that is what Mitsu intended
IS it possible mine are just seized up? IDK so I did some investigation and searching
I found that Rally Sport Direct sells SuperPro bushings. SuperPro have a replacement for both bushes on the upper control arm. The front inner is a 2 part PU bushing set that comes with the flanged 2 bolt pivot shaft. Clearly that will pivot and allow the arm to move without putting undue force on the upper arm ball joint. The rear inner is a spacer and two part PU bushing to replace the metal shell rubber spacer OEM type
So my question is ..... is this arm supposed to pivot up on that shaft and rear bushing? Would the fact mine wont pivot..then cause wear and tear on the upper ball joint, trailing arm ball joint and toe assist ball joints? Would this situation cause poor travel and compliance for the rear suspension?
Please chime in here...theory and experience , please
BTW For those interested in replacing the non spherical bushings on the rear suspension, SuperPro has both bushings for the upper control arm that I was talking about, the lower control arm ( inner and shock bushing), two kinds of bushing for the toe assist arm( including one with an offset hole in the spacer that allows more adjustment for the toe ) and the trailing arm donut.
Long post I know but it could be very important both for diagnosing non compliance and as being a trouble spot that has been overlooked . If the binding causes undue wear on the ball joints it can get very expensive very quickly. Which affects us all at some point .
I have asked Russell M at MistubishiParts.net to see if the ball joints can be sourced. They are pressed in to the arms and measure up to be the same joint on all three arms in the rear suspension , they even take the exact same dust boot which is sourceable from mitsu BTW
I look forward to some knowledgeable replies
THX
Milburn
Last edited by WRC-LVR; Aug 5, 2012 at 08:32 PM.
Aug 5, 2012, 06:27 PM
#2
The assist link mounting bolt should only move a little bit for adjustments. Did you take off the nut and take the bolt out? Could have seized to the bolt.
Mark its indexing first. If you can get it out without tearing the bushing, use a scotch pad and JB Blaster to clean the corrosion off. Re-install and see if it moves freely.
Mark its indexing first. If you can get it out without tearing the bushing, use a scotch pad and JB Blaster to clean the corrosion off. Re-install and see if it moves freely.
Aug 5, 2012, 07:37 PM
#3
Most of the rubber joints in the car are designed to flex in torsion, they aren't meant to "pivot" in the sense of the shaft rotating in the bushing. That joint not pivoting when you tried to make it is it simply doing exactly what it is supposed to do. Put the suspension together and you should be able to move the assembly with a jack without the damper on. If it doesn't move as expected in this situation, you might have something going on in there.
They do this as it eliminates "stiction" in the joint. It basically just acts like a spring that adds to the spring force to the main spring. I've seen hybrid versions of this same principle on F1 cars. They use a composite flexural beam section on the control arm that can bend a large amount and with relatively low forces in one direction and then are extremely rigid in the other two directions.
"Stiction" is simply what you learned about in high school physics where friction essentially has two values, static and dynamic. A balljoint is pretty difficult to get to move initially then "breaks away" and needs less force to keep it moving. This is also the difference between good spherical bearings and cheap ones. The high quality bearings have a lower break away torque value when properly installed. Properly installed being the key though and with the tighter tolerances used in the high quality pieces, if you have a press fit that is too tight, it can greatly increase this breakaway torque value, or even lock them up completely.
Compared to polyurethane though, I'd rather have the rubber flexural bushing used by the OEM. That bushing is so thin that the compliance it has in the non-torsion directions is nothing to be concerned about. The polyurethane however is sliding, which means when that joint goes dry of grease, it's going to have a ton of friction in it which will then make suspension movement less smooth. If you are going to replace it in a race type setup, I think using a needle roller bearing surrounded by needle roller thrust bearings would be the trick for both of those bushings as they are inline and yes, the arm "pivots" on that bolted shaft axis. The joint isn't big enough to fit anything else in there besides a sleeve bushing anyway so if you want something stiff and fancy, I think it would have to be a needle bearing setup.
I hope that helps answer the questions you had?
They do this as it eliminates "stiction" in the joint. It basically just acts like a spring that adds to the spring force to the main spring. I've seen hybrid versions of this same principle on F1 cars. They use a composite flexural beam section on the control arm that can bend a large amount and with relatively low forces in one direction and then are extremely rigid in the other two directions.
"Stiction" is simply what you learned about in high school physics where friction essentially has two values, static and dynamic. A balljoint is pretty difficult to get to move initially then "breaks away" and needs less force to keep it moving. This is also the difference between good spherical bearings and cheap ones. The high quality bearings have a lower break away torque value when properly installed. Properly installed being the key though and with the tighter tolerances used in the high quality pieces, if you have a press fit that is too tight, it can greatly increase this breakaway torque value, or even lock them up completely.
Compared to polyurethane though, I'd rather have the rubber flexural bushing used by the OEM. That bushing is so thin that the compliance it has in the non-torsion directions is nothing to be concerned about. The polyurethane however is sliding, which means when that joint goes dry of grease, it's going to have a ton of friction in it which will then make suspension movement less smooth. If you are going to replace it in a race type setup, I think using a needle roller bearing surrounded by needle roller thrust bearings would be the trick for both of those bushings as they are inline and yes, the arm "pivots" on that bolted shaft axis. The joint isn't big enough to fit anything else in there besides a sleeve bushing anyway so if you want something stiff and fancy, I think it would have to be a needle bearing setup.
I hope that helps answer the questions you had?
Last edited by 03whitegsr; Aug 5, 2012 at 08:38 PM.
Aug 5, 2012, 08:00 PM
#4
The assist link mounting bolt should only move a little bit for adjustments. Did you take off the nut and take the bolt out? Could have seized to the bolt.
Mark its indexing first. If you can get it out without tearing the bushing, use a scotch pad and JB Blaster to clean the corrosion off. Re-install and see if it moves freely.
Mark its indexing first. If you can get it out without tearing the bushing, use a scotch pad and JB Blaster to clean the corrosion off. Re-install and see if it moves freely.
Sounds like you are talking about the toe assist link here. That one is good on my car. In fact I have the SuperPro bushing on that with the offset hole spacer. so i can dial in toe much easier. No worries at all on that and the bolt moves etc easy to dial it in and index it to the marked graduations.
The arm im talking about is the upper control arm. No issue getting it off the car at all. Once off the car the rear inner bushing that is to the back of the car on that arm is a simple bushing. no issue with that. It is mounted witha simple bolt/nut arrangement. Not frozen at all. It is the forward mount for the upper arm with the small 2 bolt pivot shaft sticking thru it. It is mounted to the body by 2 bolts on either side of the bushing. It is about 3 inches long Im positive that should have twisting movement in it. Except mine ( both sides of the car )appear to have no movement..which means the upper arm doesnt want to move well at all. I believe that puts more pounding stress on the trailing arm ball joint .
Since it is replaceable (at least by SuperPro ) it stands to reason the shaft rotates in the bushing. But if Mitsubishi bonds the rubber to the shaft then it wont move much at all. Reason and understanding of the geometry of how it would move pivoting the arm up and down on the line bisecting the rear inner bushing and the front inner ( 2 bolt shaft thru bushing ) would seem to indicate that it would not be bonded.
However if that little front shaft is bonded or frozen the upper arm wont move very far up and down, limiting suspension travel, camber change ( and negative gain ) It seems to me it must be mine are frozen.
I have attached the parts diagram from Mitsubishiparts.net....I outlined the little 2 bolt mount for the upper control arm in pink. That bushing and shaft is available from SuperPro. It should be able to spin in the bushing to allow the upper control arm to pivot up. If Mitsubishi bonded the rubber in that to the shaft it would be to limit the ability of the shaft to spin thereby limiting the travel of that arm up and down. I also outlined the toe assist arm in yellow and circled the bushing that is available from SuperPro with an offset spacer in it to allow much more toe adjustment.
Those people who discover the same on their cars might expect that the ball joints on the trailing arm, toe assist arm, and upper control arm might wear out faster. The ball joint on the trailing arm on the passenger side on my car failed and I went looking as to why.
Let me know if you concur.
In the meantime, I will be ordering the SuperPro bushings for both the upper control arms and replacing the frozen parts as well as the simple bushing on the arms.
Once they are done I will report back as to the ability to spin them. I am not expecting they move easily but do expect they should be fairly easy to twist with pliers or a wrench on the mounting tabs. I will also report on the change if any of the car under bump and droop , and the compliance of the rear suspension on the road with no other changes.
Best regards,
Milburn
PS Bonus pic of my ride at a local shop. Zoom in on the front fender
Yes that is a little carbon fiber Dragon !
Last edited by WRC-LVR; Aug 5, 2012 at 08:14 PM.
Aug 5, 2012, 08:27 PM
#5
Most of the rubber joints in the car are designed to flex in torsion, they aren't meant to "pivot" in the sense of the shaft rotating in the bushing. That joint not pivoting when you tried to make it is it simply doing exactly what it is supposed to do. Put the suspension together and you should be able to move the assembly with a jack without the damper on. If it doesn't move as expected in this situation, you might have something going on in there.
They do this as it eliminates "stiction" in the joint. It basically just acts like a spring that adds to the spring force to the main spring. I've seen hybrid versions of this same principle on F1 cars. They use a composite flexural beam section on the control arm that can bend a large amount and with relatively low forces in one direction and then are extremely rigid in the other two directions.
"Stiction" is simply what you learned about in high school physics where friction essentially has two values, static and dynamic. A balljoint is pretty difficult to get to move initially then "breaks away" and needs less force to keep it moving. This is also the difference between good spherical bearings and cheap ones. The high quality bearings have a lower break away torque value when properly installed. Properly installed being the key though and with the tighter tolerances used in the high quality pieces, if you have a press fit that is too tight, it can greatly increase this breakaway torque value, or even lock them up completely.
Compared to polyurethane though, I'd rather have the rubber flexural bushing used by the OEM. That bushing is so thin that the compliance it has in the non-torsion directions is nothing to be concerned about. The polyurethane however is sliding, which means when that joint goes dry of grease, it's going to have a ton of friction in it which will then make suspension movement less smooth. If you are going to replace it in a race type setup, I think using a needle roller bearing surrounded by dual needle thrust bearings would be the trick for both of those bushings as they are inline and yes, the arm "pivots" on that bolted shaft axis. The joint isn't big enough to fit anything else in there besides a sleeve bushing anyway so if you want something stiff and fancy, I think it would have to be a needle bearing setup.
I hope that helps answer the questions you had?
They do this as it eliminates "stiction" in the joint. It basically just acts like a spring that adds to the spring force to the main spring. I've seen hybrid versions of this same principle on F1 cars. They use a composite flexural beam section on the control arm that can bend a large amount and with relatively low forces in one direction and then are extremely rigid in the other two directions.
"Stiction" is simply what you learned about in high school physics where friction essentially has two values, static and dynamic. A balljoint is pretty difficult to get to move initially then "breaks away" and needs less force to keep it moving. This is also the difference between good spherical bearings and cheap ones. The high quality bearings have a lower break away torque value when properly installed. Properly installed being the key though and with the tighter tolerances used in the high quality pieces, if you have a press fit that is too tight, it can greatly increase this breakaway torque value, or even lock them up completely.
Compared to polyurethane though, I'd rather have the rubber flexural bushing used by the OEM. That bushing is so thin that the compliance it has in the non-torsion directions is nothing to be concerned about. The polyurethane however is sliding, which means when that joint goes dry of grease, it's going to have a ton of friction in it which will then make suspension movement less smooth. If you are going to replace it in a race type setup, I think using a needle roller bearing surrounded by dual needle thrust bearings would be the trick for both of those bushings as they are inline and yes, the arm "pivots" on that bolted shaft axis. The joint isn't big enough to fit anything else in there besides a sleeve bushing anyway so if you want something stiff and fancy, I think it would have to be a needle bearing setup.
I hope that helps answer the questions you had?
I did not try moving the suspension with a jack but expect it to twist some then. Still I think it is to limit the travel, and help the toe assist arm stay in a range of motion that it will be effective in.
do you know if the rally cars swap this or change to a needle bearing setup?
Can you model that in your 3d suspension software ?
I appreciate your comments and insight to this. Even at 58 I find myself learning every day
Aug 7, 2012, 01:20 AM
#7
Evolved Member
That bush you have highlighted in pink has the rubber bonded to the outer shell and the inner shaft mount. If it can spin freely then it has broken free of the rubber and is buggered.
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Aug 7, 2012, 02:40 PM
#9
Yogi_B since you are from down under, do you know if the rally guys replace that one bush with the SuperPro one that is available? Any way you can find out what other changes have to be made if you do? Im guessing if you replace it wiht something that spins ( ie PU bushing), then you have to increase the rear spring rate to compensate
Last edited by WRC-LVR; Aug 7, 2012 at 02:45 PM.
Aug 7, 2012, 02:50 PM
#10
Someone else take a look....but im pretty sure that they have done that bushing allowing the upper arm more freedom to move and then are relying on their other modifications to supply the extra spring.
It is hard to see which way that blade arm pivots though..rotten angle :-)
Last edited by WRC-LVR; Aug 7, 2012 at 03:03 PM.
Aug 7, 2012, 03:12 PM
#11
Most of the rubber joints in the car are designed to flex in torsion, they aren't meant to "pivot" in the sense of the shaft rotating in the bushing. That joint not pivoting when you tried to make it is it simply doing exactly what it is supposed to do. Put the suspension together and you should be able to move the assembly with a jack without the damper on. If it doesn't move as expected in this situation, you might have something going on in there.
They do this as it eliminates "stiction" in the joint. It basically just acts like a spring that adds to the spring force to the main spring. I've seen hybrid versions of this same principle on F1 cars. They use a composite flexural beam section on the control arm that can bend a large amount and with relatively low forces in one direction and then are extremely rigid in the other two directions.
"Stiction" is simply what you learned about in high school physics where friction essentially has two values, static and dynamic. A balljoint is pretty difficult to get to move initially then "breaks away" and needs less force to keep it moving. This is also the difference between good spherical bearings and cheap ones. The high quality bearings have a lower break away torque value when properly installed. Properly installed being the key though and with the tighter tolerances used in the high quality pieces, if you have a press fit that is too tight, it can greatly increase this breakaway torque value, or even lock them up completely.
Compared to polyurethane though, I'd rather have the rubber flexural bushing used by the OEM. That bushing is so thin that the compliance it has in the non-torsion directions is nothing to be concerned about. The polyurethane however is sliding, which means when that joint goes dry of grease, it's going to have a ton of friction in it which will then make suspension movement less smooth. If you are going to replace it in a race type setup, I think using a needle roller bearing surrounded by needle roller thrust bearings would be the trick for both of those bushings as they are inline and yes, the arm "pivots" on that bolted shaft axis. The joint isn't big enough to fit anything else in there besides a sleeve bushing anyway so if you want something stiff and fancy, I think it would have to be a needle bearing setup.
I hope that helps answer the questions you had?
They do this as it eliminates "stiction" in the joint. It basically just acts like a spring that adds to the spring force to the main spring. I've seen hybrid versions of this same principle on F1 cars. They use a composite flexural beam section on the control arm that can bend a large amount and with relatively low forces in one direction and then are extremely rigid in the other two directions.
"Stiction" is simply what you learned about in high school physics where friction essentially has two values, static and dynamic. A balljoint is pretty difficult to get to move initially then "breaks away" and needs less force to keep it moving. This is also the difference between good spherical bearings and cheap ones. The high quality bearings have a lower break away torque value when properly installed. Properly installed being the key though and with the tighter tolerances used in the high quality pieces, if you have a press fit that is too tight, it can greatly increase this breakaway torque value, or even lock them up completely.
Compared to polyurethane though, I'd rather have the rubber flexural bushing used by the OEM. That bushing is so thin that the compliance it has in the non-torsion directions is nothing to be concerned about. The polyurethane however is sliding, which means when that joint goes dry of grease, it's going to have a ton of friction in it which will then make suspension movement less smooth. If you are going to replace it in a race type setup, I think using a needle roller bearing surrounded by needle roller thrust bearings would be the trick for both of those bushings as they are inline and yes, the arm "pivots" on that bolted shaft axis. The joint isn't big enough to fit anything else in there besides a sleeve bushing anyway so if you want something stiff and fancy, I think it would have to be a needle bearing setup.
I hope that helps answer the questions you had?
Aug 7, 2012, 11:43 PM
#12
Evolved Member
Yogi_B since you are from down under, do you know if the rally guys replace that one bush with the SuperPro one that is available? Any way you can find out what other changes have to be made if you do? Im guessing if you replace it wiht something that spins ( ie PU bushing), then you have to increase the rear spring rate to compensate
For my evo i've replaced just about all the bushes with spherical bearings, the bushes in the rear upper arm i've gone with the HardRace spherical bearings bushes. Can't really say i've noticed a big difference doing all this but every little bit helps.
So personally I feel if you just changed that bush you are talking about with say a spherical one I doubt you would notice anything.
Aug 10, 2012, 05:11 PM
#13
GSR - I'm biting. What is it we're looking for?
I spy:
1. Blade RSB mounted in the trunk.
2. HyperCo spring bearings.
3. Potentially after market rear UCA bushing.
4. Mystery rod end under front of UCA.
5. Random rivets in body.
6. Aero panel in the front of the wheel well.
I spy:
1. Blade RSB mounted in the trunk.
2. HyperCo spring bearings.
3. Potentially after market rear UCA bushing.
4. Mystery rod end under front of UCA.
5. Random rivets in body.
6. Aero panel in the front of the wheel well.
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