Technical: A-arm ball joint tolerances?
02-24-2005, 06:29 AM
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Technical: A-arm ball joint tolerances?
I've measured play on my front A-arm ball joints using the "lock pliers" test. The movement is about 1mm on each side, give or take. (These are the late model cast arms.)
Assuming this is just wear of the nylon bushings, I suspect that this might be a good time to put in something like one of the Rennbay rebuild kits. Any thoughts or recommendations about going down this route?
Am I being overly cautious? How much movement would you consider acceptable before deciding to rebuild?
Thanks for your advice,
-Mark
Assuming this is just wear of the nylon bushings, I suspect that this might be a good time to put in something like one of the Rennbay rebuild kits. Any thoughts or recommendations about going down this route?
Am I being overly cautious? How much movement would you consider acceptable before deciding to rebuild?
Thanks for your advice,
-Mark
Last edited by Mark944na86; 02-24-2005 at 08:17 PM.
02-24-2005, 12:57 PM
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You shouldn't be able to feel any up and down play in the ball joint.
If you are measuring 1mm of up and down play with the control arm installed on the car I suggest you remove the control arm from the car and verify the play in the ball joint. If there is any play, I suggest you disassemble and inspect the ball joint. You will probably find that the upper bushing is badly worn. In my case, the upper bushing was in pieces!
I was initially very pleased with the RennBay ball joint kit and wrote a review:
Product Review - Rennbay ball joint kit
However, the rebuild didn't last very long though. After about 6 months, the upper bushing had been "squeezed" out the top of the ball joint. Here is a picture comparing the "squeezed" RennBay bushing to a new one. The original Rennbay bushings were black, new ones are blue:
I don't think this was the fault of the RennBay ball joint kit though. I had let the original ball joint wear too far. The control arm pocket, where the upper bushing sits against, had become elongated slightly and was no longer round because the upper bushing had disintegrated to the point where there was metal to metal contact.
In this case, this control arm was not rebuildable. If you let yours go too far, your control arms will also become non-rebuildable.
Regards,
Jim
If you are measuring 1mm of up and down play with the control arm installed on the car I suggest you remove the control arm from the car and verify the play in the ball joint. If there is any play, I suggest you disassemble and inspect the ball joint. You will probably find that the upper bushing is badly worn. In my case, the upper bushing was in pieces!
I was initially very pleased with the RennBay ball joint kit and wrote a review:
Product Review - Rennbay ball joint kit
However, the rebuild didn't last very long though. After about 6 months, the upper bushing had been "squeezed" out the top of the ball joint. Here is a picture comparing the "squeezed" RennBay bushing to a new one. The original Rennbay bushings were black, new ones are blue:
I don't think this was the fault of the RennBay ball joint kit though. I had let the original ball joint wear too far. The control arm pocket, where the upper bushing sits against, had become elongated slightly and was no longer round because the upper bushing had disintegrated to the point where there was metal to metal contact.
In this case, this control arm was not rebuildable. If you let yours go too far, your control arms will also become non-rebuildable.
Regards,
Jim
Last edited by jpapanas; 03-22-2005 at 10:07 PM.
02-24-2005, 07:52 PM
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Thanks for your advice.
So the "lock pliers" test isn't conclusive, from what you are saying. Bummer. I've got enough on my maintenance "to do" list that I _know_ needs doing. But from what you are saying, it sounds like I should probably get under there and pull things out to inspect. It's a PITA job, particularly since you generally need a realignment afterwards (I know you can scribe the eccentrics and so on, but I don't believe that would be as accurate as a proper realignment.)
My ('89 S2) car has 17" turbo twists, added by the PO. I've just been reading that Porsche specifies that the caster blocks and eccentrics are supposed to have been upgraded to the 968 parts if 17" wheels are fitted on these cars. I suppose I should inspect for this as well if I'm under there...
Are there other rules of thumb do other people use to decide if their A-arm ball joints are due?
-Mark
So the "lock pliers" test isn't conclusive, from what you are saying. Bummer. I've got enough on my maintenance "to do" list that I _know_ needs doing. But from what you are saying, it sounds like I should probably get under there and pull things out to inspect. It's a PITA job, particularly since you generally need a realignment afterwards (I know you can scribe the eccentrics and so on, but I don't believe that would be as accurate as a proper realignment.)
My ('89 S2) car has 17" turbo twists, added by the PO. I've just been reading that Porsche specifies that the caster blocks and eccentrics are supposed to have been upgraded to the 968 parts if 17" wheels are fitted on these cars. I suppose I should inspect for this as well if I'm under there...
Are there other rules of thumb do other people use to decide if their A-arm ball joints are due?
-Mark
02-24-2005, 08:09 PM
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I would say that if you are sure that the play is in the balljoint and if you cannote any play, it's time. If there is play, it starts hammering it apart, the worse it gets the quicker it will kill it too. Also look at the ball and see if it is pitted, that will just eat the new bushings, and as noted previously, check to see that the new bushing will be properly supported, if out of round significanly, there will be no support and the new bushing will be destroyed i short time. Good luck and it can be done with a bench vice if there is enough room for the arm and a few sockets.
02-24-2005, 08:22 PM
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The rule of thumb is that if there is any play in the ball joint it should be rebuilt. The problem is that the ball joint is kept tight by the lower spring. As the bushing wears the joint stays tight until it is worn past where the spring is able to keep pressure on it. At 1mm of play the top bushings is 1mm past its useable wear point.
The newer blue bushings have a glass fiber filler inside the plastic which makes them a bit more forgiving of slightly worn pockets. The Grey ones that come with the super deluxe kits have an even higher glass fiber content.
You can check for play in the bushings by just removing the pinch bolt from the ball pin and sliding it out of the spindle. That way it is free from the spindle and you can feel the play by hand. To do this, jack up the car. Take off the wheel. Remove the pinch bolt and slide the arm / ball joint downward out of the spindle. Push the spindle off to one side and feel the ball joint for play. You will not loose any noticeable alignment adjustment with this because you never disconnect the arm.
The newer blue bushings have a glass fiber filler inside the plastic which makes them a bit more forgiving of slightly worn pockets. The Grey ones that come with the super deluxe kits have an even higher glass fiber content.
You can check for play in the bushings by just removing the pinch bolt from the ball pin and sliding it out of the spindle. That way it is free from the spindle and you can feel the play by hand. To do this, jack up the car. Take off the wheel. Remove the pinch bolt and slide the arm / ball joint downward out of the spindle. Push the spindle off to one side and feel the ball joint for play. You will not loose any noticeable alignment adjustment with this because you never disconnect the arm.
02-25-2005, 06:13 AM
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Travis,
Thanks for the tip -- smart way of checking the joint in situ.
Would you guess 1mm past where the spring is able to keep pressure on it is indicative of only slightly worn pockets?
-Mark
Thanks for the tip -- smart way of checking the joint in situ.
The newer blue bushings have a glass fiber filler inside the plastic which makes them a bit more forgiving of slightly worn pockets. The Grey ones that come with the super deluxe kits have an even higher glass fiber content.
-Mark
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02-26-2005, 02:34 AM
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OK, so I should get a kit, and quickly.
But the big question for me is: why? Why are the ball joints shot on this (relatively) mildly driven '89 s2 with 145K kms (87K miles)? This seems very premature compared with the age and mileage other people are getting before replacement...
I know that lowering a car can prematurely wear the ball joints.This car is lower than my US model car, but I have believed it to be stock euro spec (although I have been finding it hard to get a simple measurement to verfiy this). If it's been lowered, then it's not been by much -- they're pretty low to start with.
OTOH, the wheels have been changed to 17" turbo twist by the PO. I know this puts some additional strain on some of the suspension parts, e.g. Porsche recommends the upgrade to the 968 caster blocks and eccentric bolts. Could this also have accelerated ball joint wear? Are there any tell-tale signs for wear of this type?
-Mark
But the big question for me is: why? Why are the ball joints shot on this (relatively) mildly driven '89 s2 with 145K kms (87K miles)? This seems very premature compared with the age and mileage other people are getting before replacement...
I know that lowering a car can prematurely wear the ball joints.This car is lower than my US model car, but I have believed it to be stock euro spec (although I have been finding it hard to get a simple measurement to verfiy this). If it's been lowered, then it's not been by much -- they're pretty low to start with.
OTOH, the wheels have been changed to 17" turbo twist by the PO. I know this puts some additional strain on some of the suspension parts, e.g. Porsche recommends the upgrade to the 968 caster blocks and eccentric bolts. Could this also have accelerated ball joint wear? Are there any tell-tale signs for wear of this type?
-Mark
02-26-2005, 02:46 AM
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The 17" wheels will have little to no effect on the ball joint wear. Your style of driving has the most effect. Aggressive driving, especially on bumpy roads, causes premature wear of most suspension components, as compared to daily street driving.
02-26-2005, 04:06 AM
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Would putting in a Geometry Correction Kit with the long shaft pins create problems if the car _wasn't_ lowered?
I was thinking about the GCK kit in case the car actually has been lowered, and that's exacerbating the problem...
-Mark
I was thinking about the GCK kit in case the car actually has been lowered, and that's exacerbating the problem...
-Mark
02-27-2005, 08:29 AM
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I've measured my front wheel centre-to-fender vertical distance at about 13.25"; from what I have read this indicated the car is at stock (non-US vehicles) height. From the Canadian Rennsport DE rules (http://www.rennsport.ca/A_driving/tech_eng.html):
-Mark
944/968 Front A-arms Check
Vehicles affected: 944 Stage II Cars (1985 & 1/2 or later, all 968's, or earlier 944's that have retrofitted cast aluminum lower front suspension). The problem is seen on 944's that have been lowered and driven aggressively.
If a 944/968 has been lowered below factory specifications, it causes undue forces to be applied to the ball joint and the lower suspension member, increasing the possibility of failure of either component when driven aggressively. Installation of shorter or aftermarket springs with lower profiles also can contribute to the problem by changing the suspension geometry. Multiple failures of this type have been reported across Zone 1 in the past year.
In the interest of maximizing the safety of all entrants at our events, Rennsport will comply with the Zone 1 regulation and request that all subject cars that were lowered, be set to stock factory ride height. Ball joints and control arms should be checked and replaced if necessary.
Technical inspection for the Rennsport event will include a check for conformation to stock ride height for all 944/968's equipped with the cast lower suspension arms. Stock height is defined as a minimum measurement of 13.0 inches from the center of the front wheel to the lower edge of the fender directly above the wheel centerline. Vehicles not meeting this specification will not be permitted to participate in the Rennsport Driver Education Event.
Vehicles affected: 944 Stage II Cars (1985 & 1/2 or later, all 968's, or earlier 944's that have retrofitted cast aluminum lower front suspension). The problem is seen on 944's that have been lowered and driven aggressively.
If a 944/968 has been lowered below factory specifications, it causes undue forces to be applied to the ball joint and the lower suspension member, increasing the possibility of failure of either component when driven aggressively. Installation of shorter or aftermarket springs with lower profiles also can contribute to the problem by changing the suspension geometry. Multiple failures of this type have been reported across Zone 1 in the past year.
In the interest of maximizing the safety of all entrants at our events, Rennsport will comply with the Zone 1 regulation and request that all subject cars that were lowered, be set to stock factory ride height. Ball joints and control arms should be checked and replaced if necessary.
Technical inspection for the Rennsport event will include a check for conformation to stock ride height for all 944/968's equipped with the cast lower suspension arms. Stock height is defined as a minimum measurement of 13.0 inches from the center of the front wheel to the lower edge of the fender directly above the wheel centerline. Vehicles not meeting this specification will not be permitted to participate in the Rennsport Driver Education Event.
