Challenge for the new year: Troubleshoot brakes, smoothen ride
01-07-2008, 04:02 AM
#1
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Challenge for the new year: Troubleshoot brakes, smoothen ride
So I have two problems with my beloved shark that might or might not be related, but drive me absolutely crazy,
1. I can't seem to get this beast to ride smoothly. The body vibrates, not the steering wheel. This is most likely a rear wheel/tire issue. Rear tires are almost brand new.
Balancing did not help, I know I have one rear tire that's not 100% round, and recently banged the opposite wheel on a curb. The rims had been straightened last year, but I don't know whether any of them are out of round again. Also, the car sits a lot, so the first few miles, the ride is even worse...
2. The brakes have a strange intermittent behavior: Sometimes the car brakes smoothly, while other times, it jerks to a stop at various degrees of jerking. Similarly, when I brake from high speed sometimes the whole car vibrates violently, but not always. And the rear brakes squeak at times.
These problems have been there for a while. Bill and I already replaced the discs (Zimmerman) and pads (factory, with factory silencers). No change whatsoever!
Recently, we looked at the rear brakes, and found that the pads don't wear exactly evenly on the inside and outside of the discs.
Unfortunately, I don't remember when the brake fluid was last changed. But I think Bill and I did that at some point not too long ago - Bill: Do you remember???
I don't know, if #1 and #2 are related in any way. I suspect not, becaue that one rear tire is always a hint out of round (Yokohama, must have come that way), and the brake problem was the same with the previous tires, the bent wheels, etc.
I'm wondering how you guys would approach solving these two issues.
Also: Is there anybody in the Bay Area who could lend me two straight, round and well balanced rear wheels for a few days to test things out?
Thanks!
1. I can't seem to get this beast to ride smoothly. The body vibrates, not the steering wheel. This is most likely a rear wheel/tire issue. Rear tires are almost brand new.
Balancing did not help, I know I have one rear tire that's not 100% round, and recently banged the opposite wheel on a curb. The rims had been straightened last year, but I don't know whether any of them are out of round again. Also, the car sits a lot, so the first few miles, the ride is even worse...
2. The brakes have a strange intermittent behavior: Sometimes the car brakes smoothly, while other times, it jerks to a stop at various degrees of jerking. Similarly, when I brake from high speed sometimes the whole car vibrates violently, but not always. And the rear brakes squeak at times.
These problems have been there for a while. Bill and I already replaced the discs (Zimmerman) and pads (factory, with factory silencers). No change whatsoever!
Recently, we looked at the rear brakes, and found that the pads don't wear exactly evenly on the inside and outside of the discs.
Unfortunately, I don't remember when the brake fluid was last changed. But I think Bill and I did that at some point not too long ago - Bill: Do you remember???
I don't know, if #1 and #2 are related in any way. I suspect not, becaue that one rear tire is always a hint out of round (Yokohama, must have come that way), and the brake problem was the same with the previous tires, the bent wheels, etc.
I'm wondering how you guys would approach solving these two issues.
Also: Is there anybody in the Bay Area who could lend me two straight, round and well balanced rear wheels for a few days to test things out?
Thanks!
01-07-2008, 06:36 AM
#2
Nichole,
Max permissable run out on the inner and outer rim beads is 1 mm as shown on page 73 of the technical specification booklet.
Tyre/wheel balancing need to be done dynamically axially, whilst rotating, ensuring that the wheel is also balanced laterally due to width of the tyre/rim, so as they don't wobble from side to side in the vertical plane.
If the tyre is out of round then this will impart out of balanced forces from the tyre rotation into the body. I could not find the max out-of-round specification for high speed tyres. As "google" search should give you some ideas.
Tails 1990 928 S4 Auto
I have problems with my brakes when they are overheated as they tend to feel as though there is grit caught between the pads and the disks. If the disks are bright and glazed they can be deglazed using a emery cloth rotating disk on the disks while they rotate and this can solve the problem.
Max permissable run out on the inner and outer rim beads is 1 mm as shown on page 73 of the technical specification booklet.
Tyre/wheel balancing need to be done dynamically axially, whilst rotating, ensuring that the wheel is also balanced laterally due to width of the tyre/rim, so as they don't wobble from side to side in the vertical plane.
If the tyre is out of round then this will impart out of balanced forces from the tyre rotation into the body. I could not find the max out-of-round specification for high speed tyres. As "google" search should give you some ideas.
Tails 1990 928 S4 Auto
I have problems with my brakes when they are overheated as they tend to feel as though there is grit caught between the pads and the disks. If the disks are bright and glazed they can be deglazed using a emery cloth rotating disk on the disks while they rotate and this can solve the problem.
01-07-2008, 08:40 AM
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Nicole,
Hard to say what the issue is with the brakes, but if you have uneven pad wear, it could be that you have a little air trapped in the line on the one side that isn't wearing so much and this can also cause a pulling sensation under heavier braking. I would advise that if you have not changed your brake fluid in the past couple years, it's time.
As for the tires, get them "road force" balanced. Any good tire shop should be able to do this for you. You should ask them to record the lateral and radial run-outs for you (it's part of the process). This will check your wheel and tire for true and round. But once you have them balanced, don't do any burnouts as this may cause your tire to slip on the wheel and make it become unbalanced once again!
Hard to say what the issue is with the brakes, but if you have uneven pad wear, it could be that you have a little air trapped in the line on the one side that isn't wearing so much and this can also cause a pulling sensation under heavier braking. I would advise that if you have not changed your brake fluid in the past couple years, it's time.
As for the tires, get them "road force" balanced. Any good tire shop should be able to do this for you. You should ask them to record the lateral and radial run-outs for you (it's part of the process). This will check your wheel and tire for true and round. But once you have them balanced, don't do any burnouts as this may cause your tire to slip on the wheel and make it become unbalanced once again!
01-07-2008, 09:01 AM
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There is a thread somewhere on here about bedding in the brakes. That could give the sometime vibration when braking issue.
I don't know if the rears are floating calipers or not, on the newer cars, but if they are then the floating pins may need servicing. That would also cause sometimes vibration and sometime not as well.
A cheap way to see if your wheels are bent is to jack up the car and place something heavy very near the rim. Then rotate the tire. You will see the gap get larger and smaller as you rotate it. 1mm will be very easy to see.
I don't know if the rears are floating calipers or not, on the newer cars, but if they are then the floating pins may need servicing. That would also cause sometimes vibration and sometime not as well.
A cheap way to see if your wheels are bent is to jack up the car and place something heavy very near the rim. Then rotate the tire. You will see the gap get larger and smaller as you rotate it. 1mm will be very easy to see.
01-07-2008, 09:22 AM
#5
+1 on getting the tires high-speed balanced on the car. Any performance wheel/tire shop should have the equipment to do it and it's well worth the expense. If you're getting uneven pad wear it might be time to rebuild the calipers. There are multiple moving surfaces inside the calipers and problems with any of them will cause them to move erratically and unevenly. Heat buildup can sometimes make it worse or better depending on where the problem lies, which could explain why it's intermittent.
01-07-2008, 08:57 PM
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I have never seen high speed balancing on the car offered here in the US. Did it in Germany all the time, but never heard of or seen it here.
My tendency would be to first make sure the wheels are really round - which would mean shaving the out-of-round rear tire just enough to be even. But I haven't found a place in the area that does that.
BTW: Bill and I tested the roundness of the rear wheels as 69gaugeman describes. That's how we found that one tire is a bit out of round.
Regarding the brakes: I wish I could tell for sure, but I have a strong suspicion that the problem is caused by the rears - the ones that also squeak sometimes. But I'm not 100% sure.
My tendency would be to first make sure the wheels are really round - which would mean shaving the out-of-round rear tire just enough to be even. But I haven't found a place in the area that does that.
BTW: Bill and I tested the roundness of the rear wheels as 69gaugeman describes. That's how we found that one tire is a bit out of round.
Regarding the brakes: I wish I could tell for sure, but I have a strong suspicion that the problem is caused by the rears - the ones that also squeak sometimes. But I'm not 100% sure.
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01-07-2008, 09:03 PM
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Ride height is minimally lower than spec. I doubt it is connected with the above issues, as it has been like this for a long time - long before the brake and vibration issue started.
01-07-2008, 10:17 PM
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Nicole, I think Roger Kraus Racing still has a tire shaving machine- he is distributor for race tires. Most high-end tire shops have on-car balancing machines- just make sure they don't try it if you have a limited slip diff- it fries the clutches because they usually do one wheel at a time...
01-07-2008, 10:19 PM
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01-07-2008, 10:21 PM
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Nicole,
Hard to say what the issue is with the brakes, but if you have uneven pad wear, it could be that you have a little air trapped in the line on the one side that isn't wearing so much and this can also cause a pulling sensation under heavier braking. I would advise that if you have not changed your brake fluid in the past couple years, it's time....
Hard to say what the issue is with the brakes, but if you have uneven pad wear, it could be that you have a little air trapped in the line on the one side that isn't wearing so much and this can also cause a pulling sensation under heavier braking. I would advise that if you have not changed your brake fluid in the past couple years, it's time....
The great philosopher and engineer Phineus Hydraulic suggests in his teachings that the pressure in a system is the same at all points under static conditions. An air bubble won't change the pressure at one pount without changing the pressure at all points. Air as a vapor is compressible, so air would lead to a "spongy" pedal, but can't cause some pads to clamp correctly and some to be loose.
The Most Likely cause of uneven pad wear (from side to side in the same caliper) is one or more sticking pistons. Pistons stick when corrosion attacks the piston or the caliper where the parts normally just get close. Debris flying around in the brake system sometimes gets in that same small gap, sometimes causing the piston to **** slightly and get wedged in the bore.
Regular fluid changes (like once a year) will help avoid internal corrosion, but won't actually cure the effects once they are apparent. A system with fluid changed every year will never experience corrosion problems and will likely never have any hydraulic failures.
If there's debris in the caliper, it's sometimes possible to get it out by removing the caliper and invertiing it so the bleed srews are down. Completely remove the screws one at a time, starting with the inner. Flush as normal with the power bleeder. with both cavities flushed, replace the calipers in normal position and bleed the air out the top as you would normally.
If these steps don't give you the correct resultas, you'll need to rebuild or replace the calipers.
01-07-2008, 10:49 PM
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I seldom just jump in with a criticism. I usually slide it in slowly, twist it around some, and retract it gently. Put it back in the woodshed at the Girl Scout summer camp, behind the ax, and nobody is thw wiser.
The great philosopher and engineer Phineus Hydraulic suggests in his teachings that the pressure in a system is the same at all points under static conditions. An air bubble won't change the pressure at one pount without changing the pressure at all points. Air as a vapor is compressible, so air would lead to a "spongy" pedal, but can't cause some pads to clamp correctly and some to be loose.
The Most Likely cause of uneven pad wear (from side to side in the same caliper) is one or more sticking pistons. Pistons stick when corrosion attacks the piston or the caliper where the parts normally just get close. Debris flying around in the brake system sometimes gets in that same small gap, sometimes causing the piston to **** slightly and get wedged in the bore.
Regular fluid changes (like once a year) will help avoid internal corrosion, but won't actually cure the effects once they are apparent. A system with fluid changed every year will never experience corrosion problems and will likely never have any hydraulic failures.
If there's debris in the caliper, it's sometimes possible to get it out by removing the caliper and invertiing it so the bleed srews are down. Completely remove the screws one at a time, starting with the inner. Flush as normal with the power bleeder. with both cavities flushed, replace the calipers in normal position and bleed the air out the top as you would normally.
If these steps don't give you the correct resultas, you'll need to rebuild or replace the calipers.
The great philosopher and engineer Phineus Hydraulic suggests in his teachings that the pressure in a system is the same at all points under static conditions. An air bubble won't change the pressure at one pount without changing the pressure at all points. Air as a vapor is compressible, so air would lead to a "spongy" pedal, but can't cause some pads to clamp correctly and some to be loose.
The Most Likely cause of uneven pad wear (from side to side in the same caliper) is one or more sticking pistons. Pistons stick when corrosion attacks the piston or the caliper where the parts normally just get close. Debris flying around in the brake system sometimes gets in that same small gap, sometimes causing the piston to **** slightly and get wedged in the bore.
Regular fluid changes (like once a year) will help avoid internal corrosion, but won't actually cure the effects once they are apparent. A system with fluid changed every year will never experience corrosion problems and will likely never have any hydraulic failures.
If there's debris in the caliper, it's sometimes possible to get it out by removing the caliper and invertiing it so the bleed srews are down. Completely remove the screws one at a time, starting with the inner. Flush as normal with the power bleeder. with both cavities flushed, replace the calipers in normal position and bleed the air out the top as you would normally.
If these steps don't give you the correct resultas, you'll need to rebuild or replace the calipers.
Tires that are out of round can be "trued" by most competent tire shops.
As you stated, the wheels can also be "trued".
Start with the obvious, then work forward. you said the rears are where the problem is, take steps to correct this first. As for the brakes, start with a fluid flushing, then look at the calipers......but get some miles in before you blame the calipers.
Good Luck----
--Russ
01-07-2008, 10:50 PM
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I seldom just jump in with a criticism. I usually slide it in slowly, twist it around some, and retract it gently. Put it back in the woodshed at the Girl Scout summer camp, behind the ax, and nobody is thw wiser.
The great philosopher and engineer Phineus Hydraulic suggests in his teachings that the pressure in a system is the same at all points under static conditions. An air bubble won't change the pressure at one pount without changing the pressure at all points. Air as a vapor is compressible, so air would lead to a "spongy" pedal, but can't cause some pads to clamp correctly and some to be loose.
The Most Likely cause of uneven pad wear (from side to side in the same caliper) is one or more sticking pistons. Pistons stick when corrosion attacks the piston or the caliper where the parts normally just get close. Debris flying around in the brake system sometimes gets in that same small gap, sometimes causing the piston to **** slightly and get wedged in the bore.
Regular fluid changes (like once a year) will help avoid internal corrosion, but won't actually cure the effects once they are apparent. A system with fluid changed every year will never experience corrosion problems and will likely never have any hydraulic failures.
If there's debris in the caliper, it's sometimes possible to get it out by removing the caliper and invertiing it so the bleed srews are down. Completely remove the screws one at a time, starting with the inner. Flush as normal with the power bleeder. with both cavities flushed, replace the calipers in normal position and bleed the air out the top as you would normally.
If these steps don't give you the correct resultas, you'll need to rebuild or replace the calipers.
The great philosopher and engineer Phineus Hydraulic suggests in his teachings that the pressure in a system is the same at all points under static conditions. An air bubble won't change the pressure at one pount without changing the pressure at all points. Air as a vapor is compressible, so air would lead to a "spongy" pedal, but can't cause some pads to clamp correctly and some to be loose.
The Most Likely cause of uneven pad wear (from side to side in the same caliper) is one or more sticking pistons. Pistons stick when corrosion attacks the piston or the caliper where the parts normally just get close. Debris flying around in the brake system sometimes gets in that same small gap, sometimes causing the piston to **** slightly and get wedged in the bore.
Regular fluid changes (like once a year) will help avoid internal corrosion, but won't actually cure the effects once they are apparent. A system with fluid changed every year will never experience corrosion problems and will likely never have any hydraulic failures.
If there's debris in the caliper, it's sometimes possible to get it out by removing the caliper and invertiing it so the bleed srews are down. Completely remove the screws one at a time, starting with the inner. Flush as normal with the power bleeder. with both cavities flushed, replace the calipers in normal position and bleed the air out the top as you would normally.
If these steps don't give you the correct resultas, you'll need to rebuild or replace the calipers.
Alright smartypants
... on reflection, you are, of course, correct. 
However, after re-reading Nicole's description, I thought of a few causes that could link #1 and #2. Nicole, you should inspect to make sure your calipers are not loose. You should also inspect the suspension components (ball joints, suspension arms, shocks. If any of these things were loose, it could cause a jerkiness in the braking and a poor ride.
01-07-2008, 10:51 PM
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There is a thread somewhere on here about bedding in the brakes. That could give the sometime vibration when braking issue.
I don't know if the rears are floating calipers or not, on the newer cars, but if they are then the floating pins may need servicing. That would also cause sometimes vibration and sometime not as well.
A cheap way to see if your wheels are bent is to jack up the car and place something heavy very near the rim. Then rotate the tire. You will see the gap get larger and smaller as you rotate it. 1mm will be very easy to see.
I don't know if the rears are floating calipers or not, on the newer cars, but if they are then the floating pins may need servicing. That would also cause sometimes vibration and sometime not as well.
A cheap way to see if your wheels are bent is to jack up the car and place something heavy very near the rim. Then rotate the tire. You will see the gap get larger and smaller as you rotate it. 1mm will be very easy to see.
They are not floating calipers.
--Russ
01-07-2008, 10:55 PM
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Nicole,
depending on just how "short" the sidewalls of your tires are (say a 25 aspect ratio), you might purchase wheel chocks for low profile tires, if you do not drive your shark much.
I believe they are advertised in Panorama for sale.....
they claim to limit flat spotting.....this may help you as well.
--Russ
depending on just how "short" the sidewalls of your tires are (say a 25 aspect ratio), you might purchase wheel chocks for low profile tires, if you do not drive your shark much.
I believe they are advertised in Panorama for sale.....
they claim to limit flat spotting.....this may help you as well.
--Russ