98 V70 front end wobble

[skloon]

Clean the mating surfaces, swap rear wheels to front torque in two steps and see how it is

[98v70dad]

Clean the mating surfaces, swap rear wheels to front torque in two steps and see how it is

OK. Thanks. I've already done that - no change.

[sleddriver]

Apparently taking the brake caliper off to replace the left wheel bearing made the wobble (pulsing?) much much worse. It now also pulses when I put on the brakes at high speed when it didn't before. I have rebuilt calipers, new pads and new rotors to put on next weekend. While they were off I noticed that the rotors are worn half way through. I was surprised by that since they brake just fine. They are probably warped and the calipers are probably sticking.

Why the wobble/ pulsing only happens in the 65 - 70 mph range doesn't make sense to me. Any ideas? The pulsing on braking only happens in that range too. It doesn't make sense to me. If I have warped rotors or sticking calipers they should pulse at all speeds. I have had the tires balnced 3 times and replaced once so I'm confident that has nothing to do with it.

• Rotors are now off-center after reinstallation and probably warped as well.
  -
• Rotors worn that bad mean the piston has to reach much further out to brake. Therefore less piston is now inside the bore, which means it's not as stable and thus more prone to vibration. Millimeters matter here. It can also become 'cocked' in the bore due to this over-excursion. Think about clamping the very end of an object in a bench vise vs. taking full advantage of the jaw surface area. Which is more stable?
  -
• Think of the angular velocity w of a rotor when the vehicle velocity is 65mph. It doesn't take much of a warp, nor misalignment, to vibrate. Much less tolerance than lower velocities when the angular velocity of the outer edge of the rotor is much, much lower. Therefore, it shouldn't "pulse at all speeds." Resonances are also in play here.
  -
• Finally, a square, triangular or rectangular wheel/tire can be perfectly balanced. No problem. The problem comes when you try to roll with it. Think about it....

[98v70dad]

Apparently taking the brake caliper off to replace the left wheel bearing made the wobble (pulsing?) much much worse. It now also pulses when I put on the brakes at high speed when it didn't before. I have rebuilt calipers, new pads and new rotors to put on next weekend. While they were off I noticed that the rotors are worn half way through. I was surprised by that since they brake just fine. They are probably warped and the calipers are probably sticking.

Why the wobble/ pulsing only happens in the 65 - 70 mph range doesn't make sense to me. Any ideas? The pulsing on braking only happens in that range too. It doesn't make sense to me. If I have warped rotors or sticking calipers they should pulse at all speeds. I have had the tires balnced 3 times and replaced once so I'm confident that has nothing to do with it.

• Rotors are now off-center after reinstallation and probably warped as well.
  -
• Rotors worn that bad mean the piston has to reach much further out to brake. Therefore less piston is now inside the bore, which means it's not as stable and thus more prone to vibration. Millimeters matter here. It can also become 'cocked' in the bore due to this over-excursion. Think about clamping the very end of an object in a bench vise vs. taking full advantage of the jaw surface area. Which is more stable?
  -
• Think of the angular velocity w of a rotor when the vehicle velocity is 65mph. It doesn't take much of a warp, nor misalignment, to vibrate. Much less tolerance than lower velocities when the angular velocity of the outer edge of the rotor is much, much lower. Therefore, it shouldn't "pulse at all speeds." Resonances are also in play here.
  -
• Finally, a square, triangular or rectangular wheel/tire can be perfectly balanced. No problem. The problem comes when you try to roll with it. Think about it....

One question. I've thought about all of your points myself before you posted them and agree that they are very valid points. Your comments that the rotors are probably now off center is the one that I wasn't able to decide how to avoid when I install all of my new parts in a few days. I noticed when I replaced the rotors that there was nothing that forced them to be centered. The clearance on all the bolt holes allows a good bit of slop and the one fastener that holds the rotor in place allows several mm of rotational movement. You can eyeball get them centered but nothing forces them to be centered. How is this done?

[sleddriver]

By using the lug nuts equally tightened in the hub to set the rotor in place before installing the wheel. There is a link to this somewhere; might be on another site.

[98v70dad]

By using the lug nuts equally tightened in the hub to set the rotor in place before installing the wheel. There is a link to this somewhere; might be on another site.

That makes sense, but what keeps the hub from moving back when you remove the lug bolts?

I suppose that if you align the one little "keeper" bolt to be at the top the hub would hang from it and not move. I'll look for the info, thanks for the tip. I actually was pretty thoughtful about get the rotors centered when I put them back on but didn't consider that there might be a procedure for it.

[sleddriver]

It's a friction fit: The lugnuts pull the rotor tight to the hub and friction holds it there when they're removed. Just be careful not to whack the rotor loose when reinstalling the wheel. The "key/keeper" will help a bit when tightened.

[98v70dad]

It's a friction fit: The lugnuts pull the rotor tight to the hub and friction holds it there when they're removed. Just be careful not to whack the rotor loose when reinstalling the wheel. The "key/keeper" will help a bit when tightened.

I get that its friction fit but it seems like a poor design decision to me. Rotors should be indexed into place so that they are centered and unable to be moved from that. As you say mm's count.

[sleddriver]

Agreed. Not a good place for a rotor install to go "eccentric". Especially with another one on the opposite end of the axle!