Brand new brakes vibrating again

[Spitfire007]

Some of you might remember I got new brakes on all 4 corners installed by a very reputable Indy. Installed steel brake lines as well as did a full bleed.
Felt AMAZING. Great pedal feel. More braking force it seems.

However, the rotors can't seem to handle the heat and are starting to vibrate again.
It's much worse on the highway where you'll routinely have to slow from 85 to 60 then back up to speed then slow again.

I do drive fast, and the last time I had issues like this was on a 98 740iL. Heavy car was hard on rotors and I never solved it.
My 135i never had an issue, neither did my e90 328i.

These are stock parts: Zimmerman rotors and quality pads.

What gives? I go back to the Indy for an oil change soon...


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[Akakios]

So your prior cars warped rotors all the time
Your new car with new brakes warped new rotors

The lighter cars you’re handling fine. The heavier cars you’re struggling to capture momentum and not use the brakes as much imo or you’re doing a lot of spirited drives at high speed and jamming on the brakes often which means that you’re going way too fast versus traffic speed usually.

Make sure you’re off the throttle earlier than you would the lighter cars.

Replace the rotors and engine brake more as well.

[deejayh]

So your prior cars warped rotors all the time
Your new car with new brakes warped new rotors

The lighter cars you’re handling fine. The heavier cars you’re struggling to capture momentum and not use the brakes as much imo or you’re doing a lot of spirited drives at high speed and jamming on the brakes often which means that you’re going way too fast versus traffic speed usually.

Make sure you’re off the throttle earlier than you would the lighter cars.

Replace the rotors and engine brake more as well.

this ^^^^

[Spitfire007]

Some fair points.

I've had the car 4+ years. Not nearly as much vibration with the old brakes....
I try to engine brake A LOT by grabbing 2-3 gears.

I just try to follow traffic, but you know how I-95 is....speed up slow down. Speed up slow down. It's not like I'm trying to out do others on the road.

Why wouldn't this car have adequate brakes if it's designed to be driven at high speeds on the autobahn?

I'm not abusive, I swear....maybe it's more of a cruiser and I don't drive it as such?

I'm miffed.


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[Akakios]

Some fair points.

I've had the car 4+ years. Not nearly as much vibration with the old brakes....
I try to engine brake A LOT by grabbing 2-3 gears.

I just try to follow traffic, but you know how I-95 is....speed up slow down. Speed up slow down. It's not like I'm trying to out do others on the road.

Why wouldn't this car have adequate brakes if it's designed to be driven at high speeds on the autobahn?

I'm not abusive, I swear....maybe it's more of a cruiser and I don't drive it as such?

I'm miffed.


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You mentioned 95, say no more. It’s hard to adequately judge if someone’s going to be doing 110 in one lane or 55 in the next one over in the wild wild east known as 95.

You’re doing a lot of repetitive braking honestly and heat is your enemy when dealing with brakes. It’s engineered to slow you down around town and highway, not repeat race conditions. There’s a reason they threw better brakes on the RS7.

ECS Cooling Ducts + Upgraded Brakes are the solution imo.

[Spitfire007]

You mentioned 95, say no more. It’s hard to adequately judge if someone’s going to be doing 110 in one lane or 55 in the next one over in the wild wild east known as 95.

You’re doing a lot of repetitive braking honestly and heat is your enemy when dealing with brakes. It’s engineered to slow you down around town and highway, not repeat race conditions. There’s a reason they threw better brakes on the RS7.

ECS Cooling Ducts + Upgraded Brakes are the solution imo.

Ugh. More money...


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[q2quest]

It is common for people to refer to these rotors as warped, but in my experience these rotors aren't warping at all. What you are experiencing is a high spot on the rotor from brake pad material being deposited on it. It tends to happen when the brakes are pretty hot and then you sit stopped with your foot on the brake at a stoplight or in a traffic jamb for example. When you release the brake pedal a microscopic bit of pad can be transferred to the rotor. That brake pad material attracts more brake pad material and over time you get a pretty severe pulsation when applying the brakes. I have noticed this happens MUCH more frequently on the A6s I have owned versus other cars. It is perfectly acceptable to have the rotors "turned" at a machine shop to remove this built up pad material so long as they don't remove more of the rotor than spec. Most rotors can be turned at least three or four times before they become thin enough to warrant replacement. Machine shops charge between $20 and $40 to true a rotor.

Sometimes you can cure this problem by very heavy braking on back to back runs to force the brake pads to wipe that built up layer off of the rotors. In many cases the pad material is chemically bonded to the rotor surface and this procedure is unlikely to work. But, I have had some success by finding a deserted stretch of road and doing several 60 to 10 mph slow downs at about 90% braking force. Essentially panic stops, but don't come to a complete stop. Drive the car around for a while to let the brakes cool and try to eventually park the car without touching the front brakes. Let the brakes completely cool down and hours later see if the problem isn't fixed. If not, I recommend having the rotors turned and to then do a brake bedding procedure without replacing the pads. Otherwise, we will all be going broke having to purchase new rotors and pads every time this pulsation comes back on our cars.

[Akakios]

It is common for people to refer to these rotors as warped, but in my experience these rotors aren't warping at all.

You're absolutely right, it's not actual physical warping most of the time, it's just high spots for sure.

Most brake pads these days have a break in layer on them that gets deposited on the rotor the first time after install so if you do turn them, do NOT use the old pads to help save some money.

[q2quest]

Although, if the new brake pads and rotors that were recently installed are already showing signs of friction deposits then what is the real risk of trying the turned rotors with the same pads, so long as the pads are relatively new? I know it isn't standard procedure, but what if the break in layer on the new pads was actually the problem?

[sepheroth86]

I had a similar issue with my A6.

Turns out one of the caliper pins was gummed up. Cleaned with steel wool and brake pin lube. Been good since.

[Spitfire007]

They smooth out once they cool down some. But one or two more slow downs (not stopping) and they vibrate again.

Honestly, it's pretty damn irritating to spend a smal fortune on good quality brakes to have this happen. Everything was lubed and checked It shouldn't be happening, it's a 150mph autobahn car.

I've tried the brake bedding procedure before in other cars and to be honest, it's a fine line between bedding in and effing up your brand new setup with a ton of heat.

Thanks for the insight.

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[MattyMarkey]

They smooth out once they cool down some. But one or two more slow downs (not stopping) and they vibrate again.

Honestly, it's pretty damn irritating to spend a smal fortune on good quality brakes to have this happen. Everything was lubed and checked It shouldn't be happening, it's a 150mph autobahn car.

I've tried the brake bedding procedure before in other cars and to be honest, it's a fine line between bedding in and effing up your brand new setup with a ton of heat.

Thanks for the insight.

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Bleed the brakes. Could have air in the lines.


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[Akakios]

Bleed the brakes. Could have air in the lines.


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I concur. Something’s not adding up. The rotors will always be “warped” with the material deposited on them until turned, temperature shouldn’t matter.

[Spitfire007]

I mean....could it MAYBE be control arms?
Indy says everything is fine.

I've tried to aggravate the issue with some hard stops, and it really feels like heat and a few repeated slow downs (similar to brake bedding in) leads to worse and worse vibration.

I will say: SS brake lines make quite a difference in feel. Much better than stock. So that's better.


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[sepheroth86]

I mean....could it MAYBE be control arms?
Indy says everything is fine.

I've tried to aggravate the issue with some hard stops, and it really feels like heat and a few repeated slow downs (similar to brake bedding in) leads to worse and worse vibration.

I will say: SS brake lines make quite a difference in feel. Much better than stock. So that's better.


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Many years ago on my trackday Honda, I had a somewhat similar problem.

Turns out the engine cradle fasteners worked loose, ever so slightly. I tightened the snot out of them and it has been good since.

So suspension could possibly have an effect.

My old C5 had a real soft brake pedal and putting new control arms on the front stiffened the pedal feel. I used to jab the brakes, let off, then get back on them and the pedal felt better... before I figured out it was the arms.

[MattyMarkey]

I mean....could it MAYBE be control arms?
Indy says everything is fine.

I've tried to aggravate the issue with some hard stops, and it really feels like heat and a few repeated slow downs (similar to brake bedding in) leads to worse and worse vibration.

I will say: SS brake lines make quite a difference in feel. Much better than stock. So that's better.


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Broken record here… Have you bled the brakes? Easy enough to validate if it changes anything. Also, if you never have, or haven’t in a few years, fresh brake fluid is always good!


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[Spitfire007]

Broken record here… Have you bled the brakes? Easy enough to validate if it changes anything. Also, if you never have, or haven’t in a few years, fresh brake fluid is always good!


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Yep. All new fluid, a full ABS bleed, along with new brake lines.
I think the rotors saw too many heat cycles in traffic and are fubared.
I downshift ALL the time since I come from manuals, but the ZF8 just doesn't have the drag of a manual AND is frustratingly slow to downshift so by the time it reacts I'm already on the brakes even a little, and it's too late.

The Audi is comfortable, but I think I may need a different car, even though I really don't push it.



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[MattyMarkey]

Yep. All new fluid, a full ABS bleed, along with new brake lines.
I think the rotors saw too many heat cycles in traffic and are fubared.
I downshift ALL the time since I come from manuals, but the ZF8 just doesn't have the drag of a manual AND is frustratingly slow to downshift so by the time it reacts I'm already on the brakes even a little, and it's too late.

The Audi is comfortable, but I think I may need a different car, even though I really don't push it.



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If you’ve checked everything is tight, installed correctly, lubed, bled, etc. than yeah, sounds like some warped rotors.

Sounds like your indy shop said everything is good. What is he saying about his warranty of work? Guess it might ultimately be who was responsible for properly bedding the brakes


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[Spitfire007]

If you’ve checked everything is tight, installed correctly, lubed, bled, etc. than yeah, sounds like some warped rotors.

Sounds like your indy shop said everything is good. What is he saying about his warranty of work? Guess it might ultimately be who was responsible for properly bedding the brakes


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I have not brought it up to them yet, but they are quite well known for their work on German cars, and do track prep on fancy and not so fancy cars.so they should know.
Car needs an oil change and they were closed over the weekend.


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[TheBlackMarvel]

What pads and rotors at you running? Someone asked if you had disassembled the calipers and this is also a useful point. If you’re having one side of a caliper stick, this problem will continue to repeat itself.


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[Spitfire007]

What pads and rotors at you running? Someone asked if you had disassembled the calipers and this is also a useful point. If you’re having one side of a caliper stick, this problem will continue to repeat itself.


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It's stock OEM stuff. Zimmerman rotors and textar (or whatever) pads.
They looked everything over, cleaned and lubed all the pins or whatever else they can do.
Zinc coated all the parts as well. Liked silver shiny new.

Thing is, driving around town you feel almost nothing. As heat builds up on i95, I start to feel it get progressively worse until they have a chance to cool over 5-10 miles.


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[Alabama]

However, the rotors can't seem to handle the heat and are starting to vibrate again.
It's much worse on the highway where you'll routinely have to slow from 85 to 60 then back up to speed then slow again.

I do drive fast, and the last time I had issues like this was on a 98 740iL. Heavy car was hard on rotors and I never solved it.
My 135i never had an issue, neither did my e90 328i.

To paraphrase, if the car won't adapt to the driver, maybe the driver needs to adapt to the car. Maybe try to track the car with more predictable acceleration and braking and see if the same vibration occurs. Very little discussion on AZ about driver technique.

[Spitfire007]

To paraphrase, if the car won't adapt to the driver, maybe the driver needs to adapt to the car. Maybe try to track the car with more predictable acceleration and braking and see if the same vibration occurs. Very little discussion on AZ about driver technique.

Very true; but I struggle to understand why it's doing this when I'm just trying to keep up with left lane traffic in a $68000 autobahn cruiser.
This should not be happening, as this is neither my first car, nor my first set of new brakes on a German car..
That mommy in the Hyundai isn't feeling what I am and she's got shit for brakes and drives like a lunatic.


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[Alabama]

Very true; but I struggle to understand why it's doing this when I'm just trying to keep up with left lane traffic in a $68000 autobahn cruiser.
This should not be happening, as this is neither my first car, nor my first set of new brakes on a German car.

Got it, and (like me) you're dependent on what your mechanic tells you. My one experience on the autobahn was (as you say) cruising (fast), not stop-and-go. By analogy, when qcrazy wants to determine why a pump doesn't behave as expected, he studies it under as controlled conditions as possible. Maybe you can get to Summit Point and really test out your car under more controlled conditions than I-95.

[Spitfire007]

Got it, and (like me) you're dependent on what your mechanic tells you. My one experience on the autobahn was (as you say) cruising (fast), not stop-and-go. By analogy, when qcrazy wants to determine why a pump doesn't behave as expected, he studies it under as controlled conditions as possible. Maybe you can get to Summit Point and really test out your car under more controlled conditions than I-95.

I don't even need to do that. It only took one cycle of slowing from 80mph down to 60 on this morning's drive to work for the whole car to shake....


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[Botbasher]

I mean....could it MAYBE be control arms?

DING DING DING!!!! You know what the definition of insanity is?? Checking the same thing over and over again, expecting a different result!

You have increased the braking ABILITY of the car but haven't confirmed the condition of the remaining suspension components to apply that increased braking ability to the ground.

I'm dealing with the very thing right now. Bought the car with dead rotors, so I redid the brakes and now I have a little wobble at light loading from 65-80mph and a scary shake from 120-75 where it simply disappears. What is the culprit?? Trailing arm bushings!!

When you jump on the brakes the suspension flexes from neutral to whatever and Traction Control, ABS and the inherent slop in the system go to work!

When you check the brakes for the 20th time and they are still perfect, you might want to start looking at other things that can influence braking! Struts, bushings and ball joints are the primary culprits of phantom shakes and shimmys!

There are 5 ball joints and bushings a side... that's a lot of possible flex!

Good luck in the search!

Cheers,

KS

[Spitfire007]

DING DING DING!!!! You know what the definition of insanity is?? Checking the same thing over and over again, expecting a different result!

You have increased the braking ABILITY of the car but haven't confirmed the condition of the remaining suspension components to apply that increased braking ability to the ground.

I'm dealing with the very thing right now. Bought the car with dead rotors, so I redid the brakes and now I have a little wobble at light loading from 65-80mph and a scary shake from 120-75 where it simply disappears. What is the culprit?? Trailing arm bushings!!

When you jump on the brakes the suspension flexes from neutral to whatever and Traction Control, ABS and the inherent slop in the system go to work!

When you check the brakes for the 20th time and they are still perfect, you might want to start looking at other things that can influence braking! Struts, bushings and ball joints are the primary culprits of phantom shakes and shimmys!

There are 5 ball joints and bushings a side... that's a lot of possible flex!

Good luck in the search!

Cheers,

KS

Thanks. I think we may have to go there.
Thing is, two dealers and one competent indy haven't found ANYTHING wrong with the suspension. Like AT ALL. Some bushings have been replaced, all the motor mounts are new...
So I'm kind of out of ideas.

I'm not up for dumping a ton of money into this car.
It's been dead nuts reliable, so far, which has been amazing for a 96000 mile Audi, but she needs to carry me another year or so till I get into something else like a manual M3 or a Quadrifoglio...



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[Botbasher]

Thanks. I think we may have to go there.
Thing is, two dealers and one competent indy haven't found ANYTHING wrong with the suspension. Like AT ALL. Some bushings have been replaced, all the motor mounts are new... So I'm kind of out of ideas.

I'm not up for dumping a ton of money into this car.
It's been dead nuts reliable, so far, which has been amazing for a 96000 mile Audi, but she needs to carry me another year or so till I get into something else like a manual M3 or a Quadrifoglio...

I hear ya. I can't point to the bushing and say that's it either, but with a lack of other options, it's the only reasonable culprit.

Suspensions can be a bear to diagnose because when it happens at only a certain band of speed it's very difficult, if not impossible to diagnose with 100% certainty. Reproducing that exact loading and input to the modules isn't possible! You simply need to eliminate all the other options leaving you with only one solution. You've done that!

When most places check them, they lift the car which puts normal suspensions into a bind at full droop. Things need to be checked at normal ride height to even have a chance of seeing it in a shop setting. A pure visual inspection or a crowbar test can show you really bad bushing, but they rarely find marginal ones!

I do all my own work and have a back up car, so I buy the bushings cheap and do it all over a week or two (it's been 3 now!). Bushing cup kit ($125 on Amazon and useful for any car!) and bushings are all it costs. If you buy the full rebuild kits (Drop in Arms) from FCP or ECS, it's considerably more, for nearly the same amount of work! Would your Indy do simple bushings? I got all of them (with some good shopping skills and patience) for under $150.

Now that I figured out the puzzle of what shields I need to remove to access bolts and such, I should have it done this weekend. I'll let you know if it corrects the issue for me!

Cheers,

KS

[Spitfire007]

I hear ya. I can't point to the bushing and say that's it either, but with a lack of other options, it's the only reasonable culprit.

Suspensions can be a bear to diagnose because when it happens at only a certain band of speed it's very difficult, if not impossible to diagnose with 100% certainty. Reproducing that exact loading and input to the modules isn't possible! You simply need to eliminate all the other options leaving you with only one solution. You've done that!

When most places check them, they lift the car which puts normal suspensions into a bind at full droop. Things need to be checked at normal ride height to even have a chance of seeing it in a shop setting. A pure visual inspection or a crowbar test can show you really bad bushing, but they rarely find marginal ones!

I do all my own work and have a back up car, so I buy the bushings cheap and do it all over a week or two (it's been 3 now!). Bushing cup kit ($125 on Amazon and useful for any car!) and bushings are all it costs. If you buy the full rebuild kits (Drop in Arms) from FCP or ECS, it's considerably more, for nearly the same amount of work! Would your Indy do simple bushings? I got all of them (with some good shopping skills and patience) for under $150.

Now that I figured out the puzzle of what shields I need to remove to access bolts and such, I should have it done this weekend. I'll let you know if it corrects the issue for me!

Cheers,

KS

Hey, I appreciate the insight. The one thing that makes me wonder, however, is that the whole car was smooth for about two weeks after I got the brand new brakes and now it's just vibrating horribly almost every time I slow down at highway speeds. Around town it's fine.


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[johnovision27]

At least I'm not the only one chasing crazy braking vibrations. Had my OG rotors turned, vibration was still present immediately.

I checked each hub, they're all true. The rotors, they're all true as well. The inside mounting surface on the rotor to the hub = NOT true! How that got out of whack, I'll never know. The machine shop that did the rotors wouldn't have checked that either as they use the center of the rotor to mount to the lathe.

Either way, I'm done screwing with this set of rotors so I've ordered new. Just waiting for them to show up.

I'll be keeping an eye on your journey to see if you discover any bad bushings. Mine is at 180k km, so I wouldn't be surprised if something is wearing out.

[Botbasher]

I'll be keeping an eye on your journey to see if you discover any bad bushings. Mine is at 180k km, so I wouldn't be surprised if something is wearing out.

On all my vehicles over the years, 100k miles (160k km) is about where I start to plan to eventually replace suspension bushings. If for no other reason to assure that I will not have to do it for the typical life expectancy of the vehicle ~200k+!

Some cars needed it... some didn't. Those that did, it was like driving a new car. Even marginal need cars felt better again. Amazing how driving a car for 20-50k can lull the senses and disconnect you from the road!

Planning for it far in advance also lets you do it for cheap too. Watching for sales and making one off purchases for different bits. Half the fun for me is doing the job at a fraction of the MSRP! Full suspension arm kit for my A5 was ~$800. I found bits and pieces and did it for a little over $300. Love me a good sale... especially S&D!!!

Cheers,

KS

[RLCree]

A6 Rotors weren't designed to be heat cycled like that. There is a reason the S6 got larger diameter and thicker rotors. The A series was absolutely intended to be more of a cruiser. Basically, you're driving too hard for the equipment. Autobahn designed or not. You could swap to a slotted rotor and see if that helps. You could swap to S6 brakes and that might cure it. Make sure you are driving like a normal long enough to cool them off before you park, that would help a bit. Lastly, you could just live with. They had this problem on Old Toyota's where the brakes were just fine for a specific set of driving conditions. Once you exceeded that envelope, welp, you're gonna have a bad case of warped rotors. Only option was uprading to a much thicker rotor.

[Botbasher]

So here's the wrap to my never ending vibrations on an otherwise "perfect" suspension!

Like yours Spitfire, I had looked at, inspected, touched, pushed, pulled, pried on every part of the suspension. This was of course after replacing pads and rotors for "vibrations"!

So as a final hail Mary, I decided to do the lower suspension bushing.

This was all done with the arms on the car. As long as your Ball Joints are good, this works, but if you need joints, you need arms and that's pulling them from the car.

So, I swapped the large bushing on the rear trailing, and the lower inner on the front arm (the only ones really in control) and after pressing them out, it's very obvious what my issues were and it was pretty much what I thought. They were OK enough to pass a on-car inspection, but once unloaded, they were trash!

I pushed that one out with my finger. It obviously wasn't holding anything in position. The big bushing was soft enough that I can deflect it by hand. The other side was similar. I want to get the alignment checked before any high speed testing, but there are no adjustments and it tracked 100% on basic driving. Really as long as you put it in the same place you removed it from, it's a super simple DIY with some basic tools!

It felt 1000x better to drive. Prior to this, it felt sloppy and boat-ish, I assumed that it was just the difference between the tightened A5 vs the stock S6 S6, but it wasn't. Now it feels more like my A5. Tight and responsive, well, as responsive as a stock S6 can feel! [rolleyes]

I'd give your bushings a really serious inspection. Look for any degradation and shift in position.

Good luck in your search for a solution to your vibration issues!

Cheers,

KS

315745

315746

[Spitfire007]

Interesting. Car goes for oil change tomorrow morning, so I'll ask the Indy to look over everything.
I think shock mounts are wearing as well...ugh


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[Spitfire007]

So here's the wrap to my never ending vibrations on an otherwise "perfect" suspension!

Like yours Spitfire, I had looked at, inspected, touched, pushed, pulled, pried on every part of the suspension. This was of course after replacing pads and rotors for "vibrations"!

So as a final hail Mary, I decided to do the lower suspension bushing.

This was all done with the arms on the car. As long as your Ball Joints are good, this works, but if you need joints, you need arms and that's pulling them from the car.

So, I swapped the large bushing on the rear trailing, and the lower inner on the front arm (the only ones really in control) and after pressing them out, it's very obvious what my issues were and it was pretty much what I thought. They were OK enough to pass a on-car inspection, but once unloaded, they were trash!

I pushed that one out with my finger. It obviously wasn't holding anything in position. The big bushing was soft enough that I can deflect it by hand. The other side was similar. I want to get the alignment checked before any high speed testing, but there are no adjustments and it tracked 100% on basic driving. Really as long as you put it in the same place you removed it from, it's a super simple DIY with some basic tools!

It felt 1000x better to drive. Prior to this, it felt sloppy and boat-ish, I assumed that it was just the difference between the tightened A5 vs the stock S6 S6, but it wasn't. Now it feels more like my A5. Tight and responsive, well, as responsive as a stock S6 can feel! [rolleyes]

I'd give your bushings a really serious inspection. Look for any degradation and shift in position.

Good luck in your search for a solution to your vibration issues!

Cheers,

KS

315745

315746

Thanks for this insight. This will be helpful background for Indy.

The do a lot of Porsche/audi stuff, but this car is so well insulated/isolated, that the normal noises just don't make their way into the cabin so it's hard to diagnose marginal issues until they're clearly the culprit.


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[Spitfire007]

UPDATE:
Got an oil change.
Indy did feel vibes in the pedal and steering wheel, so they replaced the front Zimmerman rotors.

I still feel a lot of vibes at highway speeds, but mostly in my seat, so must be rear rotors.
Also getting light knocks over small bumps at slow speeds, but otherwise still well dampened, maybe feeling a lottle rougher than when I got it with 37000 miles.

Indy did say everything else looked ok, nothing to note in the control arms, bushings, wheels and tires and if they WERE going bad they'd be able to spot it.

Car has a bit over 96000 miles and all of the suspension is stock original except for front lower bushings which they replaced a year ago (pressed in new bushings cuz arm was fine).

They prolly need to take it overnight and beat it on an empty highway...

So that's the update. Feels better in the front, but still not 100%. I do appreciate their warrantying the rotors.



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[Spitfire007]

UPDATE:
Car is back in to Indy for oil change and boss will take it home to really beat on it to hopefully replicate what I'm sensing.

Vibrations are back again, front and rear, under braking, and now I feel a strong thumping/ vibration under the car when going full kick-down at 75mph to 95-100.
Driveshaft carrier bearing? Indy says it might be a CV joint?
Whatever. It's just not enjoyable to drive with all that's going on, but she sure it pretty to look at...
Hopefully they find something.
If not, she's getting traded within 6months





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[A665]

The driveshaft carrier bearing bushing was the culprit of vibration issues on my A6. The stock bushing is intentionally soft so as to minimize harshness of the driveshaft movement. Works as intended, until it doesn't. Meaning that it tends to weaken over time, and at a certain point it allows the driveshaft to deviate its position past the point at which it remains silent, which results in a vibration that you can hear and sometimes feel.

[Spitfire007]

Well, Indy didn't get to drive it hard enough I guess, or fast enough on his drive home, twice and didn't find anything wrong really anywhere. He says just keep driving it till things get worse and can be diagnosed.


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