Brakes 102 - Or, Why Do My Brakes Keep Pulsating / Warping?

A5INKY

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2006 Jetta TDI, 2002 Eurovan Westphalia VR6
Just had a second car in the shop in only a few weeks with the same issue - brake pulsation. Both cars had front brake jobs done by mechanics not unknown to this forum using quality parts from trusted vendors within less than 20K miles and were pulsating badly again already. For one of those customers it had been a chronic problem over many brake jobs. In both of these recent examples the root cause was the same and had nothing to do with the brake parts.

I'm calling this instructional thread a "102" course because Wingnut has a nice 101 level how-to posted in the TDI 101 Stickies HERE. This thread is to merely expand on those basics. If you are new to brake service, Wingnut's thread is a good place to start as this thread will assume one has a good grasp on the material shown there. Also assumed will be that you are using quality parts, OEM or better. Poor part quality alone can lead to pulsation, but even the best parts can fail if what I am showing here is ignored in the service work - as was the case with these two cars.

Wingnut mentioned cleaning up the hub face before mounting a new rotor but did not explain why or what could happen if you don't. This one was not too bad:



I've seen much worse. Nevertheless, you want that surface as flat and clean as the day it was manufactured before mounting the new (or old) rotor. If you are re-using a good but used rotor, both sides of the rotor hat should get the same treatment. My die grinder mounted scotch brite pad works great and fast for this without risking good metal removal.



So what has all this to do with pulsation or warp you ask? In both of these cases, even with new rotors and proper attention to detail, the rotors were not going to spin "true". "Lateral Runout" is the proper term for side to side wobble of a brake disc as it spins. Every car has a maximum spec for it for a reason. Some are as little as less than a thousandth of an inch, though zero is always what is strived for. In the case of the subject MKIV Jetta, the spec is a maximum of 0.004" which is pretty liberal IMO.

Remember how Wingnut said that calipers and pads must move freely side to side? Well, if they are doing so properly, excess lateral runout will go unnoticed by the driver for a relatively long time as the caliper quietly shakes back and forth to the wobble of the rotor. Pulsation only starts to rear its ugly head after this has been allowed to go on long enough for the rotor to wear unevenly in it's thickness, known in the industry as rotor "thickness variation". When rotor thickness variation occurs, the caliper's piston is hammering back and forth in the caliper body violently and transmitting that pulsation to the master cylinder to be felt in the brake pedal, as well as through the suspension and steering systems to be felt in the steering wheel. Left unchecked long enough it can cause the whole car to shake and be dangerous to vehicle control. Thickness variation is all too often labeled "warpage" due to heat, materials, pad selection, driving habits, etc. Parts get improperly indicted, driver is blamed for something out of their control, another brake job gets sold. After all, by now the previous brake job warranty is up anyway, right?

OK, so we now know that thickness variation due to excessive lateral runout is the leading cause of pulsation. How do we prevent it? We prevent it by ensuring the rotors are spinning as true to the axis of the axle as possible. At the very least it needs to be within VAG's maximum lateral runout specification.

So, we have already cleaned the surface of the hub face and rotor. Next we need to bolt the two together in a way that will mimic the mounted and properly torqued wheel. I do this with a stack of hardened washers and the lug bolts:



Next step requires an accurate lateral runout measurement of the rotor face as it spins on the hub. I have a special brake rotor service dial indicator tool from Snap-On that makes easy work of this measurement. However, any dial indicator can work, just may need to get creative with how to mount it.



At this point both of the example cars measured lateral runout was well in excess of the 0.004" maximum spec on just one side of the car with new rotors properly mounted. What could cause that? The hub! Both of these cars had bent hubs and one of them had a bad bearing on the same side too. The worse of the two had ~0.005" of play in the bearing with an additional 0.009" bend to the hub face. That car scared me so bad on the initial test drive I cut it short.

Both owners had spent hundreds on multiple brake jobs while believing they had either gotten defective parts or were just simply too hard of drivers. Not so!

There is one more detail a good 102 level brake instructional should include - brake fluid maintenance. Brake fluid is hygroscopic, or water loving. It will absorb moisture from the air in the master cylinder reservoir. This moisture ends up in low parts of your brake system and causes corrosion and eventual failure of those brake parts. This is why service manuals typically recommend a brake fluid flush every two years. Keep that fluid refreshed that often and your chances of needing caliper or master cylinder replacement drops significantly. In fact, failures of these parts is pretty rare when proper preventative fluid maintenance is performed over the life of a car.
 
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oilhammer

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outside St Louis (where it's safe)
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There are just too many to list....
Excellent post.

Another reason I love these cars, so easy to get that hub surface clean since they use BOLTs instead of studs/nuts. Except for the T2s. And the T3s mysteriously use buts on the rear axle and bolts on the front :rolleyes:

But anyways, I digress. Good job! :)
 

IndigoBlueWagon

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Thanks for this. We sometimes despair of helping customers with "warped" rotors when we know the product has a good history. I'd also add that a tired caliper (sometimes due to neglecting the brake fluid) will also cause a pulsation.
 

Cogen Man

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2011 Golf TDI DSG.
Thanks for this. We sometimes despair of helping customers with "warped" rotors when we know the product has a good history. I'd also add that a tired caliper (sometimes due to neglecting the brake fluid) will also cause a pulsation.
I can see your point. On a totally unrelated topic. I just put my IDparts winter grill block on. Nuts. :D
 

Mike_04GolfTDI

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Mine: 2019 Golf R DSG, Wife's: 2015 Golf Comfortline TDI
I had a problem with pulsation that was caused by improper break in.

According to a write up I found somewhere, the main purpose of the break in procedure is to deposit an even layer of pad material onto the rotors. A lot of the friction in braking is the pad material on the rotor surface sticking to the pads. If you have a patchy, uneven layer of pad material on the rotor, you'll get pulsing, even if the rotors are not warped at all.

To get a nice even layer of pad material transferred to the rotor (this is at a microscopic level, you're not really going to see it), what you need to do is get the rotors hot during braking, but don't stop with hot brakes. So, initially you'd want to do some gentle braking. 50km/h down to 10km/h a bunch of times, without stopping completely just to get the pads to start conforming to the surface of the rotor. Next you would want to do some firm, but not hard, braking from 100km/h down to about 40km/h, but keep rolling! Don't stop with hot rotors! Do this maybe 20 times, and then give the rotors a chance to cool before stopping. Avoid using the parking brake if possible, and definitely don't use it until the brakes are cool. This should get a nice initial layer of pad material transferred, and it should be nice and even.

Obviously you'd have to do this in a controlled environment, where you won't be forced to stop by traffic, lights, etc...

Then, for the next few hundred km, you want to avoid hard braking, and avoid getting the brakes really hot if you're going to have to stop.

I replaced my pads and rotors that I had screwed up with improper break in, and did it the way I've described and they just got better and better, and now the new brakes are awesome. They have a very progressive feel, and there's absolutely no pulsing. By progressive, I mean they are not grabby in any way. The amount you press the pedal seems to correspond to how much braking force is engaged, in a very linear way. Press it a little, and it brakes a little, press it a lot and it brakes hard, and everything in between. Nice and smooth.

I'm using the cheapest Chinese made pads and rotors I could get, and they work awesome, just because I broke them in properly. My previous brakes were a little more expensive and I ruined them because I didn't know what I was doing when I broke them in.

Too long, didn't read version: Break-in matters.
 

A5INKY

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Louisville, KY
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2006 Jetta TDI, 2002 Eurovan Westphalia VR6
http://www.harborfreight.com/hand-tools/measuring-tools/clamping-dial-indicator-93051.html

I picked up one of these, pretty easy to use, mostly to check how bent my wheels are. would be perfect also for the disk runout measurement.

have you considered using on the hub directly?
That is basically a budget version of the tool I use shown in my OP. The HF one has a very good price for what you get and probably fine for the weekend worrier mechanic. I would think the base and flex section should be fine but I wonder how accurate the dial indicator could be for that price. Even then, the base is fairly universal and one could add a higher quality dial indicator and have a very good set-up for cheap.

I have used my dial indicator on the hub face. But, due to geometry, lateral runout will be more pronounced (and accuracy greater) further from the hub axis. Specs for lateral runout are always given for the center of the disc swept area, so that is where the rubber meets the road (so to speak) and where it matters most to check.
 

Corsair

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Auburn, New York
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2002 Jetta GLS TDI 5M
Dittos- Kudos and thanks to OP for a great post with great info.

fwiw (maybe encourage others to bleed their brake fluid)....
I have performed the "heavy bleeding" on brakes & clutch of my 02 Jetta every 2 years since new, as recommended by the manufacturer. All of the components that touch brake fluid are original that came with the car, except for the 4 flexible lines in the rear that I elected to change while I had the rear suspension out of the car last winter for bushing replacement. (digressing... the two front flexible brake lines are still original from 2002. I plan to change them both when I do the next front brake job.)

Thanks again for an excellent informative post!
 

waltzconmigo

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A5INKY---would you mind discussing what the cause(s) of a bent hub would be for those of us whom are non-professionals or have little experience. Thanks in advance.
 

A5INKY

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A5INKY---would you mind discussing what the cause(s) of a bent hub would be for those of us whom are non-professionals or have little experience. Thanks in advance.
Trauma.

I can only speculate. However, I would assume perhaps sliding sideways into a curb or pothole on an icy or other wise slick road would be the most likely cause.
 

meerschm

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2009 Jetta wagon DSG 08/08 205k buyback 1/8/18; replaced with 2017 Golf Wagon 4mo 1.8l CXBB
That is basically a budget version of the tool I use shown in my OP. The HF one has a very good price for what you get and probably fine for the weekend worrier mechanic. I would think the base and flex section should be fine but I wonder how accurate the dial indicator could be for that price. Even then, the base is fairly universal and one could add a higher quality dial indicator and have a very good set-up for cheap.

I have used my dial indicator on the hub face. But, due to geometry, lateral runout will be more pronounced (and accuracy greater) further from the hub axis. Specs for lateral runout are always given for the center of the disc swept area, so that is where the rubber meets the road (so to speak) and where it matters most to check.
So first step would be to check half way out the disk surface, and if that is out of spec, check the hub face?

If it is out, you also could mark the high spot of the disk with something like a Sharpie, and rotate on the hub (without securing the screw) and if it is the bent hub, the high spot should stay with the hub orientation, not where marked on the disk.

(and thanks again for sharing this)
 

waltzconmigo

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Dax---thanks for the response, this makes perfect sense. Would I be correct in assuming that the rotor and rim would also, necessarily, be bent in such an event?
 

A5INKY

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So first step would be to check half way out the disk surface, and if that is out of spec, check the hub face?

If it is out, you also could mark the high spot of the disk with something like a Sharpie, and rotate on the hub (without securing the screw) and if it is the bent hub, the high spot should stay with the hub orientation, not where marked on the disk.

(and thanks again for sharing this)
Glad you brought this up, gives a chance to discuss tolerance stacking.

Everything manufactured in quantity has to have dimensional tolerances. That is just a reality of production. Depending on the final processes, this tolerance can be significant. Further, it is possible the critical-to-function tolerances (such as brake swept area lateral runout) can result from several within-tolerance parts stacking up in an unfavorable way. If slightly excessive lateral runout is the result of both hub and rotor runout, then yes, changing their orientation to one another may bring total runout down to within the max spec. Years ago when I worked on all makes of cars and trucks, and was limited in my part quality supply (due to geography), it was common to have to "index" rotors being installed in the way you describe to insure acceptable lateral runout.

I didn't mention tolerance stacking and rotor indexing in this write up for a reason though. The parts contributing to a TDI's lateral runout (assuming a good wheel bearing) are mostly just the hub and rotor. As stated, I am assuming OE quality parts or better. The Zimmerman rotors I typically use have all been within 0.001" runout and most are only 0.0005" or less. With tight part tolerances like that, and the very wide total runout tolerance we have of 0.004", the chance if tolerance stacking leading to excessive runout on a TDI is pretty slim.

If you find excessive runout with a new rotor with everything cleaned up, then a "sanity check" might be worth your while before tackling a hub & bearing replacement. As you mention, indexing the rotor on the hub and seeing if the "high spot" follows will either exonerate or condemn the rotor. You can use a dial indicator on the cleaned hub face as a last sanity check if you want. Just be aware that lateral runout decreases to zero at the axis no matter how excessive it was at the swept area of the rotor. Last one I measured that had 0.005 - 0.006" runout at the swept area only showed 0.0015" runout at the edge of the hub face. This may appear in spec but it is not. That hub was the root cause of the issue. This is why it is important to measure in the center of the swept area when comparing to manufacturer's specs.

Dax---thanks for the response, this makes perfect sense. Would I be correct in assuming that the rotor and rim would also, necessarily, be bent in such an event?
Not necessarily. This is how wheels become bent for sure, but I would not assume it would always bent the wheel when the hub gets bent. The weakest part in the direction of the excessive stress will yield first. It would be a hell of a hit if the rotor actually was bent when that happens. The rotor would have to deflect so far as to hit either the spindle or run out of room for the caliper to slide before it would start to bend. I think the car would no longer be a roller for that to happen. The "bending" or "warping" to the rotor would come later via the mechanisms of lateral runout induced thickness variation.

Wonder how many body shops check the brakes this carefully when there is that sort of crash damage? Ha ha, nevermind - rhetorical question...
 

Aviator69

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Thanks for the info... never occurred to me to check the condition of the hub [cleanliness wise] when mounting new brakes... going to be scotchbrite-ing mine for sure when the time comes...

If you really want to be clean spray the hub down with electrical contact cleaner after SB pad use and then blow the whole thing dry with an airgun :)
 
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A5INKY

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Thanks for the info... never occurred to me to check the condition of the hub [cleanliness wise] when mounting new brakes... going to be scotchbrite-ing mine for sure when the time comes...

If you really want to be clean spray the hub down with electrical contact cleaner after SB pad use and then blow the whole thing dry with an airgun :)
Glad to help. You might reconsider the contact cleaner degreasing as it will leave the parts very prone to rust and the resultant rust-jacking that happen over time that can impart lateral runout. In fact a very thin coating of a rust inhibitor like anti-sieze that won't get runny with heat is not a bad idea for the super detail oriented. Just make sure it stays well contained to that interface. Wouldn't want anything like that near the swept rotor surface.
 

993er

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...within less than 20K miles and were pulsating badly again already.

Wingnut mentioned cleaning up the hub face before mounting a new rotor but did not explain why or what could happen if you don't.
Its a step I do automatically...another reason why I do all my own work.

BUT...if the hub surface was the reason for the pulsating brakes, why would it not pulsate immediately instead of after 20K miles.

The varying friction and thickness due to surface corrosion on the brake disc, especially the inner side that is not easily visible is another reason.
 

993er

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Brake fluid is hydrophilic, or water loving. It will absorb moisture from the air in the master cylinder reservoir. This moisture ends up in low parts of your brake system and causes corrosion and eventual failure of those brake parts. This is why service manuals typically recommend a brake fluid flush every two years. Keep that fluid refreshed that often and your chances of needing caliper or master cylinder replacement drops significantly. In fact, failures of these parts is pretty rare when proper preventative fluid maintenance is performed over the life of a car.
That is hygroscopic.

I changed my brake fluid periodically and I still had my original calipers, wheel and master cylinders on my car when it went to a friend in its 15th year. But I would also lift the caliper piston dust seals away and clean the cavity thoroughly before apply fresh silicone grease to keep corrosion away.

My brakes never dragged.
 

A5INKY

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...if the hub surface was the reason for the pulsating brakes, why would it not pulsate immediately instead of after 20K miles...
My thread describes a cascading failure. Excess lateral runout is the root cause of thickness variation which is what creates the actual pulsation. I did my best to describe it in the OP. To answer as directly as I can, lateral runout is not what is felt. Otherwise, all brakes would exhibit some pulsation as lateral runout is always present to some degree, even in brand new cars.
...Remember how Wingnut said that calipers and pads must move freely side to side? Well, if they are doing so properly, excess lateral runout will go unnoticed by the driver for a relatively long time as the caliper quietly shakes back and forth to the wobble of the rotor. Pulsation only starts to rear its ugly head after this has been allowed to go on long enough for the rotor to wear unevenly in it's thickness, known in the industry as rotor "thickness variation". When rotor thickness variation occurs, the caliper's piston is hammering back and forth in the caliper body violently and transmitting that pulsation to the master cylinder to be felt...
That is hygroscopic...
You are right, but I think maybe that I am as well:
http://ve.ntut.edu.tw/ezfiles/0/academic/5/academic_48602_2579092_29493.pdf
http://aimt.unob.cz/articles/08_02/08_02%20%281%29.pdf

Since hygroscopic is the property descriptor most oft used to describe that particular characteristic of brake fluid, I will edit my OP so as not to distract from the overall intent.
 

A5INKY

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B4 Passat in the shop now for brake work. Very poor braking strength, no parking brake. None of the pads/rotors were metal to metal, but all were close. Once I got everything apart I found paper-thin rotors (unevenly worn in the front from calipers not floating for a very long time) with rear brakes obviously doing next to no braking judging by the heavy rust and rust pitting on the rotors. None of the calipers would compress. When I got them off, gritty rust colored fluid dripped out of them.

Safe to say this car had not been getting good brake service for some time, and most definitely had not had the fluid flushed in way too long if ever. It's tough to ask a customer to spend so much to make the brakes safe on what they had hoped was going to be a cheap used TDI. Especially when previous quality brake service would have prevented the lion's share of this repair bill.

Just another example of the importance of proper service work, especially preventative fluid flushing. Had this B4 had a flush at least every 2-3 years this car's calipers would still be fine.
 

p377y7h33f

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I had a problem with pulsation that was caused by improper break in.

According to a write up I found somewhere, the main purpose of the break in procedure is to deposit an even layer of pad material onto the rotors. A lot of the friction in braking is the pad material on the rotor surface sticking to the pads. If you have a patchy, uneven layer of pad material on the rotor, you'll get pulsing, even if the rotors are not warped at all.

To get a nice even layer of pad material transferred to the rotor (this is at a microscopic level, you're not really going to see it), what you need to do is get the rotors hot during braking, but don't stop with hot brakes. So, initially you'd want to do some gentle braking. 50km/h down to 10km/h a bunch of times, without stopping completely just to get the pads to start conforming to the surface of the rotor. Next you would want to do some firm, but not hard, braking from 100km/h down to about 40km/h, but keep rolling! Don't stop with hot rotors! Do this maybe 20 times, and then give the rotors a chance to cool before stopping. Avoid using the parking brake if possible, and definitely don't use it until the brakes are cool. This should get a nice initial layer of pad material transferred, and it should be nice and even.

Obviously you'd have to do this in a controlled environment, where you won't be forced to stop by traffic, lights, etc...

Then, for the next few hundred km, you want to avoid hard braking, and avoid getting the brakes really hot if you're going to have to stop.

I replaced my pads and rotors that I had screwed up with improper break in, and did it the way I've described and they just got better and better, and now the new brakes are awesome. They have a very progressive feel, and there's absolutely no pulsing. By progressive, I mean they are not grabby in any way. The amount you press the pedal seems to correspond to how much braking force is engaged, in a very linear way. Press it a little, and it brakes a little, press it a lot and it brakes hard, and everything in between. Nice and smooth.

I'm using the cheapest Chinese made pads and rotors I could get, and they work awesome, just because I broke them in properly. My previous brakes were a little more expensive and I ruined them because I didn't know what I was doing when I broke them in.

Too long, didn't read version: Break-in matters.
that's what cured my problem. as soon as i finished the first few break-in runs with ceramic Akebonos, the warping/pulsating annoyance was gone and never came back.

i read an article that mentioned "panic" breaking as being the worst thing to do to your rotors. it's when you slam the brakes and keep at it after the car has stopped. pad material simply bakes onto the rotor, to the point that it's a visible stain on the surface.
 

jason_

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grand rapids michigan
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2015 s wagon dsg
This is interesting. I've never done anything fancy.

Cars, light trucks, med trucks, semis.

Replace what's worn and drive.

Only issue I had with warping was heavily stopping 30K# at a corner (only 1 out of 6 drums had electric on trailer) with a baby 1ton dually, and cutting into a deep water puddle.. Hot rotor didn't like the cold puddle.

Sent from my rooted HTC Supersonic using Tapatalk 2 Pro
 

Ton

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Free Union,VA
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early 2001 jetta
I got the pulsating going on and the wire going to the wear pad indicator is torn. How do I fix this- buy a part from the dealer? Any help is appreciated. Thanks.
 
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meerschm

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2009 Jetta wagon DSG 08/08 205k buyback 1/8/18; replaced with 2017 Golf Wagon 4mo 1.8l CXBB
http://www.myturbodiesel.com/wiki/mk4-vw-jetta-tdi-golf-new-beetle-diy-index/#brakes-suspension

has some good info.

as does

http://forums.tdiclub.com/showthread.php?t=77522

Brakes are important, and a proper job needs good diagnosis. (inspection to see what exactly the condition is. on an almost 15 year old car, there are a few things that could need attention. Has the car had regular service of the brakes, including changing the brake fluid every two years?

at a minimum, you probably need new disks. with disks, new pads are a good idea, and these will come with the wire attached.

you will want to understand why the disks got this way. did they just rust from too many years on the car? did one of the caliper pins stick? Is there a caliper piston sticking?

if you know how to work Google, you can search for "2001 Jetta front Brakes"

and find some u tube videos, more diy info, and sources for the parts.

the local dealer will have them, but many auto parts places will have good parts as well. you can buy parts which are too cheap, and will not last, but also very good ones that will provide good service.
 
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Ton

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Free Union,VA
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early 2001 jetta
I just put new Bosch pads and new Bosch rotors on and the pulsating went away. I greased the pins. The old rotors were 4 years old and rusty but they don't have much wear on them- Carquest brand. Thanks for the help.
 
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