# Zimmerman Cross-Drilled Cracks FYI,



## FreeStage3 (Mar 18, 2002)

everyone talks about the Zimmerman Cross-Drilled rotors cracking, well here is 1 more post to prove it. I participated in a road course track event on both Saturday and Sunday. total track time was 3 hours of abuse. i am running 12.3 Zimmerman Cross drilled with Porsche Boxster 4 piston calipers and Mintex C-Tech pads. these pics show the results:
























these pics are of the drivers side which was had cracks on both sides. the passenger side had 2 cracks but only on the outer side, nothing on the inner side. the track had 4 hard right hand turns and only 1 hard left hand turn. 
matt


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## Marty (Jul 14, 2000)

*Re: Zimmerman Cross-Drilled Cracks FYI, (FreeStage3)*

Mmm, stress cracks... not a good thing.


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## Y2KVR6GTI (Aug 16, 1999)

*Re: Zimmerman Cross-Drilled Cracks FYI, (FreeStage3)*

Ouch! I hate even thinking how bad that could have been if the rotor disintegrated at Speed.


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## VDUBBINDizzy (Jul 23, 2001)

*Re: Zimmerman Cross-Drilled Cracks FYI, (Y2KVR6GTI)*

Luckily this was a small motorcycle track that's only 1.35 miles longs. But it was hard on the brakes for sure. My stock rear pads were about a half an inch thick on Fri night. Sun afternoon, nothing but the backing plate. Wonderful VW rear pads.










[Modified by VDUBBINDizzy, 8:55 AM 2-26-2003]


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## FlashRedGLS1.8T (Apr 17, 2001)

*Re: Zimmerman Cross-Drilled Cracks FYI, (FreeStage3)*

Had a little fun, eh?
Also, what's the debate, people are trying to say they don't crack?
They are cross drilled, they are going to crack.
Just curious, how many miles did you have on them and what pads
were you running?


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## FreeStage3 (Mar 18, 2002)

*Re: Zimmerman Cross-Drilled Cracks FYI, (FlashRedGLS1.8T)*

quote:[HR][/HR]Just curious, how many miles did you have on them and what pads
were you running?[HR][/HR]​approx. 5000 miles running Mintex C-Tech pads
matt


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## FlashRedGLS1.8T (Apr 17, 2001)

*Re: Zimmerman Cross-Drilled Cracks FYI, (FreeStage3)*

Thanks.


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## VDUBBINDizzy (Jul 23, 2001)

*Re: Zimmerman Cross-Drilled Cracks FYI, (FreeStage3)*

And 100+ hard miles at the track.


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## FreeStage3 (Mar 18, 2002)

*Re: Zimmerman Cross-Drilled Cracks FYI, (VDUBBINDizzy)*

here are some more pics after some more abuse. i replaced the rotors today with some more Zimmermans because thats all i could find quickly. the cracked ones are being replaced under warranty and as soon as possible i will find something else.
Notice how the crack closest to the hub has traveled to the other crack and has gotten bigger. the other problem is that it was expanding enough to to scrap my caliper. this happened to both the driverside and passengerside.























notice the crack. on one side close to the hub there is black paint, on the other side of the crack is rust. 








notice the rub marks on the OD of the rotor where it was coming in contact with the caliper








fyi,
matt


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## FlashRedGLS1.8T (Apr 17, 2001)

*Re: Zimmerman Cross-Drilled Cracks FYI, (FreeStage3)*

quote:[HR][/HR]







[HR][/HR]​








Are you sure it's only happening when it's heated?
Better yet, did you buy the exact same rotors for it to happen again?


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## ShyGuy (Sep 4, 2002)

*Re: Zimmerman Cross-Drilled Cracks FYI, (Marty)*

Stick with Brembo! Do they make 12.3" rotors for our car?


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## FreeStage3 (Mar 18, 2002)

*Re: Zimmerman Cross-Drilled Cracks FYI, (ShyGuy)*

i am looking for a different MFG but all could get locally were the Zimmermans. the dealer wanted $170 EACH for OEM TT rotors.







i will be seeing ECS at the APR BBQ today in Auburn so i will discuss the 13" setup with Tom.
matt


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## germanrox (Mar 30, 2001)

*Re: Zimmerman Cross-Drilled Cracks FYI, (FreeStage3)*

would cryo-treating help prevent this? I have the 11" zimmermans on my mk3.


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## ShyGuy (Sep 4, 2002)

*Re: Zimmerman Cross-Drilled Cracks FYI, (germanrox)*

I think the reason they crack is because of bad cross-drilling.


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## Marty (Jul 14, 2000)

*Re: Zimmerman Cross-Drilled Cracks FYI, (FreeStage3)*

They crack from stress concentrations around the holes when they expand and contract from heating and cooling.


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## 95' GLX VR6 (Feb 15, 2003)

*Re: Zimmerman Cross-Drilled Cracks FYI, (FreeStage3)*

You should never race with Cross-Drilled Rotors. F1 Cars race with them, and after each race, they throw them out. Unless you plan to buy new rotors for each race, stick with slotted.


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## FlashRedGLS1.8T (Apr 17, 2001)

*Re: Zimmerman Cross-Drilled Cracks FYI, (95' GLX VR6)*

The rotors on F1 cars are very very different from what ours are.
They are carbon and ours are steel.
Plus they race with rubber tires and change them 1-3 times a race
so maybe we shouldn't race with rubber tires.


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## 95' GLX VR6 (Feb 15, 2003)

*Re: Zimmerman Cross-Drilled Cracks FYI, (FlashRedGLS1.8T)*

The effect of the cross drilling technique is the same, whether the rotors are made out steel, carbon, iron, platimun, gold, I don't care, the they will start to crack from drilling holes in them if you decide to race. The carbon rotors crack too. It is the idea of what cross drilling does to the rotor, not what the rotor is made out of. Just because they are made of carbon iron, platimun, or gold, doesn't mean they haven't been weaken when you drill them. 
Like Marty said, its the expanding and contracting of the rotor due to heat. Any material expands and contracts due to heat.


[Modified by 95' GLX VR6, 7:35 PM 3-4-2003]


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## FlashRedGLS1.8T (Apr 17, 2001)

*Re: Zimmerman Cross-Drilled Cracks FYI, (95' GLX VR6)*

I know that but,even if they didn't drill them they 
would be changed out.
It really doesn't have anything to do with them 
being cross drilled.
Done.
You would care if you had gold cross drilled rotors.


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## a2vwnick (Oct 25, 2000)

*Re: Zimmerman Cross-Drilled Cracks FYI, (95' GLX VR6)*

quote:[HR][/HR]The effect of the cross drilling technique is the same, whether the rotors are made out steel, carbon, iron, platimun, gold, I don't care, the they will start to crack from drilling holes in them if you decide to race. The carbon rotors crack too. It is the idea of what cross drilling does to the rotor, not what the rotor is made out of. Just because they are made of carbon iron, platimun, or gold, doesn't mean they haven't been weaken when you drill them. 
Like Marty said, its the expanding and contracting of the rotor due to heat. Any material expands and contracts due to heat.

[Modified by 95' GLX VR6, 7:35 PM 3-4-2003][HR][/HR]​usually the problem is the rotors are drilled AFTER they have had their final temper, not before. read a materials book and you will see why this is a problem.


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## 95' GLX VR6 (Feb 15, 2003)

*Re: Zimmerman Cross-Drilled Cracks FYI, (a2vwnick)*

Even rotors that are cast in place crack the same way.


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## 97passatvr6 (Apr 2, 2003)

*Re: Zimmerman Cross-Drilled Cracks FYI, (FreeStage3)*

I wish I would have read this before today cause last night I just ordered a set for the front and rear with PDR pads.







Do they crack just from them be used extremly hard or is this gonna happen from normal driving conditions also?I use my gears more than my brakes so hopefully they last longer than 5000 mi. I was gonna consider doing an autocross this year but now I don't know.


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## EvilRocco (Mar 15, 2002)

*Re: Zimmerman Cross-Drilled Cracks FYI, (97passatvr6)*

Just a little question for everyone here... This come from my experiance with having the same cracking comming into play with vented rotors. Start thinking how hot do your rotors get, 50 deg C 100 deg C
take a look at some info from http://site153.webhost4life.com/coolinbox/forum/topic.asp?TOPIC_ID=1479 .
Here is a run down of types of materials

Carbon/carbon brake: A braking system in which both discs and pads are manufactured from carbon composite material. Utilized in every form of racing where they are not outlawed, carbon/carbon brakes offer significant reduction in rotating mass and inertia along with much greater thermal capacity and dimensional stability in use. The disadvantages include cost, a certain amount of lag time while heat builds up (especially in the wet) and some difficulty in modulation. Contrary to popular belief, the coefficient of friction is no better than that of state of the art carbon metallic pads and cast iron discs. A major advantage on super speedways is the reduction of gyroscopic precession on corner entry. 

Carbon metallic: This is a trademark of the Performance Friction Corporation. Pad friction compounds containing large percentages of pure carbon along with various metallic elements. Pioneered by Performance Friction Corporation these compounds offer very constant coefficients of friction vs. temperature characteristics along with increased thermal capacity. The disadvantage is that, since they both operate at higher temperatures and their temperature rises to operating temperature faster than other compounds, they increase thermal shock to the disc and increase thermal conduction to the caliper pistons and brake fluid. As a result, it is recommended to not use drilled discs with carbon metallic pads. 
Thermal shock or disc exposure to extreme temps causes a break in the bonds of the metals used in the discs which can cause cracking.
Thermal shock is different from bluing which is a result of thermal stress on cast iron rotors, but is normal for brakes that are exposed to hard braking, it will however lead to shorter rotor life

oh and just a side note those rotors wernt they desinged for a car with single piston calipers not 4 piston... hint hint extra heat alot of it


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## Ultimate1.8Turbo (Mar 31, 2003)

*Re: Zimmerman Cross-Drilled Cracks FYI, (FreeStage3)*

i have stock brakes now, but I plan to buy the ECS Tuning kit ASANeeded. Should I avoid the cross drilled rotors because of your cracking problem???? I realize that the ECS rotors are nothing like the Zimmermans, but I don't want to run the rick either way.. I will probably never see a race track, and I love the look of cross-drilled, so to cross drill or not to cross-drill that is the question??????????? thanks


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## FreeStage3 (Mar 18, 2002)

*Re: Zimmerman Cross-Drilled Cracks FYI, (Ultimate1.8Turbo)*

talk to ECS about their cross drilled. i do not have any experience with the ECS crossdrilled rotors so i can not answer your question. 
matt


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## rromasko (Aug 8, 2002)

*Re: Zimmerman Cross-Drilled Cracks FYI, (FreeStage3)*

That sucks man, I have cross drilled in the rear and have had no problems.
I think I will get the slotted up front when it comes time.
Thanks for the info!


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## LC5P_GLX (Jul 4, 2001)

*Re: Zimmerman Cross-Drilled Cracks FYI, (rromasko)*

Hey guys.... Sorry for jumpin in here, but another 'texer from the Passat forum recommended I do a search on Zimmermans before buying them, and I found this post.....
I was told buy Dave @ Germanautopart.com that the Zimmermans are "cast" with the drilled holes and that htey are not actually "drilled" which we know weakens the rotor...
How true it this? My ride is a 93 Passat GLS, daily driver, no track will be seen in this car (well that my wife will know of...







) I like a 'sporting' drive on the highway to work, but if there's a chance those rotors will disintergrate, I won't get them...

cheers!


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## kwokA3T (Sep 3, 2002)

*Re: Zimmerman Cross-Drilled Cracks FYI, (SoulJer74)*

first only porsche iron rotors have cast holes ... 
second your zimmermans' are not really compatible w/c-tech pads - this pad design (w/thermal insulator) will cause v. high rotor temps when used under track conditions ... the cracks resulted from v. high localized "hot spotting"/v. rapid thermal expansion ... 
you may want to try pagid track pads & more substantial rotors - pls see http://www.bira.org for some info & ideas ...


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## ATS (Jan 19, 2002)

*Re: Zimmerman Cross-Drilled Cracks FYI, (kwokA3T)*

Humm, I have rear Zimmerman with Mintex Pad on my rocco, and I have have about 5000 Miles on it and I have no issues of cracking, I do beleive some people on the list pointed out that RACING with cross drilled patterned rotors is a bad idea.


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## Scirocco53 (Mar 9, 2002)

*Re: Zimmerman Cross-Drilled Cracks FYI*

Why are the rotors cracking??? I go through a full season on one set of home drilled rotors. My first set was 11" Brembo's. Never had any cracks. I used Hawk Black HP+ with those when I had a booster (power brakes) The switched to Hawk Blue 9012 when I had a standard master. The second set was the Zimmerman rotors that were also home brews, and that set I ran for 2 seasons with the same pads (9012) There were a few cracks on those rotors. I now have 2 piece 11" rotors with Willwood Dynalites and they have even more braking. I can only immagine that the Porsche calipers would be a lot better, but I already have the Willwoods.
Oh wait, I just realised that I have a massive 4" brake duct that cools the assembly. Maybe that is a solution for you guys.


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## 2KGTI-t (Apr 20, 2001)

*Re: Zimmerman Cross-Drilled Cracks FYI (Scirocco53)*

the rotors are drilled thats the problem... they are not casted with the holes... all the drilling does is weaken the metal... anyone know if cryo-frozen rotors would be better?


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## Scirocco53 (Mar 9, 2002)

*Re: Zimmerman Cross-Drilled Cracks FYI (2KGTI-t)*

The reason I cross drill the rotors is that it exposes more surface area for the rotor to cool. There is more exposed area to shed heat in the cylinder that the drilled hole has, than leaving it undrilled.


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## TarmacSpecial (Mar 6, 2003)

*Re: Zimmerman Cross-Drilled Cracks FYI, (FreeStage3)*

All I can say, is the sickest car I ever rode in was a Ford Cosworth Esocrt RS Group A rally car with the FIA intake restrictor removed. The brakes were AP's and the rotors were SLOTTED, and they can last an entire season. If that's not an endorsement I don't know what is.
Most modern motorcycles use drilled rotors, street or track. However, they weigh less, and tend to have similar rotor sizes to cars, the pads and calipers are designed to absorb alot of heat, and they get alot more air to cool them off. For example my bike is running twin 6 piston calipers with 330mm cross drilled floating rotors on the front. I'm on the fourth or fifth set of pads, and the rotors are still in great shape.


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## reflexgti (Dec 19, 2000)

*Re: Zimmerman Cross-Drilled Cracks FYI (Scirocco53)*

The cracking could also be attributed to the car that it's on. Freestage3 is tracking a 2900 lb A4 chassis VW with over 300 hp. The car is probably reaching speeds greater than the Scirocco and so the brakes have to slow down a heavier car from greater speeds repeatedly.


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## a2vwnick (Oct 25, 2000)

*Re: Zimmerman Cross-Drilled Cracks FYI (2KGTI-t)*

quote:[HR][/HR]the rotors are drilled thats the problem... they are not casted with the holes... all the drilling does is weaken the metal... anyone know if cryo-frozen rotors would be better?[HR][/HR]​in theory they should. the cryo process is all about getting rid of the stressed areas in the metals latice structure.
edit: but is it worth the price? i dunno, i think its like 56 bucks each to have a rotor cryoed, i would rather just get sloted rotors in the first place.


[Modified by a2vwnick, 10:45 AM 4-16-2003]


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