You say rim, I say wheel; you say tomato...

Monday, August 31, 2009 by David Horvath
One of my pet peeves is the modern usage of the term "rim"  to describe aftermarket alloy wheels.  Perhaps this is one of those long standing debates that will never be resolved but it's important to use the correct terminology when discussing parts. 

The rim is the outer barrel portion of the wheel where the tire is mounted. 

The term wheel applies to the entire assembly so anyone who says they are going to purchase some rims for their car is not using the correct terminology.

If they intend to purchase an entire assembly, they should say they are purchasing wheels, not rims.

It's a small point but it still bugs me when I hear it used incorrectly.

Perhaps looking at the origin of the word rim would help clear things up.

I believe a lot of the confusion goes back to the very early days of automotive history when it was common for cars to use something called detachable rims.  These early vehicles had wooden wheel centers much like what you would have seen on a horse drawn wagon.

yellow wheel

Mounted to the outside of the wooden center was a removable assembly made up of the steel rim, a rubber tire and a rubber inner tube.

This design was intended to make it easy to dismount the rim and tire as a complete unit.  The rim itself was secured to the wooden wheel center using retainer bolts threaded into the wood. as seen in this close-up.
rim bolt

When you got a flat tire, it was a 'simple' matter of pulling over and switching out the rim and tire assembly. Here's a nice series of vintage photos showing the process:

Here's the damaged flat tire on the steel rim. You can make out the dark rim retainers along the edge of the wooden wheel rim. These would be un-bolted with a wrench.


Here's a nice close-up of the rim retainers. The nut 'floated' in the seat of the retainer so they could spin freely. When tightened, they clamped the edge of the steel rim down against the wooden wheel center:


Once they were removed, the entire rim and tire assembly could be lifted off of the wooden center. 
rim removed

Then it was time to slip the new tire and rim assembly back on the wooden center. It was so easy you could wear your Sunday best coat and gloves!


Many multi-piece alloy wheels are still constructed from separate rim sections and center discs like this O.Z. Racing three-piece wheel:

The centers drop into the rim sections and are bolted in place from the front of the wheel.


So in reality, you purchase wheels, not rims

I want to send out a special thanks to Mr. John M. Daly for allowing me to use some  detailed photos from his website, the  E-M-F 30 Homepage.

For more info about detachable wheels and to learn about the history of the E-M-F 30, check out his organization's website:

It's a wealth of information about this fascinating vehicle and its history.

Disc Brake Challenge Part V: Bleeding The Brakes And Bedding-In The Pads

Friday, August 21, 2009 by David Horvath
With the new brake pads and rotors installed, it's time for Samuel to bleed any air out of the brake lines. The first step is to check the condition of the brake fluid currently in the lines.

Step 1: Checking the fluid

Brake fluid is an interesting substance. It's actually a specialized type of hydraulic fluid and it does require inspection and or replacement over time.

You can't just top it off and forget about it. It should be checked regularly and flushed/replaced at least every 18-24 months depending on the condition of the fluid.

The brake fluid used in most automotive applications is hygroscopic. This simply means that over time, it will absorb moisture from its surroundings. It literally soaks up moisture from the atmosphere like a sponge.  The rubber brake lines on most cars and trucks can allow small amounts of moisture from the surrounding atmosphere to penetrate through their walls and into your brake fluid.

That can be extremely dangerous because of the high heat generated by the braking process. The fluid inside your calipers and wheel cylinders will be exposed to intense heat and any moisture trapped in the fluid can boil off forming gas bubbles inside your brake lines.

Any air or gas bubbles in your brake lines can compress and cause your brakes to fade or even fail to stop the vehicle under hard braking conditions.  

Checking your fluid is a simple matter of looking at it. Most normal brake fluid starts out as a clear liquid. As it absorbs moisture it will start to turn dark over time.

If your fluid looks like strong tea or coffee, it's time to change it ASAP.

Start by finding the brake master cylinder. It's typically located somewhere on the vehicle's firewall just behind the engine. 

The engineer that designed the location of the brake master cylinder on the 2002 Dodge Grand Caravan should be run out of town coated in tar and feathers. This has to be the worst location I have ever seen on a modern vehicle.  It's way up under the windshield cowl and you can barely access the filler cap.

master cylinder

The brake fluid reservoir sits on top of your master cylinder and it's translucent. That's so you can see the color of the fluid without actually opening the cap. If it looks like it's full of coffee or strong tea, it's time for a fluid change.

I sucked out some fluid using a clean syringe and hose to check the color. 

I did this part because brake fluid is a very caustic substance. You want to wear eye protection and you need to be careful not to let it drip. It will damage your car's paint and it will eat a hole in your clothes too! 

Our fluid didn't look all that bad. This is about what you would expect if the brakes haven't been looked at for a couple of years. This had ATE SL-6 fluid in it to begin with and it had a very light amber color to it. This is only a shade darker.

The fluid Samuel later drained from the lines was a different story.

STEP 2: Draining The Master Cylinder Reservoir

The next step was to suck out as much of the old fluid as possible from the master cylinder reservoir using the syringe and tube. Samuel dumped the old fluid into a clean gallon container that formally contained washer fluid.

All of the old fluid was taken to the local hazardous waste recycling facility and he clearly marked the bottle USED BRAKE FLUID.  

Then he topped off the reservoir with brand new ATE SL.6 brake fluid.

We have used this fluid before and it works well with the ABS brake system on the van. Even with the sticking caliper it held up very well to the excessive heat and abuse.

Samuel had to use a spare section of PVC drain pipe I had in my plumbing spares box to reach the filler neck.

Once again, my sincere thanks to whoever engineered the location of this reservoir! You can get a good idea of where it sits in this photo.  Jeesh! Obviously, ease of maintenance was the last thing on their mind when they decided to place this up under the windshield apron!!

filler neck

STEP 3: Bleeding The Brake Lines

Samuel then took our brake fluid bottle and a section of polyethylene hose and started to bleed the brakes while his sister sat in the van, pumping the brakes when prompted.

This led to some wonderful big brother, little sister banter as they attempted to synchronize their activities.

You want to use a clear or translucent hose and container so you can see the fluid as it is forced out of the brake bleeders. This is critical.

Following the instructions in the shop manual, he started with the rear passenger's side brake drum.

He worked his way from the bleeder furthest away from the master cylinder up to the driver's front caliper as he bled all four lines.


You can see here how much darker the fluid was in the actual brake lines. It looked just like coffee!

The bleeding procedure is pretty much the same on all vehicles.

  • The first step is to remove the rubber covers from all four brake bleeders. These just pull off the nipple.

  • Clean down the bleeder valve and surrounding area with brake cleaner spray. This will help keep dirt or other contaminants out of your calipers and wheel cylinders.

  • You want to attach your hose to the brake bleeder nipple after you place a small wrench on the bleeder.

  • Next, have the person in the vehicle pump up the brakes until the pedal is firm and then hold the pedal down. This keeps the fluid pressurized in the lines.

  • Then, as they are holding the pedal down, the person bleeding the brakes gently turns the wrench to open the bleeder valve.  This forces the old fluid out  into the line and into your recycling container.

  • At first you will see very dark fluid and perhaps some air bubbles in the fluid. Some of the bubbles are from air moving through the threads of the loosened bleeder valve.  A drop of clean brake fluid on the threads will stop that and you may need to do that a few times during the bleeding process.

  • Once the pressure forces out the fluid and the flow stops, the person bleeding the brakes turns the bleeder valve shut and instructs the person in the vehicle to pump it up again.

  • The cycle repeats until you no longer see bubbles or dark fluid coming through the translucent tube.

  • You then move on to the next brake line until they are all flushed and filled with clean fluid.

Once the fluid was changed out, Samuel put the wheels back on and torqued the lug nuts to the recommended spec in the owner's manual.

Step 4: Burnishing/Bedding-in The New Pads:

We then took the van out for a test drive (with me driving of course) and we bedded in the Hawk HPS pads following the burnishing/bed-in instructions printed on the box.

The bedding-in process is extremely important with new brake pads. It allows the pad compound to properly mate with the rotor surface and when done properly, it creates a nice, even, transfer film of pad compound on the rotor surface. Here's a handy link explaining the importance of properly bedding in your brake pads:

Bedding-in Brake Pads and Rotors

Step 5: Letting The Brakes Rest

After performing the in ital bed-in procedure, it's important to let the brakes completely cool down. We parked the van and let it sit for a few hours before driving it again. Samuel was very happy and proud of himself. He was a bit uneasy when he started, but it went off with only a few hitches and the van's brakes work great now! Great job son! Now you can help me tackle the body work on my car!

Disc Brake Challenge Part IV: Installing The Hawk HPS Brake Pads And Calipers

Saturday, August 8, 2009 by David Horvath
With the rotors and hubs checked for excessive run-out, it's time for Samuel to move on to the brake pads. The set we selected for this vehicle are the Hawk HPS Performance Brake pads. We have had these on previous family vehicles and even my wife noticed the difference. She specifically requested these pads for the van.

The Hawk HPS pads feature a Ferro Carbon compound that give you nice initial bite, a high level of friction when hot or cold, built in shims, and a smooth, firm, pedal feel.

Even before the caliper started binding, she complained that the previous brakes felt "soft or mushy" and that was when the brakes were new.  Installing the Hawk HPS pads has vastly improved the feel and performance of the brakes. 

After this brake job, she says she feels a lot safer and more secure with this specific rotor and pad setup.

I'd also like to point out, I personally selected and purchased the pads, rotors, and fluid for this brake job out of my own pocket. These items were not provided by the manufacturers as samples etc...

Step 1: Double And Triple Check the Pads

Samuel pulled the pads out of the box and carefully inspected them again to make sure they were the correct size, shape and model. These come nicely packaged with the installation instructions  and burnishing bed-in) procedures right on the box. That's a nice touch for sure!

hawk pads

The shims on these pads are actually riveted to the back of the backing plate so they are secure and won't slide around. They also look to be a lot larger than the O.E. shims. We later found them to be very quiet even during the bed in procedure. There wasn't a hint of noise when braking. They also have the factory style wear indicators on the inboard pads. These were a perfect match for the O.E. calipers.

Step 2: Replacing Clips And Loading The Hawk HPS Pads

Samuel then replaced the small, steel noise elimination clips on the caliper brackets with new ones. These came with the caliper hardware kit we purchased at a local parts store (the same kit that had the caliper pin bushings and boots). 
caliper clips
They appeared to be in good shape but these small clips should always be replaced. They will help eliminate vibrations and noise and they are inexpensive parts.  Brakes develop a lot of heat and these small steel parts will fatigue as they get old. Replacing these small metal clips and pins is cheap insurance against noise issues.

With the new clips in place, Samuel then loaded the new pads into the caliper bracket and checked the clearances by sliding the assembly into position over the ATE brake rotor.

Make sure you don't get any grease or other contamination on the brake pads as you handle them. Any contamination on the face of the pads can interfere with the bed-in process.

pad install

Step 3: Bolting Up The Caliper Bracket

The pad and bracket clearance checked out so he inserted the caliper bracket bolts and snugged them by hand being careful not to cross thread them. The manual also recommended lightly coating the bolt threads with medium strength thread lock compound which he applied before installing them.

bolting bracket

Once they were snug, he torqued the bolts using a Gorilla Hand Torque Wrench to the specific torque setting listed the vehicle shop manual. 

Always follow the proper torque specs and instructions in your shop manual! Failure to do so can lead to brake damage or failure! Don't take chances with your brakes.

Step 4: Prepping The Caliper

The brake caliper piston needed to be retracted so it would fit over the new brake pads and rotors.

Check your vehicle's shop manual for details on the proper procedure for your calipers.

Some pistons (typically on rear calipers) need to be twisted back into the caliper. Others, like the front calipers on our Grand Caravan simply push back in place.

To handle this task, Samuel used his great-grandfather's trusty , rusty c-clamp. 

Something tells me this may have made its way home in grand dad's lunch box when he was still working at Studebaker.

pressing piston
It's a good idea to siphon some of the brake fluid out of the master cylinder before you do this. That way it won't overflow into your engine compartment as the fluid is forced back up the lines. Also note the caliper is still supported by the spring to make sure there is no tension on the brake line.

Step 5:  Installing The Caliper

With the piston retracted, the caliper slides right over the pads and rotor.

caliper on

Again, Samuel coated the caliper mounting bolts with thread lock compound and snugged them up by hand. Then he torqued them to the specified torque setting in the shop manual.

Step 6: Repeat The Same Procedures On The Other Side

With the caliper on, he removed the wheel nuts and the extra washers from the hub and rotor. The rotor would stay in place as he moved on to the other side of the van.

The other side went a little quicker since the rotor wasn't overheated and fused to the hub. Again, he changed gloves frequently to keep the new pads and rotors free of any contamination as he worked. He was then ready to start bleeding the brake lines in our final installment:

Disc Brake Challenge Part V:  Bleeding The Brakes And Bedding-In The Pads

Disc Brake Challenge Part III: Removing and Replacing the Brake Rotors

Thursday, August 6, 2009 by David Horvath
With the worn out brake pads off and the calipers checked and repaired, it was time for Samuel to move on to the brake rotors.

Step 1: Removing The Old Brake Rotor

This looks simple enough right? There are no stud clips so the brake rotor is just resting on the nose of the axle hub ready to be lifted off. Well, not quite, as Samuel soon discovered...

bare rotor

Normally there will be some corrosion on the hub and the rotor hat. That's to be expected.

A little tap on the back with a hammer or rubber mallet will usually knock the rotor loose but that wasn't to be this time.

The first rotor came right off the nose without any issues. After about 5 minutes of pounding and rotating on the driver's side rotor he found it wouldn't budge. 

He next tried some PB Blaster spray on the rotor. That didn't work either. It was really fused to the hub. It was the time to pull out the heavy artillery. 

I had him put on some safety goggles and I got out the largest 3-jaw puller I had in the tool box. This is not the greatest idea since it's hard on the wheel bearings but we didn't have much choice. It just wouldn't break loose using normal means.

jaw puller

After a few quick turns of the wrench it finally broke loose from the hub with a huge BANG!

The driver's side overheated severely due to the sticking caliper and apparently cooked off the anti-seize compound that was originally between the hub and the rotor.

You can see the extent of the damage to the rotor. This was cooked, warped, and the brake pad compound looked like chocolate icing smeared all over the back of the rotor.

cooked rotor

Step 2: Cleaning The Hub

Now Samuel moved on to prepping the hub for the new brake rotor. This involved cleaning and checking the run-out on the exposed hub.

A wire brush mounted in a drill makes quick work of cleaning the corrosion off the hub. He sprayed some brake cleaner spray on as well.

Any debris or corrosion between the hub and the brake rotor can cause excessive run-out and vibration issues.

Eye protection is a must here!

cleaning the hub

Step 3: Checking The Hub Run-Out

This is a step most folks don't bother with but it's important. As long as everything is torn down this far, you might as well make sure the wheel bearings are not shot. 

Excessive bearing play can cause vibrations. It can also severely damage the brake rotor and brake pads. This can easily be checked using a dial indicator mounted to the strut tube. The run-out specs and instructions for this procedure will be listed in your vehicle's shop manual.

hub run-out

Step 4: Mounting The New Brake Rotor

Having established that the hub and bearings were okay, Samuel then carefully applied a thin film of anti-seize compound on the surface of the hub. He was careful not to get any on the studs themselves. You never want to put anything on the stud threads. He then mounted the new ATE Premium One brake rotors.

Before doing so, he put on a fresh, clean, pair of gloves to make sure he didn't transfer any grease or anti-seize compound onto the new rotors. Any contamination on the rotor surface can transfer to the new brake pads and keep them from bedding in properly!

The ATE Premium One brake rotors have a nice Meta Cote protective coating on them. The unique pattern of the slots minimizes noise, maintains an even, clean surface on the pads, and eliminates fade during heavy braking. The slots also aid in wet braking conditions.

They are nicely packaged and due to the Meta Cote surface, they are ready to install right out of the box.

Some rotors are not anti-corrosion plated and will come packed with a thin film of protective oil on them that needs to be cleaned off before installing them.

On those rotors, you will need to clean off the packing oil with brake cleaner spray and a lint-free cloth before installing them. You should only clean off the portion of the brake rotor that will make contact with the brake pads. 

The oil can stay on the brake rotor hat and inside the cooling vents (if it's a vented rotor).  As the rotor heats up, that will burn off and the resulting residue will help protect the rotor from corrosion. It's just like curing a cast iron skillet. If you clean it off the entire rotor, any exposed area not in contact with the brake pads will rust and turn an ugly orange/rust color very quickly.

Step 5: Checking The Rotor Run-out

The next step is also very important. You want to check the rotor run-out to make sure it wasn't damaged or bent. Excessive run-out will cause brake vibrations and a pulsing in the brake pedal. Samuel attached the rotors to the hubs using three of washers and nuts per rotor. 

It's critical to do this check before the rotors are driven on to make sure they are true.  Most rotor manufacturer's will not warranty a rotor for warping or run-out issues once they have been driven on.

The typical allowable run-out spec is .004" (.10mm) maximum.

Here Samuel is checking the run-out using the outer edge of the rotor.

rotor run-out

Now that the rotors are checked and ready to go, it's time for him to move on to the next step...

Disc Brake Challenge Part IV: Installing The Hawk HPS Brake Pads And Calipers

Stay tuned...

Disc Brake Challenge Part II

Wednesday, August 5, 2009 by David Horvath
With the parts checked out, it's time to start tearing down the brakes. Refer to your vehicle's shop manual for the proper wrench sizes for your vehicle. 

Step 1: Removing the caliper retaining bolts

Samuel started by removing the two bolts attaching the brake caliper to the sliding pins on the caliper bracket. These were pretty tight and required some coaxing.

removing caliper bolts

If the bolts are stubborn, spray some penetrating oil on them and let them sit a few minutes. Once you have the bolts loose, make sure you hold onto the brake caliper so it does not drop off. 

Step 2: Removal of the Caliper

Typically the caliper will stick to the caliper bracket assembly.  It may take some coaxing with a screwdriver to pry it away. Again, keep one hand on the caliper so it does not fall!

Never allow the caliper to hang loose on the brake line or hose! It can kink or damage the hose!

prying off caliper

It will swing away from the bracket and brake pads.

Note how much thinner the inboard pad is.  These were past due for replacement.

Step 3: Support the caliper

Once it's loose, you want to support the caliper on a piece of stiff wire or rope. I have an old spring that works great. Samuel just hooked one end in the caliper bolt holes and hooked the other end onto the strut housing. You want to keep the brake line loose so there is no weight on it.
caliper support

Step 4: Removal, Inspection, and Lubrication of the Bracket/Sliding Pins

For this step, Samuel broke loose the two bolts securing the caliper bracket to the hub assembly.  There is one on the bottom shown here and another one at the top. With those bolts removed, the whole bracket comes off.
bracket removal

Note the small rubber boot highlighted by the arrow. This is one of two sliding pins that allow the brake caliper to 'float' freely back and forth to equalize the pressure applied through the brake pads to the brake rotor surfaces. That's why this caliper type is called a Floating Caliper.

He gently popped the rubber boots off and removed the pins from the bracket. He then carefully inspected and cleaned the pins and sockets with brake cleaner spray. The pins should not bind up and they should slide in and out of the socket freely. 

He then dried them off and applied some high-temperature brake grease to the pins and re-installed them. This procedure will vary depending on the vehicle and caliper type. Refer to your specific shop manual.

One of our pins had a torn boot on it which allowed dirt and grime to get to the pin and into the grease.  This caused the caliper to bind up and it was applying more pressure to the inner pad.  We had a caliper pin repair kit handy and I walked Samuel through the replacement of the pin and the boot.  Look how thin the inner pad was!

inner pad

Stay tuned for Disc Brake Challenge Part III:  removal and replacement of the rotors!

Brake Job Part 1: The Set Up

Tuesday, August 4, 2009 by David Horvath
Well, my son Samuel finished up the brakes this past Saturday and they are working fine. The rear drum brakes were in good shape so he only had to work on the fronts. The whole process took about two hours from start to finish and he's justifiably proud of himself. I'm going to break this up into a few posts so let's get started!

By the way; Samuel was under close adult supervision during all procedures. He also wore protective eye wear and gloves when required. When working on your vehicle, always refer to a good, vehicle specific, shop manual to review the procedures before you start.
Follow all safety procedures in the shop manual and read all of the instructions that come with the parts you are installing.

Step 1:  Safety first!

The first step was placing chocks behind the rear tires of the van. These keep the van from rolling backward when it's jacked up in the air. Never jack up a vehicle without chocking the tires. Even a slight movement backward can cause the vehicle to slip off the jack. 

Since he was only working on the front brakes, I had him apply the parking brake as well. This locks up the rear brakes which will also help to keep the rear end fixed in position.

The next step is to break the lug nuts loose. You want to do this before you jack up the vehicle. The weight of the vehicle will hold the tire and wheel in place while you are applying force to the nuts. The whole wheel will just spin if you attempt this with the wheel in the air.

Here's Sam using a Gorilla Power Wrench to accomplish this. It's much easier if you are lifting up on the power wrench. You have more leverage that way.

You only need to loosen them enough to get them moving and then snug them lightly back against the wheel. Do this one nut at a time.  Don't unthread them all the way yet! You'll do that once you jack up the vehicle.
breaking nuts loose

Step 2: Jacking Up The Vehicle

With the wheel chocks in place behind the rear tires, it's time to jack up the vehicle. Refer to your vehicle's owner's manual or your shop manual for the proper jacking points under the vehicle frame.

Carefully set the jack under the proper point making sure there are no wires or lines that could be pinched or damaged!

Here Sam is using a Tire Rack Aluminum Service Jack to lift up the corner of the van. Note the van is on a nice smooth, level surface. 

jacking up the van

Step 3: Jack Stands

Another important safety device is a set of jack stands. Make sure they are rated high enough to support the vehicle weight you are working with. These supports go under the frame of the vehicle to support the weight and to give the vehicle a stable connection to the ground.

It's never a good idea to leave the full vehicle weight on the jack. Most jacks are mounted on rollers that could move causing the vehicle to shift as you work on it.

Once the jack stands are in place you can slowly lower the vehicle off the jack and onto the stands. Do this slowly and watch the stands to make sure they don't shift.

They should be sitting flat on the ground. After they are properly seated under the vehicle, the load should not shift easily. I typically move my jack back up to within 1/4" of the frame just as a backup should something shift unexpectedly.

Step 4:  Remove Lug Hardware and Wheel/Tire

Now the tire and wheel is up in the air and you can remove the lug nuts or bolts. This is pretty straight forward. The Gorilla Power Wrench comes in Handy for this as well.

removing lugs

If you have aftermarket alloy wheels, you may see centering rings sticking to the hub. Make sure you remove them carefully using a flat blade screwdriver. 

removing centering ring

Step 5: Look at the parts!

This is the point of no return. Once you start taking the calipers and rotors apart, there's no turning back. Now is the time to carefully inspect your new replacement parts and to compare them to the parts on the vehicle. You don't want to go any further if you don't have the correct parts right? 

Samuel will be replacing the pads and rotors with Hawk HPS performance brake pads and  ATE Premium One Brake Rotors. He's also going to be replacing the fluid with ATE SL.6 Brake Fluid

He inspected the parts and checked them against the ones on the van. Everything checked out and they look like the parts on the van. He's ready to move on to our next blog post: 

Brake Job Part II: Taking it all apart 

Disc brake challenge: easy enough for a 13-year-old???

Friday, July 31, 2009 by David Horvath
Automotive repair, even on newer vehicles is nothing to be afraid of. To prove my point, I'm going to post a series of reports about my son.

He's 13 and he will be performing his first brake job.  If he can do it with a few simple hand tools, you can too!

The vehicle in question is our family's 2002 Dodge Grand Caravan SE. Last weekend he replaced a bad ABS sensor lead and this week he will be installing a new set of ATE Premium One brake rotors and a set of Hawk HPS performance brake pads on the front. He will also be flushing the fluid and replacing it with ATE SL.6 Brake fluid. 

I'll be standing by, taking photos, and documenting his progress. Stay tuned for the play-by-play in the coming week.  Here's a list of some of the items he will be using:

ATE Premium One Slotted Rotors

ATE SL.6 Brake Fluid

Hawk HPS Brake Pads

Tire Rack Aluminum Service Jack

Gorilla Adjustable Torque Wrench

Gorilla Power Wrench

Pull Those Stud Cips!

Friday, July 31, 2009 by David Horvath
One of the most common issues we hear about is wheel vibrations after new tires and aftermarket alloy wheels are installed.

More often than not, the vibrations are caused by little washers attached to the brake rotor or brake drum. These locking washers are called stud clips.

These are found mostly on domestic vehicles produced by GM, Ford, Chrysler, Saturn, and even on some imports like Jaguar.

They seem innocent enough but they need to be removed before installing aftermarket wheels.

During vehicle assembly, these little clips are installed to hold the drum or rotor in place against the hub as the vehicle moves down the assembly line in the factory.

They do a great job of keeping the rotor from falling off before the caliper and brake pads are installed but once the car or truck is assembled, they serve no important function. The clamping force of the wheel and lug hardware is what keeps the assembly together after that point.

Here's what they look like on the hub. They are the small, toothed washers placed around the base of  the studs.  Notice they are only on one or two of the studs:

stud clips

They are easy to miss and if they are left on there when you install new alloy wheels, they will cause big problems! Any rust or debris on the surface should also be cleaned off with a wire brush. This rotor surface needs a little bit  of prep work before a wheel can be installed on it.

Although they are pretty thin (approx 2-3mm), they will keep the wheel mounting pad from sitting flat on the brake rotor or brake drum. Typically the factory only uses one or two on each hub so the flat mounting pad of the wheel will only make contact with one side of the hub once the lug nuts are torqued. It will feel like the wheel is mounted securely but once you start driving on it, the forces on the wheel from rotating, turning and braking will cause the wheel to rock back and forth on those stud clips.

Imagine trying to stand and balance on a flat metal disc that's sitting on two golf balls. You would have a difficult time staying balanced as you shifted your weight back and forth across the disc wouldn't you? Now you're getting the picture right?

Since the stud clips are normally made from stainless steel, they are harder than the alloy wheel. As the wheel rocks back and forth, the stud clips will quickly dig into the back of the alloy wheel's mounting pad.

The clips actually wear round indents or recesses in the back of the wheel and the resulting gap also creates a space between the lug nuts and the lug seats on the wheel face. The lug nuts are no longer torqued tight against the wheel!

You will soon notice a vibration while you drive the vehicle, especially when you turn or when you apply the brakes. The forces on the wheels change dramatically as you turn or brake and the wheel will rock back and forth violently on the now loose lug nuts and studs.

If allowed to continue, the vibration and rocking back and forth can damage the wheel and the studs. Here's a severe example. You can see the indents from the stud clips highlighted in red, as well as the damage to the lug openings of the wheel highlighted in green. The lug holes are actually elongated and chewed up from the violent vibrations against the studs. stud clip damage

The imprints of the stud clips can be seen at the 9 o-clock and 3 o-clock positions. If driven on long enough, this could cause severe damage and even failure of the studs! Once the lug seats are damaged, the wheel is ruined. 

It is critical to remove the clips before installing any aftermarket alloy wheel.

It's a simple process to remove them. You just pry them up with a flat bladed screw driver and cut them off with tin snips or twist them off with a pair of pliers.

This important little step can save you a lot of heartache.  It will also save your vehicle and wheels from damage.  Here is a handy link for wheel and tire installation. Check it out before you install your new aftermarket wheels.