How to overhaul the front brakes on your Wrangler TJ

[Chris]

Les, a good friend of mine who I had recently helped with a rear axle swap, found that he had some pulsing in the brake pedal when he applied the brakes. We took a look at the recently installed rear drums and bled them, just in case. No help....the pulsing was still there. A week later, we found ourselves on the trail with another local Jeeper who also just happens to be everyone's front end alignment guy (at least those who can appreciate a Jeeper doing front end alignments on lifted vehicles). We got to talking about the brakes and he mentioned that he had noticed that a front rotor on Les' TJ was looking a bit warped when he last aligned it, just a couple of weeks ago.. Les came over to borrow my jack stands, the floor jack, and some advice so I took some picture of his TJ while he wrenched on it.

Be sure to safely support your vehicle when you are doing work near or under the vehicle while the tries are removed. I keep a pair of 12 ton jack stands (yeah, they are a bit of overkill) for this job and they do very well. They easily support a lifted TJ's frame with room to spare. Because of their higher weight rating, they also provide a much better footprint than the smaller 4 or 6 ton jack stands. I like the increased stability they offer even though they cost a few bucks more. They are well worth it, in my opinion.

We raised the side of the TJ with the floor jack (and a block of wood) and then slipped the jack stand under the frame. This was repeated on the other side and we now had the vehicle supported for the brake job. With the floor jack providing a bit of support, Les removed both front tires.

With the tire removed, remove the two caliper mounting bolts, as shown in the above picture. These bolts hold the caliper in place while allowing it to move back and forth so it can center itself on the rotor during braking. If memory serves me, it takes a 13mm socket. This should be the only wrench you should need for this project.

Before you remove the caliper, take a minute and look at how it sits on the mounting brackets. When you assemble the caliper, after installing the new pads, you will want it to look the same way. Now, with the two caliper mounting bolts removed, grab the top of caliper and pull it back and away from the rotor. The bottom of the caliper will pivot a bit on the mounting bracket as the caliper pulls away from the rotor. At this point, the brake dust is rather "all over" the place so I always suggest using a rag to help keep things a bit cleaner. You'll have a chance to use some brake cleaner in a bit.

With the caliper out of the way, the rotor should slip off of the hub. Of course....this does not always happen, as Les discovered while taking the other rotor off. That one was stubborn to say the least (now I know how those Jeepers that live in the rust belt must feel when ever they have to remove something from their Jeep). The rotor was held in place with some rust between the hub and the rotor. We tried some PB Blaster, letting it sit for a while in hopes that it would break down the rust. I grabbed a 3 pound hammer and gently tapped around the center area of the rotor. No luck. We used some more PB Blaster and got a bit more aggressive with the hammer. Still no luck. We tried tapping from the back of the rotor (I don't advise doing it this way) but still had no luck. Out came the propane torch. We went through a few cycles of heating the rotor (not the hub) and tapping with the hammer. It finally let go!

We decided it was a good idea to clean up the rusted surfaces with a die grinder. Les used a small wheel to get rid of the rust on both the rotor and the hub. He finished it off with some emery paper, making sure both of the surfaces were relatively clean from rust. Be sure to wear safety glasses or goggles when using power tools. Those little grinding stones and wire brushes will not respect your eyes!

Brake rotors can be "turned" on a machine that will clean up the existing surface. To do this, a small portion of the rotor is actually machined away. If you have extremely deep gouges in the rotor's surface, such as what occurs from running the pad's backing plate (ie., metal on metal) on the rotor, you may not be able to have such a rotor turned. Les' rotors had no such problems and from what we believed, they were just a bit warped. As can be see above, there is a minimum thickness spec stamped into the rotor and this measurement must be met once the machining is finished. If the rotor thickness does not meet the minimum specification, the rotor can not be used (and a new one must be purchased). The cost of turning the rotors was $12 and was done at the local Checker Auto store.

NOTE: Around 2001 or there about (I don't think anyone knows the exact date), Chrysler changed the dimensions of the rotor and the unit bearing. In doing so, auto parts stores sometimes don't realize that there are two different rotors (they list a single part number) or they have the part numbers listed for wrong year(s). It is also possible that your TJ got some of the last "old style" rotors but your friend, with the same year TJ as yours, has different ones (depending on when it was assembled).

So the point is that the thickness of the rotor hat, that part that slips over your wheel studs, is different between the two rotor styles. The difference is about 1/8" and can be easily detected with a ruler. Lay the rotor on a flat surface with the hat up. Put a ruler down through the large hole in the middle of the rotor and note the measurement. Take the ruler (or the rotor if you wish) with you to the auto parts store when you get your new rotors and make certain the new ones share that same measurement. If they are wrong, they will still mount on your vehicle just fine....but when you slip your tire onto the studs and tighten the lug nuts, it will bind and you will NOT be able to rotate your tire.

Since Les was replacing the pads at the same time, we needed to remove them from the caliper. The pad that snaps into the piston (of the caliper) is removed by pushing it in the directions of the yellow arrows, as seen in the above picture. You can see the metal clips that are attached to the pads backing plate. These clips hold it securely in place. Just push hard on the back of the pad and it will pop out as shown above.

Although Les was replacing his pads with Performance Friction pads which greatly improves the braking performance (I installed them on my TJ when I did my rear disc conversion), his existing pads still had sufficient material to allow for continued use. In the above picture, you can see two grooves cut into each of the two pads. These are wear indicators. When you can no longer see the grooves, your pad material is just about gone and you should replace them with new pads. I don't remember if there is a core charge on the backing plates or not so just to be safe, take your old pads with you when you go to the auto parts store, just in case.

The other pad is removed by prying the clips out of their grooves with something like a screwdriver. The pad in the pic above is just about out of the caliper. I put little yellow dots on the picture to denote the tabs that must be carefully pried out of their slots. This backing plate also has a couple of small round pins on the back of it which center the pad in place on the caliper housing.

With the pads removed, Les uses a can of brake cleaner to remove the dust and such from the caliper. Spread a couple of newspapers (or a catch container) under the area to catch all of the junk that drips off.

Since the rotor and pads have worn down over time, the piston will be sticking out of the caliper housing a bit too far. If left this way, you would not be able to put the caliper back onto the rotor once the new pads were installed. An easy way to correct this problem is with the help of a c-clamp. Place a piece of scrap metal (or thin wood) on the front of the piston (where the pad goes) and VERY carefully tighten the c-clamp to push the piston back into the caliper housing.

If you have ABS brakes, follow the information in Note 1.

If your TJ has non-ABS brakes, you can still follow the procedure in Note 1 or you can follow the old style method outlined in Note 2, the difference being you won't be opening your bleeder screw for the old method. If it has been a while since you ran some fresh brake fluid through your lines, now would be a good time to do so....following the information in Note 1 and you will be able to flush out the old fluid as you bleed the brake lines.


NOTE 1: It is extremely important to open the bleeder screw when compressing caliper pistons or wheel cylinders during brake maintenance. When a caliper piston is pushed in, brake fluid gets forced backward, up into the system. Since the caliper is the lowest point in the system, dirt and corrosion naturally accumulate there. When this grime and dirt finds its way into the HCU portion of the ABS system, it can cause valves to stick. This can lead to: a vehicle pulling one way or another; accumulators sticking open, which leads to low pedal; compensator ports plugging, which leads to dragging brakes; and of course, it can make the ABS light come on due to all of the above. When you have finished pushing the piston back into the caliper, close the bleeder screw. You will need to bleed the brake lines later on.

NOTE 2: When a caliper piston is pushed in, you will be moving brake fluid back into the brake reservoir. Depending on how much you compress each caliper, and depending on how full the reservoir actually is, you can easily overflow the reservoir. Now would be a good time to open the hood and check your reservoir. You may have to remove some of the brake fluid (I always keep an old turkey baster in the garage for these kind of jobs) so as to prevent it from running all over the place. Remember, brake fluid and paint do NOT play well together. You do NOT want to get it on your Jeep's paint.



As this point, it is time to reverse the process and put everything back together. Les retrieved his rotors from the Checker Auto store and found that there was plenty of rotor left (ie., no problem meeting the minimum thickness specification). He also picked up his Performance Friction pads from AutoZone (about $38) and so was ready to go.

One last thing....I almost forgot. Don't forget to lubricate the caliper mounting bolts with some brake lubricant (no, this is not a joke). It is a special lubricant that comes in little 1/4 ounce tubes. Sometimes they include it with the brake pads. If not, spend a dollar and pick some up. It is much thinner than the regular grease you use on your suspension components. Spread the lube along the length of the mounting bolts. This allows the caliper to easily slide back and forth on the mounting bolt (wihch it is suppose to be able to do in order to compensate for pad and rotor wear).

The mounting bolts are NOT to be torqued too tight. My factory service manual states 11 ft. lbs. (Yes...that is NOT very tight at all). If you cranked them down too far, you will strip the threads out in the mounting bracket, as others have unfortunately discovered. Also....don't replace these bolts with just any old bolt. The length is critical.....too short, they won't hold the caliper in place....too long, they will protrude through the mounting bracket and cut into the rotor.

If you followed the information in Note 1 (above), you need to bleed your brakes. It is an easy process so grab a friend and you'll be done shortly.

If you installed a new pair of Performance Friction pads, you will need to break them in. This consists of a series (about 10) of rapid braking stops from about 40 MPH down to a full stop. After the first round of ten, drive around and let the rotors cool down a bit. After 5 minutes or so of no or low braking effort, repeat the rapid stopping sequence another 10 times. During this entire process, you should notice the braking performance improves as the Performance Friction pads are broken in. After the second set of 10 stops, you are done. As I said earlier, I highly recommend these pads to anyone that is running a lifted vehicle with bigger tires. Les noticed the improvement right off. Best $40 mod you can make, in my opinion.

That is about it. With everything back together and the pads broken in, all you have to do now is enjoy those new brakes!

 

[mrblaine]

Nice write up Chris. I'd like to add a few notes to help future readers to keep them out of a bit more trouble.

First, the alignment guy who said the rotors looked warped is full of crap. Rotors do NOT warp. They may exhibit symptoms that convince you they are, but at the end of the day, they don't and can't because of the material they are made from. What does happen is they are mounted with something behind them that causes them to be worn out of true as they run through the pads but again, not warped.

Another way we see them ruined is from a bent rear axle which wobbles the rotor through the caliper as you drive. Leave it that way long enough and it will wear a high and a low side into the disc, but again, not warped.

They can also be damaged by sticking a layer of friction material to them after a hot stop and holding the rig in place with the service brake which wears down the rest of the rotor later on producing a condition known as DTV or Disc Thickness Variation, but again, not warped. Most of those conditions cause brake judder which most believe comes from a "warped" rotor and typically as long as it talks, walks, and quacks like a duck, its pretty much a duck to the impetus continue to explain that rotors don't warp is not as important for everyone so I don't do it as often as I should because it generally just doesn't matter because the rotors have a problem and folks just want it fixed.

Second thing is the bleeding. It should be done before the pistons are pushed in for new pads. The crap that settles in the caliper bore needs to be flushed out so it doesn't get trapped and cause a sticky piston issue. Always bleed and flush the system first, then disassemble, clean, and replace parts.

The application of the brake lube should not be done on the bolts themselves. The guide sleeves they go through to mount the caliper to the knuckle just gets clamped in place to the side of the knuckle. What does need to be lubed is the guide sleeve. Pop it out of the rubber dust boots, add some silicone brake lube if you can't move the sleeve easily back and forth with your fingers and then put them back in the boots. Don't forget that adding any lubricant to the threads on a bolt reduces the torque value needed to achieve the same clamping force. Clean and dry threads work best in this application for the 11 ft lbs of torque.

Last thing is to remove the outer pad first and then put the clamp on the face of the inner pad. Pistons are phenolic and any off angle force can damage the piston. Since the pad is what they are designed to push against, pushing against the pad will never hurt them. Also makes it easier to remove the inner.

 

[TheFrenchMan]

First, the alignment guy who said the rotors looked warped is full of crap. Rotors do NOT warp. They may exhibit symptoms that convince you they are, but at the end of the day, they don't and can't because of the material they are made from. What does happen is they are mounted with something behind them that causes them to be worn out of true as they run through the pads but again, not warped.

I agree with everything mrblaine said except for this statement because it is plan wrong in my opinion. Rotors can warp. Usually a "warped" rotor is not warped as mrblaine stated. It's usually something else, but saying a rotor can't warp is almost comical in my opinion. My father has worked for AutoSpecialty for the last 30+ years in the R&D department as the brake and clutch specialist.

EDIT: This is a quote from my father 5 minutes ago.

"99% of vehicles that are only stopping their own weight will probably never ever warp a rotor. It's going to be someone who towing a very heavy trailer down a hill without trailer brakes that severely overheat their brakes that then cool very quickly. With friction comes heat, with heat metal expands. Cool that metal quickly and it will warp. Unless your rotors made of Adamantium, then science doesn't apply to your situation!"


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[mrblaine]

I agree with everything mrblaine said except for this statement because it is plan wrong. Rotors can warp. Usually a "warped" rotor is not warped as mrblaine stated. It's usually something else, but saying a rotor can't warp is almost comical. My father has worked for AutoSpecialty for the last 30+ years in the R&D department as the brake and clutch specialist.

EDIT: This is a quote from my father 5 minutes ago.

"99% of vehicles that are only stopping their own weight will probably never ever warp a rotor. It's going to be someone who towing a very heavy trailer down a hill without trailer brakes that severely overheat their brakes that then cool very quickly. With friction comes heat, with heat metal expands. Cool that metal quickly and it will warp. Unless your rotors made of Adamantium, then science doesn't apply to your situation!"


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http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths

 

[TheFrenchMan]

http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths

No offense, but I think I'll trust the man that specializes on the subject for the last 30+ years. He tests complete brake systems for several of the major car manufactures. (Ford, GM, and Chrysler just to name a few). He is also the one that came up with the recall fix for GM in the late 90s when they were having ABS problems caused by CB and other radio interference that cause an ABS stop when the tires weren't locking up. If they call him for advise, I think I'll trust it also.

I'm sure the quality of the rotors play a big factor in that. A quality rotor probably won't be as susceptible to heat warping the rotor.


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[mrblaine]

No offense, but I think I'll trust the man that specializes on the subject for the last 30+ years. He tests complete brake systems for several of the major car manufactures. (Ford, GM, and Chrysler just to name a few). He is also the one that came up with the recall fix for GM in the late 90s when they were having ABS problems caused by CB and other radio interference that cause an ABS stop when the tires weren't locking up. If they call him for advise, I think I'll trust it also.

I'm sure the quality of the rotors play a big factor in that. A quality rotor probably won't be as susceptible to heat warping the rotor.


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And I'll put more credibility in your posts when you quit referring to me as comical and plan wrong. There are reasons rotors aren't made from steel. Ask your dad to tell you why that is.

 

[TheFrenchMan]

And I'll put more credibility in your posts when you quit referring to me as comical and plan wrong. There are reasons rotors aren't made from steel. Ask your dad to tell you why that is.

When did I say rotors are made from steel?
You said "rotors can't warp" which is wrong in my opinion and a professionals opinion. I'm sorry if that upsets you. You are a very knowledgeable guy and I'm sure are way smarter than me, but even you can be wrong. They can warp under right conditions but is very unlikely. Like I said before I agree with almost every you stated before, just not that fact that "rotors can't warp" because they can. I'm not trying to offend you and I apologize if that's how it comes off.

Edit: Just an explanation....When someone tells me the world is flat it's comical to me. You don't have to take me seriously, your opinion of me means nothing. This is a topic meant to help people, and if I see someone give incorrect advise in my opinion I will give my two cents. Just as you did. People can do their own research and come up with their own conclusions. I know recently there has been a big "rotors don't warp" after some guy wrote a paper on it, but that's was just to address the more common problems that people always associated with a "warped rotor". So the better title would be "its not always a warped rotor" I edited my earlier posts to try not to offend. Have a wonderful day everyone!


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[mrblaine]

When did I say rotors are made from steel?
You said "rotors can't warp" which is wrong in my opinion and a professionals opinion. I'm sorry if that upsets you. You are a very knowledgeable guy and I'm sure are way smarter than me, but even you can be wrong. They can warp under right conditions but is very unlikely. Like I said before I agree with almost every you stated before, just not that fact that "rotors can't warp" because they can. I'm not trying to offend you and I apologize if that's how it comes off.

You didn't say that rotors are made from steel, I told you to ask your dad why they aren't and once he explains that to you, your understanding of my position will be much better. I'll stand behind my rotors can't warp statement until you show up with a set off of your rig that are warped from heat. Until then....

 

[TheFrenchMan]

You didn't say that rotors are made from steel, I told you to ask your dad why they aren't and once he explains that to you, your understanding of my position will be much better. I'll stand behind my rotors can't warp statement until you show up with a set off of your rig that are warped from heat. Until then....

That's nice, I stand behind the vast majority of the of the auto industry that knows and has dealt with warped rotors when they are indeed warped. We will just have to agree to disagree.
"Kevin bacon was not in footloose!"


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[mrblaine]

That's nice, I stand behind the vast majority of the of the auto industry that knows and has dealt with warped rotors when they are indeed warped. We will just have to agree to disagree.
"Kevin bacon was not in footloose!"


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http://www.brakeandfrontend.com/warped-rotors-myth/
http://www.skimmydiscs.co.uk/blog/warped-brake-discs-myth/
http://www.mossmotors.com/SiteGraphics/Pages/brake_discs.html

I can readily change my statement to you not being able to warp a rotor but at the end of the day, the end result is exactly the same with both statements so I will continue to know them as true.

Your dad may be able to come up with a set of very specific conditions on a brake dyno where it is possible to produce a rotor that looks like a vinyl record left in the sun, but you and I won't ever be able to do the same nor will anyone else with a vehicle mounted rotor.

BTW- tell him how disappointed I am that Autospecialty rotors are so difficult to get in the US. They were the gold standard and I'd like nothing better than to be able to use them in all of my brake products provided they are still produced onshore. Just an awesome product with near zero defect and return rates at a fair price.

 

[TheFrenchMan]

I can readily change my statement to you not being able to warp a rotor but at the end of the day, the end result is exactly the same with both statements so I will continue to know them as true.

Your dad may be able to come up with a set of very specific conditions on a brake dyno where it is possible to produce a rotor that looks like a vinyl record left in the sun, but you and I won't ever be able to do the same nor will anyone else with a vehicle mounted rotor.

BTW- tell him how disappointed I am that Autospecialty rotors are so difficult to get in the US. They were the gold standard and I'd like nothing better than to be able to use them in all of my brake products provided they are still produced onshore. Just an awesome product with near zero defect and return rates at a fair price.

I can use Google also. All the links refer to the one paper written by one guy. He has a theory that I do actually agree with. For many years auto mechanics have been replacing "warped" rotors when they in fact are not warped. Unsuspecting customers that don't know any better it would seem perfectly logical. Rotors get hot spots and the fiction material will build up which creates high spots which will cause a pulsating pedal. That is not warped, that is a rotor with too much lateral runout.

But flat out saying rotors don't or can't warp is ridiculous and comical to me when the the very large majority know it as fact.

Either way, whether it's actually warped or just excessive fiction material building up on the rotor the public will continue to refer to it as a warped rotor. Both would have similar side effects and the cause would be the same.

How anyone couldn't believe a rotor could deviate from its axial plane just a few thousandths of an inch from excessive heat boggles my mind. It wouldn't have to be "vinyl record left in the sun" in fact you probably wouldn't be able to tell with the naked eye.


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[mrblaine]

I can use Google also. All the links refer to the one paper written by one guy. He has a theory that I do actually agree with. For many years auto mechanics have been replacing "warped" rotors when they in fact are not warped. Unsuspecting customers that don't know any better it would seem perfectly logical. Rotors get hot spots and the fiction material will build up which creates high spots which will cause a pulsating pedal. That is not warped, that is a rotor with too much lateral runout.

But flat out saying rotors don't or can't warp is ridiculous and comical to me when the the very large majority know it as fact.

Either way, whether it's actually warped or just excessive fiction material building up on the rotor the public will continue to refer to it as a warped rotor. Both would have similar side effects and the cause would be the same.

How anyone couldn't believe a rotor could deviate from its axial plane just a few thousandths of an inch from excessive heat boggles my mind. It wouldn't have to be "vinyl record left in the sun" in fact you probably wouldn't be able to tell with the naked eye.


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Ask your dad to explain Disk Thickness Variation to you and why it isn't a build up of friction material.

Then ask him what cementite is and why we care. If you're going to use your pop as a resource, the you should use all of his knowledge and quit bastardizing it with yours.

 

[mrblaine]

Early on when I was developing the brake kits, my partner wanted to try a more cost effective solution. I agreed to try them as a test and to only use them if they passed. My test vehicle lives up in the mountains and made daily commutes to the bottom of the hill, or if you are familiar with the area, Big Bear to the IE. He was an enthusiastic driver and had 35's on his rig and agreed to be a guinea pig for us and work them hard and he did.

After a couple of weeks, we pulled him in for an inspection but not because there were any symptoms of judder because he had none. What we did find was fairly astounding and hammered home just how thermally stable cast iron in certain alloys really is. He had overheated the rotors so much and so often that there were a series of blue spots around the rotors separated by shiny stripes that started from the rotor hat and moved outward in a radial pattern.

It took a few minutes to understand what we were seeing but we found that the blue spots were the spaces between the rotor vanes and the shiny stripes were on top of each vane. What had happened was the area between each vane had gotten hot enough to either move inward a small amount or the area on top of the vane had hardened to the point that it was a high spot.

We put them on lathe and measured run-out and could not find any discernible amount higher than our indicator went which was less than 1/10th of a thou.

Each blue spot also had a crack running roughly through the middle of it also in a radial pattern. The evidence of excessive heat was all over the place at every aspect of that set of rotors with the single exception being excess run out. They had been abused mercilessly and still ran true or true enough to not cause judder.

For the record, this was a cheap set of import rotors and that test finally convinced my partner as to why one should use quality parts even if it costs more.

 

[TheFrenchMan]

Ask your dad to explain Disk Thickness Variation to you and why it isn't a build up of friction material.

Then ask him what cementite is and why we care. If you're going to use your pop as a resource, the you should use all of his knowledge and quit bastardizing it with yours.

"Jack of all trades, master of none."
My 66 year old father who has been specializing in the subject for the last 34 years, just read all your posts and this was his response. I'm done trying to explain commen sense things to a person. Ask any brake mechanic if rotors warp and you will get your answer. Happy jeeping


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[mrblaine]

"Jack of all trades, master of none."
My 66 year old father who has been specializing in the subject for the last 34 years, just read all your posts and this was his response. I'm done trying to explain commen sense things to a person. Ask any brake mechanic if rotors warp and you will get your answer. Happy jeeping


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I had immense amounts of respect for his knowledge until that last comment. Most brake mechanics I know are just parts replacers. They wouldn't know the difference between DTV and excess run-out if you beat them over the head with a sample of each.

Here are some of my experiences with brake mechanics and every one is true.

We have to turn all rotors out of the box because they ship to us warped. I worked at the police mechanics shop and that is what they do.

Oh no, if we ever get into a situation where the front brakes are able to lock up the tires, we install an adjustable proportioning valve in the front circuit to stop them from being able to do it.

No Loctite on the caliper bracket bolts so the caliper falls off at speed, not once, but multiples of times with many different shops that do installations.

I don't need to read the instructions, I'm a brake expert and you sent me the wrong rotors.

Repeatedly I've had them tell me that rotors warp in the box and have to be trued up.

You need to put 10 psi residual pressure valves on rear drum brakes to keep the shoes out in contact with the drums.

Over and over they build custom systems and use front brake calipers on the back and wonder why their bias is FUBAR.

If it is alright with you and your pop, I'll not be using them as a resource and until you bring me a rotor you warped on your rig, we'll just have to disagree.