Write-Up: Replacing rear rotors and pads. (lots of pics)

98riv wrote:

I broke this bolt on the drivers side.

.

Right now I have zip ties holding it in place. I tried to drill the old bolt out and I also tried to use an easy out, but neither worked. Should I just drill a slightly larger hole and try to tap it or is the zip ties good enough. I know the correct answer is to retap the hole, but if the zip ties don't pose a threat then it would be an easier fix.

Is the hole you drilled for tapping that bolt back out on center?

You don't want to drill it out but so far, the member is aluminum and needs all its metal. I had a similar problem on my car.

What I did: spray a penetrating oil on - not PB Blaster but rather Deep Creep and give it a day or so to work, then back out the old bolt stub.

You might also consider Penetro 90.

If this would not have worked then most likely I would have tapped threads into the stub and used a stainless bolt and the strap to hold the cable down. Eventually that stub would loosen but it really isn't going to go anywhere in the meantime between when I tap threads in it to hold a shackle and when I can get around (next brake job?!?) to removing it. And I don't have to keep checking a zip tie to see that something didn't pop it off.

Alternatively for the time being do you think you might use a stainless band clamp (such as for radiator hose or CV boot) to strap it down? Not sure, really.

great (+) write-up.

I replaced the rear rotors on Mel's riv with US made Wagners. There was a vibration/judder while braking and the wear pattern showed the pads were applying pressure only to about 1/2" on both rotors ! The pads were still in great shape though. The previous owner had replaced them at some point as the caliper bolts were coated with copper anti-seize. All the bolts were in amazing condition. The discs were GM OEM and very warped. The caliper bolts got wirebrushed to get rid of the antiseize, which was replaced with red loctite. The other bolt got brake lubricant on the centre and loctite on the threads.

I've only driven on the new discs about 15 mi, but it seems the wear pattern is the same as before, only about 1/2" getting worn. Judging by the photo and my green riviera, it seems the first 1/3 of the rotor doesn't see any contact, but the rest should be wearing to the outer edge, which definitely isn't the case here. What could be causing that ? The calipers and pads seemed to be in great condition.

Jason wrote:

great (+) write-up.

I replaced the rear rotors on Mel's riv with US made Wagners. There was a vibration/judder while braking and the wear pattern showed the pads were applying pressure only to about 1/2" on both rotors ! The pads were still in great shape though. The previous owner had replaced them at some point as the caliper bolts were coated with copper anti-seize. All the bolts were in amazing condition. The discs were GM OEM and very warped. The caliper bolts got wirebrushed to get rid of the antiseize, which was replaced with red loctite. The other bolt got brake lubricant on the centre and loctite on the threads.

I've only driven on the new discs about 15 mi, but it seems the wear pattern is the same as before, only about 1/2" getting worn. Judging by the photo and my green riviera, it seems the first 1/3 of the rotor doesn't see any contact, but the rest should be wearing to the outer edge, which definitely isn't the case here. What could be causing that ? The calipers and pads seemed to be in great condition.

I am thinking you might have a bent caliper bracket, you might want to get a digital caliper and check that the brake caliper is sitting square over the rotor. Might be able to correct it by filing the points where it botls onto the backing plate so the angle's right. Think about this carefully, of course, before you do it.

The thing I usually see is someone had tried to prise apart the caliper without using a tool that screws in the puck, or using a mallet to get the caliper off when the pads are holding it in place. Prising without screwing in puck gives you uneven inner vs outer pad wear. Removing caliper with assist from a mallet will bend the bracket, it's a relatively mild casting so that it is quieter than any common casting.

Albertj

Did you replace your pads as well or just your rotors?

I did NOT change the pads. They had about 80% material left and did not seem abnormally worn, almost the width of my little finger's nail. I figured the pads wear to the correct "shape" after a while. I really haven't braked all that much with them in 15 miles.

Albert is right about someone likely deforming the calipers during an attempted install, although it would take a lot of force to do it. I once bent a 9" C-clamp on mine before I know about rotating the piston. No damage in my case, but I wouldn't put it past someone to damage a caliper this way.

What you are describing, if I understand correct, is a 1/2" ring of contact (wear) around the rotor disc. Is this toward the inside or outside of the disc? Seems to me this is the result of someone replacing the pads previously - using the bent the brackets. This probably caused the outside edge of the pad to wear faster than the inside, resulting in tapered pad wear, or a flat spot on the pad. Usually when the calipers flex during braking, the pads wear at an angle, but in your case the caliper or bracket is already bent, so it could explain the 1/2" contact area caused by the flat spot on the pad.

New calipers or brackets are needed. They shouldn't be that much $.

correct, there's only a 1/2" ring of contact. It's in the centre of the pad.

I would think a more likely cause would be that the rusty old rotors affected the condition of the pads. Maybe not so badly that it is obvious but enough to only contact the rotor in the center. I would buy some new pads and install them.

The wear is in the center of the pad - that doesn't sound like a bent caliper or bracket. I agree with bigdave. Try replacing the pads, or keep them on and see what happens over time. If you want to speed up the bedding process, try applying p-brake at highway speeds.

I'll give it a few days to settle, then change the pads if necessary. Thanks.

AA wrote:

The wear is in the center of the pad - that doesn't sound like a bent caliper or bracket. I agree with bigdave. Try replacing the pads, or keep them on and see what happens over time. If you want to speed up the bedding process, try applying p-brake at highway speeds.

Agreed, although it'd help to see a picture. I admit that without a picture I was kinda talking thru my hat.

Albertj

Driver's side

Pax


On my riv it goes almost to the edge. The passenger side is worse.

My re-informed guess is the following limited list.

1) different makes of pad have different contact area, you would profit from taking off the wheel to see if the contact area you have matches the contact face of the pads you installed.

2) if the caliper pucks were ever pushed in without simultaneously twisting, you need to be aware that doing so tends to make them bind. The binding limits the movement of the pucks in the calipers when the brakes are subsequently applied.

3) If you installed the pads on used rotors without burnishing the rotors on a lathe to make sure they were flat -- then you naturally get wear where the high spot on rotor hits the high spot on pad.

I think the fix is one of the following:

1) if you have a small bubble level (the little disc ones, they are a dollar or so at a harware store or home center) you can sand the pad faces flat - use the level to verify the levelness of a table then sand each pad flat and true. In practice how this works is you sand a little using a figure-8 motion then check the level of the pad. You are done when there's no glaze on pad face, pad face is level, pad pairs are about equal thickness (check with caliper) and pad is level as measured with the little bubble level. Clean them by vacuuming the dust off then wiping with a clean rag wetted with dry gas (use the cheap stuff it's just denatured alcohol, do not use HEET which IIRC has additives) or brake cleaner. At the same time you must also service the rotors. Use a caliper to measure rotor thickness; if the rotors are thick enough to turn then please do so. If not then please replace.

2) replace rotors and pads with new, and consider getting high-spec rotors - the AIMCO or Bendix higher grade (premium) ones or the Delco ones should work -- this is not an exhaustive list -- rockauto.com does a decent job of telling you what's economy vs. daily driver vs. premium. The lowest you want is "daily driver." You prefer "installation ready" they are likely flatter (by a micron or two).

hope this helps, let us know what you decide to do...

Thanks. The rotors are new Monroe/Wagner premiums, made in the USA. I didn't realize they had outsourced to China, so I returned the ones I had and had the parts store find old North American made stock. They currently have less than 100 km. I changed the rotors but decided to re-use the pads because they were nice semi-metallics with a lot of life left. I was hoping they would "level" quickly. The driver's side pattern has thickened noticeably since installation, but not the pax side.

Mel is taking the car on a weekend trip which will put approx 500 km on it and I'll drive it to work next week. If the wear pattern hasn't adjusted by next weekend, I'll change the pads out for new ones (which I have in the garage) and reassess.

I don't know how the previous owner compressed the piston when he did the brakes. Is there any way to address binding short of getting new calipers ?

Jason wrote:

Thanks. The rotors are new Monroe/Wagner premiums, made in the USA. I didn't realize they had outsourced to China, so I returned the ones I had and had the parts store find old North American made stock. They currently have less than 100 km. I changed the rotors but decided to re-use the pads because they were nice semi-metallics with a lot of life left. I was hoping they would "level" quickly. The driver's side pattern has thickened noticeably since installation, but not the pax side.

Mel is taking the car on a weekend trip which will put approx 500 km on it and I'll drive it to work next week. If the wear pattern hasn't adjusted by next weekend, I'll change the pads out for new ones (which I have in the garage) and reassess.

I don't know how the previous owner compressed the piston when he did the brakes. Is there any way to address binding short of getting new calipers ?

since your rotors are new they might be able to be trued, if you know a shop seriously consider having that done

and now you see for yourself why re-using pads has issues

chinese quality is improving but we need to employ more americans (that is broadly writ canadians, u.s. citizens and mexicans) or else we all will be loooking in the windows of store after store loaded with "cheap" merchandise we can't afford and the store owners will be wondering why sales suck

the OE pads used to be semimets but are now Raybestos ceramic IIRC, used to be sold as "CarQuest Blue" as well. Not that expensive is you shop around and buy right, try rockauto.com for price reference price won't be much different locally

If it were mine, I would take the car up to speed and stab the brakes hard a few times to see if there are issues with the rears locking up. If not, I'd do a couple p-brake engagements from 60+ mph and see how the car decelerates (I don't recommended your lady do this). If okay, and the pads do in fact have life left in them, I don't see the harm of keeping everything the way it is and letting things work themselves out. Eventually either the pads or the rotor surface will wear together until there is full contact. Keep in mind wear may not be perfectly consistent between both sides of the car over time, but rear pads and rotors do tend to last a long, long time.

Other than checking for wear and rotating the rear pads once in a while, I find the rear brakes to be a very low maintenance item on our cars, and have seen no problems reusing parts when replacing the others.

the harm of leaving things as they are is probably not *huge* but is avoidable for the effort of trueing the rotors and replacing the pads. I've done both, and for my style of driving the extra 1-2 years I get out of a set of true rears with good rotors is worth it. As they are now they will wear down but won't wear *right* and you'll be back under there sooner rather than later.

The other nice thing about using good rotors to begin with is they may well be true-able when it's time for new pads - if trued on a good lathe you'll get that much more use out of them, not like getting a set of rotors for free but you can imagine it is like that if you want.

Jason, in your first post re: this issue, you said both sides were showing the wear issue, but in the photos above it seems one side has already started to work itself out. Would you agree?

yes, I agree. The driver's side contact patch has increased since the installation.

After a few high speed stops, the other side should follow suit. The rears really don't do a whole lot until you are braking hard from freeway speeds, so they take longer to show wear.

AA wrote:

After a few high speed stops, the other side should follow suit. The rears really don't do a whole lot until you are braking hard from freeway speeds, so they take longer to show wear.

last comment on this unless I'm directly asked.

The contact patches will increase over time to include the pad face area.

The rotors will assume a topology that instead of being flat as measured normal to the rotor surface will be a function of the initial uneven height minus a degree of pad and rotor wear during break in. Life of the installation will be shorter as a result. Shorter by how much depends on initial conditions and brake use. I really can not say whether the difference will be enough to care about, nor whether the difference is enough to give a pull.

update: both side rear pads have taken a normal wear pattern on their own, in about 500 km of driving.

Working on the Riv, new rear rotors....one of the rear caliper boots is ripped.

Ordered a rebuild kit...looks like a new rubber grommet thingy, and metal ring...

How in the heck do I replace the rubber boot on the rear caliper? Anyone ever had to do that???

Figured I'd ask BEFORE i try to tear into it.

Gracias amigos!!!


Moderator...I searched!!!

If you're talking about the accordion-like boots on each side that let the caliper move, they aren't bad. The one side just has one boot that'll pop off and a button on the other end that you shouldn't have to touch. The other one goes all the way through so it has a boot like the single one that you take off first, then pull the metal sleeve out (may be kinda tough depending on the condition of the grease or lack thereof), and then you can collapse the boot into itsself and push/pull it through the caliper end. Getting the new boots on is easier because you will have cleaned the sleeves really well and used some new brake service grease. getting the new boots on may be slightly tricky, especially if you're trying to keep your hands clean by using gloves. The easier way is to basically just press (compressing) the boot evenly into its seat and hopefully it'll kinda pop itsself around the lip. The two-piece boot on the one side of the caliper will have two lips to seat on, the caliper and the sleeve. Take care of seating the boot to the caliper first. The pin is easy. Play with it. They won't tear on you.

I know this is windy and won't make any sense unless you're looking at the caliper but I recently did it so it's still pretty fresh in mind. If you have issues, pics with arrows are awesome!

yeah, it's the part which goes around the actual piston itself, not the two longer rubber sleeves on the back side. It's accordion shaped too though.

Does it just pull out too, and the new one pops in place? I'm just concerned about the metal ring which comes with the repair kit...

BTW, been working the car since Thursday, took oil pan off yesterday...was lying on my side....SORE as hell now! I'm getting too old for this sh*t!