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Old 10-01-2018, 04:25 PM   #11
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Thank you all too. I appreciate any and all information so I can fix this problem so it doenst happen again.
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Old 10-01-2018, 04:38 PM   #12
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Booster,
Thank you very much for the information. I have never experianced that much shaking in my life, worse than any headbanger concert. It felt like the whole rv was going to fall apart.
I have another question: I tried metalllic pads on different car I owned and they never seemed to stop the car any better, BUT they really tore up the rotors!
Have you found out that also to be the case in your experience?
Thanks again
Dave

When we changed our pads, it was from the ceramic Chevy Pads, and we actually got slightly less better, less effort, braking. In normal driving it is noticeable, but not large, but the hotter the brakes get the larger the improvement is. Ours are Hawk Performance pads, so I can't speak for the effort or feel of other brands, but I don't recall anyone complaining about effort going up.

We have high end rotors, also, and after about 30K miles they hardly look worn oat all from the semi-metallic pads, so it appears that the good parts work well together.

The dirty wheel thing is what happens with semi-metallic pads, although the high end pads are significantly better better than the low end ones. We did a 6K mile trip this spring that included lots of mountains and curvy roads, so the brakes got a lot of work, and by the time we got home the front wheels were dirty, to be sure, but you could still see the paint color through the grunge. I am fine with that, as long as they stop so well.
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Old 10-01-2018, 04:59 PM   #13
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The mechanics not being able t duplicate the issue is really common for this problem, as you need the long, steep, brake taxing terrain to generate the problem. Sometimes it is not even the Rockies that are the worst, as we found out on the Smoky Mountain Parkway a few years ago. We got the brakes hot enough to smell when we stopped at the bottom on the west end, which had never happened anywhere else. That stretch going down to there is curvy and downhill, with straights in between, so tougher to do the downshifting thing without a lot of up and down manual shifting as you go from 45mph to 20mph over and over again. Our upgraded brakes were not at all damaged by getting that hot and were smooth and effective all the way.
I find it difficult to believe that rotors that warp from excessive heat return to such a true state that it can't be measured in the shop. I have no engineering credentials to support it, but IMO, if the rotors are true when measured cold, the juddering syndrome has less to do with detritus on the rotors and more to do with permanent hot spots on the rotors with different coefficients of expansion and contraction than expressed by the main body of the rotors.
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Old 10-01-2018, 05:09 PM   #14
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I find it difficult to believe that rotors that warp from excessive heat return to such a true state that it can't be measured in the shop. I have no engineering credentials to support it, but IMO, if the rotors are true when measured cold, the juddering syndrome has less to do with detritus on the rotors and more to do with permanent hot spots on the rotors with different coefficients of expansion and contraction than expressed by the main body of the rotors.

Go back and read my explanation of what if causing the juddering.


It is NOT because of the rotors warping, it is because of uneven brake pad transfer to the rotors. It is highly likely the rotor stay relatively true during the episodes, and the fact that they check OK once cool would back that up. The different thicknesses of brake pad transfer heat up differentially which gives varing coefficient of friction. It would extremely odd to find a rotor that had different coefficients of thermal expansion in different area, IMO.


If you don't believe what I say, call up some high performance brake manufacturers like Hawk and as them. I talked to at least a half dozen of them when researching what to do to eliminate the problem and all of them agreed. It is caused by uneven pad material transfer, top end semi-metallic pads are the best for this application and will cure the problem if bedded properly, high end (alloy) rotors will last longer.
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Old 10-01-2018, 06:32 PM   #15
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Booster is absolutely correct - brake rotors almost never warp (read Carroll Smith's books on race car prep). This is well proven in racing - the pad material welds/bonds onto the rotor and actually makes the rotor thicker. The problem is that the build-up is not uniform resulting in thickness variation which is what causes the shuddering, not warping. They may seem to feel better when they cool down but that is mostly the change in coefficient of friction as the rotors cool - and polishing the excess pad material off the rotors. Most pad material is designed to clean/polish the rotors (some have more abrasive built-in than others) and so mild braking when in cooler temperature ranges tends to polish off the built-up pad material and can eventually make nearly clean rotors.

I also agree that drilled rotors are a bad idea, as Booster said, they tend to have cracks showing up at the holes. Slotted are ok as they don't tend to crack as much but it is still a trade-off - reducing the contact area vs allowing air movement for cooling. I have the very best quality smooth non-grooved/drilled rotors I could find on mine.

Aside from engine braking, on long downgrades I try to brake fairly hard to drop speed quickly (say, from 60 to 40 or 50) and then get off the pedal and let them cool a bit, then as speed rises on a downgrade, repeat as needed. And NEVER use long and smooth braking like you might in your car..... that is the way to really cook brakes.

Dave
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Old 10-01-2018, 07:07 PM   #16
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Very well stated, Dave. I would add only on thing about the slotted rotors, and that is that the slots can help the pads keep the transfer layer clean and renewed a bit better than plain rotors. The best rotors I have ever used are what we have in the Roadtrek, which are the no longer available Quiet Slot rotors from Hawk. The have shallow, less than an inch long less than 1/8" wide assymetrical slots scattered around the rotor face so very little loss of surface area. They seem to do a really good job of keeping the rotor surfaces uniform, to the point is almost looks like gunmetal colored paint on them. I wish someone still made that style of rotor, but they don't have the foo-foo appearance that many confuse with good braking so they apparently don't sell well. The current Hawk rotors are just OEM quality that are drilled and slotted, and Hawk will tell you not to use them on a heavy duty application.
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Old 10-02-2018, 06:01 AM   #17
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I will add one more thing here in relation to having rotors that measure too much runout, usually more than about .004" total indicator reading.


From what I have seen with our own vehicles, and also plenty of the others around here in Minnesota is the brake pulsing (that happens all the time, not just when hot, so is rotor runout caused) magically shows up after a tire rotation or replacement. Most of the time, the runout is caused by rust or other debris getting caught between the rotor and hub when the wheel is taken off, as many vehicles just float the rotor and hold it in place with the wheel and lugnuts. There will normally be rust and dirt around the mounting surface of the rotor to hub or on the inside of the rotor that can fall right into the slightly open mounting area. Impact wrench tire removal really can make the debris and rust come loose if it needs to beat a few times on tight or rusty lugnuts. This will normally not happen if you have rotors that have a couple of small flat head screws holding them tight, but of course most of those screws have been thrown out or broken off after a few years.



Lots and lots of people have spent a lot of money getting rotors turned to fix a problem that didn't need to be fixed with turning, IMO. The problem went away, of course, but primarily because the mechanic cleaned the surfaces when he put the rotors back in.
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Old 11-18-2018, 05:28 AM   #18
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Very well stated, Dave. I would add only on thing about the slotted rotors, and that is that the slots can help the pads keep the transfer layer clean and renewed a bit better than plain rotors. The best rotors I have ever used are what we have in the Roadtrek, which are the no longer available Quiet Slot rotors from Hawk. The have shallow, less than an inch long less than 1/8" wide assymetrical slots scattered around the rotor face so very little loss of surface area. They seem to do a really good job of keeping the rotor surfaces uniform, to the point is almost looks like gunmetal colored paint on them. I wish someone still made that style of rotor, but they don't have the foo-foo appearance that many confuse with good braking so they apparently don't sell well. The current Hawk rotors are just OEM quality that are drilled and slotted, and Hawk will tell you not to use them on a heavy duty application.
From the post titled "Chevy brake update" from 2014:
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Front rotors HUS8659

Front pads HB322Y.717 The Y is the compound code for the LTS pads

Rear pads HB494Y.670 The Y is the compound code for the LTS pads
We've been having brake issues for a while now and I've just gotten around to resolving them. After a lot of research on this site and the Yahoo group I decided to try to duplicate booster's setup. The first post in this thread was very informative, I could easily have chosen the wrong rear rotor if I had not read it.

I was able to order the HUS8659 rotors for $50 ea from eBay seller drivetrainoverstock, they weren't available anywhere else at a reasonable price and they are not on Hawk's website. The seller has 8 more available so if someone wants them they should grab them (or you could wait for me to be the guinea pig to make sure they are genuine).

Pads were still available thru Amazon at a reasonable price. Also the 177-0928 ACDelco brand rear rotors were available from Amazon directly for less than $40 each. These are the correct ones for our 60S semi-floating rear axle and are ACDelco's top-tier offering, supposed to be exactly what came on the van from the factory.

Similar to what booster found in 2014 I could not find a Quiet Slot or similar type for the semi-floating axle but did find one for the 70S full floating axle (Raybestos 56828PER). There is a full slot version for the semi but they were off brand and about $150 each, hopefully I'll have the same good results booster did with the Hawk pads and OEM rotors on the rear.

I expect to get the parts in in a week or two, then it's finding the time to install them...
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Old 01-10-2019, 11:41 PM   #19
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A member here, Dicktill, had a recent problem when he checked the rear brake pads on his 2009/2010 Chevy Roadtrek 190. The inside pad on each side of the rear was severely worn with the outside pads looking good. The rear rotors, which were drilled and slotted, each had a crack, from a hole, on the outside of the rotor braking surface.

After checking all the sliders, piston movement, etc that would normally cause such an issue, nothing bad was found. At that point is was complete mystery as to why the uneven pad wear.

Longer story shorter, it was discovered that the rear rotors were not the correct ones for his van which has the standard, non locking, semi-floating version. The rotors were for the same van with a full floating rear axle.

The different rotors are nearly indistinguishable from each other unless you measure a couple of places, the diameter of the center hole, and the overall height when laying flat. The full floating version of the rotor appears to put the braking surface further inboard in relation to the wheel mounting surface, so the sliders don't have enough travel to center up and use both pads.

Here are the dimensions for the two styles
Semi-floater axle-center pilot of axle hub only comes through the rotor a small amount-will be non locker and not used on the towing package. Tag would carry a 60s model number
Center hole at 4.63" diameter
Height at 86mm (3.38")

Full floater axle-center of axle hub protrudes through the rotor at least an inch and 6 bolts in the hub protrusion-locker and used in towing package. Tag will carry a 70s model number
Center hole at 4.84" diameter
Height at 91mm (3.58")

As can be seen from the numbers, you can't put a semi-floater rotor on a full floater axle because it won't go over the hub.

You can put a full floater rotor on a semi-floater axle and it will go right on, but with a small amount of clearance to the hub diameter. You won't notice anything amiss, most likely, because the wheel studs will center up the rotor. The pads appear to have gone in OK too with the wrong rotor on the semi-floater.

Most of the rotor listings, like at Rock Auto, will mention either the center hole diameter or the height in the listing, but not mention that the axle is what determines which to get. You need to either remove a rotor and measure it or identify the axle type by the hub protrusion so you get the correct rotors.

In the case of this example, the brakes had been upgraded with a kit that included rotors and pads for all four corners of the van. The kit apparently had the wrong rotors for this van, and also apparently didn't give any indication of any other option. A visual at install very likely wouldn't show the very minor difference between what was coming off and the new ones.

The good is that it is likely no serious damage is done except to the pads and rotors, and the worn inside pad appears to be a sure fire way to tell if there is an issue.

We hope this is an isolated occurrence and isn't happening to anyone else, and I have never heard of anyone who had inside pad only wear, at least that I remember. It is, however, something to keep in mind when you buy rotors, as I could also imagine mixed stock could be an issue.


Booster thanks for this info as I am in the process of replacing rotors + pads on my 2003 chevy 190 popular, 8 bolts on the hubs that protrudes a couple inches from the wheel.

I have 2 questions for you and all who have info on this subject and hope it will help others getting their rigs safer;

1- Where did you get your dimensions data for the rotors ? There is not much to find on ACdelco.com besides the part numbers that I looked up using my VIN. So I got my pn from acdelco and then the specs from rockauto.com and cannot verify their source.

2- Can you explain to me what is the difference between center hole vs center bore diameter ? The reason I ask is because acdelco (OE) rotor pn 1771039 and acdelco (PRO) rotor pn 18a1206 are both supposed to fit my rig but, according to rockauto specs they have identical center hole dia. (118.04mm-118.11mm) but have different center BORE dia. (113.0mm and 118.1mm).
Strangely it looks like the same delta you talked about between semi and full floater axles.
Thanks again all for your insight.
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Old 01-11-2019, 12:42 AM   #20
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Booster thanks for this info as I am in the process of replacing rotors + pads on my 2003 chevy 190 popular, 8 bolts on the hubs that protrudes a couple inches from the wheel.

I have 2 questions for you and all who have info on this subject and hope it will help others getting their rigs safer;

1- Where did you get your dimensions data for the rotors ? There is not much to find on ACdelco.com besides the part numbers that I looked up using my VIN. So I got my pn from acdelco and then the specs from rockauto.com and cannot verify their source.

2- Can you explain to me what is the difference between center hole vs center bore diameter ? The reason I ask is because acdelco (OE) rotor pn 1771039 and acdelco (PRO) rotor pn 18a1206 are both supposed to fit my rig but, according to rockauto specs they have identical center hole dia. (118.04mm-118.11mm) but have different center BORE dia. (113.0mm and 118.1mm).
Strangely it looks like the same delta you talked about between semi and full floater axles.
Thanks again all for your insight.

Actually, I don't think either of the those rotors are right for your van, assuming you have the hub sticking through the wheel like you mention. That hub would indicate that it is a full floating Dana 70s axle. You could confirm by checking to see if you have a factory transmission cooler in front of the radiator, which would indicate that you have the trailer towing package which is the cooler plus the Dana 70s. Does you axle still have the tag on the rear of the driver side axle tube, just inside the spring perch? It would say 60s or 70s for the model number. I don't even see the 1771039 listed on Rock Auto for a 2003 unless I missed it.



If you do have the 70s, you would want a center hole/bore (don't know why they would have different measurements on them unless one said "maximum" center hole diameter which would just add manufacturing tolerance). Some of the rotors on Rock Auto do have that callout. The full floating 70s would take the a rotor with a 122.7mm or 4.84" center hole. The 118mm should be for the 60s semi floater. The 70s will have the height at 91mm plus or minus a little, while the 60s would be at 86mm. I got these dimensions from comparing a lot of sources as there was a lot of variation, and likely bad application data. Some even listed some rotors for both axles and they had the height half way in between the two stock specs. The Rock Auto spec area that you get from clicking on the part number after searching by vehicle looks to be just cut and paste from AC Delco. Unfortunately, they don't have the specs on all the different rotors.



Aside from the above dimensions, when you look at the specs for the rotors, they will sometimes say they are for the 10.5" ring gear axle, and that would be the 70s which it sounds like you have. Rock Auto does have some called out that way.


Just noticed the pic. That is a full floating axle, so should be a Dana 70s.


That is one rough looking rotor. Maybe the color of the pic vs my screen is off, but it looks like it has been very hot. Be sure to check the caliper sliders and pistons to make sure nothing is stuck, as there looks to be a lot of rust around that area.
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