New disc brake squealing
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Depends on the source/mfgr but some pads come with either a thin coating or a thin shim of plastic? attached to the back of the pad to act as an insulator between the steel pad base and the piston in the caliper. One other thought here is that those rotors, given what you say is their source, might not be absolutely flat. To determine how flat they are takes nothing more technical than a straight edge laid across the contact surfaces. The other thing is that if they are solid rotors and not drilled in any way then debris can build up on the brake surfaces from the pad shedding dust and that might produce some noise.
As for checking the centering of the caliper on the rotor, that can be accomplished with the use of a flat feeler gauge tool. Just open the tool up and fan the feeler leaves, then create a stack of them and insert the stack between the rotor and the pad until it only barely goes or not at all and then move to the other side and check that using the same thickness of feeler gauge leaves. Any major differentiation between the thicknesses shows up and you need to shim the caliper using thin washers to move it back or forth, depending.
Nick
As for checking the centering of the caliper on the rotor, that can be accomplished with the use of a flat feeler gauge tool. Just open the tool up and fan the feeler leaves, then create a stack of them and insert the stack between the rotor and the pad until it only barely goes or not at all and then move to the other side and check that using the same thickness of feeler gauge leaves. Any major differentiation between the thicknesses shows up and you need to shim the caliper using thin washers to move it back or forth, depending.
Nick
A couple of thoughts commended themselves to my attention after I logged off last night.
One is, are those rear rotors physically attached to the axle flanges or are they just hung in place on the studs and more or less captured by the caliper fitting over them? Some kits include rotors that are drilled for flat head mounting screws that secure them to the axle flange; others don't because the axle flange itself isn't drilled and tapped for that purpose.
Two is, what type of rear end are you using, the factory 10 bolt or a 9" Ford or ??
Thing with the GM OEM rear ends is that the axles are held in place by a horseshoe shaped keeper that slips into a groove cut in the inboard end of the shaft. You get to them by dropping the cover and having a pan handy to catch all the rear end lube that will come drooling out when you remove the bolts. Why I am mentioning them is that they wear. Worn keepers will allow the axle to walk in and out to a greater degree than would be the case if they were new. Not all that much unless they have been seriously abused but even a small amount of axle to and fro can act to move the rotor. As you point out, once the caliper captures the rotor that stops the movement and makes things go quiet; until your foot comes off the brake pedal and the noise returns.
I am Not saying this is your issue by any means but you can test for it by gently grabbing the axle flange and pulling or pushing on it. There should be some movement as that is necessary to have when you go to try and extract the keepers. For that entire exercise, I would suggest a service manual or a serious amount of video how to viewing showing multiple versions of how the job is done. Excess back and forth is subjective to the tester and I am not personally sure that there is a hard value for how much travel is too much.
Nick
One is, are those rear rotors physically attached to the axle flanges or are they just hung in place on the studs and more or less captured by the caliper fitting over them? Some kits include rotors that are drilled for flat head mounting screws that secure them to the axle flange; others don't because the axle flange itself isn't drilled and tapped for that purpose.
Two is, what type of rear end are you using, the factory 10 bolt or a 9" Ford or ??
Thing with the GM OEM rear ends is that the axles are held in place by a horseshoe shaped keeper that slips into a groove cut in the inboard end of the shaft. You get to them by dropping the cover and having a pan handy to catch all the rear end lube that will come drooling out when you remove the bolts. Why I am mentioning them is that they wear. Worn keepers will allow the axle to walk in and out to a greater degree than would be the case if they were new. Not all that much unless they have been seriously abused but even a small amount of axle to and fro can act to move the rotor. As you point out, once the caliper captures the rotor that stops the movement and makes things go quiet; until your foot comes off the brake pedal and the noise returns.
I am Not saying this is your issue by any means but you can test for it by gently grabbing the axle flange and pulling or pushing on it. There should be some movement as that is necessary to have when you go to try and extract the keepers. For that entire exercise, I would suggest a service manual or a serious amount of video how to viewing showing multiple versions of how the job is done. Excess back and forth is subjective to the tester and I am not personally sure that there is a hard value for how much travel is too much.
Nick
Thanks for the help Nick.
1. The rotors are attached to the axle flanges like standard rotors. The calipers are hung by brackets that come in the kit. The axles need to be pulled to mount the brackets.
2. It is the factory GM 7.5. Everything is a fresh rebuild including a yukon posi unit.
Unfortunately I got side tracked by other loose ends today and wasnt able to take a look at the brakes. But i did go for a decent spin and the brakes made little to no noise at all. Then at the end of the ride they made some noise when braking. So i am hoping to have a chance tomorrow to take a look at the pads and see how they are wearing in, i know i have a lot of dust on the wheels. They still work great.
Nick, in order for me to accurately check caliper centering. Wouldnt I needed to have done this when pads were new? And also pistons fully retracted? I believe from memory when I push one in it forces the opposite side out
Not necessarily. If the pads have worn evenly, which you can determine by measurement of the thickness of the pad material on each pad, then measuring for equal spacing between the pad and the rotor should work as described. It would help for sure to have both the pistons retracted evenly to the same depth (or height if you wish) but trying to bottom them both as far as possible will probably produce the results you have just described so probably just get them to the same height for each side in their respective bores and go from there..
As a total alternative you could always just keep driving them as is and see if the squeech disappears due to wear and bedding in. From what you have noted, your sound seems to be starting to disappear, could maybe just have been a case of a hard pad on a hard rotor. Pads and rotors are supposed to be compatible in terms of what pad material is used with what type of rotor metal so who knows if that was the case for your kit?
Nick
As a total alternative you could always just keep driving them as is and see if the squeech disappears due to wear and bedding in. From what you have noted, your sound seems to be starting to disappear, could maybe just have been a case of a hard pad on a hard rotor. Pads and rotors are supposed to be compatible in terms of what pad material is used with what type of rotor metal so who knows if that was the case for your kit?
Nick
On the front set, are they D52 or D50 pads? The pins need cleaned and slightly greased before install. On the D52 or D50 pad you need to bend the two ears slightly before install and on the pad next to the caliper piston you add the anti-squeak. You also have to clean the rails the caliper slides on and the hardware and needs to be slightly greased. Use wheel bearing or specialized high temp 500*F grease.
Did you true the rotors or rebuild the calipers?
When ever you get high dusting that is a caliper not returning properly and the caliper is dragging the pads when not applied. Usually the pads drag because your hardware kit is old, dirty, rusty or not greased. The other reason is the caliper piston is getting stuck in the bore because of rust or dirt left in the bore prior to the new pads.
Who made the rear kit? You mention cheap pads and that could be it also. I worked on these cars when they were new. We always used Raybestos Semi Metallic, high quality rotors and always turned them, even if new out of the box. We never had any comebacks.
Cheap pads will dust out, wear fast and or uneven, plus poor braking when wet or prolonged or hard braking like in an emergency setting.
Plus some times you do every thing right and still squeaks. I used to do the sheriff vehicles, and just on one black and white... Everything was 110%... Yet that thing squeaked every time...
Most annoying thing didn't matter what you did and Squeak... Squeak... Squeak !!! And I was chief mechanic, did all the brakes, over 20 vehicles, complete set tires, shocks and new brakes every year. I was so glad when that one was traded off. Never could get it to stop squeaking.
If you are getting high dusting... it is dragging pads or very poor quality pads.
If you are getting rust on the outside of the wheels... it is dragging pads causing premature wear of the rotor or it is a poor quality rotor.
Did you true the rotors or rebuild the calipers?
When ever you get high dusting that is a caliper not returning properly and the caliper is dragging the pads when not applied. Usually the pads drag because your hardware kit is old, dirty, rusty or not greased. The other reason is the caliper piston is getting stuck in the bore because of rust or dirt left in the bore prior to the new pads.
Who made the rear kit? You mention cheap pads and that could be it also. I worked on these cars when they were new. We always used Raybestos Semi Metallic, high quality rotors and always turned them, even if new out of the box. We never had any comebacks.
Cheap pads will dust out, wear fast and or uneven, plus poor braking when wet or prolonged or hard braking like in an emergency setting.
Plus some times you do every thing right and still squeaks. I used to do the sheriff vehicles, and just on one black and white... Everything was 110%... Yet that thing squeaked every time...
Most annoying thing didn't matter what you did and Squeak... Squeak... Squeak !!! And I was chief mechanic, did all the brakes, over 20 vehicles, complete set tires, shocks and new brakes every year. I was so glad when that one was traded off. Never could get it to stop squeaking.
If you are getting high dusting... it is dragging pads or very poor quality pads.
If you are getting rust on the outside of the wheels... it is dragging pads causing premature wear of the rotor or it is a poor quality rotor.
I believe I have Raysbestos pads on the front. They have a thin isolator (?) on the backing plate. The rears do not have this. Not sure of the manufacturer. Cheap kit. Covid times and supply chain issues.
I can wipe the brake dust off with a finger. Noise is almost gone but still creeps up under certain conditions, not sure what exactly. I guess one down and dirty way would be to clean brake dust and see if comes back. I will try to pop a wheel tonight and see what’s going on in there
The thin isolator pad can stay on. On the ones that are bear I just spray them down. The old stuff was blue, smelled like fish oil, but seemed to work ok.
Sounds like maybe just got cheap pads.
Sounds like maybe just got cheap pads.
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