Uneven brake feel

[Eskozki]

Hello,

the symptoms are similar to a warped rotor, but the rotors are new and not warped. When applying brake only slightly I can feel that the pads bite more on certain spots of the rotation of the rotor. When I did the brakes, I did notice the notch on the piston, but on the haynes manual it didn't tell the orientation for the notches on the pistons. In what orientation should the notch be? When I brake hard the brakes feel good and there is no pulling to any direction. Other than that I dont see I did anything wrong when doing the brakes.

[924RACR]

So... what makes you think they're not warped, the fact that they're new? Or have you put a dial indicator on 'em and spun 'em?

I just went through this on my wife's WRX, with a pair of new Bosch rotors from Rock Auto. They were out 1-2 thou. After checking a million things, I finally put the dial indicator on them, then grabbed another pair from O'Reilly's down the corner, problem solved.

It's hit or miss, I have two pairs of rear Bosch rotors on that and other cars without issue, but damn I was pissed when I isolated that.

[944 Ecology]

As Vaughan states above, new doesn't mean good.

Also, the face of the hub that the rotor is mounted on needs to be absolutely clean. A 1 mm bit of rust can translate to a 3 mm wobble in the rotor surface (where it meets the pads).

[walfreyydo]

Your first mistake is using a Haynes manual and not the factory service manual (which is freely available to download)

The Haynes manual does not discern very well the differences between all the models, especially when it comes to the different components like brakes, M030, 8v vs 16v... or the correct orientation of the notches...

Vibration when braking is usually warped rotors but could also possibly be caused by other issues, wheel bearings for instance.

[Eskozki]

I think they're not warped because they're new. Manufacturing a rotor that is even on a flat plane shouldn't be a challenge with modern tools and equipment, but maybe there is the issue with using to little material, so that you dont have any room for error and can't machine them to be flat again. At work we had an issue with some centrifuge drums that should all be identical, but due to using too little material they had been machined to different dimensions. Only a slight difference, but enough to make it so that some parts fit only a specific drum.

Thanks for the info, I'll check with a dial indicator at some point if they're warped.

[walfreyydo]

Check your wheel bearings as well, make sure the caliper bolts are tight.

Wheels/tires balanced? (this should create a shake all the time not just under braking)

[Monkey Wrench]

It's possible to ave runout because of bit of metal on the lathe that they were originally turned on or dirt during mounting, or possibly the metal normalized since they were turned.

check with a dial indicator. you can also measure the thickness at various spots. give the wheels a shake, if you find any free play or can' remember it ever being done, maybe repack the bearings, inspect them, readjust.

be extremely fussy about cleanliness, get any teeny tiny bit of dirt in the bearings and that will destroy them. I'd replace the races as well, if you need to replace bearings.

there is no such thing as an OEM bearing, automakers dont make bearings anyway, so I'd look for recognizable brand and avoid "made in china" ones if you can.

If the tub or tube of wheel bearing grease was left open around the shop, I'd be very careful of it possibly already being contaminated.

[924RACR]

Originally Posted by Eskozki

I think they're not warped because they're new. Manufacturing a rotor that is even on a flat plane shouldn't be a challenge with modern tools and equipment, but maybe there is the issue with using to little material, so that you dont have any room for error and can't machine them to be flat again.

You're assuming they can't get warped on the way to you.

I'm telling you, exactly that happened to me just last month; my new (WRX) rotors had 0.001-0.002" runout, and it was a disaster. I'll keep 'em for next time, get 'em turned before use, but they're junk for right now, had to get others.

[Monkey Wrench]

I remember my dad running into that on a honda, he had taken the rotors in to be turned and got them on and they were .010" out. the guy hadnt; mounted them in the turning lathe right.

so I said are you going to take them back and complain, No he said, because they are just going to say they are too thin and I have to buy new rotors..

So he didn't take them back and complain , no, too stubborn for that.. instead he went and got a motor from a furnace or something with a pulley and wrapped a V belt around that and the studs.. then he took a disk sander and held it up there with the wheel spinning.. next thing I knew he had that licked and the brakes worked just fine.. ;-) he just had a special talent of never giving up.

I dont know if its done commonly but it made me realize it might not take too much of a jig to actually turn them right there in place. a clamping fixture to hold an angle grinder or similar maybe? i think you could also grind rubber and make tires run true as well..

[walfreyydo]

Originally Posted by 924RACR

You're assuming they can't get warped on the way to you.

I'm telling you, exactly that happened to me just last month; my new (WRX) rotors had 0.001-0.002" runout, and it was a disaster. I'll keep 'em for next time, get 'em turned before use, but they're junk for right now, had to get others.

This is true as well. Parts quality makes a huge difference. If you are going with the cheapest rotors (or any other parts) you can find on R0ckAut0... dont do that.

I would recommend quality rotors such as Sebro or Zimmerman if you havent already gone that route.

You can also take the new rotors into most auto repair shops and have them turned/checked instead of buying new ones.

[Monkey Wrench]

looks like there is quite a range at RO, I see 25 different choices. all Junk? maybe ;-)

[924RACR]

Yeah, I got Sebros from Pelican for my 931; the WRX rotors from ******** were Bosch, would've expected they'd be good... but they weren't. Never wasting my money on those again.

Others have said Raybestos (for daily drivers) is pretty good.

The ironic part? I f'in work for Bosch. But not on those brake parts... (I do controls)

[Monkey Wrench]

I was very happy to get a replacement master cylinder with the reservoir for under 20 dolllars for my Volvo recently. Yesterday on my way to work the pedal almost hit the floor. turned out that the reservoir which looked exactly like the volvo one but without the volvo name on it ,, well it cracked along a heat welded seam leaked the fluid, got air int he brake lines. I couldn't see the crack, but proved it by blowing into it with the other holes covered.

I put the old reservoir back and bled the brakes again.. its ok now.. I have a new master cylinder on the way by rush.. which I wont need, but sometimes that's just the way the cookie crumbles. ..

[Jfrahm]

look for bent wheels

[cockerpunk]

warped rotors arnt real. well they are, but they dont cause brake petal pulses. the caliper is floating, the rotor can be warped all over the place, but it wont cause back pressure in the caliper unless the rotor thickness is significantly varying around the rotor. which basically, doesnt happen until you ....

... beded your pads badly. the transfer layer is unequal around the rotor face. do you use your handbrake?

the most obvious solution is to hit the rotors with a bit of sand paper, and re-bed the pads. get a nice, thick, even, transfer layer.

https://www.motortrend.com/how-to/1808-nuts-and-bolts-warped-rotor-myth/

[walfreyydo]

Originally Posted by cockerpunk

warped rotors arnt real. well they are, but they dont cause brake petal pulses. the caliper is floating, the rotor can be warped all over the place, but it wont cause back pressure in the caliper unless the rotor thickness is significantly varying around the rotor. which basically, doesnt happen until you ....

... beded your pads badly. the transfer layer is unequal around the rotor face. do you use your handbrake?

the most obvious solution is to hit the rotors with a bit of sand paper, and re-bed the pads. get a nice, thick, even, transfer layer.

https://www.motortrend.com/how-to/1808-nuts-and-bolts-warped-rotor-myth/

Im pretty sure warped rotors are a real thing, this is why rotors get "turned" by alot/most automotive shops which is basically a lathe that removes material to bring the rotor back into spec, assuming there is still enough thickness on the rotor itself to remove some of that material. The uneveness in the rotor is what (usually) causes pulsing when applying brakes. Youll notice the pulsing tends to disappear at lower speeds and is more prevalent at higher speeds.

Not to discount the buildup of material cause as pointed to in the article, that can also be an issue. Youll also notice that the article states warped rotors are "rare". I would agree to disagree, and warped rotors are most commonly caused by improper wheel lug torque pattern (for instance tightening in a circle instead of a star pattern), or brake caliper issues (uneven brake pressure due to problem with caliper or sticking caliper). The dealership I used to work for turned rotors quite often, and I have experienced it on many/most vehicles I have owned as the rotors reach end of life, not to mention my own 944. Having the rotors turned or replaced almost always resolved the issue...

Cant say for sure this is the OP's issue though.

[924RACR]

Warped rotors absolutely are a thing, and mine were bad at 0 miles, verified by dial gauge on the upright to rotor surface.

Data doesn't lie.

[cockerpunk]

Originally Posted by walfreyydo

Im pretty sure warped rotors are a real thing, this is why rotors get "turned" by alot/most automotive shops which is basically a lathe that removes material to bring the rotor back into spec, assuming there is still enough thickness on the rotor itself to remove some of that material. The uneveness in the rotor is what (usually) causes pulsing when applying brakes. Youll notice the pulsing tends to disappear at lower speeds and is more prevalent at higher speeds.

Not to discount the buildup of material cause as pointed to in the article, that can also be an issue. Youll also notice that the article states warped rotors are "rare". I would agree to disagree, and warped rotors are most commonly caused by improper wheel lug torque pattern (for instance tightening in a circle instead of a star pattern), or brake caliper issues (uneven brake pressure due to problem with caliper or sticking caliper). The dealership I used to work for turned rotors quite often, and I have experienced it on many/most vehicles I have owned as the rotors reach end of life, not to mention my own 944. Having the rotors turned or replaced almost always resolved the issue...

Cant say for sure this is the OP's issue though.

no, turning the rotors solve the problem because they remove the old deposits and cementite metal crystals. its not that they true up the rotor, its that they give you fresh austenitic iron for the brake pads to connect with.

warped rotors, are not a thing. we've known this for 50+ years. its a floating piston system, warp will not effect brake pressure.

[cockerpunk]

Originally Posted by 924RACR

Warped rotors absolutely are a thing, and mine were bad at 0 miles, verified by dial gauge on the upright to rotor surface.

Data doesn't lie.

oh they will have runout. face runout as measured with a dial gauge doesnt mean anything.

its not whats causing a brake pulse.

its a floating caliper, it will follow the runout. thats why its a floating caliper.

[Monkey Wrench]

I'm surprised at the comment. I would think that a caliper that's trying to follow a warped rotor would cause vibration..
nicer to replace rotors or have them turned, but I've swapped pads and given the rotors a good scrub with sandpaper and gotten away with it a lot of times.

I dont know if it happens wiht toe porsche rotors but the bendix brakes in my volvo 740 use a one caliper arrangement. the slide pin did not wear out but the hole in the caliper did , it caused them to rattle when I hit a bump unless i was stepping on the brakes, then it was quiet as normal.

I got rebuilt calipers and they rebuilt them , sure, but they never re-bushed the hole so it was still the same issue.. in my case I just sent the "rebuilt" one back and found a better one that way.

I'd maybe observe how worn out that hole is and if it looks bad maybe try a different caliper or maybe it can be reamed out for a bushing to be fitted.

maybe if the rotor is warped and the calliper is vibrating due to that it could cause the slide pins to wear..

I do more city driving,, if I did more highway or high speed driving . or especially racing, Id be a lot more fussy.. no doubt it's more comfortable when all is perfect. Im generally not scared by some slight vibration, I'm used to driving junk cars.. I know what the cause is , perfect is more expensive.. it would be nice ( and more safe) to put brand new tires every year but I don't do that either, its all cost related.