automotive brake question for the experts

[sailor55330]

So, I'm towing home and when I applied the brakes, I got a wobble in the steering wheel. Felt like a really bad tire balance shake. Absolutely nothing at roadspeed without brakes. I haven't driven the truck when not towing to see if it only happens with the trailer attached. I had this once before, but accompanied with a pulsing in the peddle. That was solved by new rotors and pads, which I got 60k out of so no real complaints. My gut tells me that this is also rotor related from towing, which is highly dissapointing as I put new high performancerotors on the truck 15k miles ago that were drilled & slotted to stop this exact thing from happening when towing. Rotors are easy enough to replace, just disspappointed that if that is the cuprit it's happened so soon on "performance" rotors.

[Bfun220]

Sounds like rotors to me.

[sailor55330]

Me too Bfun. Weird thing is there were no panic stops or anything out of the ordinary other than about 10 miles of 8-10 mph driving, most of which was constant speed and very little brake application. Test driving tonight to confirm and try to duplicate tonight.

[akorcovelos]

Check for frozen slide pins on the calipers. If they are stuck or stiff they will do exactly what you’re describing, and subsequently warp the rotors and wear only one side of the pads.

[Ytmsn]

Rear discs? Coming from speed to a stop sign or turn with a load will really heat them up. Then while they're already hot, braking while pulling into the loading area and then backing down the ramp will heat them up. Then a dunk in the lake.. Maybe it caused a small warp. Maybe. Or a water hole or splash of some sort on the front hot rotors? It doesn't take much. There is a lot of heat generated,and a splash or dunk isn't good for them. Just a thought.

[sailor55330]

Yes. Rear discs. Truck tires didn’t get wet on the ramp (good ramp!) as I don’t have to back in that far and no rain over the last several days—good theory though. Test drive tonight and under normal braking nothing. Harder stops a little noticeable—repeated hard stops duplicates it. At this point pretty sure it’s rotors in the front. Only thing that has changed are new tires 3 days before the trip. I checked for a thrown wheel weight but all looks good

[cmattj]

Yep you got it. Front warped rotors shake the steering side to side. Rear pulsate the vehicle forward and back at slower speeds stopping.

Performance ( drilled/ slotted ) rotors can distort when heated just as easy . The most common is due to this fancy looking rotors are lighter.
The key is heat dissipation as related to the weight of the rotor, and it’s ability to exhaust heat quickly when turning. ( internally cast vanes differ by who makes the rotor).
A factory 12lb Toyota rotor is less prone to temperature warping than a lighter aftermarket rotor.
When and when not to machine rotors.?

Do they shudder all the time cold or hot? Those are good candidates for machining. They have memory in distortion.
Only after driving and hot?
You can’t heat up a rotor and machine it right? So if only shudders when warm , then machining them is only 60% percent effective, and short term as well.
Get Heavy OEM front rotors and matching OE pads ( material match ) and you’ll have the best combo.
PS turn up your brake controller if electric or have your surge master bled.

[sailor55330]

Thanks cjmatt . Once again you’ve gone above and beyond to explain things. Back to oem it is. So there’s about an hour gone from the weekend

[jhnmdahl]

First, skip the drilled rotors unless your car is for "show" instead of "go". Pads haven't really off-gassed since the 70s, and the holes simply create weak spots for stress cracks and remove mass that could help absorb or conduct heat. Slots aren't likely necessary either, but do less harm than drilling. Matt has a lot of good advice on this.

Second, make sure the hub surface the new rotor mates to is very clean - use a wire brush if you have to, and remove any scaling or dirt. When you install the new rotor/wheel, don't just go by feel - use a torque wrench and torque the lug bolts/nuts to the recommended torque in whatever star pattern is appropriate for your number of bolts.

Third, some things can mimic a warped rotor, like a worn out link in a multi-link suspension. I had an old car on which I messed with the brakes for ages before discovering the exact symptoms you describe were the result of a worn sway bar link and control arm bushing.

John

[sailor55330]

First, skip the drilled rotors unless your car is for "show" instead of "go". Pads haven't really off-gassed since the 70s, and the holes simply create weak spots for stress cracks and remove mass that could help absorb or conduct heat. Slots aren't likely necessary either, but do less harm than drilling. Matt has a lot of good advice on this.

Second, make sure the hub surface the new rotor mates to is very clean - use a wire brush if you have to, and remove any scaling or dirt. When you install the new rotor/wheel, don't just go by feel - use a torque wrench and torque the lug bolts/nuts to the recommended torque in whatever star pattern is appropriate for your number of bolts.

Third, some things can mimic a warped rotor, like a worn out link in a multi-link suspension. I had an old car on which I messed with the brakes for ages before discovering the exact symptoms you describe were the result of a worn sway bar link and control arm bushing.

John

Good advice. I always clean the mating surface (and the new rotor) and definitely use a torque wrench on everything I can, even the oil drain plug.

[smokymance]

Working in places like TRW and Brembo for the past 13 years i also agree with all the stuff mentioned here. Most of the aftermarket rotors as mentioned are pure junk. Drilling almost does nothing, and slots are for metal and debris pick up, which at the end of the day just equals a shorted pad life. Most of the hot judder noticed as brakes heat up are from components expanding. A poorly developed rotor will expand and cone at different rates and places compared to a properly designed and manufactured OEM rotor. This leads to disc thickness variation across the whole brake surface thus the pedal pulsations that the driver feels. Also, as noted above, a improperly working caliper ( sticky slide pin etc) will create drag on the rotor while off brake, causing uneven wear on the rotor, on that "high spot"' as discussed . This on top of any lateral run out the system has due to improperly torqued wheels, hubs etc etc, will cause uneven rotor wear, yielding to more cold and hot judder. This is just the beginning! We can talk about graphite flake counts, machining operations, pad composition etc etc! Long story short, as described by cmattj, buy OEM stuff and torque stuff right

[sailor55330]

Well new rotors and pads installed. We’ll see how it goes. The wheel wobble seems to be eliminated but I have to admit my stopping distance is now greater. Just have plan better

[sailor55330]

Well new rotors and pads installed and torqued to spec. We’ll see how it goes. The wheel wobble seems to be eliminated but I have to admit my stopping distance is now greater. Just have plan better

[liquid]

[cmattj]

Killing me buddy..
No worries as tomorrow we will discuss material composition as it relates to iron rotor friction and proper break in of brake pads.
I know ... nail biters