2003 XC70: pulsing brakes...

[carboncow]

I did my brakes last fall which included turning the rotors (within spec) and new ceramic pads in the front. This spring I also did the rear brakes with new rotors, organic pads and new e-brake system.

About a month after that rear brake job I started to get a mild pulse in what I believe is the front brakes when applying the brake...first noticed when coming off highway exit ramps and now more pronounced around town. In the case of the highway exits the rear brakes will most likely not even been called into play at first...so I'm about 93% sure the concern is with the front brakes.

It starts with a pulse felt at the pedal and then becomes pronounced at the steering wheel as more pressure is applied.

I had a similar issue with an old Vw that required me to annual turn the rotors and replace the pads...and it was explained to me due to my 40K miles of highway driving that the organic pads leave deposits from the excessive heat of exit ramp stops...but that doesn't apply now that I'm driving my XC70 on freeway especial with ceramics.

Is this is symptom of caliper issues? The pads are to new to see uneven ware associated with calipers not sliding correctly and thus creating uneven wear.

What are you theories to consider?

[chrism]

I had this same issue on my V70. I couldn't decide if it was front or rear. I checked all the rotors and the run-out was within tolerance. But of course I was checking them when cold vs hot and i know that they can sometimes warp when they're warm and then return to nearly straight when cool. I was telling my local Volvo independent mechanic about the pulsing. He said if you fell the pulsing in the steering wheel, it's the front. If you feel it in the seat of your pants, it's the rear. He was right, in my case it was the rear and a new pair of rotors fixed the problem. In your case, if you feel it in the steering wheel, the problem is likely the fronts.

I have found in recent years that machining the old rotors often doesn't work out well. The cost of new rotors is generally not a whole lot more than machining the old, which makes a strong case for purchasing new.

[oragex]

not quite sure either about turning the rotors...

do the rotors look thoroughly clean?

also, the wheel lugs must be equally torqued or the brake disc can warp.

[carboncow]

There does look like a little bit of buildup on the rotors. I'm going to pull them this week and give them a sanding/cleaning and put them back on...as well as inspect the sliders and pad wear.

I'm not against a crappy turning getting out of hand over time and being the cause...now that you guys say this it makes me think maybe my NAPA needs to look at the lathe! That is where all my cars have been done over the last 5 years and had constant issues like this only for the last 5 years and I've been doing DIY breaks for 24 years.

I'm not a fan of the "warp" theory as it takes a tremendous amount of heat to truly (in my opinion) warp a rotor. I read a guys post years ago who raced Porsches and he went into the science of why you most likely are not warping your rotors with street driving...and I tend to agree with what he wrote, but I could be wrong!

I'm going to check the run out as much as I can and see if my crappy NAPA could be to blame. I'll most likely be getting new rotors!

[scot850]

Our 2006 XC70 when purchased from Volvo dealer used, had the front rotors replaced 5000km before we bought it. Straight out the box the front rotors pulsed. Took back to the dealer and they machined the front rotors and fitted ne OE pads. They warped again within 10000km and have been replaced with new OE rotors. Occasionally get slight pulsing on light breaking.

Fitted new Zimmerman rotors all around on our 1998 V70XC, and got pulsing almost immediately. The supplier would not replace, so had them turned and 5 years later they are still ok.

Sometimes it is just bad luck!

Neil.

[chrism]

"...Fitted new Zimmerman rotors all around on our 1998 V70XC, and got pulsing almost immediately...."

I'm not a real aggressive braker, but I've had just as much, if not not better, luck with the cheap Advance Auto store brand rotors as I've had with the pricey "designer" brands.

[carboncow]

I agree and since I dive 30-40K via highway I can get 2-3 years out of my front brakes. For daily driving I've noticed no difference between rotor brands.

[regent]

I support what oragex mentioned: lug torqueing is critical, especially on new or newly machined rotors. Cleanliness makes a lot of difference, too: a small burr or just a bit of deposits on the new rotor's mating surface to the hub flange will surely spoil the job.

With the ceramic pads, did you do bedding-in?

I would like to check the axial run-out at the hub and with the rotor on to rule out possible warpage in the hub assembly. Since, in your case, the pulsation appears to be growing, it looks like the famous uneven rotor thickness...

[carboncow]

What is the "famous uneven rotor thickness..." and what would cause it.

I doubt the issue is cleanliness or a "burr" as they were fine for the first 5-6+ months...unless somehow that could intensify the wear. Regardless I wirewheel the hub always before installation.

I'm pretty conistant on most lug installation using a torque wrench as I rotate my tires almost monthly due to the amount of travel.

I also think my bed technique is as good as any. if you look up the specs for most aftermarket manufacturers they tell you light driving for the first 500 miles but that's imposible for most who highway drive even once they do an embed. The first few times you come off an entrance ramp (even modulating) the temps can get high...thus why I always heard organics could leave deposits due to high heat.

Again if I can find time this week I'll pull the discs to see what I can tell.

[regent]

Uneven (non-uniform) thickness or thickness variation: http://www.stoptech.com/technical-suppo ... ther-myths