Q45 high speed brake vibration

[jgregory43]

I have replaced both front rotors and brake pads and left idle bar, and still have vibration when braking at higher speeds.
I see that it could be a broken belt in tire, but I think that would still wobble or have a vibration no matter speed, and I hear it could be shocks in front, and anthr says it's out of line or not balanced. I am looking for solid potential ideas of what it could be.

thanks

[hannibal]

rotate wheels. see if the problem moves.

[szh]

Try a good balance on your tires too at a reputable place - using a force-balance system like the Hunter GSP9700.

If the problem goes away and comes back fairly soon (like within a few hundred miles ... certainly well less than 1k or 2k miles), I would agree that broken tire internals (belt, rubber, etc.) are a possible culprit - they shift around as the tire rotates and quickly unbalance the tire again.

BTW, what is the brand of tire? Are you using a brand/model with sufficient load capacity (at least 94 or higher - preferably closer to 98 or 100) and speed rating (at least H or better)? And keeping the tire pressure at around 36 psi or so (plus or minus no more than 1 or 2 psi)?

Z

[AZ89two4Tsx]

Make sure your control arms and ball joints are in good shape. Seeing as you've replaced stuff near there, I'm assuming they are.

My guess is tire(s) as well.

[szh]

Make sure your control arms and ball joints are in good shape. Seeing as you've replaced stuff near there, I'm assuming they are.

Good point! The upper links on a first-gen Q45 require replacement every 25k miles or so ... if they are in bad shape, then the car will not handle well at all.

Z

[jgregory43]

Thanks for all the good possible solutions, when I find the culprit, I will pass it along for your information to put in your back pocket.

[szh]

Thanks for all the good possible solutions, when I find the culprit, I will pass it along for your information to put in your back pocket.

Good!

What year is your Q45?

Z

[Jesda]

What kind of rotors? Cheap ones are not balanced.

[jgregory43]

well after tire rotation and balance, the problem still present. The car is a 2003 Q45 and actually not a vibration, more of a pulsation, not noticable at higher speeds, but slower speeds you can feel a pulsing sensation like brakes pulse.
Could this actually be a ABS issue?

[sstroudwku]

Did you clean the Hub surface before installing the new rotors? Even a slight bit of rust can off center the rotor and cause a pulsation. I would have the rotors turned using an on car lathe, something like a procut warthog or similar that has a compensating head.

[jgregory43]

yes and they were brand new rotors and pads. Hubs appeared clean. Vibration/pulsation only happens when braking

[sstroudwku]

yes and they were brand new rotors and pads. Hubs appeared clean. Vibration/pulsation only happens when braking

new does not mean within runout spec. I don't have enough fingers and toes to count how many new rotors I've machined for this exact complaint. Not saying this is 100% the fix, just saying it's typically the cause of higher speed brake pulsations. Get a dial indicator out and measure the runout.

[jgregory43]

point taken, but problem was present before replacing rotors and pads, this is why I replaced rotors and pads, as it felt more like a pulsation rather than a vibration, but noticed more pulsation at slower speed.

[sstroudwku]

Ok, now we're getting somewhere. Have you noticed any noises from the ABS module?

[jgregory43]

nothing

[sstroudwku]

Very curious now, wish you were near I'd love to look at this. I crave interesting cars. I was given two cars last week that hadn't run in over a year and had them both running by the end of the week. I love challenges.

[jgregory43]

was a chudder I think thats what they called it. My buddy is a mechanic and he is stumped as well.

[AZhitman]

Simple stuff to check as well - loose caliper bolts?

Did anyone check runout on the actual hub? (caliper off)

Also, have you disconnected the ABS sensors individually?

Beyond that, I'd be looking at the ABS internals.

[Jesda]

I had a very similar issue on my Cadillac Seville. Entirely different car, yes, but it turned out to be badly worn wheel bearings.

Check the runout on the hubs.

[alms24sebring]

Rear rotors warp too. Did you do brakes all around?