car brakes...

[TMM]

well, i was driving around today in my '01 toyota tacoma, and came to a situation where i needed to brake somewhat hard [at about 50 mph]. when i did so, i experienced a quite noticeable vibration. however, earlier in the same drive i had braked hard-ish at a slow speed and i noticed nothing. i only noticed something at a higher speed, around 40-55 mph. what bothered and confused me was that the front brakes were replaced with double-caliper disks and pads about 1000 miles ago, the truck has relatively new pads and shoes, and the disks were also ground maybe 700 miles ago to fix the same issue. so, i was wondering - could it be the fact that i had a large load in the back? there was some firewood and about 4-500 pounds of rocks in the back at the time[for traction]... haven't noticed it with just the rocks in the back... because i can't think of any other reason the brakes would have issues again so soon.
thanks,
~tmm

[Paddy]

I'm no mechanic, but I'd pull the wheels and look at the drums and shoes and see what's up.  Or maybe one of the shoes has a broken spring and is hangin' loose and chatterin'.

[Brad Johnson]

Heavy load? Fast (maybe panic?) stop? Questionable traction?  I bet you were on the verge of losing traction without realizing it and were feeling the ABS system pulsing.

Brad

[TMM]

well, i'm no mechanic either, so i'm not trusting myself to remove the wheels and look at something that i'm not even really familiar with. the rear drums have these covers on them so i can't see what's up, and the front of the truck was on wet ground when i parked and i didn't feel like crawling around on cold soggy ground.

the truck doesn't have ABS. i do know what ABS sounds and feels like, though, and ABS is far more "chattery" and my vibration was a true vibration that i could feel, and it felt more "wobbly"...

~tmm

[Declaration Day]

what bothered and confused me was that the front brakes were replaced with double-caliper disks and pads about 1000 miles ago
~tmm

Do you mean double-piston calipers?

I'd check for a warped rotor.

[RoadKingLarry]

Several possibilities, fro disc brakes that get a vibration or chatter when brakes applied could have a warped brake rotor/disc. that could also be amplified by and sometimes caused by a tire that is out of balance or has a flat spot or bulge. Old and worn shocks can also exacerbate this kind of problem.
It isn't to hard to warp a rotor on some cars and light trucks if the lug nuts are over tightened or tightened out of sequence. If you are not up to checking it your self take it in and get it checked, it won't get better by itself and could lead to serious control problems.

[Hawkmoon]

Warped rotors that have been cut to remove the warp are very likely to warp again almost instantly, because when they get cut the result is a flat surface with uneven thickness. One semi-hard stop that heats them up does the rest ...

[Sergeant Bob]

Were your dogs barking? Maybe the rear wheels were losing traction?

[TMM]

yes, what i meant was double piston calipers.

the tires are not old or bulged, they've been used for as long as i've driven the truck with no issues. hasn't ever sat for a long time either.
if the disks were warped, would i notice it only during a hard brake, or all the time?
the wheels were definately not losing traction. i know that sound and feel, and it was not present.
i haven't noticed it since this one incident, but i'll keep a watch for any other vibration. if i notice some, i'll have it checked out.

~tmm

[Declaration Day]

If you have a warped rotor, you'd definitely feel it more during a hard brake, because your pads would ride against the uneven surface at a much faster / harder pace when you hit the pedal.  You might notice it while braking from slow speeds too, depending on the severity of the warp.