I have been posting various questions relating to my 1990 240 wagon's vibrating while braking problem.

I feel lots of vibration through steering wheel while braking at high speeds. My front rotors are only 2000 miles old. I replaced with Brembos several months ago.

My research led me to believe that either my pins or my rotors are stuck, leading to premature warping on the front rotors. (lug nuts are properly tightened at 85 lbs)

I am tempted to just replace the rotors and pins, bleed the brakes and hope that warping won't continue. I don't really want to replace the calipers because the brake lines can be hard to remove. On-the-other-hand I don't want to buy new rotors again in two months.

Is there a way to be certain that calipers are bad?

see www.stoptech.com
Very unlikely to have warped rotors per se....
It IS possible to have a stuck rotor and not have a hot caliper/dragging pad. I just replaced a left rear ATE caliper on an 87 760T where the outside pad was worn about 1/2 and the inside pad almost wore out, down to about 2mm. I could SEE the rotor flexing as the free piston pushed on the stuck piston/pad!!! I couldn't push the stuck piston in and it wouldn't come out with air pressure (If it was an antique/unobtainium I could blow it out with a grease gun and then clean out the grease..BTDT!).

Point is that one way to diagnose a stuck caliper is to look at brake pad wear...if one is wearing faster than the other, the other piston is generally stuck, won't go out. Of course it's possible one piston is stuck/won't go in, in which case it continues to press on the rotor and won't release...then you'll get a hot caliper.

Stuck rotor? I take it that is a typo, but if not what do you mean?

Rotors on Volvo do not float.. Mac

Leave your Brembo rotors on the hubs and pack lugs with large nuts for spacers, use lug nuts to tighten rotor to hub. have them remachined, this will true all parts to hub bearings. If wheels are tight to turn release bleeder nipples, if they free up it will be hoses constricted, if not pistons sticky. Fitting new rotors to warped hubs will not guarantee proper braking. You have gone this far and really should overhaul calipers. Not releasing properly will definately warp rotors. Regards Jack McIntyre.

"Is there a way to be certain that calipers are bad? "

IMO, it's not likely to be a caliper. But you can test by taking a 2 to 3 mile drive when the car hasn't been driven for an hour or two, then feel the calipers on each side.

If one is much warmer, jack it up, pull the wheel, and see if you can retract the pads easily with a pair of channel-lock pliers, or pry back with whatever. (No need to remove the caliper from its mount.)

Remember that each pad has an upper and lower piston, thus 4 per side.

When did this problem start, relative to the new rotors?

The Control Arm bushings (Rear—Fronts are usually OK) may cause braking vibrations, especially if they're 13 years old.
--
Bruce Young,
'93 940-NA (current)
'80 GLE V8 (Sold 5/03)
'83 Turbo 245
'76 244 (lasted only 255,000 miles)
73 142 (98K)
'71 144 (track modified--crusher bound)
New 144 from '67 to '78
Used '62 122 from '63 to '67

If the pistons in your calipers are sticking the rotor will get really hot after driving.Your car won't roll freely either,and your car will feel really slow(like driving with the brake on).
If you have vibration in the pedal when braking there may be crud on the hub behind the rotor.Did you replace the rotors yourself? If so were the pistons easy to push in when you put the new pads in?I always scrape off all the rust and use a lot of brake parts cleaner.I like to use new hardware as well,it's only $5 for both front brakes.
--
philvo '86 245 215k,'90 240 196k,'87 SAAB 900 SPG 213k

Other than vibration, why do you think calipers might be stuck? Is one wheel warmer than the other after driving? Usually a stuck caliper will pull the car to that side when driving. Front end suspension and steering component wear can cause vibrations while braking.

If you really want to see if the caliper is frozen, pull the wheel, remove the caliper from the holder and put a piece of wood in the caliper for where the rotor would be. Apply the brakes and see if the caliper grips and releases the wood. If it does, it's not frozen. I still think you've probably got suspension problems (bushing, ball joints, tie rod ends) if your only complaint is vibes under braking.

HTH,

someguyfromMaryland