I recently had a odd issue with my 05' grand prix. I was following a coworker to his house and he decided to pick the pace up a little bit. I didn't know the roads very well so I braked pretty aggressively for a blind corner and the steering wheel felt like it was going to jump out of my hands. It felt like the rotors were warped badly. The rest of the trip it did fine, and has since then. No pulsation at all, until this afternoon as I was getting off of the interstate and got on the brakes just as I hit the seam where it transitions from asphalt to concrete. It shook until I got it to a complete stop. Then no pulsation or vibration at all stopping at several red lights. I do get a slight vibration through the wheel when at highway speeds and I brake lightly so I have no doubt the rotors are a little warped. I rotated my tires about a month ago and noticed no looseness in my normal checks of the ball joints and tie-rods. So far I've came to the conclusion that it only happens when I hit the brakes semi-aggressively on a bumpy surface.
Could a tie-rod or ball joint have suddenly gone bad? Could the strut be bad? It certainly doesn't wallow or bounce but I wonder if during a hard hit with most of the weight transferred to the front the strut is letting spring bounce uncontrolled. It mostly seems to be coming from the right front. It doesn't help that the wheels I have on it are around five to eight pounds heavier than the stock wheels which are surprisingly light at around 17#'s iirc.
Also while changing the wife's oil yesterday (99' gp) I noticed a pretty good amount of oil on everything underneath. Never had a leak before so I tried to trace it up but couldn't find a definite cause. There was oil dripping off the oil pan bolts but it looked like it was dripping down higher than that. I'm thinking valve cover gaskets but it looked dry from up top. If it's the oil pan gasket could the wind cause the oil to curl up the block making it appear like it's coming down from above?
Struts on the 05 is my guess, unless you are having an ABS event that doesn't trigger a light. I can't remember if those have regular or electric PS.
The 99... I have never seen an oil pan or valve cover that doesn't leak, especially on the FWD's. Remember those era W bodies have a fire hazard recall because of the spark plug looms holding on to the oil and then dripping onto the manifold causing a fire.
In reply to Ranger50:
Well it's a comp g so that came with the magnasteer II system. I guess I'm leaning strut as well but I'm going to check everything out as soon as I have a chance.
I'm aware of the recall, as far as I know the fix dealers perform is remove the goofy looms and replace them with a more conventional loom. I've been meaning to address this since I received the letter. I was wondering if I should still let the dealer do this or would I be ok doing it myself because I don't trust dealers for squat. Generally the only time anyone works on any of my cars is if it's tranny related because I still don't understand all the black magic voodoo that goes on in there. I just don't trust anyone else to touch my cars. Would I be liable if I fix it myself and we sell the car (no plans to it is paid for and runs good) and it burns down?
I THINK you'd be OK if you gave the purchaser full disclosure that the GM dealer had not performed the recall work. It would then be up to him to follow up with an authorized dealer for the free work (I'm presuming it's free if it's a recall) or not, at his option. I would also presume that the car's VIN would show the necessary work not yet done, so any future dealer would (I know, I'm doing a lot of presuming here...) mention it in the hope of getting the job & maybe other service work.
One other question you might consider asking yourself is, what if you fix it yourself and it burns down while you still own it? Would your insurance pay up? I'm asking this one out of complete ignorance, but as it happens I have the same outstanding recall issue on an 00 Impala.
To my knowledge the reason for the fire is because of a crappy vc gasket that leaks. I believe there is an upgraded valve cover gasket that doesn't leak but G.M. found it was much quicker and less costly for them to remove the catch can of a wiring loom thus letting the oil run harmlessly down the engine instead of collecting and dripping on the hot exhaust manifold catching fire. I'm going to go ahead and replace the gaskets even though it's a huge pain, to try and fix the real issue instead of just treating the symptoms.
Good question about the insurance though I'd imagine showing that you or I didn't have the work preformed at a dealer would give them the leverage they need to wiggle out of paying.
after reading several dissertations by acknowledged leaders in the brake product world....
... it seems that what most of us refer to as rotor warp is really uneven transfer material .... i.e. pad bedding that has worn off unevenly...
this one from stoptech is one of the better ones
http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml
In reply to wbjones:
Wow that is a very good read thank you.
I have been running Satisfied ceramics and they have preformed beautifully, they had a bedding or break in coating applied to them. I followed a procedure which is very similar to the one outlined in the article. Basically three stops from 40 to 5 followed by three stops from 60 to 5 followed by not braking for several miles to let everything cool off. I did notice one thing I did wrong according to the article; I reused my old rotors and because they never showed signs of pulsing or "warping" I just scuffed them up with sand paper which according to the article is a no-no. They are getting a little long in the tooth now and I'll probably check the rotor with a mic when I get time to investigate further.
In reply to nicksta43:
The recall is free and takes all of .2 for the technician to do, so it is about 30 min out of your day to have it done.
As to the car burning down.... I have one in my yard that burned down and GM said that they had NEVER had an instance of it happening. But about 4-6mo maybe a year before the recall, my wife complained that it did indeed burn down.
Autotragics in the GM FWD line are butter easy, except the CVT and 4T40's. The dealership guys have them down for rebuild without ever removing the trans from the car. 
I'd wager something is lose/worn in the front. I had a similar experience with my '72 Capri. Someone I trusted told me the same thing. Something is loose. Go find it and fix it. Took me a while, but finally I found that one strut gland nut had worked lose. Just a little loose, not all crazy lose with the strut jumping up and down. But lose enough that it could move in the housing under just the right conditions. Once I fixed that, the front end shimmy was gone.
On the leak- if it's not valve covers and it's not the oil pan, I'd guess a seal somewhere. I'd look around all the seals and see if there's a mess by one. Look at the underside of the hood. A leaky seal by a pully will sometimes spray a mist of oil on the underside of the hood in a straight line. Helps narrow it down.
Take care,
Ed
(edit) Oh, I don't doubt that you have some brake issue, but it sounds like more than that to me. "Warped" rotors on an otherwise solid front end sure can shake things, but in my experience, it's pretty consistent. It's there or it's not. Less when slower, more when faster. Not there then gone again.
I'm not too familiar with those suspensions, but Id check for cracked and loose bushings. Its definitely something that's just slightly loose.
I ran into kinda wierd problem with my '90 240sx. The steering wheel would randomly move about a 1/6th rotation left or right under braking or some hard cornering. Turns out my lower control arm mounting points were starting to slot. Or had been for a while. The bolt that passed through the subframe and LCA bushing was 1/2 turn loose and slotted the subframe. Ive never seen another 240 do it. You'll probably find something like that.
~Alex
