Weird shuddering...

[sluggo42]

Around town and at lower speeds the car is very normal, but when I;m going 70-80 down this long hill on the freeway, when I hit the brakes to slow down, the car goes into a heavy shuddering and shaking that is kinda scary. I took it to a brake guy and he told me everything looks OK, but I don't think so. Could it possibly be the front suspension? It's a stock 91 with TEMS.
I still think it's the brakes.
What are some good rotors and brakes? Does anyone think buying used brakes is a stupid concept?
I'm kinda ignorant on what this car should have as far as brakes and suspension. I'm not a racer, and I'm stock, so I don't think I need racing parts.
Also lastly, and forgive the length of this post, but I'm wondering.. does a 3" catback on an auto tranny do enough to actually "feel it" in the seat of the pants?

Thanks for your thoughts guys...

 

[crimson88]

i just finished the brakes course at my automotive school. shuddering when braking means your rotors have a thickness variation. if you just feel it in the steering wheel, it probly the fronts. if its the whole car like you said, it most like the backs or all 4. ask your brake guy to measure the runout on the rotors. if its more than .0003 inch, tell him to machine them.
hope this helps..

 

[1992supraman]

Tires out of balance? Mine did the same sort of thing when I would brake from 80+ until I bought new wheels and tires. Just another thing to check.

 

[Cz.]

Does your car have ABS? It may be the ABS system kicking in, what condition are your tires in?

Also a 3" system will make a difference, don't know if you'll "feel" the difference through an auto since I've never drove one.

 

[ms07s]

Might also want to check your drive shaft for play. When my center bearing took a crap it would shudder on decel. 3 inch exhaust is nice, but it really wakes up with the addition of a downpipe and high flow cat.:naughty:

 

[radiod]

I would tend to lean towards a brake pulsation myself as well. There are lots of times that you won't notice a brake pulsation until you get up to highway/freeway speeds. Does the shuddering feel like it's coming from the front (through the steering wheel) or from the back (through your seat)? If you can differenciate those two at all, then you know where to look. Like crimson said, it doesn't take much thickness variation at all to make a noticeable difference in the braking. Typical replacement under GM warranty (I work at a dealership) is around 0.003" and you can DEFINITELY feel it at that point.

 

[hvyman]

either brake pulsation or steering rack bushings. i lean towards the bushings. if its pulsation you will feel it when ever your on the brakes light or hard.

 

[cuel]

Brakes. Either get the rotors machined(runs about $10 each), or buy new ones(around $20 each). I'd buy new ones, myself. The Wagner thermo-quiet pads from O'riellys and Advanced are a decent pad for a good price. You need new pads when you machine rotors, or change to new ones.