Scion tC Forums banner
1 - 20 of 23 Posts

·
Registered
Joined
·
124 Posts
Discussion Starter · #1 ·
ok heres my problem


everytime i break during a bumpy road my break paddle starts to shake. i wanna kno what causes this problem and should i take it to the dealers right awy?
 

·
Registered
Joined
·
413 Posts
Yup, ABS. The ABS system in the tc is extremely sensitive (overly so IMHO) and will cause your break pedal to shimmy and you'll hear an aweful noise. My pedal even goes to the floor usually which IMHO is a huge safety risk. What if I hit some uneven patch of pavement when braking and the ABS kicks in, drops my pedal to the floor, and causes me to hit the car in front of me since I can't control my brakes?
 

·
Registered
Joined
·
4,964 Posts
Might want to get that checked, Simplespirit... Mine never goes to the floor.

Also - if you're rolling on the stock tires the ABS will kick in a lot more than if you have better tires.
 

·
Former '05er
Joined
·
12,467 Posts
Why? Mine does exactly the same thing over washboard bumps while attempting to stop. It's especially worse with stiffer suspension. Between EBFD and ABS, the brakes (correct spelling) don't know what to do so the pedal (also correct spelling) goes to the floor and you do not stop. AMHIK.

It's a design problem, not a system fault.
 

·
Registered
Joined
·
4,964 Posts
Maybe I've never gotten into that situation before. Generally the brakes hitting the floor is a bad thing.... the only time I've ever had that happen to me is when I busted a brake line in my old Ford Taurus.
 

·
Former '05er
Joined
·
12,467 Posts
You don't drive the way I do, and you are on basically stock suspension. No replacement spring comes anywhere close to Tein SS-Ps for stiffness, and the OEM dampers aren't even in the same ballpark as the Teins. I have practically slid through an intersection while attempting to brake over washboard bumps caused by pavement wrinkling in a braking zone. It's happened more than once, and made me wish for standard brakes without ABS and EBFD. The pedal does for sure go to the floor and the wheels most assuredly do not stop the car.
 

·
Registered
Joined
·
4,964 Posts
Sounds like you need a big brake kit, Lance.
 

·
Registered
Joined
·
5,192 Posts
I kind of doubt that will make it better; if anything, it would make it worse. The brakes will lock up easier with a brake kit that applies more brake torque for the same amount of pedal travel.

The solution is to improve the compliancy of the wheels to the road; as discussed in the other thread (the really good one), the solution to better compliancy is to reduce wheel rate, reduce damping to match and reduce unsprung mass.

-Ed
 

·
Registered
Joined
·
5,192 Posts
Basically you want to leave the brakes alone, but make it so that the wheels follow the contour of the road better. Lance's problem is that on washboard or cruddy roads, the tires can't maintain contact with the road due to the stiffness of his suspension (a combination of the hard springs--i.e. high wheel rate, and stiff dampening--to control the hard springs).

Reducing the weight of the wheel & tire combination (unspring weight/mass; the car itself is sprung, since it is a load on the suspension, but the wheels, tires, brakes, axles and hubs are considered unsprung) and then reducing the stiffness of the damping and springs will allow the wheels to hug rotten and run down roads. The size of your contact patch means nothing (like on his 245s) if the wheels can't even stay on the ground; on the same token, no matter hoow good or bad your brakes are, they'll do nothing either if the wheels are in mid-air, since that automatically means lock-up.

-Ed
 

·
Registered
Joined
·
6,586 Posts
Here's something I understand: my car handles very well and does not lose traction with my current setup, so I'm not going to make any further changes to the suspension.
 

·
Ironhead
Joined
·
13,253 Posts
Originally posted by EddNog@Jan 19 2006, 01:55 PM
Basically you want to leave the brakes alone, but make it so that the wheels follow the contour of the road better. Lance's problem is that on washboard or cruddy roads, the tires can't maintain contact with the road due to the stiffness of his suspension (a combination of the hard springs--i.e. high wheel rate, and stiff dampening--to control the hard springs).

Reducing the weight of the wheel & tire combination (unspring weight/mass; the car itself is sprung, since it is a load on the suspension, but the wheels, tires, brakes, axles and hubs are considered unsprung) and then reducing the stiffness of the damping and springs will allow the wheels to hug rotten and run down roads. The size of your contact patch means nothing (like on his 245s) if the wheels can't even stay on the ground; on the same token, no matter hoow good or bad your brakes are, they'll do nothing either if the wheels are in mid-air, since that automatically means lock-up.

-Ed
nicely put, ed.

so, the ABS sensors basically think the car is sliding?
 

·
Registered
Joined
·
5,192 Posts
The ABS sensors sense what they're designed to sense--that particular wheels have stopped or come close to stopped spinning while others are still moving, meanwhile the brakes are being applied, so the wheels have locked up under braking, so then the ABS instructs the car to let loose on the brakes until the wheels unlock-up, which won't happen with wheels in mid-air, which the brakes don't know about, in effect reducing the car's braking to nil.

-Ed
 
1 - 20 of 23 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top