brakes fade at low speeds

[grn2geclipse]

i just bought a 99 eclipse rs with 69000 miles and i found that the breaks don't work very well sometimes, if i brake hard it brakes ok but then it feels like the pedal hits a wall and the cars brakeing power is cut tremendously. also on the highway the brakes shake like the rotors are warped, but i just put brembo cross-drilled rotors on it...so i don't know. i almost rear-ended a jetta because i lost alot of braking power so i'd REALLY like to fix this.
thanks for all your input.

 

[poppyseed]

your pads are shot, get new pads, for say ebc green stuff, hawk performance, akebono's new street performance pads, axxis, metal masters, satisfied, etc etc


also cut the rotors so the new pads seat correctly, and flush the brake fluid

 

[luv2rallye]

If all that is ok, check the caliper pistons for sticking (rusting in place). If not that sometimes the proportioning valve gets stuck or the brake booster isn't working (check it's hoses for leaks). A stuck proportioning valve can sometimes be freed by tapping it with a hammer while the brake pedal is pressed.

 

[smuckles]

proportioning valve gets stuck.

interesting....Hmmmmm

 

[Omega]

Did you properly torque the lug nuts? If you don't, you can cause your nice new rotors to warp.

As mentioned, I hope you put new pads on. You could also replace the rubber lines to the calipers.

 

[grn2geclipse]

alright, i flushed the brake lines and there was zero air bubbles, i checked the caliper pistons for rust, i also asked a guy at a local shop and he said it could be that my rear brakes aren't even working, i tried pulling my e-brake while brakeing hard and it seemed to make a pretty big difference in braking power, i have rear drums and i figured they just need to be adjusted, but my last car was a subaru impreza so im not sure the the adjustment is still the same. so if anybody knows how to make the rear drums work again, let me know, thanks.

 

[ddavisaf]

Your rear brakes don't help you stop very much. Majority of the braking power comes from the front brakes. How old are your brakes and what kind are they?

 

[grn2geclipse]

brembo rotors were installed maybe 8,000 or less miles ago an pads too, pads are auto parts store brand(i forget which store)

 

[goingDSMsoon]

Are you getting good vacuum to the master cylinder?

 

[grn2geclipse]

how would i check the vaccum to the master cylinder?

 

[Omega]

Get a vacuum gauge (or a spare boost) and dissconnect the line going to the booster. Start car and record reading. You can buy a tool for this too.

 

[destrux]

The rear brakes don't do much?!?

Your rear brakes are responsible for balancing the braking so you dont lock the front tires and lose control everytime you hit the brakes, plus they contribute to 20% of your braking power!

Trust me, I drove a car that had no rear brakes once... and it makes a huge difference in how strong the brakes work.

Take your rear drums off and see if they're coated with rust or brake fluid. The brake shoes should be dry also. If they have fluid on them or the drum surface is covered in rust you'll need to replace the shoes and drums. If there is fluid on them then you have bad wheel cylinders, and you'll also need to replace those. Once everything is back together, adjust the "clickers" on the rear brakes till the brakes start making the wheel hard to turn, then go push the pedal, and back the adjuster off till the brakes just barely stop dragging. I recommend adjusting the brakes with the wheels on, you get a better adjustment because the drum is tight and not flopping around loose.

Even if your brakes are working better after you do that, I'd still replace or cut those fron rotors (I only said cut, because they are new and have no wear on them, if they were worn at all, I'd say just replace them, since cut rotors are twice as likely to warp again).... and put better pads on. I've had good luck with Hawk HP+ and EBC Redstuff, they are autocross pads, but they work great on the street and I get 20,000 miles out of them. They are a bit expensive though... usually around $100 a set.

 

[destrux]

I forgot one thing...

Never, ever, ever use store brand pads. They are garbage. Even the "better" ones. They are designed for the average cheap person that will complain to the auto parts store if they dont get 60,000 miles out of a set of $25 brake pads. They also have to be whisper quiet.

 

[ddavisaf]

The rear brakes don't do much?!?

Your rear brakes are responsible for balancing the braking so you dont lock the front tires and lose control everytime you hit the brakes, plus they contribute to 20% of your braking power!

20% isn't alot compared to 100% is it?

I know with slotted rotors you cannot get them turned. I'm assuming it's the same with cross-drilled, but I'm not sure. I'm unfamiliar with the term cut.
Your vacuum to your master cylinder would be my first troubleshooting area, your pads would be my second. Most aftermarket upgraded rotors require a certain kind of pad. My rotors require premium pads. So I use Carbon/Kevlar pads on my slotted rotors.
If you're using the incorrect pads, it's understandable that you're lost some stopping power.
Also, take a peak at your calipers and make sure they're not all rusted to hell. They should look fairly clean. If they're rusted really badly they may be getting "hung up" and not applying the correct pressure to the pads/rotors.

 

[Omega]

20% isn't alot compared to 100% is it?

Exactly.

Another thing to check is the front flex lines. They can expand and ruin braking pressure. On the other side of things, they can degrade and plug up the line. I don't know how many miles you have on the car, but it couldn't hurt to replace them... SS replacements are recomended.

Your warped rotors could be from improper torquing of the lugnuts as said. It could also be that the mounting surfaces are crudded up making the rotor not spin true.

I wasn't aware that you could put the wrong pads on slotted/drilled rotors.

I do know that because you do have slotted/drilled rotors, it can cause a vibration when braking. One of many reasons I steer clear of them. It is sad that they can be cheaper than blanks