Needing to pick the collective brain about the braking system on our babies...

[AL_Jazz]

As you guys know, I purchased my current XLR after it had rear-ended someone. Having now driven it for a couple weeks, I think I know why/how they did so. I enjoy driving, and am known to drive aggressively...so shoot me. Here is my issue...twice when I have been hard accelerating through traffic and then moved in to a right turn lane to make a turn and applied the brakes for a rapid deceleration, the brake pedal feels good for about 1/2 sec and then drops a couple inches and I can feel the anti-locks pulsating, but I am no where near a skid situation. To make it worse I have severely decreased braking during that time. This occurs until I reduce some speed or another 1/2 to full sec passes and then I can resume braking hard. If this occurred to the previous own in an emergency stop situation, I can see how they ran under the rear of another vehicle. The first time it bothered me, but I chalked it up to peculiarity. This morning when it did it a second time, it makes me think something is not exactly right. Has anyone else experienced this behavior and might possibly know the cause? BTW, no lights and no codes.

 

[graytoad]

Sorry, I have never had this situation you describe.

 

[David_B]

Did you touch the braking system during your repair?

Could be air in the ABS system, think it requires a Tech II to get it out.

 

[xlrlist01]

As you guys know, I purchased my current XLR after it had rear-ended someone. Having now driven it for a couple weeks, I think I know why/how they did so. I enjoy driving, and am known to drive aggressively...so shoot me. Here is my issue...twice when I have been hard accelerating through traffic and then moved in to a right turn lane to make a turn and applied the brakes for a rapid deceleration, the brake pedal feels good for about 1/2 sec and then drops a couple inches and I can feel the anti-locks pulsating, but I am no where near a skid situation. To make it worse I have severely decreased braking during that time. This occurs until I reduce some speed or another 1/2 to full sec passes and then I can resume braking hard. If this occurred to the previous own in an emergency stop situation, I can see how they ran under the rear of another vehicle. The first time it bothered me, but I chalked it up to peculiarity. This morning when it did it a second time, it makes me think something is not exactly right. Has anyone else experienced this behavior and might possibly know the cause? BTW, no lights and no codes.

If the ABS is activated, then one or more wheels have (or are about to) locked up. That suggests that the braking effort is sufficient to lock the wheel. Have a look at tire condition and brand?
Can you get a brake test carried out? Static brake tests have some value. Some pedal drop with ABS active is normal. Two inches is a lot though, far too much.
With engine running, XLR not moving (ie park), what happens when you put a lot of pressure on the brake pedal? It should move a distance and then not drop further. If it continues to drop, there is a leak.
In the past I have encountered what I suspect were incorrect brake pads fitted to a car. I suspect that they were racing pads, and these were very, very poor in their performance in road use. Oddly they worked well braking very hard, but if they were braked hard then gently then hard again (in a single stop situation) the second hard braking resulted in little increase over the light braking situation. Fitting pads designed for road use corrected the performance. (Some racing pad types are optimized for maximum braking effort, but have to be bedded in correctly to work properly.)

 

[Stella]

I would start by looking at the condition of all four brakes and rotors. Hopefully no leaks or stuck calipers,etc. then I would probably bleed the old fluid out replacing with new. I believe you do need to hook up to a tech 2 for certain instances.

 

[AL_Jazz]

Thanks for all the info guys. We did not touch the brake system during the rebuild as all the damage was above the bumper. I do need to replace the front tires, but they are not bad enough to cause a lock-up and skid. I am still looking at various tires and trying to decide what new shoes I want for her. When the wheels are off, I will look at the brakes and may do a pad and rotor upgrade while I am in there. If I do the upgrade, I will definitely flush the fluid. Suggestions on rotors and pads?

 

[Stella]

I did a thread under brake upgrade with pictures. I replaced mine with dba5000 two piece rotors in the front,stoptech drilled and slotted in the rear with ceramics all around. Braking is great,looks awesome, and all for under 400 bucks. They are very quick with shipping too.

 

[AL_Jazz]

I did a thread under brake upgrade with pictures. I replaced mine with dba5000 two piece rotors in the front,stoptech drilled and slotted in the rear with ceramics all around. Braking is great,looks awesome, and all for under 400 bucks. They are very quick with shipping too.

Those do look good. I am still hoping to get new wheels, and if I do, I will definitely be keen on cleaning up the looks on the brake rotors and calipers. Right now my expendable income is going into rebuilding a Lexus SC430 for the girlfriend. She wants a hardtop convertible now...