capnmorgan

I have a '00 coupe. When I hit my brake pedal a little too hard, my front brakes lock up and won't let up until the car decides when its done sliding (Doesn't matter if its wet or dry ground). Usually about 10-20 feet. I seem to remember that in my '99 FRC the pedal would seemingly fight back when my ABS was active. This car doesn't! Any ideas why this might happen? Please help! Thank you.

bluvette79

i'd pull the codes and list them here. i guess you aren't getting an abs light either?

TEXHAWK0

Are both sides locking, or just one side?
You might check to make sure the front brake hoses have not deteriorated internally causing the brake pressure not to be released.
Sometimes the inside surface can deteriorate and a flap of rubber can block flow like a check valve, so the caliper cannot release.

capnmorgan

Thanks ya'all. I don't know about the corrosion/deterioration I'll have to have a look at that Yeah I was trying to remember if the light kicked up on me or not. I don't think it does. Surely it couldn't just be a fuse could it? Thanks again...

Bill Curlee

If its not MECHANICAL, its most likely a problem with the EBTCM. Theres a microprocessor inside the module that does all the computations and tells the BPMV what valves to open/shut and when to run the pump to apply pressure to selected wheels.

Holding pressure on a set of wheels seems like it would be a sticking poppet valve in the BPMV or wrong signals being sent to it.

If you dont have any DTCs and you dont see the MESSAGES, the EBTCM may not be working correctly. If the micropressor isnt working, dont try to send it to ABS fixer unless you call him first. I dont thing that part of the EBTCM is repairable.

The best way to troubleshoot this issue is with a TECH II.

BC

capnmorgan

Thank you Bill. That's a very in depth answer lol. I still have the car and still have the same issue, i just tru really hard not too get in situations where I'll need to lock em up! Sure appreciate your reply brother.

k24556

WOW! 12 years and no cure? Since you said the fronts lock up, do you know for sure the back brakes are not? When you brake weight transfers to the front, so the rear brakes should lock up if ABS and/or the proportioning valve is not working. That’s what happened in pre ABS cars. IF just the fronts, then you should see some ABS codes, which you can do with the DIC on the dash.

If you had a tranny or clutch job done, it is likely the rear brake lines, which route inside the torque tube tunnel were damaged by lowering the drivetrain, and no fluid pressure is getting to the back brakes b/c the lines are kinked. Another possibility is a bad front wheel bearing which will cause funky outputs from the wheel speed sensor.

Pull the ABS fuse. If the rear wheels lock up then you will know that either the ABS is funky, or there is a caliper or hydraulic problem. in the front circuit.

FormerBiker

If it is the ECBM, good luck. Mine went out on my 2k FRC and I looked for 4 years and could not find a replacement. That unit was one year only and not repairable.
There is a long thread here describing the issues with the ECBM.

Fortunately I was able to afford a C7 in 2017.

Bill Curlee

Using the built inC5 DTC reading routine, What DTCs are being displayed??? You must use the internal C5 DTC reading routine or a TECH2 or expensive aftermarket DTC reader to see most Body and Chassis DTCs. Also, read the DTCs when the problem happens (before you turn the ignition OFF). Some EBTCM DTCs reset when the ignition is cycled on to off and back on. If there are message in the DIC, press and hold RESET until all the messages go away.

Post up all the DTCs present. Especially the DTCs for the EBTCM.

Bill

punz

When my passenger front wheel kept locking up when braking hard, the issue was a frayed wheel sensor wire at the bearing. Was able to solder it and caulked it to seal it since taping it was not doable.

capnmorgan

Thank you all for your input. I thought i saw a wheel speed sensor write hanging a while back... I'll have to see if it's messed up. So a bare/cut wire could cause the abs to pull my pedal to the floor instead of pushing against my foot as it should??

I haven't checked my codes lately as I've been replacing the clutch for the last month lol... but i remember looking up my codes and didn't see anything that triggered a "oh that makes sense" code pop up.... the car has done this since i bought it in '08.

k24556

No. Pedal all the way to the floor is something else. Possibly pad knockback ( a problem sometimes seen at the track under heavy braking), air in the system, or a fluid leak.

usually when a wheel bearing goes bad and the sensor no longer sends a signal, ABS will kick in early and unexpectedly. Yes the pedal will go deeper a bit, but you will still have brakes.The brake booster can make pedals feel funky when they go bad as well.

Regardless of what goes wrong with a wheel speed sensor, you should get a DTC set if they aren't reporting wheel speed properly.

With the engine off key off, can you pump the brakes to a hard pedal, put a lot of foot pressure on the brake and get to a point where the pedal is NOT moving at all? If you can't pump up the hydraulic portion of the system, then you have a hydraulic problem. Now the next thing to do is to see if the ABS is working OK. Drive down the road, hit the brakes hard and see if you can get ABS activation. Then "feather back" on the brakes to reduce hydraulic pressure so ABS turns off, but keep enough pressure to continue braking. This is called "threshold braking" and is how we kept braking control before ABS. You had to feather brake pressure to keep the rear wheels from locking up. If this works OK and no wheel speed sensor codes, then you have ABS, and probably a little air in the ABS system . The air in the ABS can be hard to get out unless you can do an automatic bleed.

k24556

Continuing the thought of a wheel bearing going bad. The wheel speed sensor has a tone ring that rotates with the axle part of the bearing, and the sensor is fixed in the housing. When a bearing goes bad, especially in the front, the clearance between the tone ring and the sensor increases. Eventually the sensor does not pick up tone ring impulses and will give a slow wheel speed output. There may not be a code because a signal is being produced..

The front wheel bearings usually go out more than the back bearings. Also bad rear wheel bearings are harder to diagnose because of the axle shaft.

The ABS will then activate under lighter braking conditions, and your deeper pedal feel may be an artifact of the real problem. I like to remove the wheel, and the brake calipers in the front, to check for smooth proper bearings. In the back, I like to drop the upper control arms and remove the axle from the bearing before checking, so the axle does not affect bearing inspection.