98 Dodge Ram, brake mystery

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Old 08-11-15, 07:03 PM
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98 Dodge Ram, brake mystery

First of all, thanks to those who take the time to read and a bigger thanks to those who offer help.

98 Dodge Ram 1500.
4 wheel drive.
Auto Trans.
Approx 170,000 miles.

Brake line rusted through and leaked inside the frame near the gas tank. I didn't have time to fix it right away, so I crimped the line and drove it the rest of the week, sporadically, not every day. When the brake line failed, the red brake light on the dash as well as the antilock brake light came on.

I replaced the lines all the way back to the wheel cylinders, including the "splitter?" with the rubber hose. Bled the brakes, and all was fine. Brakes worked great, good "pedal", no issues. The brake and antilock lights did stay on for awhile, and I was told that the lights would have to be reset by someone with the proper equipment.

After about maybe a couple hundred miles of town driving, using the brakes a fair amount, the antilock light went out, but the red brake light stayed on. At about this time, the brakes developed a throbbing, when the brakes were applied. I initially thought maybe a rotor was warped, so I raised up the front end and spun the wheels by hand while my wife gently applied the brakes. They seemed to grab the rotor smoothly, no uneven grabbing. ( Not sure if that's a good test or not, but thought I'd try it).

So, questions:

Is there something that could have been triggered in the antilock system that is making the brakes throb? My wife thinks that the issue had something to do with the brake line replacement- I feel that since the brakes were good once I changed the lines and bled them, that it must be something else. I am going to bleed the brakes again in case some air got into the lines, but I've had brakes with air in the lines and they didn't throb at all, the pedal was just mushy.

Any suggestions as to what to check, and how to check it? Is there some way to "reset" the antilock system if that is the issue?

Again, thanks in advance for any help!
 
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Old 08-11-15, 07:28 PM
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You have ABS sensors on each of the front wheels and stuck into the differential that talk to your ABS module. It is located under the hood at the firewall on the driver's side sitting on top of other computer stuff. Unplug the module and give it time to reboot. It may turn the brake light off. If this module goes south it all has to be redone as it is VIN specific. Let us know about how the reboot works.
 
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Old 08-11-15, 07:57 PM
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There is a sensor going into the differential? I'll have to look at that tomorrow. I don't remember seeing any when I was working on the brakes....

I tried unhooking the module. Unplugged it, let it sit for about 30 seconds. Pushed the brake pedal in for about 15 seconds. Put the plug back on and took it for a ride. Didn't change anything at all.

If there was a broken wire, or bad abs sensor, would the anti-lock light stay on?

Thanks much for the advice!
 
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Old 08-12-15, 01:43 AM
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Yes, if the sensor in the differential has gook on it, it cannot read revolutions of the axle. It is located at the top of the differential on the input side, held in with a small clamp and nut. You'll see the wire from it.
 
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Old 08-12-15, 03:26 AM
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there can be several reasons for the brake light to be on like low fluid level in the master cylinder, combination valve piston not centered or emergency brake applied if that's the only light that's on it probably one of those and likely to be a combination/proportioning valve not centered due to you having had a leak it likely moved to prevent you from losing all your brake fluid so fast and is now not centered some have a button you can push on while bleeding to keep it centered sometimes you just have to create a leak on the opposite side or the front brakes in this case to re center the piston then bleed the system like normal.
would start by figuring out why the light is on and getting that fixed and then see if you continue to have any throbbing of the brake pedal and also if you hear any other noises to indicate its from the antilock brakes or just a rotor or drum issue.
 
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