As I'm leaving for work this morning, hit the brakes and pedal nearly bottoms out- at the same time, the brake and ABS lights illuminate on the dash. If I pump the pedal twice, third time pedal is back to correct travel and normal braking.

No leaking brake fluid. Reservoir is full, pulled the rear drums and all looks fine, decent pad left and no leaks.

No code(s) thrown- i have no clue where to go from here with troubleshooting, including the ABS. I've read that a bad speed sensor could account for the lights, but no code? And how could that affect actual braking?

Heeelllppp....

 

Couple of possibilities. Disassemble and check your front calipers to ensure that they slide freely when the brakes are applied. The other item could be that your master cylinder seals are starting to go bad and may need replacing.

 

The warning lights were probably triggered by the "combination valve" which is a proportioning/metering valve with a differential pressure switch that get activated when the front and rear line pressures differ significantly. Normally that would indicate a leak or air in the lines but it could also be the master cylinder as AtomicDog wrote.

 

What you describe sounds like you blew the hard brake line next to the gas tank(they rust out to the point of bursting). Are both sections of the reservoir full? If this happened it will drain the rear but the front will be full.
Did you press the brake pedal to see if the shoes move?

 

I didn't check for movement, yes- both cylinders are full and no leaks evident.
The fluid reservoir was low several months ago (again, no leaks- looked like just typical as you'd get with pad wear over time and neglecting to check the level). I filled it up and had no issues since, so I didn't think it was low enough to let air in the system. If air did get in the lines, wouldn't this have manifested before now?

Could it be the ABS module? I'd think there would be a code (?).

Should I bleed the system even though its been fine for months since I noticed the low reservoir? Fluid is dark and probably due for a flush/refill...

Replace the master cylinder?

If this were your truck, which direction would you go? Thanks to all for the reponses.

 

What is your truck's year, make and model (4x4 or non-4x4) and how long do you plan to keep the truck? Is the truck in decent condition with little rusting issues on the frame? The newest 2nd gen Dodge truck is about 23 years old now. Personally, when I work on these trucks, I tend to approach them with the mindset of a restoration if its a truck I plan to keep. The hard brake lines should be replaced at some point on these trucks, as they tend to rust and leak with age. You can either purchase a 25' roll of steel brake line along with a double flaring tool and flare/bend and replace the lines yourself or purchase a set of pre-bent steel or stainless steel brake lines (Inline Tube, Fine Lines, Classic Tube, etc.) and install them yourself. I'd also purchase a new master cylinder and install it, as these are common to fail over time. I also used DOT4 fluid, as it has a higher boiling point than DOT3 fluid.

 

That's a text book example of a failing master cylinder. It may not do it again for a bit then surprise you when it does. The earlier fill of the master cylinder is to replace fluid that is compensating for worn pads. Eventually your mater will fail completely. A few times you'll be able to pump it up, but the mater is going out.

 

If the brake and abs lights are on it set a code. You can't read the code unless you have a scanner that reads abs codes. You can ground out one of the pins on the obd2 port and count the flashing light to get codes. This procedure should be in the service manual. Try hitting the brake like the time it failed and see if it happens again. Hold pressure on the pedal and see if it creeps down. If it does you need a mc.

 

Thanks for the replies, sorry for the delay posting back- moving this past weekend.
Truck is a 2000, 2500 extended cab, 8' bed with the 5.9 gasser. Florida truck from the factory- and I bought it here back in 2004. It's been a solid hauler for me, zero rust of any significance other than some surface inside the bed since I pulled out the bedliner but haven't had the time to do the Raptor Liner. Nearly 300k, still runs great but obviously burns a couple quarts a month- so not bad. I plan on running it till the proverbial wheels fall off since 8' beds are impossible to come by and I'm the guy that owns a truck because he uses it like a truck. Brake lines all appear to be in good condition despite the age (I had to lift the bed to replace the fuel tank sender a couple of years ago and all looked fine).

Would Advance or AZ have the scanner to read the ABS codes? Or should I replace the master cylinder. Booster and master were replaced just a few years ago. Booster is good, if I pump the pedal three times to get it up and firm (did I really say that) then start the engine it drops as I understand it should. I can keep pressure on it when "up" indefinitely and pedal doesn't drop. If I let off and idle forward a few seconds, gotta pump it a couple of times again.

Replace the master cylinder?

 

Advance where I live will read ABS codes...... I think that varies by location.