1996 Dodge Ram brake problems (long)

A brief rundown: Truck is a 1996 Dodge Ram 2500 Diesel 4x4 with 4 wheel ABS; 230k miles.

Blew a brake line 2 years ago, replaced it, no problems. Some of the other lines looked crusty at this point.

Sent the truck to the body shop to have a complete respray, at that time they installed new fenders because the originals were rusty. In order to do this they had to unbolt the front wheel ABS pump from the fenderwell and did God knows what with it.

I get the truck back from the shop and my dad said the brakes sucked. So I investigate, and indeed they do. A line that ran from the proportioning valve to the front ABS pump (truck has separate front and rear ABS pumps) was rusted, allowing a pinhole leak.

The next weekend, I replaced that line and the three rusty lines that run from the ABS modules down to the frame rail. I also replaced the master cylinder. Front calipers are 2-3 years old. Rear wheel cylinders are 6 months old. All hard and soft lines on the truck are less than 3 years old.

Bleed the brakes out, and they are okay. Drive the truck around for a day, hit the brakes HARD. ABS kicks in and the pedal drops to the floor. Ever since then, no matter what we try, we can not get a good brake pedal back. Pedal slowly sinks to the floor with moderate pressure, and does not build adequate pressure until very late in its throw.

If you unplug the ABS module, the truck will lock the wheels up but the pedal is on the floor when they lock up. If you leave the ABS module plugged in, the ABS works fine, but again the pedal is on the floor before the brakes work well.

I followed the factory bleed procedures and have bled the brakes both with vacuum and manually. I have not pressure bled them yet.

Only item left to be touched is the proportioning valve. My ace mechanic suggests that may be the problem, but I have a HUGE problem throwing parts at a "maybe"

Any suggestions?

Here's something an old mechanic told me once for bleeding abs when you dont have special tools.

Go find a nice safe area with a grass or gravel runoff area right off the shoulder, put the two outside wheels on it going a decent speed, and push the brakes until the abs kicks in. You shouldnt have to slow down very hard to do this. Just ride the abs until it comes to a complete stop. Do this a few times from a decent speed, and then go home and try bleeding it out again.

If that doesnt work you'll have to find someone with a better idea, hah!

a few comments from an industry insider:

1. those front calipers suck balls. if they're original with 230k on them, the bridges are likely as stiff as warm taffy. time for replacement calipers. new, not remans. EDIT: I see you replaced them a few years ago. It is possible that remans have lost some stiffness compared to a new part.

2. if you had rust in a line between the MC and the ABS, you've now got an ABS valve with filters full of crap, and perhaps some of that crap has gotten past the filters and is ripping up (or has already ripped up) some of the seals in the ABS valve. This can lead to long pedal travel as the fluid accumulators (where the ABS dumps excess pressure from a locked wheel to get it unlocked) will fill up before building pressure at the wheel ends. Probably time for a new ABS unit.

3. When I bleed an ABS car, I do just what Vigo said. Bleed it, go do some ABS stops, then bleed it some more. Don't be a Bob Costas about stomping on the pedal either, as it's important to get ABS activation on all hydraulic circuits. That truck is a 3-circuit, ie each front is separate, and the rears are tied together.

ps

1. On an ABS car, flush the fluid completely every 2 years, regardless of mileage. Don't let the MC reservoir go empty during this process. When flush is complete and reservoir is topped off, go out and make a few ABS stops to get clean fluid through the entire ABS valve. I was shocked at what a difference it made to the pedal feel on my Probe GT, with no other changes to the brake system or the tires.

Mr. Corvair:

The brakes were fine to the point where I did exactly as described: Got going about 50 on a county road, jammed on the brakes. ABS worked, pedal dropped, and its been bad ever since, with no end of bleeding and parts repairs.

I made sure the brake fluid was running clear before I stopped bleeding the system (before I test drove it on that fatefull day 3 weeks ago), and have bled the system a few times for various reasons since I bought the truck 2 years ago, so the system has been relatively clear. As to where the debris came from, I have no idea.

What you say about the accumulators could definitely be a problem. The truck stops fine, but has TONS of pedal travel.

Plan for the weekend goes as follows:

1. Hit up junkyard for some misc fittings and a new used prop valve (see next few steps).

2. Pressure bleed brakes by applying air pressure to master cylinder reservoir and opening bleeders.

3. If step 2 does not work, disassemble, clean, and inspect proportioning valve, repeat step 2.

4. If step 3 does not work, remove all ABS components from engine bay. Make new brake lines running from proportioning valve to bulkheads on frame. Bleed brakes. Remove ABS bulb on dash cluster. Celebrate.

Please dont warn me about removing/disabling the ABS. I am willing to accept the risks. I am not willing to shell out dozens of dollars for new ABS components, ASSuming they are even available.

Also, had calipers apart/inspected this summer and all is good and sliders move freely. Had rear brakes apart this week. All is clean, inspected, adjusted, and under 6 months old.