Hi all.

I have a 04 Cummins DRW 6 Speed. Had the truck for years, no real issues until now.

If I drive it from cold, it drives totally normally. BUT, after a few kms the brakes start dragging, almost to the point where I cant accelerate in 6th! I mean ALL four corners drag - as if I am pressing the brake pedal.

I did a short 6 km run today on an errand. Everything fine for a while until on my way back home it got to the point where she wouldn't take 6th, and I could smell hot brakes. But, after another couple of clicks, the dragging went away, and by the time I got home everything was freed off and other than hot rotors, the brakes were perfect again???

The brakes when not dragging like this work great, with nothing out of the ordinary.

Anyone had experience of this? Hydro boost on it's way out? I did fit a new master cylinder a couple of years ago, and have done a few thousand clicks since then on a couple of long trips, but like I say, the brakes work perfect other than this weird issue.

Any ideas?

Thanks.

 

Disk or drum in the back?

 

Discs.

 

That seems rather strange...... Are there any codes? Does the ABS function normally while the brakes are dragging??

 

No codes at all. I just went for a drive until it started dragging, and then read for codes. No lights warning lights, no codes. The ABS appears to function normally, although if I brake hard enough I can get the rears to lock slightly - but there's no weight in the back at all. ABS light goes off at engine start as it should.

If I pump the brake pedal with the engine off, it gets hard. With my foot on the pedal, and starting the engine, the pedal drops, and with a pump or two it feels normal again. No leaks or obvious issues around the booster, pedal assembly. No strange feel in the pedal or noises coming from the hydro boost or power steering. Power steering action fluid level all good, no leaks etc.

Is it at all possible that one hanging caliper ( not that I feel anything from stone cold ) could be causing slight heat build up in the fluid, then over pressure causing all the calipers to drag? I just jacked the truck up after a run long enough to cause the dragging, and with the engine off all four wheels cannot be turned by hand. I pumped the brake pedal with the engine off to (release the pressure in the hydro boost system?), but you still could not rotate any wheel. If I leave it to sit a couple of hours, I am pretty sure it will be fine again - but that doesn't explain how, on my way home earlier, the dragging went away on it's own whilst driving and braking in traffic?

 

Behavior with engine off is normal.

There are no check valves in the system, so, fluid expansion due to heat would just go back to the master cylinder.

Why all four are holding some pressure is a real head scratcher. Gotta be either the abs pump, or something up-stream from it..... after that, it's all just individual fluid circuits.

 

Thanks for your input buddy. I just went for another drive until the brakes started to bind. Got back to the house and jacked the front and back up off the ground. I couldn't spin the wheels by hand. I then loosened the two nuts holding the master cylinder to the hyrdobooster, as I wondered if the master cylinder was somehow causing the problem. Once the master cylinder was pulled away from the booster the wheels were able to be rotated by hand, but still stiff (still hot). It is possible that the master I replaced has some how developed a fault and isn't releasing properly, but I'll need to crack the brake lines at the master to be sure, and I don't have time right now. But even that doesn't make sense, as the brakes are fine for the first few miles at least, if the master was hanging up somehow, I'd think you'd feel it in the pedal maybe, and you'd think the problem would show it's self straight away after setting off.

If that proves a dead end then as you say, what else can it be other than the ABS pump as that's the last point where all lines heading to the four corners meet.

I got a sneaking suspicion, this sort of problem leads down the parts cannon path!!!!

I'll report my findings.

Thanks again.

 

Yeah, and that's why its a head scratcher.... If it was a purely mechanical issue, you would think the brakes would be stuck all the time..... I suppose the question becomes, what changes in the brake system during the time you are driving, and they start dragging....... Personally, I can't think of anything that would explain it mechanically.