Isolating failure in hydroboost system - 2002 2500 CTD

I'm having power brake problems, and am trying to isolate what is wrong - pump, hoses, or hydroboost unit. Basically, from time to time I find myself with the ability to slow down but not stop. I can stand on the brakes, and the truck will stop, but there's a chattering type feel through the pedal, like it's trying to grab but doesn't.

I found instructions on line to troubleshoot the system, but to be honest I followed those instructions and still couldn't figure out what was wrong. Those instructions were asking me to tell if the power assist was there after so many pedal stroke or so much time (IIRC), but I couldn't tell any difference in pedal feel. Even driving down the road when the problem occurs, the pedal feels the same except there's no stopping power. It's not like old vacuum assist systems, where it's like stepping on a rock if the power assist fails.

The truck has always had a "loose belt" sort of sound from the steering during cold weather, but until recently the brakes seemed to be unaffected by that. Last weekend I tried "changing" the PS fluid by cycling two quarts of new fluid through using the turkey baster method. That was no help at all.

I'm trying to avoid throwing money at the problem and replacing parts that are good. Can anyone comment on a good way to figure out what is failed/failing on my 2002 2500 CTD truck?

Thanks in advance for any help,

Sounds like an ABS problem. Pull the fuse for the abs pump (light will come on) and see if it still happens.

Most likely a failing wheel speed sensor.

How do you figure that? He would have a light on the dash if there was an issue with the ABS/wheel speed sensor but would most likely still have brakes. Brakes generally don't fail from wheel faulty wheel speed sensors. But just for giggles - is there an ABS light on the dash?

That said, an '02 model year truck would probably only be RWAL. For that system, the speed sensor is on the rear diff.

Obviously the first thing to do is to verify the p.s. fluid level and make sure it's full. You said there was a noise on cold start sometimes? Could be the belt slipping/going away, that's a relatively cheap/easy fix. Maybe try that and see if that helps? Not likely though if it's an intermittent problem but obviously sometimes noises disappear when the truck warms up to operating temp. Same with the pump - if it was the pump or hoses, the problem would most likely be there all the time.

If not the belt, then it's probably the booster. Probably a good idea to replace the hoses if you change it.

Sorry couldn't be more help. Maybe Guitar Jones will chime in, he'll probably know more.

It does feel like ABS kicking in when it happens, but there are no lights on the dash to go with it. I think. The whole dash could be lit up and I might not notice, since at that point I'm basically looking at what I'm going to hit if I can't get it stopped. It's easy to reproduce so I can sure test it out and look at the dash while it's happening.

The belt is fairly new, and the fluid is full since I just flushed it.

I was able to find internet posts complaining about the cold weather behavior from others that said changing to ATF+4 makes it better. So maybe the pump is OK after all.

I'm about at the point of just replacing everything in the system to be sure whatever is failing is fixed.

FWIW the truck has < 80k miles on it.

What does the belt have to do w/ anything? The PS pump isn't run by a belt on the Cummins. Doesn't the PS pump also serve as the hydroboost pump on these trucks?

If you had a failed sensor or a failure in any part of the ABS system, it would give a code and the ABS light would be on until it was fixed, no if and or buts about that.

Are the service brakes in good condition? Fluid full, clean? Pads/rotors have enough meat on them? I have replaced frozen calipers on older trucks/Jeeps, not totally uncommon. The pulsing you feel could be a warped rotor from overheating. Maybe check the rotor surfaces to see if one is glazed or rusted on one side or looks chewed up in some way. You didn't mention any pulling to one side so that's probably not likely but doesn't cost anything to look. If you're feeling adventurous, maybe get a helper to press the brake pedal while you crack a bleeder or two to see if the fluid gushes out.

If the hydraulic side of the brakes check out, you might ultimately need to have a scan tool put on it. It's an '02 which would be a DRB III. I don't remember what functionality there is (if any) to monitor the brake system on those trucks so I can't say exactly what someone might do but it might help to pinpoint something.

Yep, that's true, my mistake on the belt, did not put it together. I did some reading to edumicate myself and found the link below. Could be a bad vacuum pump/seal behind the P.S. pump. I would bet this is your issue. Bad vacuum pump = no brakes.

Click this link here.



Yes.

I had a steering issue a while back and changed the PS pump on mine ('01 2500 CTD). I got a rebuild kit off ebay for the vacuum pump and rebuilt it myself. Not hard to do at all and a heck of a lot cheaper than a new vacuum pump. I wasn't having any issues related to the vacuum pump, but they mount together and to ensure there wasn't an oil leak, I removed both. Figured I might as well rebuild the vacuum pump while I had it off.

Ha, that's right, and yes it does.

To the rest of the responses:

The truck is hardly ever driven, the brakes are fine other than this problem. There is no pulsing when the brakes work, only a feeling like an ABS pulsation when I don't have power assist.

I saw posts about the vacuum pump while reading up on how to pull the PS pump, but they weren't clear what the vacuum pump has to do with brakes. The booster is only connected to the PS pump.

I just looked at the booster, it has two high-pressure lines and one return line. One HP line goes to the pump, the other looks like it runs up front to the steering box.

^ more reading leads me to believe the vacuum pump is used for HVAC control on the truck. Also if the vacuum seal was going bad, the truck would be spurting oil.

The PS pump is driven off the vacuum pump. But unless the shafts broke a bad vacuum pump shouldn't affect his ps pump. And that's definitely not an intermittant.

ABS sensors can indeed give false readings and trick the system into an abs stop WITHOUT throwing codes r lights. It's actually pretty common around here, a little saltwater gets into the wiring and throws the resistance off or you get rust jacking that opens up the gap between the sensor and tone ring. You end up with a sensor that does pass the self tests for open or short and still generates readings, but they are off.

You need a scanner that can access the abs data to narrow down which sensors are acting up. But disabling the abs will narrow this down to an abs problem or not.

Knowing how abs works helps here too. The system can (and does) cut the pedal off from what ever wheels the computer thinks is sliding. If he has multiple sensors giving false readings he may very well have no brakes.

Thanks ruderunner, that definitely sounds like something I need to investigate this weekend. Luckily I don't have to rely on the truck but I need to get it fixed because there's nothing worse than having a vehicle that isn't usable when you need it.

With an ABS capable scanner, you should be able to see which wheel sensor thinks a wheel is locked up. It won't throw a code, because it thinks it is doing its job. I've only done it with Fords, though - I haven't looked at Dodge ABS.

Your wrong as I've had this happen to my truck... once I pulled the fuse, stops perfectly fine. I have a bad wheel sensor that never once threw a code.

To the OP, pull the abs fuse under the hood and try it. The sound you have is probably a ps pump going bad. If it goes or gets week, you will have a hard time steering and stopping. I've been through it all before. On the vacuum pump, I've done rebuilds and even went new and mine still leaks... nothing left to replace. I recently had the seal blow out in the steering box... guess that's what happens when you run big tires on a heavy front end.

You were all right, I pulled the fuse and went for a drive without it happening once. Normally it happens before I get to the end of the spur I live on (about 100 feet). Now to get the codes pulled and the thing fixed.

Thanks to everybody for the help, you saved me some $$$ for sure

Dealer and some repair shops have scanners that can get abs data. Local parts store won't. There likely won't be a code, someone will have to watch the live readings.

Sensors themselves are usually easy to change, some can be a bit pricey.

Missed the cold weather and noise from the pump... mine does the same thing when it's really cold, goes away after it warms up. This is with the new pump. Not sure why, but hasn't been an issue for the past 3 years it has done it.

I'm surprised but I guess it's possible.

Please reply and let us know what you find if/when it has a scan tool on it. I would ask whoever looks at it to take it for a ride with the scan tool to monitor what happens rather than just deleting codes.

There likely are no codes. You must watch the data to see which sensor is dropping out.

The truck sits most all the time so I may be able to tell which sensor is bad by looking at it, if it's caused by rust from moisture trapped under the truck. It looks like there's 3, 2 front, one rear center. Even if I just go for broke and replace them all it's still a good bit cheaper than the hydroboost unit.



FWIW I saw at least one thread during my searches saying someone had changed from PS fluid to ATF and the cold weather noise went away.

When I changed mine out I used PS fluid, mostly because it's clear and I was doing the job with a turkey baster hoping the fluid would get clear once I had the old stuff all gone. It never did. I've never had it cause a problem in the cold, the steering's just a little stiffer and noisy.

I've got a trick for telling if it's a front and which side. Will post a how to this evening.

That will be great, thanks.

Sorry for the delay, got hung up at works quite late the last 2 days.

Anyways, since you can get the problem to occur pretty consistently, that's a big help. You'll need a straight, fairly smooth road with minimal traffic. Drive the vehicle and apply the brakes in a fashion that makes the problem occur (hopefully under 30 and not a panic brake situation)

when doing this, take your hands off the steering wheel (keep close and ready to grab)

Note wether the steering pulls to one side or the other when the pedal starts to shake (abs kicks in)

The abs will release the brake on the wheel it thinks is slipping, this means an imbalance from side to side. The side that still has brake will pull the steering that way. Basically if the steering pulls right then the left front sensor is suspect.

Do this a few times to rule out road conditions, if it always pulls the same way on braking that kind of confirms it. If it pulls a different way each time well this doesn't work.

No pull? possibly both front sensors are no good, or the rear sensor or?

This all assumes the vehicle drives straight and true to begin with.

If the above test is inconclusive, you will need a scanner or have to shotgun it.

Thanks, that makes perfect sense.

I haven't fooled with it since pulling the fuse to be honest.

You can leave it out. But BUT you lose abs, and have a light on.

Change the fluid.

I flushed the system with clean regular power steering fluid (replaced the steering pump on mine) and filled with MOPAR +4 POWER STEERING FLUID ($9.99 a qt at Pep Boys before the 20% off coupon) while running the returns into a bucket and keeping the pump full with a helper turning the steering wheel and pumping the brakes and the cold weather noise is pretty much GONE ...

Did that when I replaced the pump... I had to flush the system for it to be covered under warranty. Made no difference at all.