RABS or Vacuum Pump or Both?

[IDIDREW]

Ok,

The brakes operate BUT I use almost everything I have to push on the pedal to stop the truck and even then it doesn't stop all that fast or well. It is a super sketchy white knuckle inducing driving.

Brake Booster and Master Cylinder were replaced, Brake Calipers were rebuilt and rears are new. System was bled. **the RABS unit was not bled although I suspect it to be bad.

The e-Brake light on the dash has lit up (usually indicates a vacuum issue correct?)

1. It appears that there are NO power brakes
-I think the Vacuum is not sufficient or non existent.

2. Since the RABS was not bled there may be some air in the system AND since the truck sat for so long (10 years) it may also be bad.

3. I think I need to diagnose the Vacuum Pump (will most likely replace it), Test it and then continue onto the RABS unit by giving the original a bleed and then testing to see if it is toast.

RABS = Spongy brakes

No Vacuum = No power brakes

Am I missing anything here?

 

[madpogue]

The primary purpose of the brake failure warning light on the dash is to warn you of hydraulic brake failure (i.e. no brakes, slam into a busload of nuns and schoolkids...). It also comes on when you apply the parking brake and when there is insufficient vacuum. So your combination of conditions - hard pedal plus brake warning light - indicates a vacuum problem.

You do need to bleed the RABS valve if you've opened up the hydraulics. Best to re-bleed all points, in reverse order of distance from the M/C (RR, LR, RABS, RF, LF). That's most likely a separate issue from your hard pedal.

Does the truck have A/C?

 

[IDIDREW]

The primary purpose of the brake failure warning light on the dash is to warn you of hydraulic brake failure (i.e. no brakes, slam into a busload of nuns and schoolkids...). It also comes on when you apply the parking brake and when there is insufficient vacuum. So your combination of conditions - hard pedal plus brake warning light - indicates a vacuum problem.

You do need to bleed the RABS valve if you've opened up the hydraulics. Best to re-bleed all points, in reverse order of distance from the M/C (RR, LR, RABS, RF, LF). That's most likely a separate issue from your hard pedal.

Does the truck have A/C?

Yes, there is AC but it is not connected (electronically, I unplugged it and removed the Belt). I removed the belt as I was concerned about hurting the pump due to a lack of refrigerant.

In addition to checking on the vacuum pump I think I need to take a look at the vacuum hose. They look good on first glance but I could have missed something. I am most likely going to replace that hose, too much at risk to take a chance that there is a leak.

My goal is to take my family in this truck and not knowing will keep me up at night.

Thanks!

 

[OLDBULL8]

Simple test for brake Vacuum is to pull the Vacuum hose off the booster with the truck running, hold your finger over the check valve, it should try to suck your finger into it, you should hear a suction when you pull it off.

 

[DaveBen]

Many Vacuum leaks occur where the hose transitions from the frame to the front hubs. Vacuum switches the hubs for the ESOF (Electronic Shift On the Fly).

 

[snicklas]

Many Vacuum leaks occur where the hose transitions from the frame to the front hubs. Vacuum switches the hubs for the ESOF (Electronic Shift On the Fly).

Dave,

Too old of a truck. We get that fun on the 99+ SD trucks. The old IDI truck don't use that system. Sone days, I wish ours didn't either.

 

[DaveBen]

Thanks Scott. I lucked out, I have manual four wheel shift. So they did not have ESOF.

 

[snicklas]

Not the vacuum like the SD's. My Excursion has the ESOF vacuum hubs. I had to replace the big seals and need to get a lockout. For the most part it is fine, but takes time and money for the seals and lockouts. In the very near future I am doing ball joints again......

 

[IDIDREW]

Pulled the vacuum line from the booster. There was absolutely no vacuum showing up on the gauge. Dead as a door nail.

 

[madpogue]

Pull the line from the vacuum pump and check there. You want to narrow down whether it's the pump or a vac line. There's also a distribution box (aka vacuum manifold) where the vacuum splits from the pump to the HVAC and the sensor.

 

[OLDBULL8]

IF PEOPLE WOULD JUST PUT THERE TRUCK INFO IN THERE SIGNATURE AND KEEP IT THERE, A MORE INTELLIGENT DIAGNOSE COULD BE MADE.

 

[IDIDREW]

IF PEOPLE WOULD JUST PUT THERE TRUCK INFO IN THERE SIGNATURE AND KEEP IT THERE, A MORE INTELLIGENT DIAGNOSE COULD BE MADE.

Agreed and Done,



I replaced the Vacuum pump and the brakes are working as they should but the brake pedal would slowly press down to the floor.


Next, went after the RABS unit. Replaced that and bled it. Finally the brakes felt as they should have been.

All in all it was a quick set of bolt on and go fixes. Truck runs great.

Thanks all.