I am dealing, again, with the old brake light/abs light issue. Two years ago, a vacuum leak was fixed at the cruise control, which fixed the light issue. Lately, I have noticed that if I held my foot on the brake pedal for an extended period of time, the brake light would come on. Once removed, the light would go back off. Now, if I brake for any extended time, or just hold the pedal, the lights will come on, and the pedal will get hard. I have been tracing the vacuum lines, and have done these things so far;
1) Replaced the 3/8 inch line from the vacuum pump to the brake booster
2) Capped off the line going to the blend door- it would appear that I am losing some vacuum there.
These things have helped a little, but the problem still persists- the lights come on after holding the pedal down longer. I plan to trace and check the vacuum line to the transfer case and to the CAD.
Back when the first leak was fixed, I also installed a new master cylinder and a new brake booster. They were both quality parts, not from advance or auto zone. Could I be having a problem with the booster, or do you think that I still have a vacuum issue? What about the small box underneath the ABS unit? What is that, and can it cause problems? It has a vacuum line going to it.
Has anyone added a vaccum reservior before the booster? It would seem that the amount of vacuum and its effect is marginal in these trucks.

 

Well, I think that I found my problem, and it is a lesson to all who have the brake light/abs light issue- a vacuum line to the CAD had pulled lose. Before throwing money at ABS sensors, follow all of your vacuum lines. A loss in vacuum, even when the cruise and 4WD work, will trigger the lights. I would still be interested in ideas on a vacuum reservoir.

 

Hodge, I would probably look more to a auxiliary vacuum pump like the Furd PS used. They used to be fairly inexpensive, and would shut off when they reached full vacuum.

As for a spare reservoir, it still wouldn't fix the leakage, just make it appear OK for longer.

 

I found the leak. The brakes are working good now, and the lights are off.

 

The Ford electric vacuum pumps are $89 from Napa and very long lived and reliable.
Don't know why Dodge went with such a complicated and expensive vacuum pump especially after they switched to hydro assisted brakes.

 

That's a great idea..........anybody figure out a way to delete the vacuum pump and still have a way to drive the PS pump? I've changed half a dozen seals in the vacuum pump and would like to not do it a gain. It's amazing how much oil gets dumped all over the bottom of the truck from a bad vacuum pump oil seal.

 

The 4BTs that were put in at least the Chevy P30 stepvans had PS only, no vacuum. I'm actually heading the other way when I do my conversion, though thinking about it, I might just do the Furd PS electric pump. Didn't know Napa carried them.

There was just a 4BT PS pump only on fleabay.

 

How many miles are you getting before you have to change the seal again??

 

I looked it up and it appears that the Ford electric pump generates only 17 in of vacuum. The FSM calls to replace the stock pump if vacuum is below 25 in. The electric one is too weak, it appears.
I started having weaker exhaust brake response, suspecting weak vacuum. Measured it at 22 in, looks like the pump needs replacement.

 

Seems to me that 22 inches would be plenty.
Vacuum pumps rarely fail in the vacuum making dept, they just start leaking oil. The vanes are easy to replace and only $25 but I've never ran into any that were very worn down.
The whole pump is ridiculously expensive but http://www.fixinrams.com/id14.html is the best bet.

 

Well, I'm not done dealing with this. The brake light is coming on after a very short push of the brakes, and goes back off as vacuum is built back up. I have been through all of the vacuum lines, and was ready to pull the pump today, before I decided to check the amount of vacuum generated- a constant 28 inches. So, I went and bought a brake booster, and will put it on tomorrow. The current one is only about 3 years old, but crazier things have happened.

 

Since you're getting excellent vacuum readings it sounds like the low vacuum sensor is bad.
Not sure how it triggers the warning light but is has to be either open or closed.
Unplug the sensor and if the light comes on you'll know the light comes on with an open signal.
If so short across the sensor wires and see if the problem goes away.

 

I replaced the brake booster this morning, and the only way now that I can get a brake light is if I pump the brakes numerous times at idle- so, I believe that they are working as well as the factory system will allow. The pedal feels better, it brakes better, and it passed inspection.