Southtowns27

Truck is in my sig... The other day while towing my trailer I was slowing down coming up to a stop sign and the brake pedal got REALLY hard, the vacuum assist was gone. The next intersection I came to it was fine and has been fine for a couple days. Tonight, I went to move my truck from one driveway to the other and at first the brakes were fine, then all of a sudden, no more vacuum and a VERY hard pedal. If I ran the RPM's up the vacuum came back and the pedal became normal again. At idle, I'll push the pedal and the vacuum is gone in less than 10 seconds. Grr. Are there any common vacuum leaks on these trucks? Is the vacuum pump just plain toast?

chariotdriver

The vacuum pump in these trucks usually works great; it's main flaw is the seal cuts a groove in the coupler and it starts leaking engine oil---alot. It's a great exterior lube system covering most of the underside of the truck and I've fixed both of mine. I'm guessing you should look at any check valves; usually one on the pump itself (in 96, Dodge shipped a few w/o the valve and oil was getting sucked up into the HVAC controls causing a recall worth lots of $$) and I'm not sure if the valves are anywhere else in the system. A light should also come on with a low vacuum; the sensor is on the driver's side of the engine compartment. If none of the above is a problem then look at the vac-booster itself or your brake master cylinder; are they original? It is 12 years old and things will take a dump from time to time; with the exception of the excellent 12V engine which seems to go forever.
Hope this helps, cd

infidel

It's very common and probably the main reason Dodge switched to hydro-boost brakes in '97, vacuum pump just can't keep up with continuous braking at low rpms.

Easiest solution is to just be aware of it and give it a little more fuel.
If you need the brakes a lot at idle speeds up the idle.
Lastly another easy and cheap solution is to install a vacuum reservoir tank.
Need only to tee the tank into any vacuum line with one hose.
Hard part with this though is finding a place to put it

sal09

im not trying to steal your post but i have the same problem when i put it in 4lo. when i go to slow down the brakes get really hard. im thinking about trying the tee idea

infidel

Probably easier to make your own vacuum tank then to locate and buy one.
About a foot of 4" or "6 PVC or ABS pipe with a cap glued on both ends will give plenty of storage. Just drill and tap one port for the hose before you glue the last cap on. This way you can clean out chips.
Or you can get inventive, many things can be made into a vacuum tank. Old fire extinguishers, propane bottles, etc come to mind.

Southtowns27

Great suggestions guys, I'll have to do that. It makes sense since it only seems to happen to me at low RPM.

dozer12216

Need to look for vacuum leak. Vac resivor will not cure a leak, just delay.