By Bruce W. Smith. Turbo Diesel Register Magazine Issue 129 Pages 44-48.
The simple vacuum pump found on ’91.5-’02 Turbo Diesel engines serves a number of different functions.
Because a diesel has an open intake system, this pump provides the vacuum needed for the proper operation of the four-wheel-drive system, cruise control, HVAC, and on ’94-’02 models, a booster for the power brakes.
The vacuum pump is one of those parts that goes totally unnoticed until a pesky, messy oil leak from under the engine catches our attention. That leak is typically traced back to where the power steering pump’s shaft goes into the rear of the vacuum pump.
The Purpose of 5.9L Cummins Vacuum Pump
The vacuum pump gets its lubrication via a direct feed from the engine. If the shaft seal fails, it becomes an instant high-pressure engine oil leak.
Bob Marinos is a Cummins service tech with more than 35 years of experience working on diesels. He is also a Dodge Ram owner, so he speaks from both personal and business experience. He discovered his early-production ’98 truck’s vacuum pump was the culprit behind the annoying oil spots on his garage floor.
Repair of Leaking Vacuum Pump
Removing and re-sealing the vacuum pump on the 12-valve engine isn’t technically that intricate of a task, but it does take a little know-how to make the job go quicker. “What makes the pump removal on a 12-valve a little more difficult, time-wise, is the Bosch injection pump blocks easy access to the vacuum/power steering pump assembly.”
“The easiest and most efficient way to remove the vacuum pump on the older 12-valve engines is to physically separate the power steering pump from the back of the vacuum pump while it’s in the engine bay. However, getting at the four nuts that hold the two pumps together can be frustrating to a first-timer. But once you’ve done it, the next vacuum pump repair is so easy.
Marinos says that some 12-valve owners doing this repair for the first time pull the power steering pump and vacuum pump out as one unit. Ultimately, this makes aligning the drive gear cogs easier during reassembly on the bench.
Take Care with the Drive Cogs
A word of caution from Bob, “The vacuum pump’s drive cogs are normally broken when someone tries to just replace the power steering pump instead of removing the two pumps as a unit. It is very difficult to align the cogs with the vacuum pump mounted to the engine if you haven’t done this a few times. Often, those who don’t know any better just crank down the connecting bolts and do the damage. When you bolt the two pumps together on a bench, up-ended, make sure the drive parts are indexed and fully fit together before tightening anything.
“Either way, the vacuum pump assembly has to be unbolted, slid out of the timing cover and tilted upward to get it out of the engine compartment. Then it can be put on the bench to make the repairs.”
Bob tells us about this repair on the 24-valve engine, “Owners of 24-valves have it a lot easier. The VP-44 injection pump does not interfere with removal of the power steering pump, and it can be easily separated from the back of the vacuum pump. Then the two bolts that hold the back half of the vacuum pump can be removed and that section pulled off so it can be put on the work bench and re-sealed.”
Cost Saving: Do It Yourself
Many dealerships charge four hours labor and $100-plus for the re-seal kit, potentially putting the out-of-pocket repair costs between $400-$500. However, repairing a leaking vacuum pump is one of the simpler of Cummins repair tasks. It just takes time and a little patience.
Using a few simple hand tools, a do-it-yourselfer that is willing to invest the 3 to 4 hours it takes to do the re-seal (depending on whether it’s a 12-valve or 24-valve engine) can buy a generic kit for less than $30 at Geno’s Garage.
[Special thanks to Dunks Performance (541-726-1006) in Springfield, Oregon, for letting us watch over their shoulders during the rebuild.]
