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How to Repair Cummins 5.9L Vacuum Pump Oil Leak

Solid Seal

Bruce W. Smith
Oct 6, 2017
Photographers: Bruce W. Smith
Cummins’ 5.9L diesel engines have many wonderful traits, from the simplicity of their design to the durability and reliability of their internal components. However, the powerplants also have parts that require attention from time to time to help promote a longer service life and trouble-free operation. One item that requires occasional tender loving care is the vacuum pump.
Because a diesel has an open intake system, the pump provides the necessary power for a Dodge Ram pickup’s vacuum-operated mechanical functions (four-wheel-drive system, cruise control, HVAC, and, on earlier models, the brakes).
It’s one of those parts we rarely pay attention to until oil leaking from the engine catches our attention and is then traced back to the area where the power-steering pump’s shaft fits into the rear of the vacuum pump. This is a very common problem, and one that shouldn’t be ignored for too long. That’s because the pump gets its lubrication via a direct feed from the engine. If the shaft seal fails, the result is an instant high-pressure oil leak.
Photo 2/22   |   “Diesel Bob” Marinos leans over a 5.9L Cummins engine while removing its vacuum pump.
That was the biggest concern when “Diesel Bob” Marinos, a Cummins service technician with more than 30 years of experience, discovered his early-production ’98 Dodge Ram 3500 dualie’s pump was leaking. Removing and resealing the vacuum pump on the 12-valve 5.9L engine technically isn’t too tall a task, but still, it does take a little know-how to get the job done quickly.
“The Bosch injection pump is the thing that makes the vacuum-pump removal a little more time-consuming, because it blocks the vacuum/power steering pump assembly,” Diesel Bob says. “The easiest and most efficient way to remove the vacuum pump on the earlier 5.9L engines is to physically separate the power steering pump from the back of the vacuum pump while it’s in the engine bay. Getting at the four nuts that hold the two pumps together can be frustrating for a first-timer. But once you’ve done it, the next go-round is easier,” Bob says.
The vacuum-pump assembly is then unbolted and slid out of the timing cover and tilted upward to get it out of the engine compartment so it can be put on the bench to make the repairs. “On the 24-valve engines, the power-steering pump can be easily separated from the back of the vacuum pump, and then the two bolts that secure the back half of the pump can be removed and that section pulled off so it can be resealed.”
The biggest benefit for a Dodge Ram owner tackling this repair in his own garage is the cost savings. Many dealerships charge four hours’ labor and $100-plus for the reseal kit, potentially making the out-of-pocket repair costs range between $400 and $500.
On the other hand, a DIYer willing to invest the time it takes to perform the reseal operation themselves can buy the kit (PN 4089742) for less than $20. Doing the work takes less than four hours using simple handtools.
Photo 3/22   |   Here is a look at the vacuum pump and Cummins reseal kit.
Photo 4/22   |   The first step in reaching the vacuum pump is removing the intake manifold. Diesel Bob’s ’98 Dodge Ram 3500’s pump seeped oil for a couple of months before he decided it was time to reseal it.
Photo 5/22   |   One of the best tools for removing the four 15mm nuts that hold the 5.9L engine’s power-steering pump to the back of the vacuum pump is a half-moon wrench. The nuts are in an awkward, tight location, and it’s hard to see in that space, so this makes the job a lot easier.
Photo 6/22   |   Cummins vacuum pumps tend to leak oil where the power-steering shaft enters the rear of the housing (arrow). The typical cause for the leak is a failed shaft seal inside the vacuum pump’s bearing housing.
Photo 7/22   |   A 9/16-inch wrench is used to loosen the engine-oil feed line that provides the pump’s lubrication. There will be a little oil dripping out when the line is removed, so have a rag or pan underneath to minimize the mess.
Photo 8/22   |   The vacuum-pump rebuild kit is very simple. It consists of two O-rings, the shaft seal, and the gasket that goes between the power-steering pump and the vacuum pump. Be sure to check the kit to make sure all four are present before removing the pump.
Photo 9/22   |   When rebuilding a part with new seals and O-rings, it’s prudent to give it a good cleaning to prevent dirt or debris from getting on the delicate sealing surfaces.
Photo 10/22   |   The vacuum pump is actually made up of two parts: The pump assembly and vacuum-pump bearing housing. Once the two 13mm bolts that hold the two elements together are removed, a light tap with a hammer will separate them. The pump section is set aside and not touched.
Photo 11/22   |   Here’s the culprit that caused our pump’s leak. The shaft seal is worn just enough to let oil seep past the power-steering pump’s driveshaft.
Photo 12/22   |   Pro tip: Diesel Bob places a 15/16-inch wrench under the case’s ears to keep it level on the workbench then uses a 7/8-inch deep socket and hammer to carefully drive the seal retainer out of the housing. It only takes a couple of light taps.
Photo 13/22   |   Invert the bearing housing and place the cross-shaped coupling plate back in the bottom of the bore. It doesn’t matter which side of the cross plate is facing up.
Photo 14/22   |   Once the O-ring is removed, a 1¼-inch socket is used to carefully drive the old seal out of the housing and reinstall the new one. Pro tip: Clean the retainer before installing the new seal—and leave a little solvent on the inside to help the seal slide into place. The solvent dries, leaving the seal firmly locked in place. (Don’t use oil, as the seal could work itself free, creating huge oil-leak problems).
Photo 15/22   |   The new O-ring “snaps” into place. Bob uses new engine oil to lubricate the seal and bearing retainer before reinstalling them.
Photo 16/22   |   Thumbs are perfect tools for initially setting the seal retainer back into positon (O-ring-end first) in the housing. Doing it this way facilitates aligning it squarely and without damage to the aluminum piece.
Photo 17/22   |   After the retainer is partially in the bore, Bob lightly taps it into the housing until it seats firmly against the lip ridge. He also uses a special drive tool, but a 36mm deep socket (or equivalent size) works just as well.
Photo 18/22   |   Once the retainer is in place, the cross-coupling plate must turn freely, and the O-ring shouldn’t be twisted or pinched.
Photo 19/22   |   The O-ring that seals the two case halves together rarely fails. But it’s good to replace it with the one included in the reseal kit, using fresh engine oil as a light lubricant.
Photo 20/22   |   The bearing and pump housings are aligned with a dowel pin that must seat in the hole or the two halves will not seal. The drive must also be aligned with the cross coupling before cinching down the two bolts.
Photo 21/22   |   Cummins specifications call for 22 ft-lb of torque for the bolts that hold the two sections together.
Photo 22/22   |   After the power steering’s drive is cleaned of any old residue, the resealed vacuum pump is bolted back into the timing cover housing (the pump shaft is turned until it aligns with the cam gear). Then the gasket is set in place and the power steering pump-drive’s dog rings are aligned so they slide into the slots of the vacuum pump’s cross plate. Cummins requires 18 ft-lb of torque on the nuts that join the pumps together and 57 ft-lb for the two bolts that secure the assembly to the block.

Sources

Dunks Performance
541-726-1006
http://dunksperformance.com/

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