You Have a Mechanic Problem

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My mechanic did some tweaking with my gearbox and slowed the rpm on my pump. He figured, and I agreed, that slowing the rpm wouldn't hurt anything. Possibly, I thought, it might take longer to build vacuum. I thought it made good sense economically because it would save money by making the pump last longer. A few months later, we opened up the pump and it can best be described as "washboardy," almost like there are now rolling waves in the cylinder of the pump. Did we do something wrong or did I get a faulty pump?

Gene Strasburg

Gary, Ind.


Your problem has a simple answer: You are running the pump too slow. That's right. Running your pump too slow can cause the vanes to skip and bounce inside the cylinder, causing the washboard effect. It might also be that the pump is not getting enough oil. This also causes the vanes to skip and bounce. Obviously, the oil is intended to make the vanes run smooth and easy inside the cylinder.

How to fix it? First, the cylinder must be re-bored to the perfect circle it had at the outset. Then check the operator's manual to determine the manufacturer recommended rpm for the pump. Double-check the gearbox or however your system is set up and reset it so you have the proper rpm. Vacuum pumps, like any piece of machinery, are designed and manufactured to operate in a certain way. To vary from manufacturer's specifications usually causes problems.

This was not a pump problem, but a mechanic problem. Stick with your operator's manual, and if you've lost it, call the pump dealer or the pump manufacturer. They'll be glad to answer any questions concerning
pump specifications.

Where there's smoke ... there's probably the wrong oil


I drove out to the work site the other day, started the pump and, after a short while, it began to smoke. When I examined the pump, it was hotter than I expected. For some reason, the pump overheated. What can you tell me?

Skip Cuthbert

Toledo, Ohio


As we just talked about running the pump too slow, what could be better than to have the opposite situation? In this case, there are two possible solutions to your problem.

The first is you're running the pump too fast. Adjust the rpm to meet the pump specs. Heat generated by the fast rotation of the rotor holding the vanes causes oil in the pump to smoke. Friction caused by the vanes moving too quickly in the cylinder can result in the pump overheating.

If you find the pump is running at or around the proper rpm, the problem is with your oil. Either there is not enough oil in the pump or you are using the wrong type of oil. Using the wrong oil may cause your pump to smoke. The manufacturer specifies which oil is best suited for your pump. They know what type of oil best lubricates the vanes in their pump. Each manufacturer makes its vanes out of a different composite material. When I've asked for a further esxplanation, this is the best answer I've received.

When it comes to vanes, the secret stays with each manufacturer. They have tested the pumps and have recommended oils best suited for their vanes. Different composite materials respond differently to the various oils available.

If overheating is allowed for an extended period, it can cause damage to the cylinder. The cylinder itself can go out-of-round and the efficiency of the pump will fall drastically. This will either result in re-boring the cylinder or replacing the pump.


The two problems mentioned above don't have to happen. When you buy a new or used truck, know what to expect from the various working components. If the truck seller or dealer cannot provide an operating manual for the pump, call the pump manufacturer. They will be happy to send you one. Be prepared with the right information resources and you'll save time and money over the long haul.


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