The last thing one wants to worry about is a loud noise coming from their truck and not knowing why it is happening or where it is coming from. Without proper maintenance and potential improper installation, the Power Take-Off (PTO) itself is subject to making noises that may sound like whining, clattering, clicking and grinding. It is important to note that the sounds one may hear of these noises may not be from the PTO itself but from somewhere else in the system. PTOs also sometimes accentuate vibrations caused by the diesel engine that have led companies to develop technologies to help mitigate and smooth out those expected vibrations.
PTOs now in the market have focused on reducing noise and making sure that drivers are more comfortable allowing them to get their work done. Parker Chelsea has developed QT GearTM technology, a solution to mitigate noise, that can be applied to nearly all PTOs that are engine driven by a live PTO drive gear in the transmission.
Even though the technology is in place, there still may be unique sounds coming from the PTO itself. Here is more information on what might be causing the specific noise types you hear if the PTO is the root cause of the noise.
When looking into a new installation and hearing a whining noise coming from the truck, a potential cause could be from the PTO having an improper backlash. What improper backlash entails is less than .006” clearance between the (transmission) PTO driver gear and the PTO input gear as measured at the pitch line using a dial indicator. This can cause rapid heat buildup and gear tooth breakage. For an existing installation, the whining noise (pitch sound) change could indicate a possible bearing failure.
A probable cause for hearing a clattering noise coming from the truck with a new installation can be the result of the excessive backlash. Excessive backlash is created from more than .012” clearance between the (transmission) PTO driver gear and the PTO input gear as measured at the pitch line using a dial indicator. This will lead to eventual gear tooth failure from insufficient contact. In the scenario of an existing installation, it is important to make certain the cause of the noise is from the PTO. It can be determined by disconnecting the driven equipment and running the PTO. If the source of the noise is determined to be from the PTO, make sure to check the bearings and shifter mechanism.
Clicking is most commonly caused from a damaged gear tooth. The clicking noise itself typically indicates that either one or two gear teeth are damaged only. The frequency of a click can help indicate the size of the gear at issue, with a fast click being due to a small gear and a slow click being due to a larger gear. If a grinding noise is heard, this would be an indication that all the teeth are damaged.
The common cause of grinding noise can be traced to operator abuse when engaging the PTO. To properly engage for a mechanically shifted PTO, the operator should depress the clutch and then wait for the transmission gears to come to a stop before engaging the PTO. To properly engage for a “hot shift” PTO, the operator should make sure the engine RPM’s are below 1200 before engaging the PTO. For both new and used installation, a grinding noise could indicate that the shifter cable or lever isn’t adjusted correctly. Make sure to check for the correct adjustment of the clutch brake on the transmission.
Noise on Allison Transmissions
Typically, the combination of diesel engines, automatic transmissions and PTOs can result in significant noise via rattle and/or vibration. It becomes more recognizable when using heavy-duty transmissions behind turbo-charged engines and is enhanced by using neutral lock up. (The neutral lock up compresses the disks within the transmission torque converter, eliminating the cushioning fluid that is normally found between these disks.) Please note that this noise is not harmful to the PTO or the transmission. When the engine RPM is raised or lowered, or a load is applied to the PTO, the noise will usually disappear and go away.
PTOs generally do accentuate torsional vibrations and therefore can be heard on a truck application. Companies have been putting in place their own technologies to help mitigate noise from these vibrations. Even with general PTO noise, the rare whining, clattering, clicking and grinding noises may occur. One will have to distinguish from a subjective matter if the PTO sounds like it is making one of these noises and from there will need to be determined if that noise is from the PTO or another part of the system. Learn more about Parker Chelsea’s QT Gear and PTO support material for the proper product PTO series and technologies for each unique application.
This article was contributed by Michael Mabrouk, marketing leadership associate, Chelsea Products Division, Parker Hannifin Corporation.