Helpful guide for your Auto Clutch™, TwinDisc® or Rockford® PTO
This Tech Tip focuses on the basics of spring- loaded automotive style clutches as used in wood chippers.
Many of our engine customers operate diesel driven power units that have industrial PTO clutches. To support them we sell PTOs, clutch packs and replacement parts. Like with everything else, clutches have a different terminology than engines. There are two main kinds of industrial clutches. The most common kind is the traditional over-center power takeoff clutch or PTO. These are manufactured by; Twin Disc®, Rockford™, NACD®, WPT Power® and others. We stock WPT Power, Rockford, NACD and aftermarket Twin Disc to make sure our customers can get what they need when they need it. We discuss these over-center PTO’s elsewhere on our site in
- Tech Tip #48: Maintaining your Rockford and Twin Disc PTO,
- Tech Tip #67: How to Remove A Troublesome Pilot Bearing,
- Tech Tip #73: How to Make Your Twin Disc or Rockford Power Takeoff Last Longer, and
- Tech Tip #93: What Do I Need To Find The Right Parts For My PTO Clutch,
The other style clutch is called the “automotive style”. This consists of a spring-loaded assembly similar to what you might find in a pickup truck. It is often used on wood chippers and tub grinders manufactured by Bandit Industries®, Morbark®, and Vermeer®. Chipper manufacturers tend to select automotive style clutches because the spring-loaded clutch is easier to engage and disengage than the traditional over center PTO. While Twin Disc, Rockford, NACD and WPT Power do have automotive style clutches (in fact, most Ford powered chippers run Rockford automotive style clutches) the prominence of these brands with equipment manufacturers ebbs and flows. Newer brands like Auto Clutch and Stein had become common on diesel powered chippers, however in the recent past we believe that their failure to support the non-equipment manufacturing customer market has made getting the correct components quickly and cost effectively more of a challenge. While we still carry and support replacement products to support our WPT Power, NACD, Twin Disc and Rockford clutch owning customers, finding the right Stein and Auto Clutch and Stein components requires a more nuanced approach. Give us a call an we can help you find what you need.
Common Clutch Nomenclature For Automotive Style PTOs.
Clutch Cover. This is an outer shell constructed from stamped steel. The clutch cover contains four main components. The pressure plate, the diaphragm spring, pivot ring, and drive strap. The pressure plate is a cast piece that provides the pivot point for the diaphragm. It also provides the friction surface for the clutch disc and a mounting surface for the drive straps. The diaphragm is a spring-steel disc that is sandwiched between the outer cover and the pressure plate. The steel pivot ring is attached to the clutch cover, creating the fulcrum point for the diaphragm. The drive straps are used to attach the pressure plate to the clutch cover, allowing the plate to disengage from the disc.
Clutch Disc. This is the most critical part of the system. The transmission input shaft goes into the spines of the disc and slides backwards and forwards as the clutch is engaged. Clutch discs have a hub in the center with a number of internal teeth or “splines” to mate with the transmission input shaft which is also splined. The clutch disc also contains a number of torsion springs or idle-stage dampers. Most clutch discs are round and made from an organic material. Recently though, drag racing technology has migrated to the industrial clutch field. Increasingly clutch discs are shaped in paddle format that contain a Kevlar friction material on each paddle.
Clutch Kits. Most of our customers replace automotive-style clutches as a complete kit assembly. This includes the pressure plate, the disc, and the pilot bearing. As a complete assembly everything will mate together well for many thousands of hours of use. We recommend this approach as opposed to piecemealing the assembly so that newer wear components don’t wear out pre-maturely due to maintaining older worn components. This also tends to avoid some of the individual component variations that don’t work with certain separate components which are typically not well labeled if at all by the manufacturers.
How to order? When ordering a clutch kit from us simply give us the numbers from the inspection plate on the cover to the PTO. Older Rockford PTO’s will have a number beginning with PTA and newer Rockford or NACD PTO’s will have an Assembly Number resembling 4-25754 or 42574AM that starts with a “4”. Auto Clutch numbers are similar to 1300 HD. If the plate is gone, advise the brand of the engine, the diameter of the clutch disc and the ID (from bottom of groove to bottom of opposite groove) of the spline on the friction disc. We can take care of the rest!
Manufacturers names, symbols and numbers are for reference purposes only and do not imply manufacturing origin.
