ELECTRICAL REBUILDER’S ASSOCIATION — Technical Document $S201603B www.electricalrebuilders.org DENSO PASOS STARTER — Completely Different But Strangely Familiar ____ BYBOB THOMAS ost or us love to see a Denso offset gear reduction recessed in such a way that it will be a challenge to remove. (OSGR) starter show up on the front counter for Once the field case and armature are out of the way, you rebuilding. Aside from their easily accessed can get to the planetary gear assembly. When you remove the solenoid contacts and brushes – most of the cover plate which also supports the armature’s recessed bearing component parts in these starters seem to last forever. The drive (see Figure 10), there is a good chance that a large strange- clutches can be rebuilt without any special tooling and a minimal ly-shaped spring washer will stick to its back side. It is very amount of parts. Denso has a long history of making service and easy to miss it. This is what Denso calls a slip disk shock repair components available to the rebuilding industry through absorber (see Figures 11 and 12). More about it later as well. their warehouse distributors. The OSGR starters are generally just But when removing this part, remember to make a note of its plain easy to repair of rebuild. orientation, which is easy to forget when it comes out stuck to Denso’s OSGR platform is a proven design that has withstood the bottom of the cover plate. Then remove the planet gears to the test of time for three and a half decades. It could be argued expose the drive clutch. that pound for pound, they perform as well or better than any other starter ever made. A multitude of vehicle and equipment manufacturers of all types have used them in a wide range of applications. But someone once said that “all good things must come an end.” In this case, it actually started to change about nine years ago. That is when Denso introduced the PA90S series starter for diesel applications. They are smaller, lighter and stronger than their OSGR predecessors. The PA90S is a series-wound planetary gear reduction starter for diesel-powered medium duty trucks and equipment. The part number of the one we have here is 428000-6110 (see Figures 1 and 2). It first appeared on Dodge Ram pickups with diesel engines in 2007 and is rated at 3.0kW. As you can see in the third photo (see Figure 3), it is noticeably smaller than its OSGR cousin. Interestingly, this PA90S starter can be used to replace the 228000-2292 in the photo, Lester 17548. Some sources show they will interchange. However, I suspect that may depend upon the amount of room that is available for a bulkier OSGR starter in the post-2007 trucks and the installer’s willingness to accept it. Rebuilding a PA90S is not going to be much more difficult than rebuilding an earlier Denso starter once you gain some experience with them. In fact, other than the gear set, the two starters have more in common than you might think. Sadly, some key component parts like brushes and solenoid contacts are not yet available, most likely due to lack of demand. Hopefully that will change. To disassemble this starter you must begin by removing the brush holder screws and through bolts. That allows you to remove the commutator end housing, brush holder (see Figure 4), armature (see Figure 5) and field case (see Figure 6). Like many of the small engine Denso starters of the past, the pole shoes are riveted into this case. These coils are quite different too, wound from a heavy flat wire. However, note that the wide side of the flat wire is parallel to the housing (see Figure 7). You can see that there are just three turns per coil. As a protection feature, Denso has built four fusible connections into these coils, two where the positive brushes attach (see Figure 8) and two where the coils attach to the field case lead (see Figure 9). They are there to prevent a critical failure. But you have to wonder for whom. It obviously cannot benefit of the end user. Once these fuses burn open, the starter is disabled until the fields are replaced or repaired. More about that later. Note that the armature’s drive end support bearing is Figure 1 – This Denso PA90S starter has been used on Dodge Ram diesel pickups since 2007. Figure 2 – The 428000-6610 or Lester 19029 as viewed from the drive end. An ERA Publication. ©2015, Electrical Rebuilder’s Association. All rights reserved. No portion of the guide may be reproduced in Page 1 any way, or stored in any electronic retrieval system without the prior written consent of the Electrical Rebuilder’s Association. www.electricalrebuilders.org Figure 3 – The PA90S (right) is significantly smaller than the OSGR starter. Figure 6 – The pole shoes on the PA90S starter are riveted into the case. Figure 4 – The PA90S brush holder may look familiar due to similarity to OSGR brush holders. Figure 7 – Note the way that these field coils are wound, the number of turns and the size of the wire. Figure 8 – Here you can see one of the fused field coil connections Figure 5 – The PA90S armature’s DE bearing will be a to a positive brush. challenge to remove. An ERA Publication. ©2015, Electrical Rebuilder’s Association. All rights reserved. No portion of the guide may be reproduced in Page 2 any way, or stored in any electronic retrieval system without the prior written consent of the Electrical Rebuilder’s Association.