A while back, my Porter-Cable model 450 compact router went crazy.  When I flipped the switch on, it started normally for a second or two, and then ran away into the stratospheric RPMs by the sound of it.  I checked the brushes, blew out the dust, even rapped it a couple of time with a mallet.  No joy.  It still ran at frighteningly high speed.  Now this machine only had about a dozen hours on it, but was outside the warranty period, so I was unwilling to write it off.  I probably should have, as you will see later.  Hopefully this blog will help those with a similar failure on their hands to benefit from my experience, save a couple of bucks, and even maybe come away with a better router.

I found a few references on the web, in various blogs, about these models losing speed control, but nothing about why or how to fix it.  So I took a small vacation from common sense and decided to try to fix the router myself.
 

                          Fixed speed Porter-Cable 450 name plate

Let me start off by saying that Porter-Cable and DeWalt are owned by the same parent company, so it should be no surprise that these two 1.25 HP routers share many components.

This is the original name plate.  The router is a fixed speed model regulated electronically to 27,000 rpm.  I started by opening up the top case, taking care to photograph the wiring from all possible angles so I had at least a fighting chance for reassembly.

Close up view of the wiring under the top cap

There are two closed modules tucked deeply into the assembly, and I figured (incorrectly) that replacing one or both would cure what ailed it.  Next, I went hunting on the web for replacement parts.  What I quickly learned was that the P-C 450 is nearly identical to the DeWalt DWP611 variable speed router.  All the components, critically including the motor, share a part number.  What differs between them is one of the two control modules.  Also the top cap on the DWP611 allows for the speed control thumbwheel that the P-C does not have.  Otherwise, as it turned out, the dimensions are identical.  Oh, and the DeWalt case is yellow while the P-C is black. 

Side by side view of the tops of the P-C field case (left) and the DeWalt field case (right)
with the electronics removed.  The P-C still has the brush holders attached.

 

So I ordered a replacement for the module with the shared part number.  The other module has a different part number owing to the fact that the DeWalt has speed control.  I ordered one of those as well.  Both modules were placed on back order, so it took a month or so for them to arrive.  Installation went well, and I became the proud owner of a resurrected variable speed hybrid P-C/DeWalt 1.25 HP router.  The big moment had arrived - testing it.  Plugged it in, stationed a fire extinguisher nearby, and flipped the switch.  Yup, you guessed it; the router started normally for a second or two and then ran away to some ridiculously high rpm.  Failure!  Time to dig deeper into this puzzle. 

 I reasoned that if the new “DeWalt” configuration had speed control, then it must have embedded in it a means of sensing speed.  For that matter, the original P-C configuration must have had a similar, perhaps identical, sensor.  After a bit of on-line research, I discovered that there is a magnet mounted at the top end of the motor shaft that interacts with a sensor on the closely adjacent circuit board.  Getting to it meant tearing apart the top end again, and then pulling the motor armature out of the casing.  After disassembling the top end, and easing the armature out of the case, I found no magnet at the top end of the shaft, only the threaded stud.  Peering down into the field case, all I could make out were a few bits of sparkly something.  I could also, with effort, pull out bits of rubber.  Everything else down there looked like it had melted, as I would confirm later.

View up into the motor housing with the field coils removed.  The red circle highlights
where the speed control magnet should seat, but shows a fused mess instead.

Going back to the assembly diagram published by the parts supply house, I saw that the top bearing is held in place by a rubber spider, and the magnet screws onto the threaded end of the armature shaft.  I ordered a new magnet, spider, and plastic field case.  Backordered again, I waited six weeks for these parts to arrive.

 

                   From left to right, the new magnet with its threaded nylon insert,  the 
                   new rubber spider bearing holder, and the new field case showing the 
                   bearing seat.  The magnet sits between the armature bearing and the 
                   yellow plastic field case. 

To swap field cases, the bottom end of the field case has to be snapped off, and the field coils removed from the case.  It is a snug fit, but I found that the field coil assembly is heavy enough that I could literally shake it loose from the case.  Now, with complete access to view inside the top end of the case, I could easily tell that it was in fact fused.  I am guessing that the magnet somehow got loose enough on the shaft that it started rubbing the plastic walls around it and friction melted them while shattering itself in the process.  No magnet, no speed sensor, hence no speed control.  I tossed the old field case into the trash along with its fused magnet pieces and rubber spider remnants. 

The new spider fit easily into the new, now yellow, field case.  I threaded a new magnet onto the motor shaft stud, added a drop of Loctite for good measure, and inserted to armature for a test fit.  After removing the armature, I inserted the field coil assembly into the new case.  This took a fair amount of patience and strength since there are some critical alignment channels with tight clearances.  Once the field was seated, I re-installed the armature, and then snapped on the lower cover.  Once again, referring to my stack of photos, I re-assembled the top end. 

Finally, time to test, once again!  With fire extinguisher handy (it IS an electrical device in a shop full of sawdust, just for you skeptics), I turned on the switch.  Success at last, controlled rpms from 1 to 6 on the dial, and nary a sound of a misaligned bearing or armature.  

To summarize: Inside 12 weeks, I ended up repairing the P-C 1.25 HP fixed speed router while also upgrading it to a variable speed DeWalt-like variable speed 1.25 HP router, all for $118.16 plus tax and about $20 shipping.  Buying a brand new DWP611 locally would have cost roughly $125 plus tax and taken two hours.  But where is the fun in that? 

Of course, had I known to just buy the magnet, spider, and field case in the first place, and settled for the original fixed speed, it would have been a lot cheaper, about $25 plus $20 shipping.  And a couple hours of my time, which for me is free.  YMMV. 

The Bottom Line
I list in the table below the part numbers of the replacement pieces, the vendor I obtained them from, and the cost as of early 2025.  If you have a P-C 450 Type 1 with speed issues, and only wish to fix it without upgrading, then those three parts (numbers 21, 58, and 9 in the table below) are all you will need.  If you wish to upgrade to variable speed at the same time, or just for the heck of it, you will also need the variable speed module, the Gacc module, and top cap (parts 13, 14 and 20 in the table below).  The armature and field coils are merely listed as evidence that electrically the two router models are equivalent, so don’t buy them.  There are of course other suppliers for DeWalt and P-C parts.  I just happened to settle on MM Tool Parts, but I take no responsibility as to whether parts are currently available anywhere. 

So, if your DeWalt DWP611 or Porter-Cable 450 router loses speed control, a broken magnet is a likely cause.  Easy enough to fix for a few dollars if you can brave disassembling the whole tool and have a lot of time on your hands.

Or just buy a new one - it is so much easier.     Cheers!