The Mighty Powr-Lok

<body topmargin=0 leftmargin=0 marginheight=0 marginwidth=0> <table cellpadding=0 cellspacing=0 border=0><tr> <td valign="top" colspan=2 height=90 BGCOLOR="#006633" TEXT="#F7F7FF" bgproperties="fixed" background="079005a0ddvuru.png"> <div> <A HREF="http://www.vernco.com/index.htm" TARGET="_top" TITLE="http://www.vernco.com/index.htm"><U><B>home</B></U></A><B>     |     </B><FONT SIZE="5" COLOR="#FFCC66" FACE="Arial" ><B>Vern</B><B>co.com</B></FONT></div> <div> back to<B>  </B><A HREF="http://www.vernco.com/id18.htm" TARGET="_top" TITLE="http://www.vernco.com/id18.htm"><U><B>Projects</B></U></A></div> <bR> <div> <A HREF="http://www.vernco.com/id173.htm" TARGET="_top" TITLE="http://www.vernco.com/id173.htm"><U><B>Site Map</B></U></A></div> <div> </div> </td> </tr><tr> <td valign="top" width=150 BGCOLOR="#669966" TEXT="#080000"> <div> <A HREF="http://www.vernco.com/rearaxle/" TARGET="_top" TITLE="http://www.vernco.com/rearaxle/"><U>Full-Floating Rear Axle</U></A></div> <div> <A 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it.  The stock front differential was completely installed in the axlehousing, ready to go.  I went to the big 4x4 Swap meet in Puyallup, Washington.  Next thing I knew, more of my children's college fund was going towards Willys parts.</div> <bR> <div> I have scanned two Willys Service Bulletins covering the Powr-Lok unit.  The first 8 page bulletin has an excellent description of how a Powr-Lok works, in addition to information found in the service manual.  There is also a single page bulletin with updated details of the plate arrangements.  The very last page is a blowup of that bulletin's illustration.  That last bulletin is from 1967 so it is possible the information has been updated since then, but it certainly supersedes the 1965 manual reprint that I have.  In fact, the 1965 manual only shows the details for the Model 44 Powr-Lok and none of the other models:</div> <div>  </div> <div> <A HREF="id683.htm" TARGET="_top" TITLE="Bulletin 500 p. 1"><U><IMG SRC="5ed7d9d0.jpg" border=0 width="125" height="157" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></U></A></div> <bR> <div> I like the writing style of this bulletin's author, and give him a big tip of my orthopedic hat.  There is more to a Powr-Lok than I thought.  The clamping force varies depending on available traction, relative wheel speed and torque.  It is not simply a fixed clutch between the two axleshafts.  It even unlocks to a certain degree when one wheel over runs the other in a curve.  Read through the bulletin again after looking at the pictures I've added below.  The bulletin references two types of Powr-Loks.  This is the later style with the flat clutch plates.  </div> <bR> <div>  <A NAME="powr_lok_side_gear"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A></div> <div> It is time to scatter the Powr-Lok pieces across the workbench and see what makes her tick.  The picture below shows the special side gear in the Powr-Lok.  To the left of the picture is the mating piece  called a Differential Ring.  Both the Ring and Side Gear are splined to the axleshaft.  There is no relative rotation between the two parts, but they are free to travel along the axleshaft splines.  Note the shoulder, explained further below with the Spider Gears:</div> <bR> <div> <A HREF="id388.htm" TARGET="_top" TITLE="Ring and Side Gear"><U><IMG SRC="6137d4b0.jpg" border=0 width="125" height="75" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></U></A></div> <bR> <div> The backside of the Differential Ring has a hub with external splines in addition to the inner splines for the axleshaft.  There are two clutch packs, one for each axleshaft.  This exploded view of a clutch pack shows how alternating plates will rotate with the Differential Ring.  The remaining plates have external keys to mate with the Powr-Lok housing halves.  Some of the plates are bowed to provide spring action.  Some of the plates are different thickness, also.  Consult the <A HREF="http://photos.yahoo.com/bc/kr98664/vwp?.dir=/Powr-Lok+Bulletins&.dnm=Disc+details+bulletin+close-up.JPG&.src=ph&.view=t&.hires=t" TARGET="_top" TITLE="http://photos.yahoo.com/bc/kr98664/vwp?."><U>Service Bulletin</U></A> for the proper order and orientation of each plate, which varies by application:</div> <bR> <div> <A HREF="id389.htm" TARGET="_top" TITLE="Clutch pack exploded"><U><IMG SRC="617af4e0.jpg" border=0 width="175" height="78" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></U></A></div> <bR> <div> Here is a close-up showing two of the plates on the backside of the Differential Ring.  The externally keyed plate is free to spin relative to the Ring, which turns with the axleshaft:</div> <bR> <div> <A HREF="id390.htm" TARGET="_top" TITLE="Two plates on PowrLok Ring"><U><IMG SRC="61b645a0.jpg" border=0 width="100" height="90" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></U></A></div> <bR> <div> This shot shows the two Powr-Lok housing halves.  The half on the right has the mounting surface for the ring gear, and already has the clutch pack and side gear installed.  The other clutch pack is upside down and ready to be installed.  The clutch pack keyways are visible in the Powr-Lok housings:</div> <bR> <div> <A HREF="id391.htm" TARGET="_top" TITLE="Clutch pack and housing"><U><IMG SRC="61daf3e0.jpg" border=0 width="175" height="62" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></U></A></div> <bR> <div> Before assembling the two halves, take a look at the Spider Gears and the special shafts upon which they ride.  The two shafts are notched to fit together in the shape of an X.  Note the shoulder on the Spider Gears, which applies clamping force to the clutch pack via the Differential Ring.  The special V-shaped ramps on the end of the shaft control how much clamping force is applied:</div> <bR> <div> <A HREF="id392.htm" TARGET="_top" TITLE="Spider gear and shaft closeup"><U><IMG SRC="61faf4c0.jpg" border=0 width="175" height="76" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></U></A></div> <bR> <div> This image shows both Spider Gear Shafts installed.  You can see how the V-shaped ramps face opposite directions.  The shafts are free to wiggle side to side slightly, and apply clamping force as they climb on the V-shaped ramps in the housing.  Note the hole in the center, explained in the next paragraph:</div> <bR> <div> <A HREF="id393.htm" TARGET="_top" TITLE="Spider gears on housing"><U><IMG SRC="621af4d0.jpg" border=0 width="175" height="77" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></U></A></div> <div>  <A NAME="powr_lok_spacer"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A></div> <div> If a Powr-Lok is used in a semi-floating rear axle, mushroom-looking spacer buttons are added on each side to act like the <A HREF="http://www.vernco.com/rearaxle2/index_spacer_stock_config.htm" TARGET="_top" TITLE="http://www.vernco.com/rearaxle2/index_sp"><U>stock spacer between the axleshafts</U></A>.  This image, courtesy of Jamey Scott, shows the the profile of a spacer button.  The ball on the end of the spacer fits in the dimple at the inner end of the axle shaft.  (The axle shafts are the same whether for a Powr-Lok or stock open carrier.)  Two spacers are used, one on each side of the Powr-Lok assembly.  The two spacers are long enough to meet in the middle, acting as a solid piece, so no inward pressure from the axle shafts is transmitted to the Spider Gear Shafts.  Pressure against the Spider Gear Shafts would interfere with the variable clamping action of the Powr-Lok.  Should the spacers come out during axle shaft replacement they could be tricky to reinstall.  You might have to use superglue to secure them to the end of the axle shaft for installation:</div> <bR> <div> <A HREF="id561.htm" TARGET="_top" TITLE="PowrLok Spacer"><U><IMG SRC="91b96540.jpg" border=0 width="150" height="84" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></U></A></div> <bR> <div> Concerning the spacer buttons, not all models had provisions for them.  In my '51 Willys wagon's front axle, I recently installed an otherwise identical Powr-Lok that did not even have the holes in the Spider Gear Shafts.  There is no need for the spacer buttons on a front axle because the axle shafts are free to float endwise.  Spacer buttons are only needed on a semi-floating rear axle where the <A HREF="http://www.vernco.com/rearaxle2/index_spacer_stock_config.htm" TARGET="_top" TITLE="http://www.vernco.com/rearaxle2/index_sp"><U>tapered roller bearings push the shafts towards each other</U></A>.  Rear axles with flanged shafts (approximately 1970 & later) have different style bearings at the outer ends.  On this type, each bearing holds its own axle shaft independently so no spacer is needed in the middle. </div> <bR> <div> Torquing the housing half bolts was a bit of a challenge because of the round housing.  There wasn't a whole lot to grip.  Luckily a strap wrench came to the rescue.  You could also make some sort of spanner to engage the bolt holes for the ring gear.  Don't forget Loctite on the bolts.  The bolt heads come very close to the axle housing, so there is no room for lockwashers.  While not shown, use the axleshafts to line up each Side Gear with the respective Differential Ring before the clutch packs force them together when the bolts are torqued:</div> <bR> <div>  <A HREF="id394.htm" TARGET="_top" TITLE="Housing Halves Torqued"><U><IMG SRC="62396500.jpg" border=0 width="150" height="80" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></U></A></div> <bR> <div> With the housing assembled, this view shows how the V-shaped ramps face opposite directions.  The housing has been heat treated at the ramps, as evidenced by the dark areas.  The oval holes between the spider gear shafts help oil reach the clutch packs:</div> <bR> <div> <A HREF="id395.htm" TARGET="_top" TITLE="Heat treat view"><U><IMG SRC="625af520.jpg" border=0 width="175" height="82" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></U></A></div> <bR> <div> Here is a side by side comparison with the original Model 25 open differential from my front axle.  If you are ever scrounging through a junkyard, you can quickly identify a Powr-Lok by unscrewing the filler plug and looking at the carrier with a flashlight.  Under one of the cover bolts, you might see a metal tag specifying the special lube required, but those are often missing:</div> <bR> <div> <A HREF="id396.htm" TARGET="_top" TITLE="Carriers side by side"><U><IMG SRC="62964990.jpg" border=0 width="100" height="153" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></U></A></div> <bR> <div> Again courtesy of Jamey Scott, here is what a Powr-Lok looks like in a Model 44 rear axle:</div> <bR> <div> <A HREF="id562.htm" TARGET="_top" TITLE="Model 44 PowrLok"><U><IMG SRC="9207d670.jpg" border=0 width="125" height="103" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></U></A></div> <bR> <div> I'm pretty excited to have a Powr-Lok for my front axle.  I had looked at lots of option and I think the Powr-Lok will work best for me.  A spool or any type of full locker can make steering next to impossible  The torque sensing properties of the Powr-Lok help restrict the tendency to slide sideways in off-camber situations.  There are some limitations according to the bulletin, such as both wheels must have at least a small amount of traction for it to work, but it should be far superior to an open differential.  (Note: I have since discovered the Powr-Lok still powers one wheel somewhat, even if the opposite side has no traction)  I also like the fact that this was available as original equipment so I shouldn't be overloading the rest of the drivetrain.</div> <div>  <A NAME="powr_lok_test"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A></div> <div> The Powr-Lok has added much capability off-road.  In slow speed applications, especially on loose surfaces, the slight increase in turning force is not objectionable.  The tradeoff was a no-brainer due to the increased traction.  No pulling was noticeable at low speeds with stock rims and tires.  You might have less satisfactory results with High-School Drug Dealer (oversized) tires and rims, especially if running a greater offset.  When I tested my Jeep on the road at higher speeds (front hubs locked, but with the transfer case still in 2WD), there was quite an increase in turning force needed.  There was also an erratic pulling motion to one side.  The pulling was quite strong and unpredictable.  Unless you have a Jeep that sees only low-speed trail use, if you have a Powr-Lok in the front axle, locking front hubs are a must to allow civil handling on the road.  Turning the locking hubs requires a bit more leverage with a Powr-Lok installed.  Details of a combination windshield latch/hub turning tool can be seen in the <A HREF="http://www.vernco.com/tips/id540.htm" TARGET="_top" TITLE="http://www.vernco.com/tips/id540.htm"><U>Tips and Tricks section</U></A>.</div> 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