Servicing Suspension Linkages
Contents
1. Technical Servicing Suspension Linkages How To Maintain These Important But Hidden Bearings Shock linkages usually live in crowded nasty places They don t present the most invit _ a E F Fa i Jd ing DIY prospects but they re essential to good rear suspension performance and their by Mark Barnes employ a linkage to make shock movement progressive In other words as the swingarm moves through its arc leverage afforded by the linkage transfers that movement at an accelerating rate to the shock The goal is to provide relatively light and supple damping at the beginning of suspension travel and firmer resistance to bottoming at the deepest extreme This is the best of both worlds The rear wheel is allowed to rise easily to hug the contours of small surface irregularities maximizing traction and ride plushness But it can t just blow through the shock s full stroke in response to larger impacts such as square edged bumps or potholes on the road or landings off big jumps on a supercross track A quick reminder about fluid dynamics Liquids are non com pressible Think of a shock as two chambers connected by a set of orifices During compression oil is forced from one chamber to another with the orifices limiting the speed of this transi tion The faster the shock is compressed the harder it is for the oil molecules to crowd through those orifices picture Black Friday shoppers struggling to squeez2. shock s lower end usually hanging down below the swingarm they re regularly exposed to lots of abuse Off road bikes often subject their undersides to impact and all motorcycles pelt this PEN HE REAR SUSPENSIONS on most modern motorcycles 36 OCTOBER 2013 MOTORCYCLE CONSUMER NEWS actual maintenance needs are fairly simple Most of the work is just getting to them area with dust water and gritty crud Of course even if they were completely shielded from such threats the friction bearing surfaces would wear from use alone Linkages Need Love Too Unfortunately linkages are often neglected even by otherwise conscientious owners They re not highly visible wear and tear is totally invisible and they can be awkward to access Special tools are listed in shop manuals for bearing removal and instal lation and these are invariably quite expensive keep reading for a super cheap alternative Also the bike must be supported in such a way that the rear is completely unweighted which can be a challenge on some street bikes Still none of these factors make linkages any less needy or worthy of attention To check the condition of yours first suspend the swingarm and rear wheel If you have a centerstand that natu rally lifts the rear wheel off the ground this part is a cinch If your centerstand tends to lift the front you can have an assistant push down on the bars for this part to get the rear end up Barring either of
3. of the swingarm and try to wiggle them Check for side to side move ment which likely indicates worn swingarm bearings bushings Then check for vertical free play between where the swing arm comes to rest and where the suspension s resistance is first encountered While this can also result from swingarm com ponent wear it s most likely the result of worn linkage parts especially in the absence of lateral movement Don t make this assessment by tugging at the wheel slop detected there could be a wheel bearing issue Still while it s convenient check your wheel bearings too Note If you do detect problems with the wheel bearings or swingarm pivots these warrant your immediate attention Both will detract from suspension performance and a full blown fail ure of either could result in loss of control while riding On many bikes lubricating or replacing swingarm bearings is the same in principle as those operations on linkage bearings although disassembly is obviously more involved We won t cover it here though because swingarm removal can be so different on differ ent motorcycles Review the procedure in your service manual and see if you re up to it Wheel bearing replacement involves different procedures and tools see them in our April 2006 issue Even if you detect no slack in the system linkage bearings still require regular cleaning and lubrication A few models come with fittings to allow the use of a grea
4. replacement then you ll just be cleaning and relubricating what s already there Be aware though that seals can wear out before the bearings they protect If a seal doesn t pop out easily or if it shows signs of wear e g cracked or ragged lips it should be replaced with a fresh one These are so cheap that you should just get a new set ready before disassembly Note that these seals go in with their lips facing outward and their flat backs against the bearing races With the linkage pieces removed from the bike and the seals popped out spray contact cleaner into the bores and bearings to wash out the old grease and accumulated grit A towel passed through and rotated within each bearing may help Bearings may be of the caged or uncaged variety Caged bearings hold their needles in place behind a perforated plate An uncaged bearing s needles are only held in place at their very tips by a small lip around the race s edge If a needle gets cocked its tips will no longer be retained and it will fall out making it easier for others to do the same So when cleaning an uncaged bearing keep in mind that the old grease may play a large part in holding the needles in place when you rinse it away the needles will be more likely to get loose This isn t a big deal as long as you re ready to catch any escapees Actually with the needles out the race will be much easier to clean thoroughly But it is quite a tedious pro
5. al for details Of course if you discover that a shock bearing is in bad shape replace it Your suspension is now ready for reassembly Consult your shop manual for the proper sequence as doing things out of order may leave you without access to a bolt or nut hidden behind a part that you should have waited to install Dou ble check all torque values this is not a part of the motorcy cle you want to come apart or bind during operation With everything buttoned up your rear suspension should be silky smooth and subtly responsive This linkage less rear suspension is worlds simpler and eas ier to maintain but its PDS Progressive Damping System only approximates the progressive feel of a linkage KTM owners take heed The heim joint at the lower end of your shock should NEVER be lubricated its Teflon surface will be destroyed by the resulting grit accumulation
6. cess to replace them Get into a meditative state smear a little grease in the empty race and use tweezers to install the needles one by one If you re careful and lucky they Il tolerate gentle cleaning without evacuating Re ar Tol a This old bearing was in pretty good shape Stripped of its grease by solvent it released its needles readily Note that each needle has a small cone on each end that is normally retained by the race s edge i d 40 OCTOBER 2013 MOTORCYCLE CONSUMER NEWS With our new bearings and seals installed it s time to pack those needles and seal lips with fresh grease before reassembly Smear or brush fresh grease onto the new or cleaned bearings Most of this will get pushed out by the bush ing so there s no need to go over board Insert the seals and fill the space between their lips with grease this not only provides lubrication but it also presents an additional barrier to moisture and debris seek ing entry Install the bushings and wipe off the excess grease to avoid creating a dirt trap While you ve got the linkage off shock removal will require pulling just one more bolt the shock s top mount Do this now while it s con venient and clean lube the shock s bearings Some linkage bearing kits will include a replacement for the lower shock bearing note that its removal may require different proce dures or tools so check your owner s manu
7. cult and even more awkward than it already is due to location The rear end will also fall to the ground when you remove something So prop up the rear wheel slightly to neutralize this reverse tension before beginning any disassembly Doing the Deed First of all get the necessary supplies ready before you begin as your bike will be disabled for the duration of this project A shop manual torque wrench chassis grease all the appropriate socket and wrench sizes and new parts if indicated by rear end wiggle room should be handy along with a bearing removal installation tool if you re going to replace worn components Such tools can cost hundreds of dollars which may be worth while if you re a tool connoisseur with some money to burn no doubt they re more elegant and probably a tad easier to use than what we re about to offer as a low cost alternative But if you d prefer to spend less than ten bucks on something you ll rarely use all it takes is a quick trip to your local hardware store Special bearing tools use the mechanic leverage of a screw to apply concentrated force against press fit parts Said leverage can be obtained with a simple piece of all thread and a few nuts and washers along with some sockets borrowed from your tool ironically All Balls makes needle bearings too This kit includes all the bushings seals and bearings shown here for our example bike along with the lower shock joint and its seals
8. d will be of no real consequence as long as there are no raised surfaces Once such a bearing is out use fine grit sandpaper or Scotchbrite to remove corrosion remnants from the bore DO NOT try to hammer bearings into or out of place with a punch this will damage the bearing s race and cock the bearing in its bore Also a slip will gouge the bore The resulting trench will not cause problems but the metal berm raised around it will New bearings pressed into such a defaced bore will be squeezed out of i j ie i ae VECE Here s our all thread bearing tool clamped onto the linkage dog bone The narrow socket is set to press the bearings out into the wider socket braced against the dog bone We used a long all thread connector as our second nut on the left side the increased surface area made holding it still a bit easier For parts that can be pulled off the bike a vice works very efficiently to press the narrow socket through the bore extracting the bearings It s easier than using our tool although a third hand might be needed to get everything lined up take care to avoid accidental damage round by the raised surface rendering them useless If you have trouble slipping a bushing into a newly installed bearing the bear ing may well have been deformed by such a surface irregularity We found out the hard way on our project bike that someone who d serviced the linkage previously had done quite a bit of dama
9. e through a store entrance that would normally present little resistance to lighter traffic A linkage produces this same effect as the shock approaches its bot toming point It rushes and crowds the oil at an increasing rate as travel is used up thereby maintaining an ever firmer cushion to slow down suspension movement rather than transmitting a sudden jolt at travel s end Linkages can be designed to deliver a steeper or shallower progression rate to suite their intended use Some rear suspensions try to address the need for progressive damping by other means Instead of a linkage they utilize valving in the shock that allows oil to flow more freely at full extension and less freely at full compression You ll probably never read an article that says this solution is equivalent to a linkage setup at best they perform well for a non linkage system One such example is KTM s enduro lineup Fans of these bikes value the ease of shock R amp R literally a two bolt three minute affair the lack of linkage maintenance the reduced vulnerability to damage and the lower equipment cost Also unlike motocrossers these riders don t need their suspensions to cope with hard landings from high altitude the limitations of progressive damping shocks are less problematic without the demands of aerial acrobatics Linkages contain bushings and bearings to manage friction at their joints Because they re almost always located near the
10. g bone that we had to cut into their edge with a Dremel tool to break them loose Patience and a steady hand help mini mize damage to the bore ensure there are no protrusions In many cases it may be possible to safely hammer a bear ing out of its bore using a socket and its extension Although a bearing can at least theoretically also be installed via this same method the risk of getting it cocked in the bore is high We rec ommend using a screw action tool over a hammer and socket especially for installation If a rebuild is in order OEM parts must be ordered individu ally including bearings bushings and seals Aftermarket parts on the other hand are usually sold in kits that include all the neces sary items These are often less expensive than OEM parts and in some cases may offer superior performance and durability For our example we chose All Balls brand as they have an excellent reputation but we can t say whether our kit s components are actually better than their OEM counterparts Another respected name is Pivot Works When installing new bearings note that one side will be flat with a square shoulder and numbers etched into it while the other side will have a rounded shoulder The WWW MCNEWS COM OCTOBER 2013 39 Technical This old bearing was packed with mud and rust its needles barely turned at all latter goes in first the numbers should face outward If your bearings don t require
11. ge to the bore in the swingarm boss there were several big gouges on one side This boss is in an extremely awkward location which is probably what prompted the person to abandon good technique It also made visual inspection difficult and we didn t spot the problem before ruining a replacement bearing We had to pull the new bearing back out and smooth the bore s surface with a grinding tool and sandpaper Although the bore s condition is still less than ideal it no longer interferes with bear ing function a snug fit with no race deformation and this fix was much cheaper than buying a new swingarm The earlier bearing s movement was certainly far from smooth but it did rotate even with its race deformed because some of its needle bearings were pulverized The first new bearing we installed naively wouldn t even admit a bushing We can only assume that the prior replacement involved hammering the then new bushing into place Yikes So always carefully feel the bore s interior especially if you can t see directly into it and Here s our tool in action on the swingarm boss As that wrench gets turned the bearings are pressed from the far side into the near socket The whole thing must be held still at the all thread connec tor visible just inboard of the chain To max imize visibility the wrench for holding it isn t shown here This seal and bearing were corroded and so tenaciously stuck to the do
12. ller than the bearing s outer diameter thus allowing it to press the bearing through the bore and out the other side The other socket s internal diameter will be large enough to allow the exiting bearing free egress but small enough to maintain level contact with the linkage piece or swingarm frame boss It s just a matter of lining everything up and turning the nut on either side a pair of nuts forced together like any lock nut arrangement will provide purchase for a wrench to hold the all thread still against the turning of the nut on the opposite side Washers spread the load evenly and keep the nuts from getting caught in the sockets 38 OCTOBER 2013 MOTORCYCLE CONSUMER NEWS a We treated the shock joints to a good cleaning and some fresh grease replaced their seals and turned our attention to the linkage recesses Choose all thread that is as large strong as possible but that will still fit through the holes in your sockets The all thread can be cut to an appropriate length with a hacksaw Actually this very same process can be carried out with a table vice in many cases Obviously this won t work on a frame boss underneath the motorcycle But for linkage parts that are removed from the bike it s even easier than using all thread However during installation it may also be easier with a vice to apply great force with the bearing slightly cocked in its bore which will ruin the bearing and damage the b
13. not shown which we deemed unnecessary at this point and saved for the future For rear suspension service the bike must be supported from under the engine frame or sub frame the swingarm cannot bear weight It will however need to be supported to relieve extension pressure on the shock and linkage thereby allowing their removal Ugly old rugs come in handy when playing mechanic in the kitchen oer Ae ae si e This linkage is extremely compact to save weight and stay tucked out of harm s way relatively speaking It has actually taken quite a bit of abuse on this trials bike Linkage systems can include more segments but the principles involved remain the same WWW MCNEWS COM OCTOBER 2013 37 Technical The mounting points at both ends of this shock top shown look like they might contain nee dle bearings same as the other pivots in the system or perhaps just plain bushings but with the seals bushings and old grease removed they re actually spherical joints held in place with circlips Ours were snug and swiveled smoothly so we left them in a box Basically you ll run the all thread through the bearing the part housing it and a couple of sockets The sockets will be squeezed against the bearing on one side and the host part on the other side using nuts on the all thread On the bearing side the socket s outer diameter will be slightly sma
14. ore which is likely soft aluminum In any case proceed slowly and carefully While substantial pressure is required you shouldn t have to apply Herculean force if everything is lined up properly Also there are several ways to ease both insertion and extraction First recall that hot metals expand while cold met als contract Getting bearings in and out is easier when there s a temperature differential between the parts Use a heat gun propane torch or even just a bath of hot water seal the part in a plastic bag and immerse it in a pot of boiling water to heat the piece a bearing is to enter and leave the bearings in a plastic bag in your freezer for a few hours Then smear the bearing outer surface with a lubricant before pressing it into place Likewise heating the outer surface of the part housing the bearing prior to extraction will create a smaller heat differential between them Not only does this reduce the press fit tension but it may also break the grip of rust and corrosion at a microscopic level as the surfaces pull away from each other Speaking of rust and corrosion you may need to apply some penetrating oil to the edges of bearings that refuse to come out If stronger persuasion is necessary you can cut the bearing race with a silicone carbide Dremel bit Just a small cut will probably suffice once pressure is reapplied Be careful not to dig into the bore although a little of this is likely to be unavoidable an
15. se gun without disassembly unfortunately the vast majority do not Consult your owner s manual for a schedule of chassis lubrication but keep in mind that riding in wet dusty harsh conditions is apt to shorten the service life of bearing lubricants and subsequently the bearings themselves Also it s not uncommon to find that a brand new motorcycle may have been assembled with precious little grease in these and other load bearing components The good news is that getting your bike s rear end off the ground may be the hardest part of this process depending on your linkage s design Our example bike actually had only a small amount of tell tale swingarm free play However its linkage bearings were in much worse condition than that assessment suggested All had a gritty notchy feel when turned by hand and two were very hard to turn at all They were packed with dense sludge as though mud had been substituted for grease It was a wonder the rear suspension moved at all But so much weight and leverage are involved and so little rotation is actually required at each individual pivot that move ment was preserved just not smooth supple movement Action out back was much improved with new well lubricated bearings To do any actual service you ll need to not only support the bike s frame but also the rear wheel swingarm Off the ground those parts weigh on the linkage and try to extend the shock mak ing bolt extraction diffi
16. those possibilities you ll have to lift the bike by its frame This is accomplished easily for off road machines by hoisting them onto a stand that supports them from underneath their motors with their frame rails bearing the weight Some street bikes can be raised off the ground in this same way When this isn t possible there s another method available to the home mechanic without a hoist Use a workstand to lift the rear of the motorcycle off the ground This is only a means to an end it won t work for rear suspension maintenance because it doesn t remove any load from the swingarm Now get two tall jackstands ready near a sturdy place in the frame where you can slide a stout pipe through The idea is to have the bike s weight supported by this pipe on the jackstands once the workstand is removed Of course the area of the frame used must be strong enough to bear the bike s weight and should be free of finished surfaces that could get scuffed place towels between the pipe and the frame in any event This sounds more challenging than it really is on many bikes though some will be tricky Consider the juncture of the rear sub frame and the passenger peg supports Although it might require the removal of some plastic you can probably slip the pipe straight through above the wheel here and the bike will rest securely on it with little risk of tipping or front to back movement With the rear suspension unloaded grasp the ends
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