alanbrowne wrote:Hi all,
Recently bought a second hand RWD 6mph Puma 40.
Really good condition and all good so far, apart from at top speed I am getting a caster shimmy.
Reading on here there are various options to fix this, it has solid tyres all round so can’t lower the pressure, is it possible to program the controller to help with this?
I’ve attached a photo of it, I’m a Software developer so pretty tech savvy but it does sound like an expensive option.
Many thanks for any help.
Alan
hi i have a couple of pumas in the house and one thing i had noticed was both had shimmy at speed or after hitting a bump with just one caster wheel i tried as others have done/suggested ie increasing the preload on the bearings on the caster stem but this is a hit or miss fix too tight is awful and caster movement impeded,to loose and shimmy is worse,tried lower tyre pressure as ours have pneumatic tyres (the solids you have can be replaced with pneumatics as the standard wheel has the valve hole) to no avail one chair still does it at 6mph,then one caster wheel started making a funny horrid noise which got louder the faster you go so bought new set of stainless steel bearings and tried again chair quiet now but did notice even on the newer one the housing part of the wheel in which the bearing is seated is a very loose fit (the alloy is softer than bearing case) and shortly after the noise and shimmy returned so i risked using some threadlock(not permanent type) and reinserted same bearings and now noise and shimmy have both gone
and chairs done many more miles just fine,i do not quite understand how this worked as in my mind the wheel bearings should not be able to induce shimmy.
but only theory i have is a slight imbalance created by the small play in the bearing transmits beyond bearings and sets up vibration that caused shimmy,
threadlock is cheap whereas even used wheels on ebay are £40+ so if your wheel bearings simply push out with little or no effort the threadlock carefully applied so as to not get inside the bearings might be worth a shot and is easy job,good luck