As I continue to comb through the Internet archives of age-old Virago “Tech Tips” I am always amazed at the prolific information regarding leaking Virago Front Fork seals and the many methods that have been developed to tackle this repair. What I often wonder to myself is this…”Does anyone ever think to do any preventative maintenance by changing fork oil, and thus possibly preventing this type of failure?”. By my guess I’d say fork seals repairs take place more often than fork oil replacement. So to help those here who have never thought about why and how this type of effort might prove beneficial, I will rely on my background in petroleum fluids to explain why this might help.
As you know front forks are nothing more than fluid filled shock absorbers. Unless a dampening structure is present, a spring will extend and release the energy it absorbs from ab impact at an uncontrolled rate. The spring will continue to bounce at its natural frequency until all of the energy originally put into it is used up. Thus, a suspension built on springs alone would make for an extremely bouncy ride!
Enter the front fork (a spring shock absorber) a device that controls unwanted spring motion through a process known as dampening. Springs and hydraulic oil in your front forks slow down and reduce the magnitude of vibratory motions by turning the kinetic energy of suspension movement into heat energy that can be dissipated through hydraulic fluid. So in essence, a fork spring combo is basically an oil pump placed between the frame of the bike and the wheels. In a twin tube motorcycle fork design, the inner tube is known as the pressure tube, and the outer tube is known as the reserve tube. The reserve tube stores excess fork oil (or hydraulic fluid).
Now most of the fork oils/hydraulic fluids I’ve looked at tend to be very low viscosity (thin) oils, and most if not all contain little if any additives to protect against fluid degradation. Although heavily hyped by bike shops… many of the best known and popular fork oils represent inexpensive formulations and cost little if anything to make. We call them “sewing machine oils” in the industry because that is often times what you are purchasing in terms of quality. Most of them do little to prevent fluid breakdown and metal to metal wear. In reality… it is easier to put money into advertising rather than spending it on product quality. We all know that… right? Specifically you want a fork/hydraulic oil to posses excellent anti foaming chemistry, good oxidation resistance and heat tolerance, and above all…. excellent resistance to wear and corrosion. If you DID have a high quality oil in your forks, I guarantee that when you drained it out… it wouldn’t look too bad at all.
Have any of you ever drained old fluid out of your forks before? I’ll bet you saw really black, thick goopy oil come out of there! That’s because the old fork oil had oxidized and has thickened. And the black color represented microscopic metallic corrosion particles that acted like pumice, grinding the heck out of those poor defenseless rubber seals! Not only that, but in this degraded condition, the fork oil possessed little if any of it’s designed ability to properly dampen the spring motion. That is why you felt like your springs were mush, and you saw your seals leaking like a crying baby.
So what i recommend is this. Choose a “high end”… high quality full synthetic hydraulic oil and change your fluid every 2 years or so. The Germans make an excellent product that fits this bill, and it is called Pentose CHF 11S, and it is a primo synthetic power steering/level control fluid used in a broad range of European cars. It provides precise performance in a wide range of temperatures -40C to 150C (-40F to 302F). Be forewarned however that this stuff is very expensive. But then again… what great product isn’t! If you want an equally great/alternative product, then I also recommend using BG products Full Synthetic Power Steering/Hydraulic Fluid, part #334 (www.bgprod.com). It is an exact match for the Pentose Fluid standard, and will also deliver all the necessary fluid properties to guard against fluid breakdown and seal wear. Not only that, but both fluids contain state of the art seal conditioners, which are polymers that help the seal remain pliable and resilient even under high heat and the deforming stress of constant use.
What I recommend is this… drain out your old fork oil… spray the inner tubes with non chlorinated brake cleaner to rinse out all the metallic debris and oxidized oil, then blow the tubes dry until no more fluid or vapor comes out the drain hole. Then simply refill the tube with the exact quantity of new oil recommended in the owners manual.
I could go on and on for you by quoting some lab results of how these full synthetic European fluids peg out the chart for film strength and resistance to oxidation and wear, but space here prevents me from turning this into a research paper. Let’s leave it to be said though that if you send me an email I will “confidentially” let you know how well the oil you have been using holds up against the rest in a match of total product quality.
Until then I wish you all good riding weather. warm days and cool nights… and many miles of rides that don’t rattle your teeth!
Thanks again for your interest!