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Low friction material for a bushing

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Hi guys,

I’m a keen mountain biker and I’m getting fed up of the bushings in my rear shock wearing rapidly. Well, I don’t mind them wearing but they are quite expensive! This got me thinking, why not just make some myself and keep a bunch in the drawer so I can swap them out as needed?

So my question is, what to make them from?

The existing ones on my bike are a plastic bushing that is pressed into the shock with an aluminium shaft running through it. I have seen some people run a brass shaft (I’d probably prefer bronze myself) through a plastic bush but is there any merit in running two bearing materials against each other?

The ultimate aim would be to reduce friction as the difference can be noticeable when out on the bike (I used to run needle bearings but these seemed to come out of the box with a little play which worsened rapidly. they did make the suspension much more supple though).

I was thinking a plastic DU bush and a bronze shaft but if there won’t be any improvement over a steel shaft then I won’t bother with the added expense. I was thinking D2 tool steel hardened to somewhere around the 52 HRC mark if not bronze.

Any help would be greatly appreciated!
 

Comments

check out Vesconite I am running them as link pin spacers for my offroad buggy kinda expensive stuff. the other I have used is a nylon with moly impregnated into the material. I am no expert but this has worked for me.
 
Nylon would work for that. It won’t squeak and will last a long time. I have made them for 3 wheel ATVs and they hold up for same purpose.

Just do the bushing by itself not the shaft.
 
An off road bike gets dirty. Is the shock assembly designed to keep all the dust, dirt, and grit out of it? What it is made out of doesn't matter if it is always contaminated. Make sure that issue is addressed first. Sometimes the designers use the frame itself as the "clean space", and only have seals where the parts slide into the frame. The inside of a bike frame is not a clean place. Another issue is having oily rods out where the grit is. That is a lapping machine. After all that is considered, then think about maybe changing materials...
 
If you look at the stock bushings from Fox and Rock Shox, they are a slight press fit and come from the factory with a loctite compound on the mating surfaces. If the bushing fails, you're a mile away from destroying the mounting eyes on your shock.

When I ruin the stock bushings after a season, I go straight to RWC at enduroforkseals.com and get their needle bearing retrofit kits. I've put them on a number of bikes, raced them hard, and never had a problem.
 
Teflon will spread under pressure. I use it for telescope bearings where the very low stiction is a bonus.
I would go sealed needle rollers.
 
When I replaced the rear shock bushings in my MTB I turned some bearing bronze shock bushings and used a titanium through bolt. Seemed to work well, the previous shock had aluminum bushings with a SS bolt. The shock travel is short and the pivot movement is small, all the other suspension pivots use sealed ball bearings. A big problem with these bearings is no matter how good the seals are water and moisture get in and they get pretty nasty. The needle bearings from RWC have seals, but if you get the bike wet a lot I might opt for something simpler and use some Teflon grease to keep the moisture out. If you have a long travel rear suspension, the needle bearings would give the least friction, bearing bronze bushing may be more durable. UHMW (ultra-high-molecular-weight polyethylene) might be an option. Turning UHMW is difficult from what others have posted.
 
Thank you all for the replies - it's good to know I'not the only mountain biker!

Something like this maybe: https://www.mcmaster.com/bronze-sleeve-bearings
Hardened shaft for that to run on would be nice.
Being familiar with (dirt) motorcycle shocks, the shafts are hard chrome, but they are running needle bearing on them also.
I did consider oil impregnated bronze. I did a very quick search and couldn't find anything of a suitable size for my shock and it seems that it isn't available in bar form. That being said, it was a very [very] quick look.

An off road bike gets dirty. Is the shock assembly designed to keep all the dust, dirt, and grit out of it? What it is made out of doesn't matter if it is always contaminated. Make sure that issue is addressed first. Sometimes the designers use the frame itself as the "clean space", and only have seals where the parts slide into the frame. The inside of a bike frame is not a clean place. Another issue is having oily rods out where the grit is. That is a lapping machine. After all that is considered, then think about maybe changing materials...
That's a fair point. The modern Fox bushings come sealed with o-rings and seem to do a fairly good job of keeping the grime out. The shock and the frame is exposed to the elements however the frame itself acts as a shield so mud and water isn't directed at the bushings. The bushings are installed dry so as not to attract dirt.

If you look at the stock bushings from Fox and Rock Shox, they are a slight press fit and come from the factory with a loctite compound on the mating surfaces. If the bushing fails, you're a mile away from destroying the mounting eyes on your shock.

When I ruin the stock bushings after a season, I go straight to RWC at enduroforkseals.com and get their needle bearing retrofit kits. I've put them on a number of bikes, raced them hard, and never had a problem.
The newer DU bushes that come stock on Fox shocks are a plastic of sort and do not come with any form of retaining compound on them (see below). I can't vouch for Rockshox as I've not run any of their rear shocks before.

1546502360117.png
I have tried the needle bearings from enduro. The first one I tried was sweet and lasted about a year and a half. It made a huge difference to the feel of the bike. The next three however the shaft was a sloppy fit in the bearing so there was play in the bearing before I'd even hit the trail. Eventually the play drove me mad and I reverted back to standard bushes.

Teflon will spread under pressure. I use it for telescope bearings where the very low stiction is a bonus.
I would go sealed needle rollers.
That's good to know about teflon and it is certainly something I shall consider before using any!

When I replaced the rear shock bushings in my MTB I turned some bearing bronze shock bushings and used a titanium through bolt. Seemed to work well, the previous shock had aluminum bushings with a SS bolt. The shock travel is short and the pivot movement is small, all the other suspension pivots use sealed ball bearings. A big problem with these bearings is no matter how good the seals are water and moisture get in and they get pretty nasty. The needle bearings from RWC have seals, but if you get the bike wet a lot I might opt for something simpler and use some Teflon grease to keep the moisture out. If you have a long travel rear suspension, the needle bearings would give the least friction, bearing bronze bushing may be more durable. UHMW (ultra-high-molecular-weight polyethylene) might be an option. Turning UHMW is difficult from what others have posted.
The frame is a Santa Cruz Tallboy LT. The issue with the VPP suspension design seems to be a high range of motion in the lower link which causes rapid wear and i have seen a number of people complaining of this online. I agree that in theory a needle bearing makes more sense but from past experience they are not reliable enough. Thanks for the suggestion of UHMW though - certainly something to look into!
 
I would use a sintered bronze( oil impregnatd) and 316 stainless for your shaft. I'd turn the stainless down shy .001" then emery cloth the last .001" to achieve the finish desired. Would last unless dirt entered the equation.
 
Delrin is a plastic designed for bushings with a SS shaft. I bet most of the wear is dirt ingress into the bush. Why not machine aluminium caps with internal O rings to fit over the ends of the bush.
 
Make the bushing from 6/6 Nylon. It is easy and not expensive. If it works you could make them for others that have same issue. And a nice simple lathe project.
 
Turcite is made for just this type of application. Self lubricating but not as brittle as oilite or bronze bushings.
(link for reference - not researched as a purchasing option) https://www.boedeker.com/family/turcite
And, as pointed out before I would incorporate seals, o-rings or other method of keeping dirt out.
 
Thanks guys for the suggestions. I think I would certainly incorporate an O ring recess into the spacers and / or bushing. From doing a little more research about it would seem that the ones supplied by the manufacturer are IGUS bushes. Not entirely sure what the materials used are but they advise using a hardened aluminium shaft or stainless steel for wet environments which confirms my suspicion that there isn't a need for both the bush and the shaft to be made from a bearing material.

Another plus for making them myself is to experiment with different offsets to alter the geometry of the bike. Quite excited about making a few and doing some back to back testing!

I shall look into the availability of the various materials mentioned above and see what would be the most suitable. I like the idea of the oil filled bronze but i suspect that Derlin (or Turcite which seems to be a variant) will be the more readily available alternative.
 
Sami-
I've been out of the game for the most part since I raced the Megavalanche a few years back. Just during the train-up, I broke two fingers in my hand, sustained a neck injury that still causes big issues, got a puncture wound from a branch in my leg from crashing into a tree, ruptured the saphenous vein in my right leg (twice from riding too soon after injury), had blood clots between my shin and peretoneum, and more bruises than I can remember.

I have had 3 VPP (DW link) bikes, and all of them ate pivot bearings. Most of the cartridges are doubled for single race bearings, some use double row bearings. The doubles are very expensive and last a year (at 100 km of singletrack a week). I have not had any issue at the shock eyes on those bikes. One thing I've noticed after servicing lots of Fox (I made Fox parts in the CNC shop I worked at in "99-'00), Rock Shox, and CC shocks is that the tolerances in the bushing eye are broad. I suspect they tolerance match the mating parts. Sometimes, bushings press in and out easily, other times it's sketchy. Some of my RWC kits have fit better than others. One kit I installed on a Fox was so tight that the bearings got brinelled, so I get what you're saying. Oilite or other bronze sounds great from the point of view of this forum, but I think it is too hard and will ruin your shock eyes. If you achieved a perfect press fit with bronze, it might be okay, but I think up until now that aluminum has been the choice because it is light and soft enough to be sacrificial. Maybe hard plastic is the way to go, or some bushed combination. But combining rigid and soft material brings us back to the status quo of a soft bushing and aluminum inserts.

When I'm doing a lot of riding, I wash, oil, and re-grease once or twice a week. That keeps everything working and dialed. I just don't give crud a chance to accumulate.
 
Are the bushings the top hat bushings for the shock or the swingarm/ link bushings?

If you want the premium feel, roll your own needle bearing set up using a hardened shaft for the needles to roll on and a suitably sized hardened outer cage to press into the frame. Or make up a ton of bushings from Delrin at once and simply change them out at regular intervals. If you make up a little press kit to press them in and out it won't take long. I think Turner went with (maybe still does) bushings for the support and the limited rotation of most suspension bearings. His had grease ports for each bearing though. That by be another option - that way you'll be able to force any grit out that gets in there and lube them at the same time.
 
Vesconite was mentioned. This is a plastic invented in S Africa and used extensively in the mining industry to replace p bronze bushes in heavy earth moving equipment. The p bronze just did not make the grade.
It is also used for ships rudders and props .
 
If the needle rollers are not spinning they will wear divots in the shaft. My Jaguar uses needle rollers on the rear suspension fulcrum shafts and these only travel through about 15° it wares divots in the shaft bush. I made bronze bushes with grease channels and fixed the issue for good.
 
Have the shafts coated or plated with a low friction material such as hard chrome or titanium nitride, make the bearings from a low friction low wear plastic material such as PEEK filled with PTFE and carbon as seen here https://www.ensingerspi.com/material.cfm?material=PEEK

This combination should last a good deal of cycles, everything may be done in the home shop aside from the plating or TIN coating.
 
Have the shafts coated or plated with a low friction material such as hard chrome or titanium nitride, make the bearings from a low friction low wear plastic material such as PEEK filled with PTFE and carbon as seen here https://www.ensingerspi.com/material.cfm?material=PEEK

This combination should last a good deal of cycles, everything may be done in the home shop aside from the plating or TIN coating.
The company I work for has a sister company who can chrome plate but to be honest, I suspect that unless it was for a large batch the cost wouldn't be worth it. I am leaning towards a low friction plastic with a hardened shaft. I should be able to make these at a fairly low cost - as long as I get comparable life out of them compared to the stock ones I can have a heap in the toolbox and swap them out as needed. It's only a 10 minute job to do.

Someone suggested UHMWPE and some research into it makes me think it could be the most suitable material. It has a coefficient o friction comparable to PTFE however is much more abrasion resistant.

Whatever I use I'll look to seal them with a couple of O-rings as well as others have said.

Thank you all for your comments - they have been most helpful!
 
McMaster-Carr sells a nylon-kevlar composite that is claimed to be "ultra wear-resistant". They also have MDF-filled nylon. I have machined both using sharp HSS tools. I initially tried using a carbide-insert cutter on the composite, with poor results. If you do try the composite be prepared for long, stringy swarf.

I got the composite to experiment with making polishing bits for a machine at work, so it was deliberately exposed to abrasives. It held up quite well. However, I didn't need very accurate machining tolerances so can't say how easy it would be to make a bushing out of it.
 
Very interesting reading through this thread. I am amazed at the specialized plastics these days. In the fruit packing houses I used to work in we used 1/2" and 3/4" keystock as chain guides on the bin dumps and they needed to be cut out and changed every couple of seasons. The bins would come out of the field and be muddy and be washed in the dump so it was very muddy messy and even though the chain rollers rolled on the keystock it wore them out in no time. When we changed to UHMW guides that all went away. I never saw anybody have to change them except in a house that did radicchio. Something in radicchio it ate UHMW!

In another house we leased a cardboard box maker. We had guys from the company in and out of there all the time and I got to know them. If the boxmaker went down, the shed went down so it was a big deal and they had been struggling with the shafts in the rams that form the boxes wearing out. After going through all kinda of exotic hardened alloys they went to pins made out of Delrin. Yup, had to believe. And they made them a press fit. If it didn't shave off curls as they drove it home it wasn't right. I was VERY skeptical and kept a wary eye on it and they never went down.

So I bring this up because what if you had a Delrin shaft on UHMW bushings?
 
so here's another idea: If you go with Nylon or Delrin bushings, you can increase their life considerably by coting the mating surfaces in Plumbers Grease. It is used in a lot of Nylon plumbing assemblies and is hydrophobic (keeps the moisture out). You can then remove the shaft at intervals to clean up the outer mm or so that might accumulate detritus...
 
Very interesting reading through this thread. I am amazed at the specialized plastics these days. In the fruit packing houses I used to work in we used 1/2" and 3/4" keystock as chain guides on the bin dumps and they needed to be cut out and changed every couple of seasons. The bins would come out of the field and be muddy and be washed in the dump so it was very muddy messy and even though the chain rollers rolled on the keystock it wore them out in no time. When we changed to UHMW guides that all went away. I never saw anybody have to change them except in a house that did radicchio. Something in radicchio it ate UHMW!

In another house we leased a cardboard box maker. We had guys from the company in and out of there all the time and I got to know them. If the boxmaker went down, the shed went down so it was a big deal and they had been struggling with the shafts in the rams that form the boxes wearing out. After going through all kinda of exotic hardened alloys they went to pins made out of Delrin. Yup, had to believe. And they made them a press fit. If it didn't shave off curls as they drove it home it wasn't right. I was VERY skeptical and kept a wary eye on it and they never went down.

So I bring this up because what if you had a Delrin shaft on UHMW bushings?
I hand't considered using plastics for both surfaces. My only concern would be that if the bore was drilled off centre then there would only be <0.5mm material on the shaft so not sure if it would deform under load.

so here's another idea: If you go with Nylon or Delrin bushings, you can increase their life considerably by coting the mating surfaces in Plumbers Grease. It is used in a lot of Nylon plumbing assemblies and is hydrophobic (keeps the moisture out). You can then remove the shaft at intervals to clean up the outer mm or so that might accumulate detritus...
I hadn't considered using grease - I had always been under the assumption that plastic bearings should be run dry although I must admit I have no idea why I think that!
 
While derlin + nylon might be fantastic w/regard to low friction, there are other factors to be considered, like the load the shaft has to take when this here shock is in use! It's necessary to design for worst-case, because, you know, Murphy is always lurking in the wings......
 
I hand't considered using plastics for both surfaces. My only concern would be that if the bore was drilled off centre then there would only be <0.5mm material on the shaft so not sure if it would deform under load.
I've always thought that a bushing should be softer or harder than the shaft, but not the same. I can't think of many things that use the same material for both the bushing and the shaft from the factory?
 
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