suspension forks - drill vent hole or not?

[Galactic]

I'm in the process of renovating some suspension forks, I've undone them all and cleaned out all the gunk and rubbed off the rust. Now waiting on replacement springs before I put it all back together again. The forks rely on the springs only, no sign of any elastometers (unless they've rotted away?). My guess is the forks are at least 15 years old, but a stamp on each leg says 2000. ETA: They're Post Moderne Sporty 20" forks. There are no external signs of damage or wear, they fit together nicely with no play.

I've noticed there are neither draining nor vent holes in the lower forks, and there were a few ml of stagnant, rusty water in each leg. The lowers are ally, the uppers chromed steel, which is where the rust presumably came from, although there's no sign of any lamination or deep corrosion.

I'm very tempted to drill a 2 or 3 mm vent hole halfway down each lower leg (ie just below where the uppers end) to ensure moisture can escape. But another part of me warns that I may be weakening the aluminium alloy lowers and that I actually have no idea what I'm doing. These are the first suspension forks I've ever looked closely at, so have no idea how the moisture problem is usually solved.

Perhaps I'm expected to undo everything and take the forks apart once a year to dry and clean them?

What's the verdict, dear CUK forum? Vent hole in ally lowers a good idea or am I being mindlessly unintelligent?

Thanks

[Cyclothesist]

What make and model of suspension fork is it?
Don't drill it meantime

[Galactic]

What make and model of suspension fork is it?

Post Moderne Sporty 20"

[Brucey]

suspension on bicycles (no matter how it is achieved) tends to be problematic, one way or another. 'Maintenance-hungry' is a criticism which can be levelled at most MTB-inspired suspension systems, most bouncy forks included. IMHO the only examples of the breed that are worth having are probably those with so-called 'open bath' oil damping. Here, the main issue is not keeping water out of the forks, it is keeping the oil inside them. Needless to say, holes in the lower part of the forks are contra-indicated in this case.

[Cyclothesist]

As Brucey describes I too wondered if the fork lowers were meant to act as an oil bath - one that had long gone only to be replaced by rusty water. I wouldn't drill the forks. You could try adding a little oil after cleaning the forks. The seals are likely to be shot though. It could get messy.
Post moderne appear to be a Taiwan factory producing low end forks.

[Galactic]

The only way those forks could take any form of liquid-based suspension would be in sealed cartridges, which seems unlikely (albeit not impossible) given there's an adjustment bolt running through the lowers. The design of them would only allow dry (spring or elastometer) suspension.

Haven't drilled anything yet, there's no rush since if I mark up the position I can do the drilling at any time. I'll be putting them back together as soon as I get my new spring coils. Presumably a bit of grease around the lower parts of the uppers (where they slot inside the lower legs) wouldn't go amiss?

[Cowsham]

I'm in the process of renovating some suspension forks, I've undone them all and cleaned out all the gunk and rubbed off the rust. Now waiting on replacement springs before I put it all back together again. The forks rely on the springs only,

Why?

[Cyclothesist]

Assuming that you're not planning to immerse the forks in water (and the hubs too at that point!) why not drill a drainage hole at the bottom of the legs so that any collected water can drain immediately?

[POIDH]

I do not know that specific fork, however I have had the misfortune of being asked to 'fix' similar cheap forks.

First advice: just get rid of the fork. You will find that any 'seal' no longer does it's job, and those cheap forks rely on the seal and contact with a lower bushing (often just the fork leg). You will therefore find the fork leg will judder under braking and flex a lot. Rigid forks at a cheap price point (see your local recykabike) will work better. Even spending a few quid on a better fork that is branded, sealed and has an oil bath or damper will be so, so much better.

Second advice: they are usually greased internals, not oil bath or sealed cartridge like you get in nicer forks. So IMO, drill away and make sure you keep it greased.

Third advice: see first point.

[Cowsham]

I do not know that specific fork, however I have had the misfortune of being asked to 'fix' similar cheap forks.

First advice: just get rid of the fork. You will find that any 'seal' no longer does it's job, and those cheap forks rely on the seal and contact with a lower bushing (often just the fork leg). You will therefore find the fork leg will judder under braking and flex a lot. Rigid forks at a cheap price point (see your local recykabike) will work better. Even spending a few quid on a better fork that is branded, sealed and has an oil bath or damper will be so, so much better.

Second advice: they are usually greased internals, not oil bath or sealed cartridge like you get in nicer forks. So IMO, drill away and make sure you keep it greased.

Third advice: see first point.

I agree with the first and third bits of advice.

But I'd add a forth -- buy a rigid fork ( suspension corrected )

[DropperPost]

What's the verdict, dear CUK forum? Vent hole in ally lowers a good idea or am I being mindlessly unintelligent?

I haven't got any experience of maintaining a cheapo coil fork, although I've owned one in the dim-and-distant past, and it worked vaguely-okayish for years despite probably being half full of rusty water like yours. This is the big advantage of this type of fork - they just soldier on until something major happens, e.g. the spring breaks. Seth did a video on the most common version of this type of fork, basically praising them for being the right tool for a particular job, i.e. people who want a cheapo, low-performance, comfortable bike for general use, which they have no intention of doing any maintenance on:



You haven't posted any photos, but you mention getting rid of the rust, so I'm taking it as read that the stanchions aren't pretty? In which case, replacing the wiper seal won't give you good results, unless you try some of the exotic solutions to smoothing them out such as building up the voids and flat spots with nail varnish, and then sanding it down. (I've tried this in the past without great results.) But the fork doesn't require a good seal, so personally my approach would be to (1) keep the bike stored out of the rain and/or (2) make a 'gaiter' out of an old inner tube. I've done this on my bike's dropper posts, with outstanding results - they've worked perfectly for years despite living in a world of mud. You'd need to cable tie the top of the innertubes around the top of the stanchions and around the top of the fork legs. It won't look pretty, but it's a bit like the gaitered front forks on the old cheapo MZ motorbikes: really ugly, but go on for ever.

[Brucey]

I'm reasonably certain that the fork will be built with grease lubrication in mind. However that shouldn't put you off oil, bolts or no bolts, because bolts are very easy to seal. Usually no washer under the head, a few turns of PTFE tape, et voila! -job's a good 'un.

[Brucey]

...... and/or (2) make a 'gaiter' out of an old inner tube. I've done this on my bike's dropper posts, with outstanding results - they've worked perfectly for years despite living in a world of mud. ....

but dropper posts only to up and down a few times per ride plus it is usually fairly dark just there. These things conspire together and give as 'ersatz' inner tube gaiters a better chance. It should be possible to give proper rubber fork gaiters a 'fair go', despite them not being 'flavour of the month' just now. Forks generally see high levels of both UV light and flexing, whereas dropper post conditions (apart from the mud) are benign by comparison.

[DropperPost]

but dropper posts only to up and down a few times per ride plus it is usually fairly dark just there. These things conspire together and give as 'ersatz' inner tube gaiters a better chance. It should be possible to give proper rubber fork gaiters a 'fair go', despite them not being 'flavour of the month' just now. Forks generally see high levels of both UV light and flexing, whereas dropper post conditions (apart from the mud) are benign by comparison.

I'm pretty confident that my home-made gaiters have been through all the 'mechanical' testing you'd want, i.e. they've been used for many years with an average of, I would guess, 20 or 30 activations, per outing, with the seat spending the majority of time fully lowered, where the gaiter is crushed into a tight concertina. Both gaiters are still good as new, with zero signs of creasing, cracking or abrasion etc. (I've punched a hole at the back of each so they can open and close without pulling a vacuum.) I know nothing about the UV resistance of inner tubes though. My bikes spend most of their time under cover, so for all I know, that could well be a problem for a bike that lives outdoors.

But... your mention of using proper gaiters has reminded me that I did briefly look into putting gaiters on my own forks, but gave up as it was too difficult and my wiper seals do a good job anyway. The problem was the arch that connects the fork lowers together: in order to attach the bottom of the gaiter to the lower leg, you've got to somehow accommodate this arch, which requires a lot more than just a well-positioned cable tie. I did find a few commercial offerings online, but these rely on velcro and look a lot shabbier, more fragile and prone to mud-ingress than my inner tube/cable-tie method.

So... OP: apologies, my idea of making your own inner-tube fork gaiters is probably a non-starter. But Brucey: if you could design a decent fork gaiter that got round the fitment problem, I'd have a go at making it, plus I reckon it would sell.

[Brucey]

be realistic; 20-30 activations is about as much flexing as a fork would see in a few seconds. My experience has been that anything made from old inner tubes has a relatively short life expectancy outside, which is presumably why they use a quite different sort of rubber to make gaiters.

FWIW suspension forks on bicycles (quite sensibly) used to be designed with gaiters in mind. However, 'modern' ones are, for some reason, not. I don't think this is easily overcome.