Brompton 3 speed hub problem
 

Hello everyone,
Not sure if this should go into the mechanical forum but since it is a Brompton I thought I would post here.

I am having a problem with my Sturmey SRF3 on my C type Brompton. I am
able to shift fine into all of the gears and coast fine in gears 1 and
2, but in gear 3, there is a fair amount of drag on the pedals and if
I back pedal at all in gear 3 the hub makes a lot of bad sounds. I
consider myself pretty familiar with the older Sturmey AW hubs so I
decided to take a look and see what I could find. I checked the right
cup and it was adjusted correctly, about half a turn out from finger
tight. I took the hub apart and checked for anything that was worn or
chipped and did not find anything that looked out of place. Please
let me know if you have any ideas regarding this. Oh and it isn't the
cold temperatures which was the first thing I thought so I brought it
inside and let it warm up over night and have the same problem inside
on my work stand.

Thanks,

Chad

You have covered everything I would have checked. Don't suppose the indicator rod is sticking slightly by any chance?

Nice thought on the indicator rod, the bike is right behind me, I just tried pushing on the indicator rod and it won't go in any further. This one really has me baffled.

OK. The noises, I am unsure of.

Three causes of the pedals trying to turn on over run in third gear are:

• Too tightly adjusted cones.
  
• No lubricant and or corrosion
  
• Wrong lubricant

Use of the wrong lubricant - specifically, too heavy a grade of oil or the wrong grease. The SRF3 and the AW too require a very light grade of lubricant on the internal parts, except for the main ball races at either side which use pretty ordinary bearing grease.

So far, you've eliminated the cone bearing adjustment, broken parts and obvious severe wear,and unless you've filled it up with the wrong lube that leaves a lack of lubricant.

Dry planet pinions might make noises, but then they would be making a noise in other gears too because they rotate all the time. Of course dry and corroded pawls and dogs on the top gear set up might cause harsh noise which wasn't present in the other gears. A dry hub can make horrible noises. I recenty bought a 39 year old R20 and the hub sounded dreadful when I pedalled backwards or spun up the wheel and then stopped pedalling. I put in a good amount of 3 in 1 oil and it was cured in minutes.

If you've looked for broken parts and found none, I'd come down on a dry hub. You can trickle some light oil into the hollow axle while the bike is lying on its side or squirt it in with an oil can. If you've tried everything else, squirt some in - about three tea spoons full. If you put in too much, it will just come out and mess up the wheel. this is easily cured by washing it down. with a squirt of that citrus bathroom kitchen cleaner. This is a tremendous degreaser when used neat.

My hub has run purely on light oil for 2500 miles and is totally good, even though it is a grease type hub as all the SRF3 ones are. You just have to keep on with adding a few drops of the oil every month or so once you start on that game.

Let us know how you get on. I am really fascinated by these hubs.

There is another cause for pedals dragging, too tight chain. But yours has noise...

So, here is my experience:

The 3sp AW that came on my R20 ('76) I have never liked much. It has those same problems, dragging pedals and noisy back-pedal. I have tried everything without much success, but I *think* I know what the problem is.

You mention undoing the RH cone a half-turn from finger-tight. That may be the problem. Undo it 1/4-turn only. What I *think* happens is the inner works rubs on the shell at the RH side from too much play, producing a distinct rubbing sound. So have another look at the cones and adjust especially the left one with as little play as you can, allowing the tiniest amount of knock at the rim that you can get. This reduces the problem by pulling the inner works to the left as much as possible. But in my case that improves it for a little while only. Very frustrating.

As I said, I am not sure about my diagnosis, but it's the only thing that remains after eliminating all else. Another much older hub I have has none of these problems.

SunRace Sturmey-Archer S-RF3 hubs are lubricated from the factory with Sturmey SA103A synthetic grease. I would NOT add oil to this synthetic grease. I would never put 3 in One in an IGH in any case - it is both too acidic and it has a vegetable based component that will go rancid and turn into a very non-lubricant.

If you really think it might be a lubrication problem, open the hub and check. (I bet you'll find the internals are slathered in SA103A.)

The S-RF3 manual is located here. There is a fault diagnosis table on page 3.

HTH,
tcs

Thanks everyone for your helpful suggestions.
I have opened up the hub, disassembled completely and there is quite a bit of the factory grease inside and I did not add anything to it. or degrease anything.

Thanks for the link to the manual. The chain shouldn't be too tight since this is on a Brompton and chain tension is maintained by a chain tensioner. I will try going only a quarter turn on the right hand cone and tighten up the left one a bit more to see if that helps. Thanks for the suggestions.

If it doesn't improve, these hubs are extraordinarily cheap. As long as the dogs inside the original hub casing are sound, you could buy a new hub, open it and substitute the internal unit for the defective on in your wheel. That way, you have no wheel building to do. I just got a spare one of these for £35 built into a new wheel, so you wouldn't be paying much.

Just for clarification - re TCS's comment, I put the 3 in 1 into an ancient siezed up hub just to free it off. He is right that 3 in 1 isn't the right thing. It gums up, but mine will be cleaned out when I refurbish the bike. I will flush it out with clean mineral oil. As it was, it was totally dry and full of rust when I looked into the oil port.

The SRF3 runs very well with light weight engine oil. It is freer running and very slick in changing. I am well pleased that I did that experiment.



Over tightening cones will certainly make the pedals rotate in top gear. The manual says so, and I have seen it with my own eyes when I was experimenting with a sound SRF3.

No need to buy a whole hub. You can actually buy the mechanism (minus the hub) as a unit. You'll have to ask at a bike shop that sells S-A. They have a price list that shows it (or did last year).

Good point. I've just seen the whole hub for really low prices, but as long as the wheel, hub casing and its built in ratchet / dog thingy are ok, the internals if available will be fine. A whole hub is ridiculously cheap if not.

I'm not sure how many miles that original hub of his had done, or why it started this misbehaviour. He seems to have covered everything that would cause the problem he describes other than a failure in some part that he hasn't found yet.

The bike is only a little over a year old and I would guess has less then 400 miles on it. Currently the bike is at another shop with them taking a look at it. I told them not to spend too much time on it as I can replace the hub or all of the internals pretty inexpensively thanks to the advice given on this forum.

Four hundred miles is absolutely nothing. Mine has 3600 plus on it and I expect to see it go three times that and more. I was surprised you were having trouble even when I thought it had been hammered around for a few years on a daily commute.

Good luck anyway.

I read through a Sturmey catalog that had numerous testimonials from riders who had completed tens of thousands of miles without trouble.

The catalog was published in 1908!

tcs

how's the shifting? is it as easy to downshift as it is to upshift?
if the shifting is way tight in any of the gears open up the cable cover where it meets the pulley and try giving it some slack using the cable connector (small locknut and rod connected to the pulley chain which can be 'opened up' to give slack).

how tight is your bicycle chain? have any stiff links?

Hi Rekall,

Thanks for your thoughts on my problem, The hub seems to be able to shift between gears fine both ways. Not sure what you mean by cable cover, but I have tried tightening and loosening the shift chain adjustment either way and it does not appear to have an effect on this problem. This is also what the shop tried as well while I was still there.

Didn't seem to have any stiff links on the bike chain, and as for chain tightness, the brompton uses a chain tensioner kind of like a rear derailleur to keep the slack out of the chain so I wouldn't think that is the issue. Calhoun Cycle (a great shop) has had my bike since Friday, if they can't figure it out I will contact Sturmey and perhaps contact Brompton again (no response from them yet)

hmm, tough luck then.
quite a mystery!
keep us posted if it gets solved; i just installed an srf3 myself and no problems yet but as they say, knowledge is power :)

p.s. i did just think of something else; have you been shifting while pedaling, or allowing the bike to coast while the hub switches gears? i just learned from the shop that made my wheel that the best thing is to shift Without pedaling... dunno about the mid-to-long term effects of doing it 'the wrong way' (aside from a pretty awful noise, and feeling some awkward pedal drag).

I have shifted both while pedaling and while not pedaling, usually when pedaling though you have to loosen up a little bit to get it to shift. The hub never seemed to have any issues until this one started. Personally I think something like the axel is probably bent, which I should have checked when I had it apart, but I will wait and see what the shop says. If they give up, the next thing I will check is axel straightness and then I will have them order me new insides.

The strange thing is that it drags in 3rd, but not in 1st (both gears use the planetary system). That implies to me that you're not getting full engagement in 3rd gear, or some of the internals are contacting one another. It's tough to say without opening it up.

different sets of pawls engage the hub shell in 1st and 3rd. This is why I think in 3rd, the side which does not engage, ie which would produce the ticking while pedalling in 3rd, is the side which is dragging its pawls or something against the shell.

The dragging of the pedals around in third gear when freewheeling is a common failing if the hub is corroded, unlubricated, lubricated with too heavy oil / grease, or has the cones too tightly adjusted. I think it says that in the trouble shooter chart, but you seem to have already dealt with these issues so I am at a loss. In these cases, it doesn't happen in first gear either.

Could you go into more detail about the nature of the noises you mentioned? We aren't talking about a sharp ticking sound are we (sorry if that's patronising) because that's normal in third gear. If you spin the pedals backwards when the wheel is rotating you get a pretty buzzy sound from the hub as the pawls skip over the dogs at extra quick speed. I suppose it isn't that kind of noise we're talking about is it? Again - sorry if that is VERY obvious to you - just casting my mind over what it could be.

Thanks again everyone for the continued helpful advice. I am going to call the shop today and see if they have had any luck with the hub. If they haven't, I am going to take the bike back and tear down the hub and check the following in addition to what I have already done:
1. Check and see if somehow the axle got bent somehow, I wish I had checked this when I had the hub apart and before I brought it in to the shop
2. Degrease everything in the hub and then re-grease using SA103A if it is available at the shop, otherwise I will probably use 5w30 engine oil unless someone here tells me not to :-)

Trying to describe a noise is rather difficult, It is a lower pitched clunking sound rather then the usual tingy high pitch normally heard from the pawls. if after doing the above I still have the issue I will record it and put it on youtube or something. I have a week off over Christmas and New Years with very little to do so I should have the time to track this down which to me is now more interesting then just giving up and replacing the hub internals. However if when I call the shop and they tell me that Brompton decided to warranty the hub you won't hear me complain. :-)

If you are looking inside and the hub is well greased up with clean SA103A, I doubt there is anything to be gained in solving the noise by clearing the original lube off. If it's lubed with the right stuff - and it is, it isn't that that's causing it.

Clunking is definitely not right (as you knew of course). Only time I ever heard a rough grinding type noise was when the cable was maladjusted and at a certain setting that occured, but I think it came between second and third. If you can get third properly, it isn't that.

Just as a last ditch effort, try slackening the cable a bit more and see if that cures it. ..... I guess the mechanic would have done that, and I think you said he re-adjusted it.


Well good luck either way

Something's bent I reckon.

Bike shop called yesterday and said they had it fixed, but said it was a cable adjustment problem. Unfortunately when I stopped at the shop I put it in the test stand and the problem was still there, they were stumped but did notice that when the hub makes the awful noise you can see the indicator chain moving back and forth, that was an important detail I missed.
I brought it home and tore the hub down again and checked the axle on a pair of V blocks for straightness as someone suggested earlier, looked good. Re-assembled the hub and the problem was still there. Decided to follow the advice mentioned earlier on the forum by EvilV I believe, loosen the right hand cone a bit, tighten the left hand cone a bit which should move the "innerds" to the left more. Repeated this a few times so now I am slightly more then a half turn out of finger tight on the right hand cone and the problem has gone away.

Thanks so much for all of the help :-)

Glad you got it sorted out fafnir! I have to remember this tip.