Sturmey Archer 5-speed ( sprinter, etc. )

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Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: S.A. 5speed

Postby Brucey » 25 Aug 2014, 6:38pm

sorry I missed this before; it isn't easy to tell (ahem) but that looks like the remain of a 2/4th gear ('secondary') sun pinion from a dog-locking sprinter 5s hub (~1993-1996).

I don't know how commonplace this failure is; however I do know that they redesigned the hub to the ball-locking version in 1997.

I also think that if there is already a minor fault already in the hub (e.g. a tiny burr on the axle key, a bent control rod, a piece of crud in the wrong place, etc) it may be possible for both suns to be (very briefly) both locked onto the axle.

I have previously calculated that under normal conditions the load on the key could be up to around 2000lbs (bloke standing on the pedals, normal gearing). However if both suns get locked at the same time, the force can become enormous because there is a relatively small difference between the 4th and 5th gear ratios, and the smaller the difference, the higher the force generated. I estimated around 6000lbs for this fault condition.

Another fault condition arises if the control is bad between 3rd and 4th, which is slippage of the main clutch on the planet cage. This condition can produce extremely high shock loads through the fourth gear train. I cannot estimate these with any accuracy except to say that if they are x5 to x10 more than normal it wouldn't surprise me.

In your case the primary gearing was lower, so the loads on the gear parts would have been pro-rata higher.

I do not think that the dog-locking sprinter hub is well-supported for spare parts now; it may be possible to convert to a ball-locking arrangement; for this you will need (at least) a new axle, new sun pinions, and a few other parts, so is not an economic repair

Sun Race's current 5s hub the (W) variant uses a revised version of the dog-locking hub, but the gear ratios are different. I don't think the parts are compatible. This hub also uses a redesigned main clutch with a deeper engagement, as the previous 5s hubs (basically all sprinters) proved susceptible to clutch slippage in 4th gear unless adjusted perfectly.

I have a theory that draggy gear cables are very likely on bromptons (which will mess the 3rd to 4th shift up first) because of the fold. I've looked at several sprinters from bromptons and they all had badly worn clutches. By contrast the ball-locking sprinter on my heavily used pashley (which will have seen much higher torque loads than any Brompton) is fine.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

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breakwellmz
Posts: 1982
Joined: 8 May 2012, 9:33pm

Re: S.A. 5speed

Postby breakwellmz » 26 Aug 2014, 1:57pm

Hi.

It was a unit with fresh oil and new control rod that was reconditioned by SA specialists.The change was also`sweet`and positive in the few hundred miles i probably did on it before it broke.
I`ve lost any faith i had in a SA hub with more than three gears, hence my Shimano Nexus 7 hub being built into a 700c rim.

Brucey
Posts: 32272
Joined: 4 Jan 2012, 6:25pm

Re: S.A. 5speed

Postby Brucey » 26 Aug 2014, 4:37pm

I can understand that you might have lost faith in it, I would have too. However of the many flavours of 5s hub there have been, that is not one of the strongest ones, which is why they redesigned it after a few years. Barring the spring modification to one other version of 5s hub, only the '5 star' hub had a shorter service life than that one I think.

I would also wonder if the parts were dye penetrant inspected or not when the gear was reconditioned.

Is it back to a 3s then?

cheers
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breakwellmz
Posts: 1982
Joined: 8 May 2012, 9:33pm

Re: S.A. 5speed

Postby breakwellmz » 27 Aug 2014, 11:09pm

I`ve always fancied the Nexus 4 actually but.......

Brucey
Posts: 32272
Joined: 4 Jan 2012, 6:25pm

Re: S.A. 5speed

Postby Brucey » 28 Aug 2014, 7:28am

breakwellmz wrote:I`ve always fancied the Nexus 4 actually but.......


The Nexus 4 hub is a good hub for utility riding but...

a) it is a 'gear up' only hub. You need your direct gear to be bottom gear, so small chainring, large sprocket.

b) if you set up the gear in the normal way (3rd normal) then you will ride furthest in the second least efficient gear of the four.

c) The pinion bushings are plain and have grooves in the bearing surfaces; with standard lube these do seem to wear.

d) the gears work a bit like 5-8 in an N8 hub, but IIRC the clutching is done as per an N7 hub (inwards facing pawls inside the sun pinions that engage with steps on the axle)

e) you can't get spares for this hub any more.

f) I don't think that this hub is necessarily very good for anyone who is going to give it a lot of hammer; most utility riding is in the saddle and the rider isn't looking to get sweaty doing it. If you (say) enthusiastically ride up a single hill out of the saddle in 3rd gear then you may have used up about a year's worth of 'utility riding axle fatigue life'.

g) most of the shifters that work this hub are rubbish. The one to go for is the trigger shifter IMHO.

h) you can also use any N7 shifter with this hub, using the first four positions. The revoshift style versions are similarly poorly thought out for the most part too; the saving grace is that you can buy them and they are not too expensive.

I) the hub isn't very well sealed; corrosion in the driver ball race is quite commonplace.

j) the hubshell appears to be 'all hard' steel; I don't think it is easy to install a lube port in these hubs.

cheers
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breakwellmz
Posts: 1982
Joined: 8 May 2012, 9:33pm

Re: S.A. 5speed

Postby breakwellmz » 28 Aug 2014, 7:49am

Thanks.
I think you have succeeded in putting me off it. :wink:
I came across a bike with one in a shed of a garden we were clearing yesterday, the owner is considering getting rid of it.I`m sure it had an alloy shell.It also came with a rotary shifter, roller brake and stainless 700c rim-YUCK!