SRAM A2 Automatix; introduction to the internals

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Brucey
Posts: 32765
Joined: 4 Jan 2012, 6:25pm

Re: SRAM A2 Automatix; introduction to the internals

Postby Brucey » 18 Aug 2014, 12:43pm

I suspect that these hubs are prone to corrosion damage (the sealing etc is very little different from many other IGHs) if used in all weathers but I have not yet seen this in one of these hubs with my own eyes. Other troubles appear rare; remember that the basic internal design is well proven; automatic 2-speed hubs of this sort have been available (on and off) for nearly 50 years. I first rode one of these hubs in about 1971 when I was a nipper; they were not (certainly widely, perhaps at all) sold in the UK at that time but one of my school chums had one on a bike that had been brought back from Germany. It felt very odd indeed then to ride like that and disappointingly my chum seemed reluctant to have his dad take it to bits so he could tell me how it worked.... :wink: It is possible that the change of manufacturing plant (was Germany, now Taiwan) may have introduced some anomalies but the basic design is sound.

There are some reports of the shift point not matching the expectations of the rider, which I attribute to poor hub selection in some cases; I am not sure of the current state of affairs but there used to be two distinct models available; one for small-wheeled bikes and one for larger wheeled bikes. In any event the shift-up point is fixed in terms of wheel rpm and this is a different speed pro-rata with wheel size. If the shift point is wrong the only cure is to do something with the shift control spring.

In terms of first use I would adjust the bearings correctly, use the hub a few hundred miles, then regrease before winter comes.

I think it is best to use spoke washers when building on these hubs because the flanges are not very thick.

cheers
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garry71
Posts: 3
Joined: 17 Aug 2014, 9:10pm
Location: Brum

Re: SRAM A2 Automatix; introduction to the internals

Postby garry71 » 18 Aug 2014, 6:10pm

Thanks Brucey.
I'll have a look on Amazon for a couple of 22mm spanners. I've ground spanners down in the past but it's a right chore, so I think I'll treat myself this time.

I have some lithium-molibdenum grease which I can use for when it needs regreasing. I might put a generous dollop inside the grey cap on the sprocket side to help keep water out anyway.

Cheers
Garry

Prodigal
Posts: 106
Joined: 27 Nov 2008, 10:22am
Location: Warwick

Re: SRAM A2 Automatix; introduction to the internals

Postby Prodigal » 1 Oct 2014, 10:16pm

This is a long thread, so apologies if this is answered elsewhere. I've just fitted my Automatix hub onto my recycled hybrid. I'm running 700 x 35s/38t front chainwheel/22t rear sprocket. Slightly higher gearing than I'm used to, but I'll get used to it. Anyway, my question is that is it right that I have to stop pedalling for the hub to change down? It changes up fine, but I'm having to stop pedalling for it to change back down however slow I'm going. No big deal, but I'd like to know.

Brucey
Posts: 32765
Joined: 4 Jan 2012, 6:25pm

Re: SRAM A2 Automatix; introduction to the internals

Postby Brucey » 1 Oct 2014, 11:23pm

if you continue to pedal firmly these hubs tend to 'hold' the high gear, but they usually downshift without you having to stop pedalling altogether.

[edit; this appears to vary with the hub type; it seems to me that the type intended for use with large wheels (with a low hub rpm shift point) does 'hold' the gear more easily than the hub variant which is intended for use with small wheels.]

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

Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: SRAM A2 Automatix; introduction to the internals

Postby Brucey » 29 Nov 2014, 9:20am

I've added an update to the original posting which now includes

- link to 2015 SRAM technical documentation
- tooth counts for the gears
- comments re shift springs and service experience

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

mig
Posts: 1926
Joined: 19 Oct 2011, 9:39pm

Re: SRAM A2 Automatix; introduction to the internals

Postby mig » 30 Jan 2015, 9:04pm

within the first ten or so pages of the recent 'cycle' magazine there is an advert for a white 2 speed 'fixie' ( :roll: ) sold by a high street retailer. does anyone know if it uses this hub please? this is apparently a freewheel / coaster brake hub...?

Brucey
Posts: 32765
Joined: 4 Jan 2012, 6:25pm

Re: SRAM A2 Automatix; introduction to the internals

Postby Brucey » 30 Jan 2015, 9:20pm

I've not seen that but if it uses the SRAM automatix hub it is a two-speed freewheel hub available in coaster or no-brake versions.

This hub;

http://www.63xc.com/genng/bikesmith.htm

is a true two-speed fixed, with a normal and a reduction ratio. Shame about the ugly bellcrank though. They appear to have in essence 'reinvented' this gear;

Image
which is the sturmey archer TF hub; an 80 year old design this, itself a variant of a design that is now over 115 years old.

The TF hub is a two speed fixed with a 'normal' top gear and a 25% reduction in low gear.

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

Prodigal
Posts: 106
Joined: 27 Nov 2008, 10:22am
Location: Warwick

Re: SRAM A2 Automatix; introduction to the internals

Postby Prodigal » 14 Mar 2016, 8:45pm

Just as an update, I hardly ever used the Ridgeback onto which I'd fitted the Automatix. It got used occasionally on runs to the train station, but gathered dust most of the time, sadly. However, I recently bought a secondhand ebike kit from someone on this forum and fitted it to the Ridgeback. I raised the gearing by fitting an 18t rear sprocket and it is just about a perfect match. The lower gear with full electric assist gives me a very smart getaway, then the upper gear kicks in and I spin out at about 20MPH.

Not having to worry about gear changes makes it a very simple ride. All in all, a rejuvenation.

mig
Posts: 1926
Joined: 19 Oct 2011, 9:39pm

Re: SRAM A2 Automatix; introduction to the internals

Postby mig » 7 Apr 2016, 11:08am

would there have been any (hopefully) improvements to these hubs in terms of sealing over the course of a year? i'm still curious to give one a lash on the winter commuter.

Brucey
Posts: 32765
Joined: 4 Jan 2012, 6:25pm

Re: SRAM A2 Automatix; introduction to the internals

Postby Brucey » 7 Apr 2016, 1:03pm

mig wrote:would there have been any (hopefully) improvements to these hubs in terms of sealing over the course of a year?


doubtful. I think the brake and non-brake versions differ in this respect also. I think the key is to use the right lube inside the hub.

i'm still curious to give one a lash on the winter commuter.


and why not...?

However in my use I have found the non-external adjustability of the shift point really quite annoying at times. I have worked up methods to adjust/supplement the springs so that the shift point can be set, but it still needs to be checked, and if you adjust the gearing even slightly, the shift point needs a tweak too.

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

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[XAP]Bob
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Joined: 26 Sep 2008, 4:12pm

Re: SRAM A2 Automatix; introduction to the internals

Postby [XAP]Bob » 7 Apr 2016, 1:09pm

Yes - I'd have thought that a screw adjustment could be made (either through the hub shell somewhere, or along the axle).

It would make this a much friendlier option
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.

wouter.appleid
Posts: 2
Joined: 20 Mar 2017, 6:36pm

Re: SRAM A2 Automatix; introduction to the internals

Postby wouter.appleid » 20 Mar 2017, 6:40pm

Hi,
Thanks for your post.
i was adjusting the speed automatic shifting speed according this post:
http://bikesfornoreason.blogspot.nl/201 ... -hack.html
well i did that en i assembled everything back together but now the brakes squakes alot!
tried to grease the ball bearings in the brake arm. no change.

what should i do next?

thanks for the help!

Wouter

Brucey
Posts: 32765
Joined: 4 Jan 2012, 6:25pm

Re: SRAM A2 Automatix; introduction to the internals

Postby Brucey » 20 Mar 2017, 8:44pm

apologies if this is obvious, but a coaster brake needs (high melting point) grease in the brake itself else it will squeal like a banshee. From your description I would guess that there isn't enough grease inside it.

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

wouter.appleid
Posts: 2
Joined: 20 Mar 2017, 6:36pm

Re: SRAM A2 Automatix; introduction to the internals

Postby wouter.appleid » 20 Mar 2017, 10:03pm

well i didn't greased the rollers and ramps for brake actuation. :roll:

gonna try tomorrow :).

Brucey
Posts: 32765
Joined: 4 Jan 2012, 6:25pm

Re: SRAM A2 Automatix; introduction to the internals

Postby Brucey » 20 Mar 2017, 11:20pm

just to be clear, the brake shoes themselves need lots of grease on them too.

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