SRAM A2 Automatix; introduction to the internals

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Brucey
Posts: 31934
Joined: 4 Jan 2012, 6:25pm

Re: SRAM A2 Automatix; introduction to the internals

Postby Brucey » 19 Jan 2013, 3:11pm

I'd try one thing at a time! I'd also try the easy/reversible things first!

Note that unless the springs etc are modified, the gear change will happen at a constant road speed, so changing to an 18T sprocket will increase your maximum cadence by ~12.5% before the shift point. I'd definitely try that first if you are happy riding in a 80" top gear at speed and a 58" low gear; sounds OK to me. At present you have a 65" gear and a 89" gear; I'd find the latter slightly heavy going myself. Maybe a 21T sprocket is worth consideration; this would give 49.5" and a 68" gear, so maybe ths would suit best if you had but hills and flat to contend with.

If you want to experiment with a delayed shift in terms of road speed, yes, you will have to do something to the shift point. One way which might work well enough for a test (I've not tried it) is to simply remove the centrifugal weight which doesn't have a spring on it. This should inhibit the shift nicely (from 15mph to about 21 mph if my sums are right).

Do be sure that nothing will come adrift if you do this though; I can't remember if the pawl control plate is partially retained by the weights or not. Also note that the assembly will no longer be balanced, which may cause a problem at very high speed.

You can of course make your own spring for trial purposes, from piano wire (go to a modelling shop). It isn't a very complicated shape IIRC.

Have fun!

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

michael432000
Posts: 14
Joined: 1 Oct 2012, 8:46am

Re: SRAM A2 Automatix; introduction to the internals

Postby michael432000 » 20 Jan 2013, 6:56am

Hey, thanks Brucey, you’ve made me have a rethink.

For some reason I was thinking that the lower gear would be the main gear because presumably it is the straight-through gear and the higher gear that engages some extra mechanism would be used less frequently. My fast commute out of London and back is almost totally flat so I had not considered using the bike on hills.

However, on my 700c road bike my favourite climbing gear, as well as for standing starts, is a 42t/22t = 50.6.

And my favourite high cadence fast cruising speed gear on the flat is a 42t/17t = 65.5.

And these are very close to your suggested gear range.

52t/21t = 49.5 and * 1.37 = 68

So I definitely want the 68 gear, which is near to my current 16t lower gear set-up, and I have to decide to go for a higher 93 gear or the lower 50.6.

On my road bike the higher 93 gear equates to a 52t/15t, which is occasionally useful.

But I must surely settle for the 21t sprocket that will enable me to accelerate really fast away from lights whilst also being able to use the bike on hills.

*

I would like to be able to accelerate really fast to at least 22mph on the low gear so the spring will probably still need a little adjustment.

I have actually already taken it off. The ends of the spring currently face in opposite directions, 180 degrees apart.

The pawl control plate is indeed held in place by the weights so one cannot be removed.

Not 100% sure of the correct way to get the spring back on. Can you or anybody else remember how much resistance the weight has to overcome to engage the bigger gear? Is it quite a light resistance?

Thank you once again. At least I know a little bit about internal gear hubs now.

Brucey
Posts: 31934
Joined: 4 Jan 2012, 6:25pm

Re: SRAM A2 Automatix; introduction to the internals

Postby Brucey » 20 Jan 2013, 9:29am

you must spin really fast if you can get up to 20-odd mph on a 50" gear before needing to shift up! I'd try it with the original spring and the new gearing first; that should give an upshift on that gearing of about 100-odd rpm.

Re the spring; IIRC it has about half a turn of preload in standard form.

I wonder if the other weight could be temporarily replaced by (say) a spacer and/or stack of small washers or something?

BTW I would -for large wheel use anyway- prefer this hub to be a 'gear-down' hub than the 'gear-up' hub that it is, so that normal running in the high gear didn't incur any efficiency loss. But I guess this would prohibit it for being used easily on very small wheeled bikes.

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

michael432000
Posts: 14
Joined: 1 Oct 2012, 8:46am

Re: SRAM A2 Automatix; introduction to the internals

Postby michael432000 » 20 Jan 2013, 10:23am

I used to do regular criterium races, which is endlessly sprinting out of bends, so trained specifically for very fast leg speed on a turbo trainer.

Yes, half a turn of preload is the only way I can see it fitting. In fact there is only one obvious way to put the weight and spring back on.

It’s just that the tension seems rather weak and I wanted to be sure before I try and put that little circlip back on. It was a miracle I didn’t lose it when I took it off; took me ten minutes to find it. Guess I’ll just have to put it back on and try it.

Brucey
Posts: 31934
Joined: 4 Jan 2012, 6:25pm

Re: SRAM A2 Automatix; introduction to the internals

Postby Brucey » 20 Jan 2013, 10:56am

michael432000 wrote: It’s just that the tension seems rather weak and I wanted to be sure before I try and put that little circlip back on. It was a miracle I didn’t lose it when I took it off; took me ten minutes to find it. Guess I’ll just have to put it back on and try it.


if you are worried about losing the clip, it isn't a bad idea to take it off inside a plastic bag.

cheers
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s-o
Posts: 1
Joined: 20 Jan 2013, 2:52pm

Re: SRAM A2 Automatix; introduction to the internals

Postby s-o » 20 Jan 2013, 3:18pm

According to the specifications on SRAM:s website, the Automatix should be avaliable in “Coaster brake, Freewheel, Disc brake, Aluminum hub shell, SH Rollerbrake comp., Gates beltdrive”.

I'm looking for the disc brake version, but so far all I have found is the roller brake and coaster brake versions. To make things even more impossible I'd really like to use the 32-hole rims I already have, but the hubs on EBay and Amazon all seem to be 36h.

Does anyone here know of a reseller who might be able to find me a 32-hole, disc brake Automatix hub?

Brucey
Posts: 31934
Joined: 4 Jan 2012, 6:25pm

Re: SRAM A2 Automatix; introduction to the internals

Postby Brucey » 20 Jan 2013, 5:22pm

this;

Image

appears to be a new aluminium-shelled version of the automatix. The plastic cover appears to be the same as the one that is used on other recent SRAM IGH's to cover (but not waterproof) a disc mounting. In other hubs the open holes let lube out and water in unless plugged with something.

I've not seen this hub in the flesh yet; given that the previous A2 automatix hubs were personal import only, I should imagine that these won't be any different. In fact I've not even seen it for sale (although I've not exactly looked hard TBH).

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

AW_hub
Posts: 2
Joined: 30 Dec 2012, 6:47am

Re: SRAM A2 Automatix; introduction to the internals

Postby AW_hub » 7 Mar 2013, 4:38am

Can Jerry or Bruce tell me - for the TSR2 which I may buy, does the belt drive version mount the sprocket with the usual Sturmey Archer 3 lobe/circlip? In other words. is it easy to transfer the rear belt sprocket to the SRAM A2, which also uses the Sturmey 3 lobe/circlip for its included chain sprocket? Any special spacers needed?

Brucey
Posts: 31934
Joined: 4 Jan 2012, 6:25pm

Re: SRAM A2 Automatix; introduction to the internals

Postby Brucey » 7 Mar 2013, 10:19am

I don't know the answer to this for sure; although I don't see why they would alter the interface, I don't know that they have not.

However, the advice I'd give here is to try it and see; a belt drive sprocket is physically wider than a chain drive sprocket, and the previous A2 hub came with no spacers on the sprocket fitting, i.e. it will take a sprocket and that is all. By contrast the SA hub has room for a sprocket and two spacers which may make all the difference to being able to fit a belt drive sprocket and not.

If your belt drive sprocket is thin where it mounts, maybe it'll be OK, but there is no guarantee that the overhanging parts won't clash sideways. You will probably have to try it to be 100% sure it is going to fit.

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

grapposoda
Posts: 1
Joined: 2 Jul 2013, 2:33pm

Re: SRAM A2 Automatix; introduction to the internals

Postby grapposoda » 2 Jul 2013, 3:21pm

Hi!

I'm trying to put together an Automatix wheel and just recently managed to find the correct spacers and nuts to mount the hub properly in the frame.
Only then I noticed how surprisingly hard it was to turn the hub by the sprocket. This made me hesitant to follow through with the wheel build before consulting some internet expertise. (That would be you!) ;)


So, I've got the rollerbrake version of the hub, but no roller brake! (rather a dust cap from a Shimano Nexus hub.)
When just turning the hub shell (as when coasting) it seems to run smooth. Not quite like my single speed hub of course, but perfectly fine with a happy clicking noise.
Turning the hub by the sprocket (as when pedalling) or turning the hub in the backwards direction, the force/torque required is really substantial.
Again, I'm not expecting efficiency on par with the single speed hub, but it feels much harder to turn than compared to say a standard dynamo front hub.
This is just turning by hand too, so I expect the hub to be in low/direct/low-friction gear.

I notice the LHS of the RB hub is different from the coaster and free wheel versions, but the RHS seems identical.
I've tried loosening both LHS and RHS cone nuts (really loose) without any improvement, only more wobble.

Could anyone please give me a hint what could be the matter, or if I'm just overoptimistic about the efficiency of IGHs?
I'm a bit hesitant to pull the whole thing apart like in the first post, but if that would help I could try it and then also post a few pics of the internals of this version too. :)

Cheers!
Anders

Brucey
Posts: 31934
Joined: 4 Jan 2012, 6:25pm

Re: SRAM A2 Automatix; introduction to the internals

Postby Brucey » 2 Jul 2013, 9:18pm

IIRC the grease in my hub was kind of thick and gloopy, (what there was of it, anyway....). It may just be drag from slightly dry grease.

In any event, most hub gears 'run in' over the first few hundred miles. I'd suggest using a semi-fluid grease inside, and after you have done a few hundred miles, I'd suggest a clean and regrease.

Whipping the centre out and cleaning it/regreasing it is maybe a half-hour job. Your hub will love you for it, because cleaning like this will remove any running-in debris; without this, the grease eventually turns to mildly abrasive sludge....

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

skin and bone
Posts: 85
Joined: 18 May 2013, 11:22pm

Re: SRAM A2 Automatix; introduction to the internals

Postby skin and bone » 3 Jul 2013, 11:07pm

This is an example of why I enjoy reading the postings on this site.

michael432000
Posts: 14
Joined: 1 Oct 2012, 8:46am

Re: SRAM A2 Automatix; introduction to the internals

Postby michael432000 » 20 Jul 2014, 10:07am

I have one in good condition (not used much) with a coaster brake. The spring needs attention because it changes up even earlier than it should do.

It comes with a pair of stock Swift Folder wheels and almost new Schwalbe Big Apple tyres and inner tubes.

Free.

Anyone interested can pick up from Ilford, Essex.

Brucey
Posts: 31934
Joined: 4 Jan 2012, 6:25pm

Re: SRAM A2 Automatix; introduction to the internals

Postby Brucey » 20 Jul 2014, 11:27am

you have pm.

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

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

Re: SRAM A2 Automatix; introduction to the internals

Postby garry71 » 17 Aug 2014, 9:31pm

Hello everyone, I found this thread and forum via a reply on bikeradar.

I've just bought an SRAM Automatix Freewheel from Amazon, and am looking forward to building a 26" wheel up for use on my 20 year old Raleigh Nitro (no laughing!)

I'm interested to know how people's Automatix have been performing, and what problems you've had with it.

Are there any adjustments or lubing I should do to it now, or should I wait until it's been run in a bit?

Cheers
Garry