Yet Another Cycling Forum
General Category => Freewheeling => Folders => Topic started by: citoyen on 01 September, 2012, 09:44:45 pm
-
Does anyone have an exploded diagram of the Brompton Sachs Torpedo 3-speed hub? I'm sure a link has been posted on the forum in the past but I've not been able to find it in the archives, or on my hard drive...
d.
-
Presumably it's (internally) the same as the vanilla Torpedo hub. <fx: tappity tap>
Blimey, the Sram website is a bit of a maze. I'll extract the relevant page from one one my machine here and PM you.
Edit. Think it might be on the end of this link: http://www.sram.com/service/include-archived/sram/435 (http://www.sram.com/service/include-archived/sram/435). Go for the Spare Parts Catalogue Sram Performance Comfort 2010. Torpedo 3 speed is called T3 in there. Page 94.
-
Excellent! It looks slightly different to my Brompton-specific hub, but close enough to be useful. Thank you very much indeed!
d.
-
No worries. I might have some suitable spare bits from my collection of cannibalised 3x7 hubs in the SEECRIT BUNKER.
-
Cheers. I think I have all the bits I need though - that's partly why I need the exploded diagram, so I can tick them off!
d.
-
All parts present and correct. Now to see if I can re-assemble them without breaking anything...
d.
-
One thing occurs to me...
Obviously the big difference between the Brompton and the regular hub is the lack of a torque arm. The Brompton has narrow dropouts with flats on the axle to compensate. Thing is, I filed the dropouts of the Brompton to take a fully round axle. I still have the anti-rotation washers, but will they be enough to prevent rotation?
What would be the consequences of a rotating axle?
d.
-
Isn't the torque arm for the coaster brake? Which in your case you do not have.
Anyway, the 3 x 7 hub on the Pino features anti rotation washers and slotted drop outs. if the anti rotation washers are tabbed like mine, the should still engage in a round dropout.
-
Isn't the torque arm for the coaster brake?
Yes, I realised that shortly after posting... :facepalm:
I've put it all back together but there seems to be an awful lot of play in the bearings and I can't tighten the locknuts any further... Something not quite right. Hmmm.
d.
-
Hmm. IME of the 3 x 7, getting the fixed cone down tight is the key. The wee spring that sits underneath it sometimes gets in the way, giving an impression of it being all snug only to take up the right location, ending with stuff all wobbly. Or one of the bearing sets is misaligned, peeking out from the edge of the cone.
-
They're relatively easy to rebuild. What was wrong with yours - snapped axle key, or just skanky bearings? The balls are an odd metric size and you have to get the SRAM cages.
-
What was wrong with yours - snapped axle key, or just skanky bearings?
Both! I got replacements easily off eBay. And spares for next time...
All seems quite straightforward using the diagram. Not sure why it wouldn't go back together but I had to go out this afternoon and didn't want to rush the job this morning - the bearing cages are a bit flimsy and I want to be careful not to bend them while reassembling (btdtgtts).
d.
-
There was one bit I didn't take apart because it really didn't want to be disassembled - I can't remember exactly what, but it was deep in the planetary gears. The exploded diagrams on the SRAM website are what I used - your hub is the same as a Spectro T3.
-
Right, rear wheel successfully reassembled and refitted.
Next problem - the trigger shifter is knackered, which I'd forgotten about having not used it for so long. I could get a NOS replacement Torpedo shifter on eBay, but what other shifters are compatible? Would a SRAM T3 twist shifter work?
Also seems that the chain needs replacing and the brakes need a bit of fettling, but otherwise it looks like I have a working Brompton once again. Hurrah!
d.
-
Yes - even a Sturmey-Archer shifter will work. The Brompton plastic one is universal.
-
Excellent. I was just concerned the indexing might be different on different models.
d.
-
Rode to the station on the Brommie this morning and the reassembled wheel seems to be fine. Hurrah!
However, I realised that the problem with the chain is that it's for a 7spd (3/32") and the 3spd sprocket seems to require a 1/8", so getting the chain to engage with the sprocket was a bit hit and miss.
I went up to Bikefix during my lunch break to see if they could get me some replacement pawls for my singlespeed wheel. They didn't know, so phoned Brompton. It wasn't good news. So I'm stuck with gears (spit!) for the time being. Oh the ignominy! (Mind you, until I replace the knackered gear shifter, I can only use two of the three gears anyway, so it's not so bad. ;D )
I bought a new 1/8" chain while I was there and fitted it, so the ride home is sorted, at least.
d.
-
However, I realised that the problem with the chain is that it's for a 7spd (3/32") and the 3spd sprocket seems to require a 1/8", so getting the chain to engage with the sprocket was a bit hit and miss.
Even with the new chain fitted, I'm still getting skipping in the transmission. I initially thought this was down to shonky gear indexing but now I suspect it's more likely the combination of new chain and old sprocket since the skipping only happens under heavy pedalling - if I spin a lower gear, it's mostly fine. Going uphill is a problem though.
I've ordered a new sprocket - hopefully it will arrive by the weekend, so I'll soon find out.
It wouldn't be the cogs inside the hub slipping, would it? They didn't look worn when I had it stripped.
d.
-
The cogs should be firmly in constant mesh and should never be able to slip. The whole planetary mechanism slides in a SRAM 3-speed (Sturmeys just have a sliding dog clutch) but this should only be able to slip if misadjusted.
-
I have an old SA shifter gathering dust if that would help?
-
There is a difference in cable pull between 2nd and 3rd gears for SA vs. SRAM. The Brompton shifter works on both because it has a long cable pull. Either the SA or SRAM doesn't but I can't remember which.
-
I know Charlotte uses a SRAM shifter successfully on a SA hub, so maybe the other way round is tricky.
SRAM hubs use a less precise cable adjustment that SA, basically a case of removing slack in top gear, so you can fiddle with it a bit.
-
Regardless of compatibility issues, I'd already ordered a replacement Torpedo shifter, but many thanks for the offer, AWL!
In case anyone was wondering, it was definitely the sprocket that was causing the slippage - I fitted the new sprocket and the problem is instantly solved. Funny though - the old one doesn't look very worn - even held next to the new one, you can't see much difference at all.
d.
-
Was it a 13T? They can split radially because they're so thin, and the split opens up under pedalling pressure, causing a slip. It's not always obvious when the sprocket is removed.
-
That has happened to me before so I know exactly what you mean. I don't think this one is split but now you mention it, I shall check.
-
I know that it's and old thread but as anyone a source for replacement hub bearings?
-
https://www.cyclebrother.com/cycling-components/hubs/spareparts-for-gearhubs/sram-ball-bearing-35-and-7-gear might be appropriate.
-
https://www.cyclebrother.com/cycling-components/hubs/spareparts-for-gearhubs/sram-ball-bearing-35-and-7-gear might be appropriate.
Thank you, marvellous
saved another hub!!
BUT they only offer one postage option to the UK - £30 .........parts are just a few Euros - I'll look on their site for other stuff that I may need
(http://www.wenltd.co.uk/TZ/Hub_1.jpg)
(http://www.wenltd.co.uk/TZ/Hub_2.jpg)
(http://www.wenltd.co.uk/TZ/Hub_3.jpg)
-
You should be able to pop the individual bearings out of the cages and replace them with new balls. You just need to know the correct ball size. Open up the hub, measure them and order loose balls, job done!
-
You should be able to pop the individual bearings out of the cages and replace them with new balls. You just need to know the correct ball size. Open up the hub, measure them and order loose balls, job done!
the metal case has broken/snapped on the left bearing - you cannot see it in the image for the black "grease"
-
Feed the SRAM part number into ebay with the item location set to EU. Since SRAM pulled the plug totally in 2017 (hubs and spares) this may not be as easy as it was.
I have a feeling the balls were an odd size, possibly metric?
-
Thanks everyone - I got the outer bearings from Germany 0576 104 200
They look like "copies" and are not quite as well made as the originals
-
I have not played with a Torpedo hub but replacing caged bearings with loose balls is always an option in future. Loose balls require a little more care with reassembly (which is why manufacturers usually prefer using races) but theoretically increases durability.
-
The Sachs hubs use very few bearings - the cages intentionally have huge gaps. To use loose bearings would require oodles of balls, a bit like a freewheel. It would work but would be OTT for supporting the load and might add a bit of drag. The races are very large - the diameter of the shell, in fact.
-
I overhauled one recently. The big races use 3/16" and the small race in the driver uses an annoying 7/32". You could stick loose balls in with grease but you will need a lot of them without the cages.
Das Zweirad in Germany still has stock but will.no longer ship to Brexit Island, of course.