Bruce27

Hi Folks

Looking for a little help and giving a shot someone here might know...

The bike is a 1981 Trek with SR(Sakae)double chainring crank and a 5 speed freewheel in the back.

I’m thinking of changing from a traditional cup/cone type bottom bracket to a cartridge type bottom bracket.

I've cleaned the spindle (tapered)/bearings many times in the past but unfortunately, never took note of the numbers stamped on the spindle or measured it when I had it apart.

Before I disassemble to measure, has anyone made this conversion on their early Trek with SR double chainring crank and know the spindle length?

This would be my first conversion of this type so any information and/or warnings will be appreciated.

Thanks

Iride01 

Mainly just make certain you know what the BB shell on that bike is. If you go with a two piece Shimano crank, you'll probably have the least issues. ISIS or Octalink cartridge BB's will be the next thing I'd recommend. And any thing square taper I'd run away from.

Square taper BB's length depends on the crankset you put on it. ISIS and Octalink are more standardized about where the chain rings set on them. 2 piece Shimano cranksets even more so.

Shimano tends to do a lot of black cranksets though. But occasionally they'll produce some silver cranksets for a short time.

Joe Remi

He's trying to add a new cartridge square taper BB to his existing cranks.

An '81 - and all, as far as I know - Trek should be English thread. Pull your cranks, measure the spindle, buy a BB that length. Solved!

Joe Remi

I should add: Don't do this unless you really need a new bottom bracket. That fixed cup has been in there for 42 years and may not want to budge; cup-and-cone brackets are generally smoother than cartridge type and will last for dang near ever with new bearings and a repack now and then.

Bruce27

Thanks both Iride01 & Joe Remi. The bike bottom bracket shell is English 1.370 x 24 tpi and the width is 68 so I think I have that information.

Did want to stay with my original existing SR crank, which fits the original (and current) square taper BB spindle....trying to avoid the domino effect.

I was being lazy ....didn't want to pull off the crank to get the spindle measurement and hoping someone else here would know that dimension.

The existing BB still seems to be fine. Just thought I might try a cartridge version the next time I think about cleaning it. If that cup is going to misbehave, I'll have second thoughts about even attempting this project.

Andrew R Stewart 

Back in the early 1980s the loose ball BBs often had an axle that wasn't symmetrical, the drive side had more length WRT the bike's centerline. If your Trek has this and if you only measure the overall axle length and if you purchase a current cartridge BB unit with that same dimension listed there's a very good chance that the drive side crank won't sit the same distance from that centerline. Most current BBs are a symmetrical type.

Instead measure the drive side amount, from the frame's centerline to the axle end and just double this to come up with a symmetrically designed unit that will produce the same chainline as the OEM BB had. If you were to take the current BB axle out of the shell you could measure the axle's two ends and see if my belief is correct and what the amount of difference is. Then add that difference to the overall axle length for the replacement's size.

As usual, Sheldon Brown's website should have a good tutorial about this. Andy

If when you do remove the old parts and if they are in good condition consider just relubing and reusing them. Andy

Joe Remi

Yes and it gets even murkier because a lot of Shimano square taper cartridges are asymmetrical, too. My very vague recollection on this is the 110 and 113 are the same length on the drive side. So good luck out there!

Kontact 

Go to the crankset category here:
https://velobase.com/ListComponents.aspx?Category=115

If you can visually identify the SR crank you have, there may be spindle information posted. It is usually correct.

You can also take the dust caps and fxing bolts off the crank arms and use a caliper to measure from the bb shell to the crank and from the crank in to the spindle end, then subtract. That will give you all the numbers you need to estimate overall length and any offset. SR cranks should all be JIS taper.

Bruce27

Thank you @Andrew R Stewart @Kontact & @Joe Remi again.

The crank is an SR SAX-5RG. Unfortunately I didn't see the spindle length in velobase for that crank. I'm 99% sure the existing spindle has an extended length on the drive side, ...so current is asymmetrical.

From what I understand so far... even if I confirm that my current asymmetrical spindle is 113mm, I would need a BB cartridge (symmetrical) that's 118mm or more to keep the existing chainline. Surely don't want to be chewing up my chainstay.

I'll try measuring again. Thank you all, and if someone stumbles across this thread and has already gone through this exercise...please chime in.

Jeff Neese

I've put cartridge BBs on 4 of my vintage Treks, all of them Shimano UN55 which unfortunately are no longer made. I always changed the crankset at the same time which meant a different spindle length, but you'll need the same as you have now. What BB are you going to buy?

Bruce27

I was able to find this old SR catalog online and I think mine is the Super Apex. It looks like it could be the Double 68 D-3P 119mm.

Bruce27

Not sure at the moment. Was first trying to figure out the spindle length. I've read good things about the Shimano UN55.

Jeff Neese

UN55 is discontinued but you can still find them if you look hard enough. The replacement Shimano is a UN300 which isn't as robust, but is cheap and good enough for most people. I used one of those on my wife's Rockhopper and it's fine.

Bruce27

Thanks Jeff Neese . I see that UN300 comes with a lot of symmetrical spindle length options. Two being 122.5mm and 127.5mm. So if I'm thinking this through correctly and my current asymmetrical spindle is 119mm, the 122.5mm or 127.5mm might work?
Like others have mentioned, I really need to try and measure this out.
BTW.... I also see spacers mentioned in the instructions. Did your UN55 come with spacers?

Bill Kapaun

Maybe look at this document. You'll need to go to page 10 or so to get past cottered spindles.
https://law.resource.org/pub/in/bis/....1131.2006.pdf

Jeff Neese

If your current one is 119mm, 127.5 would probably be too big. It sounds like you have a handle on what you need to measure though. I don't remember the UN55 coming with spacers.

Bruce27

To All The Above......
Thank you for all the information you've shared in this thread. Not sure when (or if) I'm going to proceed, but you've been a tremendous benefit in helping me understand the project if I decide give it a go.
Thank you again.....

dedhed

Tange LN bottom brackets are a good substitute for a UN55

kit_fl

You need all these before ordering.
1. spindle length, 2. The bb shell width 68mm is pretty common. 3. Jis or iso taper 4. English or Itailan threading.

Garthr

I agree with Joe here, if it's not broken, and it's not, don't go fixing a problem that isn't there. Who says a cartridge is any better, or will last longer, or will be easier to maintain and such ? Point being, they aren't without their flaws or gotchas. Plus, while tapers are supposed to be standard, hah hah ... the joke is on everyone because these standards may be precise on paper, in practice they are not. I remember I had to use a cartridge with a Sugino AT whose spindle pitted and they were no longer made. I had to use a cartridge, a UN72, and of course the DS length wasn't the same, neither was how far the spindle sat in the tapers, it was further in. It was still usable, but notable. I eventually sold the bike('83 Stumpjumper) but kept the crank and BB, but never used them since.

Just saying, replacing older specifically made parts with generic fitted ones is a can of worms. Yum yum !

Besides, asking for advice is dangerous, we all love to spend someone else's money and have them do things we'd never want to do ourselves. I don't know whether to laugh or cry about that ..... seems they're kinda the same.

Road Fan

Yes, I agree!

I've had four Treks of this era and worked on several belonging to friends, and all have been 68 mm shell width, English threading, JIS square taper except for the Italian designs, and spindle length as required by the chainset. In these frames I've installed Japanese chainsets, Campagnolo. some odder Italians like Ofmega/Avocets, and French TA 5-pin and Stronglights. In the Shimano and Campagnolo cases I've done installations with cup/ball/spindle and cartridge BBs. It's all a matter of correct mechanical fitting. For the spindle length it's a matter of controlling the chainline by selecting the spindle length on the drive side, and if desired to balance the offset by selecting the non-drive side spindle length.

This took me a while to sort out and learn, but the set of parameters are not all just a crap shoot. Unrecommended choices might work but not as easily as what Shimano, TA, and Campy recommended the mechanic should do.

Kontact 

The trick with the early Treks was that a high end Japanese crankset like Superbe would be a Campy spindle taper, other Japanese would be JIS and the Ofmegas they often used were a third very different taper. Without getting the spindle taper right the spindle length isn't useful. That's why going back to the crank manufacturer specs are always the best bet.