Bottom bracket options
#1
Newbie
Thread Starter
Join Date: Feb 2021
Location: Fremont, CA
Posts: 2
Bikes: 2019 Trek Marlin 5, 18", 29
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
Bottom bracket options
Hi!
I have a 2019 Trek Marlin 5, 18", 29 and want to replace the bottom bracket. My current one is
VP-BC73, 73(shell width), BC 1.37x24T, 125.5mm (square)
Unfortunately, I can't find the exact BB. Could you recommend a replacement?
I have a 2019 Trek Marlin 5, 18", 29 and want to replace the bottom bracket. My current one is
VP-BC73, 73(shell width), BC 1.37x24T, 125.5mm (square)
Unfortunately, I can't find the exact BB. Could you recommend a replacement?
Last edited by mranton; 02-23-21 at 05:33 PM.
#2
Really Old Senior Member
IF the cranks are off, you can measure the difference between the offsets for a guide.
Here's a chart from-
https://www.sheldonbrown.com/bbsize.html
Here's a chart from-
https://www.sheldonbrown.com/bbsize.html
#3
I'm good to go!
Join Date: Jul 2017
Location: Mississippi
Posts: 14,987
Bikes: Tarmac Disc Comp Di2 - 2020
Mentioned: 51 Post(s)
Tagged: 0 Thread(s)
Quoted: 6193 Post(s)
Liked 4,809 Times
in
3,317 Posts
Shimano or anyone else that makes cartridge BB's will probably work. You put all the info you need in your OP. Just look for another BB maker that has the spec's you wrote.
You might still have an issue with how far down on the tapers the cranks sit, but as this is a very modern bike with the current for today type of square tapers, then you should be good. Just be a little leery if their description starts talking about it fitting old bikes.
73(shell width), BC 1.37x24T, 125.5mm (square)
#4
Senior Member
Join Date: Jul 2005
Location: Boulder County, CO
Posts: 4,396
Bikes: '80 Masi Gran Criterium, '12 Trek Madone, early '60s Frejus track
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 514 Post(s)
Liked 448 Times
in
337 Posts
You might still have an issue with how far down on the tapers the cranks sit, but as this is a very modern bike with the current for today type of square tapers, then you should be good. Just be a little leery if their description starts talking about it fitting old bikes.
It looks like Shimano is replacing their BB-UN26 and BBUN-55 with a new model, BB-UN300. Unfortunately, it looks like nobody has these in stock yet. You might have to shop around and consider off-brands.
#5
I'm good to go!
Join Date: Jul 2017
Location: Mississippi
Posts: 14,987
Bikes: Tarmac Disc Comp Di2 - 2020
Mentioned: 51 Post(s)
Tagged: 0 Thread(s)
Quoted: 6193 Post(s)
Liked 4,809 Times
in
3,317 Posts
There are two tapers, JIS and ISO. ISO is for vintage Campagnolo and possibly other obscure European cranks. Ask your bike shop for any 73x125.5 JIS BSA-threaded bottom bracket.
It looks like Shimano is replacing their BB-UN26 and BBUN-55 with a new model, BB-UN300. Unfortunately, it looks like nobody has these in stock yet. You might have to shop around and consider off-brands.
It looks like Shimano is replacing their BB-UN26 and BBUN-55 with a new model, BB-UN300. Unfortunately, it looks like nobody has these in stock yet. You might have to shop around and consider off-brands.
I would think that the UN-300 probably will work.
https://www.universalcycles.com/shop...&category=6042
Supposedly they are in stock.
But the OP shouldn't take my word for it being a direct replacement. They should maybe call and ask someone there what they think.
Last edited by Iride01; 02-24-21 at 01:21 PM.
#6
Newbie
Thread Starter
Join Date: Feb 2021
Location: Fremont, CA
Posts: 2
Bikes: 2019 Trek Marlin 5, 18", 29
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
Thank you for your suggestions. I went to a local Trek bike shop, and they told me that they could not find anything of the same size. They offered me a new Shimano crankset with an integrated spindle (I don't know what type it was). Total: $80 + labor. So I decided to invest this amount in tools and knowledge. I bought a bearing separator kit and 2 bearings. It was a fun project. It still works fine after 15 mi.
I wonder how to avoid problems with rare bike parts in the future? Should every single part be Shimano only?
I wonder how to avoid problems with rare bike parts in the future? Should every single part be Shimano only?
#7
Senior Member
Join Date: Mar 2015
Location: New Zealand
Posts: 1,053
Bikes: Gunnar, Shogun, Concorde, F Moser, Pete Tansley, Rocky Mtn, Diamant, Krapf, Marin, Avanti, Winora, Emmelle, Ken Evans
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 275 Post(s)
Liked 417 Times
in
218 Posts
https://bike.shimano.com/en-NZ/produ.../BB-UN300.html
that's the current gen shimano part and says they have 73mm in 123mm
So you would definately be able to find that part somewhere, eventually. Would your chainring rub on the frame if it was 1.25mm further inboard?
That's the obvious solution. For more waffling see below:
You'll notice that most NDS cups of square taper bottom brackets are not flanged. So while obviously not ideal, you can most square taper 68mm bottom brackets in your 73mm shell, and just screw the NDS cup in 5mm more. That puts your NDS crank in 5mm. Something your body can easily correct especially if using platform pedals or on a beater.
It's also worth noting that cranks will sit differently on tapers depending on wear so it's not even an exact measurement. Like if you had a 127.5mm BB, that would be totally fine. It's mm.
that's the current gen shimano part and says they have 73mm in 123mm
So you would definately be able to find that part somewhere, eventually. Would your chainring rub on the frame if it was 1.25mm further inboard?
That's the obvious solution. For more waffling see below:
You'll notice that most NDS cups of square taper bottom brackets are not flanged. So while obviously not ideal, you can most square taper 68mm bottom brackets in your 73mm shell, and just screw the NDS cup in 5mm more. That puts your NDS crank in 5mm. Something your body can easily correct especially if using platform pedals or on a beater.
It's also worth noting that cranks will sit differently on tapers depending on wear so it's not even an exact measurement. Like if you had a 127.5mm BB, that would be totally fine. It's mm.
#8
Senior Member
Join Date: Mar 2015
Location: New Zealand
Posts: 1,053
Bikes: Gunnar, Shogun, Concorde, F Moser, Pete Tansley, Rocky Mtn, Diamant, Krapf, Marin, Avanti, Winora, Emmelle, Ken Evans
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 275 Post(s)
Liked 417 Times
in
218 Posts
other factor is if the low limit of your derailer is able to shift the cage 1.25mm inboard.
#9
I'm good to go!
Join Date: Jul 2017
Location: Mississippi
Posts: 14,987
Bikes: Tarmac Disc Comp Di2 - 2020
Mentioned: 51 Post(s)
Tagged: 0 Thread(s)
Quoted: 6193 Post(s)
Liked 4,809 Times
in
3,317 Posts
Most any BSA threaded shell will have a 2 piece crank and compatible BB for it. 2 piece cranks eliminate much of the stuff that cartridge BB's couldn't do for the myriad of possible right and wrong combination of cup and cone square taper spindles and cranks.