Bottom Bracket Question

MarkInNC said:

My new XT crankset and bottom bracket arrived yesterday. I am increasing the chainring size from 44T to 48T as well as moving up a notch or two in type.

I have read the install instructions a couple of times. The BB can be used on both width hubs and has a set of washers/spacers which are used differantly for BB type. Three types are listed and I don't have a clue what they are or how to ID which I have. I have a Trek 6500 MTB. the three BB hub types that Shimano lists are: "Band", "Chaincase Stay Type", and "Bracket". Does anyone know what these terms mean and or how I can tell the one I have?

thanks,

Mark

if the BB shell is 68mm, use 2 spacers on the right side and 1 on the left. If it's 73mm, use 1 on the right. If the FD is the type where it has a piece that mounts it to the BB shell(e-type FD), remove one of the spacers and replace with the FD bracket. I'm guessing you probably have a band type FD, one that clamps onto the seat tube. So measure the BB shell width and use spacers as spec'ed above.

MarkInNC said:

My new XT crankset and bottom bracket arrived yesterday. I am increasing the chainring size from 44T to 48T as well as moving up a notch or two in type.

I have read the install instructions a couple of times. The BB can be used on both width hubs and has a set of washers/spacers which are used differantly for BB type. Three types are listed and I don't have a clue what they are or how to ID which I have. I have a Trek 6500 MTB. the three BB hub types that Shimano lists are: "Band", "Chaincase Stay Type", and "Bracket". Does anyone know what these terms mean and or how I can tell the one I have?

To describe the situation in a slightly different way:

If your BB shell is 73mm wide (you'll need a ruler), then just install your new BB as-is.

If your BB shell is 68mm wide, then you'll want to use the spacers to center the BB in the shell because you have a BB which is designed for a 73mm shell (this is common with MTB bottom brackets) -- install one of the 2.5mm spacers on each side.

You apparently (?) don't have an E-type front derailleur ... if you do, then the E-type is on the driveside, and one 2.5mm spacer is on the non-drive side.

BTW. The use of the term "Chaincase Stay Type" is a mystery to me ... is that their term or your description?

The "Band" is undoubtedly the normal front derailleur with its own clamp ...

The E-type front derailleur is what I presume Shimano/(you!) is/(are) referring to as the "Bracket" type.

Peter@vecchios said:

if the BB shell is 68mm, use 2 spacers on the right side and 1 on the left. If it's 73mm, use 1 on the right. If the FD is the type where it has a piece that mounts it to the BB shell(e-type FD), remove one of the spacers and replace with the FD bracket. I'm guessing you probably have a band type FD, one that clamps onto the seat tube. So measure the BB shell width and use spacers as spec'ed above.

Sorry. I presume THAT must be correct ... in the past, I have usually squandered (!) extra cassette spacers whose thickness I adjusted with a hand file rather than using the spacers!

For some reason, my failing recollection is that the 73mm BBs only came with two 2.5mm spacers ... but, I guess they must have actually been 1.25mm thick!

MarkInNC said:

My new XT crankset and bottom bracket arrived yesterday. I am increasing the chainring size from 44T to 48T as well as moving up a notch or two in type.

I have read the install instructions a couple of times. The BB can be used on both width hubs and has a set of washers/spacers which are used differantly for BB type. Three types are listed and I don't have a clue what they are or how to ID which I have. I have a Trek 6500 MTB. the three BB hub types that Shimano lists are: "Band", "Chaincase Stay Type", and "Bracket". Does anyone know what these terms mean and or how I can tell the one I have?

thanks,

Mark

Thank you guys, I think I have a better understanding now. The terms in quotes are terms used by Shimano. My front derailer mounts to the seat upright and I do not remember anything else in the mix, I will check, so from what you guys are saying I have a bracket type. Measure 73mm, nothing else there, no washers, 68mm, nothing else there use a 2.5mm washer on each side. (Ah, OK that makes sense, 2.5+2.5=73mm-68mm.

thanks,

Mark

alfeng said:

Sorry. I presume THAT must be correct ... in the past, I have usually squandered (!) extra cassette spacers whose thickness I adjusted with a hand file rather than using the spacers!

For some reason, my failing recollection is that the 73mm BBs only came with two 2.5mm spacers ... but, I guess they must have actually been 1.25mm thick!

Ya know, I might be thinking of the Octalink V2 BB for XT, not the newer, 2 piece type. Not sure now, I'm at home. I'll go look at one.

MarkInNC said:

Thank you guys, I think I have a better understanding now. The terms in quotes are terms used by Shimano. My front derailer mounts to the seat upright and I do not remember anything else in the mix, I will check, so from what you guys are saying I have a bracket type. Measure 73mm, nothing else there, no washers, 68mm, nothing else there use a 2.5mm washer on each side. (Ah, OK that makes sense, 2.5+2.5=73mm-68mm.

Well, no, I'm saying you have the BAND type where the integrated clamp mounts to the seat tube.

I presume that Shimano is using the term "bracket" to refer to their E-type front derailleur which was designed for some rear-suspension bikes whereby the derailleur is attached to a PLATE which has a hole that is essentially held in place by the BB cup ... BUT, having said that, you may be correct.

Regardless, the nomenclature doesn't really matter other than to avoid a small amount of confusion ... you just need to know that you may need to use the spacers to center the BB.