AZ4Mtb

Rebuild questions for a 1993 Bridgestone MB-3. I am putting new wheels, cassette and chain on my MB-3. I also need to replace the original bottom bracket. The new wheel set is from Quality Wheels with current model Deore hubs. The rear freehub is an 8-10 speed model - Deore FH-T610 . The original bottom bracket is a Tioga BB-401with 120mm spindle and I need an equivalent. Since I will need to install a 4mm spacer behind the 7 speed cassette I am trying to figure out the proper size bottom bracket to maintain the correct chainline and one that is equivalent or better quality than the original. Triple crank is still the original Deore DX meant to work with a tapered square spindle. Thanks for the help and suggestions on anything that I may be missing.

Andrew R Stewart 

So the rear axles (old compared to new wheel) are the same drop out widths? If so then the chain line of the rear cogs won't shift WRT the frame much. The high gear cog is still about the sane distance from the RH drop out inner face. What did change was the RH flange moved inwards (more dish), hence the spacer to fit the longer freehub splines. But a few easy measurements can confirm this. Either way a couple of MMs of chain line shift shouldn't be much for the system to absorb with the "wide" ring spacing of a 7 speed system.

I would set up the rear end first, measure the new rear and old crank/BB for chainline and modify the front chain line as needed with a new BB. Andy

2old

+1 with above; and Rivendell has old style, high quality bottom brackets with various widths.

AZ4Mtb

Thanks for all the helpful replies. As posted before, I am rebuilding a Bridgestone MB-3 that needed new wheels and new drive train. I am at the point where I need to figure out my proper bottom bracket spindle length as the BB also needs to be replaced. As per previous I am converting the bike from 3x7 to 3x8 while I am at it. The original component group was all Deore DX. Here is what I have obtained for the upgrade followed by what I have done so far:

New Alex DT19 Rims with Shimano Deore Hubs (8-11 speed non disk rear hub 135mm spacing).
New (old) Deore XT M739 3x8 rapid fire shifters
New (old) Deore XT M739 rear derailleur
New (old) Deore XT M735 front derailleur
New SHIMANO 8 Speed Cassette - HG50 and new HG71 Chain

While the original dropout spacing for the MB-3 is specified as 135mm I had to cold form the rear triangle to fit the new rear hub because it was about 2.5mm too tight. I could get the rear wheel in but I required me to muscle it somewhat. Now it pops into place with minimal effort and will fall out of the dropouts if the QR is opened.

The rear cassette is installed and the wheels are on and I have measured for chain line with the new hub/cassette combo. I am keeping the original Deore DX crank and just installing new chain wheels. My new rear chain line is 43.5mm and my front chain line is 47mm with the DX crank and the original Tioga BB40. The Tioga BB has a 120mm spindle and I want to replace it with a sealed cartridge setup. I am looking at the Origin8 Torqlite or the OMNI Racer JIS Square Taper BBs. Sheldon Brown's guide to BBs shows the symmetrical equivalent for a 120mm spindle as 124mm. If I am understanding all of this correctly, I've moved the chain line of my rear cassette in about 2-3mm closer to the center line of the bike with the jump from a 7 speed to an 8 speed rear hub. So, can I install BB with a 122.5 spindle and end up with a 45.5 front CL? That would leave me with a 2mm difference back to front if I am understanding the effect of spindle length on the chain line. Also, nobody seems to make a 124mm spindle anyway so I would need to go up to 127mm and that seems like the wrong direction to be headed...

Thanks again.

AZ4Mtb

I am sticking with 3x8 speed. Already have the shifters, cassette, derailleurs, chain etc. So as posted previously, I need to figure out my BB spindle length as per my previous post.

The rear cassette is installed and the wheels are on and I have measured for chain line with the new hub/cassette combo. I am keeping the original Deore DX crank and just installing new chain wheels. My new rear chain line is 43.5mm and my front chain line is 47mm with the DX crank and the original Tioga BB40. The Tioga BB has a 120mm spindle and I want to replace it with a sealed cartridge setup. I am looking at the Origin8 Torqlite or the OMNI Racer JIS Square Taper BBs. Sheldon Brown's guide to BBs shows the symmetrical equivalent for a 120mm spindle as 124mm. If I am understanding all of this correctly, I've moved the chain line of my rear cassette in about 2-3mm closer to the center line of the bike with the jump from a 7 speed to an 8 speed rear hub. So, can I install BB with a 122.5 spindle and end up with a 45.5 front CL? That would leave me with a 2mm difference back to front if I am understanding the effect of spindle length on the chain line. Also, nobody seems to make a 124mm spindle anyway so I would need to go up to 127mm and that seems like the wrong direction to be headed...

bikemig 

The shimano sealed square taper bottom brackets are good and reasonably priced. The UN 55 is a fine unit. I've installed a number of them on older bikes while running a deore triple. I've found that a 127 works fine with a deore triple. It's not like you have a lot of choice since the next size down is 122. The chain line may not be perfect but I've never lost much sleep over that. The shifting still works fine.

I've done this on 2 vintage MTBs, a 1988 Specialized Stumpjumper and a 1992 Trek 950, both with Deore XT hubs and a 127 mm UN 55 bottom bracket.