JosephShead

Hi,

Can anyone tell me the difference between a Shimano BB-UN55 and a BB-UN54 bottom bracket?

Joe

ultraman6970

The difference is just 1

Booger1

Comes with an aluminum retainer on the left...UN54 has a plastic one.Suppose to be a better set of bearings also,abec-3's instead of 1's....

JosephShead

Ok, thanks booger1. I was particularly worried, because one site said the BB-UN54 is "JIS square taper," but for the BB-UN55 it just said, "Square taper." I was afraid that might have been an unclear way of saying "ISO square taper." Another site called it a "Euro" BB. So, I asked them about that, and they said that according to Shimano and Seattle Bicycle Supply, the only difference is strength of materials, and the "Euro" was just their way of referring to 68mm bottom brackets.

I installed it this afternoon. Works fine, so I guess it's JIS, like the UN54. A store on eBay sent it to me, instead of the BB-UN54 68x113mm I ordered.

I can add that the left cup is shaped a little differently on the inside, where it goes over the bottom bracket body, perhaps to make it fit more snugly over the end. I'm using a Problem Solvers UP-CUP #54, anyway.

Joe

Garthr

The UN55 is JIS all the way.... like every other BB they've made. I wonder if they're still using that stupid unremovable collar around the drive side axle? LoL ....
I see they still have a lip on the removable cup too ..... that's still silly and makes no sense.

I'll still buy the Tange LN-3922's instead of these. No lips ... and they provide a removable DS collar.

HillRider

I think that was done to eliminate one source of squeaking that was chronic on their first designs.

Bezalel

Italy France and Switzerland are also in Europe. The only BB standard I can think of that isn't European is Ashtabula.

hybridbkrdr

Wow, I had no idea they had a Problem Solvers aluminium cup like that. Do the plastic ones break?

HillRider

They do if you torque them too tight during installation or if you try to remove them first if the drive-side cartridge is jammed firmly against them. Torque them moderately and remove the ds cartridge first and they last just fine.

JosephShead

Yeah, I'm no expert here, but the more you know, the more questions you have when you read things like that "Euro" term. But, the store was really polite, and gave much more in their answer than I was asking for.

As for the plastic ones breaking, I've heard that they last a long time, but it is plastic, and will therefore age, get brittle, and, I would assume, shatter one day down the line when you stick that BBT-22 (or Shimano TL-UN74-S) in there and crank on it.

On my other bike, I have a Shimano 500 (no, not 600) rear derailleur, which has lasted from 1974 to the present, and taken a beating. But, it had a flaw, one little fatal flaw. There was a piece of plastic that both housed the P-tension spring (corresponding to part no. 20 on the Shimano 600, in Glenn's New Complete Bicycle Manual, 1987 version, pg 173) and served as a stop for one end of the spring. That aged, got brittle, chipped, shivered, and was eventually shattered. I replaced it with a stack of two thick washers that I spent 3 or 4 hours filing down to make them fit and do the end-stop function, not to mention the time spent working out the solution to problem, and getting the materials from the hardware store. I love fixing stuff like that, though, because it thwarts the manufacturers in their effort to get me to buy another one every 2 years. I mean, hey, just my Marxist opinion.

Oh..., Uh oh..., I better stop right now, because I'm just about to start goin' on about plastic pieces in key structural roles.

HillRider

If you remove the drive side cartridge first, the plastic cup can be removed with your fingers as there is nothing holding it in place at that point. If you install it after the cartridge you only have to get it snug because it just anchors the nds end of the cartridge and isn't a structural part of the bb.

I suppose it will eventually age and get brittle but if you ride your bike even a reasonable amount, the bearings and the rest of the bb will have worn out before that happens. You may go back to reading Das Kapital in peace.

JosephShead

I understand your points about treating it nicely, and I suppose Shimano considered it to be Ok, because it is sandwiched between the frame and the BB shell. On the other hand, it seems to be the main bearing for the left crank. We can also be glad that Shimano addressed the problem with the BB-UN55.

We have different reference points regarding how long things should last. I ride a 1974 Azuki 2x5 speed, with a steel, cup and bearing bottom bracket, probably made by Shimano. It is still doing fine, with very little wear, and so are the Shimano cup and cone hubs, and the steel headset. I've ridden that bike for about 17 years, and heavily for last 4.5 years, even getting groceries with a BOB Yak. So, while there have been great technical improvements, there has also been a cheapening of some products over the past 40 years. I have high expectations, but not unrealistic ones.

Anyway, thanks for the points. They should help anyone who already has a plastic cup in place.

rogerstg

The nylon cup has no bearing interface at all. The bearings are in the cartridge itself. The purpose of the plastic cup is as a type of round shim, to add support to the cartridge, not to hold it in.

Even when people use too much force to tighten them, they only seem to crack at the outside edge. I've never seen one cracked all the way through. Of course, the entire inner portion is firmly wedged between the BB and the BB shell.

The downside to a metal cup is that they are prone to squeaking and usually weigh more than the nylon version.

HillRider

As rogerstg further pointed out, the plastic cup does not support any bearings as they are all inside the metal cartridge. The cup is just a shim and end support for the cartridge and sees no wear at all.
Good quality cup-and-cone bearings can last a long time if kept clean and well lubricated and if made of good materials. Some of the better Shimano and Campy C&C bottom brackets will last for decades and tens of thousands of miles but other maker's pitted in less than 10,000 miles no matter what you did. Same with hubs. My 7700-series Dura Ace C&C hubs have over 50,000 miles all on the original cones and races but I've seen low quality hubs pit their cones in only a couple of years.

Modern cartridge bearing bottom brackets can also be very durable. I have a Shimano Octalink bb with 32,000 miles on it and other Shimano square taper cartridge units with over 30,000 miles each still in perfect condition so "modern" doesn't mean expendable or disposable.

There is a lot of unfounded nostalgia for "the good old days" and "they don't make them like they used to". Indeed some newer stuff has been cheapened and made far less durable but the better quality new components are vastly better than their predecessors.

JosephShead

I should probably have left this alone, and I don't want to get into an arguments. I actually originally thought I could get some friends around here.

I used the term 'bearing' in a broader sense than what is usually referred to by 'bearing'. It is part of the support structure through which forces are conveyed from the pedals to the ground, through the left crank arm, spindle, bottom bracket bearings proper, bottom bracket shell, plastic cup, shell in the frame for the bottom bracket, etc. And, as I introduced into the discussion, once the plastic is in place, it is sandwiched and supported by metal parts. But, I still can't ignore my experience with that other plastic Shimano part.

Regarding the good ole days, I'll give them credit where deserved, but in building up my new touring bike (which I might give a report on, good for laughs), I can certainly say, I don't miss cottered cranks, and I like the fact that so many things are accessible with Allen wrenches, and in metric sizes, for instance.

Shimagnolo

Shimano also makes a metal cup for the UN54: https://www.universalcycles.com/shopp...3&category=347

HillRider

You have made friends and none these posts need to be considered arguments, only discussions of the merits and demerits of various components and material choices. Keep the reports coming as your build progresses.

rogerstg

This is a place where lots of information is exchanged. If you take it personally when facts and experience are contrary to your opinion, you may be in for a rough ride.

FWIW, I've learned much in some cases where my own opinions and experience were challenged by this frank exchange of information.

IME, it's actually quite the opposite. The high density nylon part is supporting the metal structure of the BB as a circular shim, held in place from sliding out by the threads. That's why even if the tool interface cracks, it has no effect on supporting the left side of the BB.

I think that a lot of the consternation about cracking the part on installation could have been avoided by Shimano properly noting the lower torque requirements in their instructions.

Iowegian

+1. I usually install the cartridge, then install the plastic cup until just touching, unscrew the cartridge a few turns, and then turn the plastic cup about 1/4 turn and re-tighten the cartridge. It's a bit of trial and error but it prevents putting any serious torque on the plastic cup.

ka0use

i was looking at my bb one day and when i saw the new plastic whatever-that-thing-is i had doubts.
seems to me it is there to support the cartridge, and, i suppose, provide a weather seal. i'm getting
the idea you guys think it isn't necessary. bearing down hard on the left crank will strain the right
side, won't it? therefore, a strong left side doodad is mandatory.

confusion reigns in my mind.

RogerB

Jenson USA still has UN-26, UN-73, UN-53, UN-54, and UN-55.

I see a lot of anecdotal conjecture all over the web, which is only partially useful. Is there any info out there about the actual, technical differences between these?

joejack951

UN-73 has a hollow axle.

hybridbkrdr

Even though I don't know everything to know about bottom brackets I can say I read that some earlier versions apparently had some kind of creak. So, I'd be somewhat hesitant to buy the 73 or 53 BUT I don't know if those were really early models.

Booger1

I have had a UN73 in my bike for many years,no creaking.

A UN 26 is a steel axle as oppossed to CRoMO for the others.
UN54 has 1 metal cup,1 plastic cup.
UN55 is metal cup on both sides.
UN 73 is 2 metal cups,and a CRoMO hollow axle.

aleks

I can add that the left cup is shaped a little differently on the inside, where it goes over the bottom bracket body, perhaps to make it fit more snugly over the end. I'm using a Problem Solvers UP-CUP #54, anyway.

Joe[/QUOTE]

I bought UN55 as replacement for BB-CT92. It has an aluminum cap that is bigger diameter than cartridge itself. When I slide cup over cartridge, it feels loose. Is it defective adapter? How it supposed to support left end?