Sram GXP External cups BB - Modification

[Dudes]

I have been through a number of above BB's on my 29er (four to six month regularity) and in my opinion the BB has a built in design flaw which necessitates regular replacement at a not so small cost. Since I have modified my BB I have had no more problems and I believe it will now last me for a number of years. Time will tell. The modification was very simple.

 

THE MODIFICATION IS POSTED LOWER DOWN

Edited December 7, 2012 by Dudes

[Swift01]

Also converted mine 300km ago and all seems well. GXP ones were lasting 500km. But after 300km I made the REAL permanent change. Went from the Noir cranks to XT. Real problem solved. Not as light but will last longer and shift better.

[PeterF]

I have been through a number of above BB's on my 29er (four to six month regularity) and in my opinion the BB has a built in design flaw which necessitates regular replacement at a not so small cost. Since I have modified my BB I have had no more problems and I believe it will now last me for a number of years. Time will tell. The modification was very simple.

 

Please share. I am running 2 bikes with GXP BB's, and I know there's a problem on the drive side. I made a foam spacer for the one bike, still have to see how well it works.

[rouxtjie]

I have been through a number of above BB's on my 29er (four to six month regularity) and in my opinion the BB has a built in design flaw which necessitates regular replacement at a not so small cost. Since I have modified my BB I have had no more problems and I believe it will now last me for a number of years. Time will tell. The modification was very simple.

Tell us more...I have done a number of hacks to improve the life of my 2 GXP cranksets...incl rubber bands to hold seal / dustcap in place because right behind sits the bearings nicely exposed.

[Bike Mob]

without telling us what the mod is this post is about as useful as a cock flavored lollipop...

 

I also a secret but I'm not telling people that I have a secret

[Swift01]

The drive side bearing is just a weak bearing. very small ball bearings and has a plastic casing holding them together. No rubber band or foam was going to save that puppie. The conversion is an actualy Enduro bearing conversion kit you can buy.

[BogusOne]

Just use a Shimano bb with the shim from an old GXP bb to accomodate the stepdown to 22mm on the non drive side.

[rouxtjie]

The drive side bearing is just a weak bearing. very small ball bearings and has a plastic casing holding them together. No rubber band or foam was going to save that puppie. The conversion is an actualy Enduro bearing conversion kit you can buy.

The rubber band extends the life, but its not a solution and my argument is this a premium brand, why the hell do I have to hack it, to get it to perform. That being said, when you chuck the enduro kit in, it improves alot and I am with you on this, standard GXP bearings are hondnaai...

[Stretch]

without telling us what the mod is this post is about as useful as a cock flavored lollipop...

 

I also a secret but I'm not telling people that I have a secret

 

lets hope it has nothing to do with the aforementioned lollipop

[Bike Mob]

lets hope it has nothing to do with the aforementioned lollipop

 

Well lets hope your wife doesn't say anything about that...

[Dudes]

Sorry, was just testing the water to see if there was any interest before I use up all my typing skill in 1 session! It is apparent to me how the old bikes (internal BB's) that I rode never had a BB issue in the many years I rode them so I needed to figure out what the problem was with these new ones. As you know, the drive side bearing has a plastic bush cum dust cover that sits between the bearing and the shaft, while the non-drive side bearing sits directly on the shaft. This plastic (or whatever it is) bush is the weak point and as it wears due to pressure, not due to friction as it is the bearing that turns and not the bush itself, the drive shaft develops play that allows dust and dirt to get into the bearing. My first attempts were to add a a few turns of plumbers tape between the shaft and the bush to eliminate the play. This would give me a few more weeks before I had to re - tape and so on. My final effort (permanent effort) was to buy a small piece of 316 stainless steel tubing from the boat shop (1 inch diameter: 25.4 mm) and I took it to an engineer friend who cut both the inside and the outside diameter to fit snugly but not tightly onto the shaft and into the bearing respectivly (perfect lollipop fit). He only had to machine about 1.5 cm length, the width of the bearing, and also left a small lip (the full tube diameter: 25.4mm) at the one end before cutting the new machined bush off from the bought piece of tube - so the operation was quick and easy. We used the old plastic dust cover (less the bush part) and made to fit over the new flange diameter of 25.4 mm. Addittionally, I use a soft felt washer the same size as the dust cover (I didn't have felt so I used a bit of my 5 mm wetsuit) between the cover and the chain ring to prevent dust ingress. I have opened it once (after 4 months) to inspect and the bearings are beautifully clean and dirt free. If I remember correclty, the bush outside diameter was 24.8 mm (with a small 25.4 mm lip (about 1mm wide) on the one side) and the inside diameter was 23.7 mm, leaving a wall thickness is 0.55 mm. I would need to whip it out to re-measure but you can measure yourselves when you make the bush. (The 22 mm diameter as someone has mentioned is on the non drive side). (Good idea Bogus One - I misread first time). Swift01 mentioned that the bearing itself is just not good. This is not true. The bearings are good. I have dismantled to individual casings and loose ball bearings to check them out and clean them (bit of a job getting the bearings back in the casings but I managed in time) and there is nothing wrong with them. The problem was simpy the play created by the pressurized plastic bush which lets in dirt and grime which in turn chows the bearings. Now there is no play .... can't find the lollipop .....at least there is a flange! OK my typing is up.

Edited December 6, 2012 by Dudes

[Dudes]

Just use a Shimano bb with the shim from an old GXP bb to accomodate the stepdown to 22mm on the non drive side.

 

Elaborate please. The shim you mention, is that a bush to build up from 22 to 25 mm? In the Sram, its the stepdown that holds the shaft in place. I am not familiar with the Shimano BB. Is it 25 mm on both sides (inside bearing). If you build up the 22 on the non drive side the shaft will wander left and right through the BB, unless Shimano have a different way to prevent that. I will take a look at one when next at the LBS.

[Dudes]

Tell us more...I have done a number of hacks to improve the life of my 2 GXP cranksets...incl rubber bands to hold seal / dustcap in place because right behind sits the bearings nicely exposed.

 

Modification posted...

[Dudes]

Please share. I am running 2 bikes with GXP BB's, and I know there's a problem on the drive side. I made a foam spacer for the one bike, still have to see how well it works.

 

Modification posted above