SRAM GXP bottom bracket premature failure

Back by popular demand, the general all-things Road forum!

Moderator: robbosmans

Post Reply
DuncanS
Posts: 143
Joined: Thu Aug 12, 2010 4:42 pm

by DuncanS

Hoping somebody has some experience to share.

I recently rebuilt my old bike as a "Winter bike." As part of the rebuild, I had a new SRAM GXP Team (English threaded) bottom bracket installed by LBS.

Shakedown ride with 10sp Red cranks, all good.

Then the wet weather came, so I flipped my SRAM/Quarq PM cranks across to this bike. Rode about 5 rides ~200km, no issues.

Then dry weather came back, so I flipped the cranks back around again. Red cranks back onto this bike. Spun the cranks and realised there was massive drag. Took them off, discovered the drag is from the drive side bearing. Feels like it is completely busted, but there is no visible damage. The bearing itself, behind the gutter seal, looks clean and greasy still. I don't think I messed up the crank installation and overloaded the bearing - I torqued fairly firm but I don't think there were any washers in the wrong place that would overload the bearings. But then again, the only other explanation I can come up with is manufacturing defect.

Side note: After the last wet weather ride, before flipping the cranks back, I heard something rattling inside the frame. I'm wondering if it's actually (a) a ball bearing, or (b) something inside the frame that lodged into the bearing (and old rivet from cable guide and a bidon rivnut could well have been floating around in there). Both don't seem particularly plausible.

I think the only solution now is to get a new BB installed. However, as the BB was supplied by me, installed by my friendly LBS, then cranks installed by me, I'm not in a rush to go back and give them the impression I'm blaming them for anything, nor any more ammunition that I'm a classic Home Mechanic :oops:

So, any ideas what might have happened?

TIA

by Weenie


Visit starbike.com Online Retailer for HighEnd cycling components
Great Prices ✓    Broad Selection ✓    Worldwide Delivery ✓

www.starbike.com



User avatar
HakeemT
Posts: 167
Joined: Thu Mar 18, 2004 7:39 pm

by HakeemT

DuncanS wrote:I torqued fairly firm but I don't think there were any washers in the wrong place that would overload the bearings.

This reads like you did use washers, correct? A GXP (68mm threaded) bracket + GXP cranks shouldn't need any washers in the first place. Did you use any spacers or wavy washers when installing the cranks?

DuncanS
Posts: 143
Joined: Thu Aug 12, 2010 4:42 pm

by DuncanS

No spacers or wavy washers. Just the gutter shield on DS and rubber shield on NDS.

I took a better look when I got home today and the bearing shield is cracked, I suspect by compression. Haven't yet figured out whether the whole bearing had been trashed or only the shield.

Image

rbrtwyn
Posts: 252
Joined: Thu Dec 09, 2004 1:57 pm

by rbrtwyn

Did your shop check the BB shell's facing before installing the BB?

BikeAnon
Posts: 399
Joined: Sun Mar 02, 2014 6:36 pm
Location: NY USA

by BikeAnon

The bearings are very inexpensive, and can be replaced at home with simple tools.

I suspect that bearing is 24x37x7mm. Pairs of those bearings are well under $20.

EDIT: it might be 25x37x(6 or 7mm). The dust-cover might fill in the extra mm. http://www.the-climb.net/2011/09/truvat ... ckets.html

- Remove the cup.
- On the "inside" side of the cup, insert a socket that just barely fits into the hole.
- Hold the assembly in your hand
- Hit the socket hard with a hammer.

You won't damage the cup. You will be able to generate enough force to pop the bearing out.

Press in a new one carefully by hand.

Finish the job by placing the cup on a piece of soft wood, threaded-side down.

LIGHTLY tap the bearing in with a proper sized socket, and light taps with hammer.


More info that might help:
http://forums.mtbr.com/drivetrain-shift ... 89495.html
http://velonews.competitor.com/2008/12/ ... rame_85783

As for why some bearings "go bad" quickly... I've had some that lasted years through all manner of conditions, and one (this year) that was wrecked in a single winter ride.

DuncanS
Posts: 143
Joined: Thu Aug 12, 2010 4:42 pm

by DuncanS

Well well, it seems I did have a couple of spacers on the spindle! See below the gutter seal:

Image

Shield however was not trashed - I saw the split retainer ring and thought it was a crack:

Image

With all that out of the way, the balls look good but they stop firmly at exactly the interval of the ball spacing, so it really seems like I've notched the race or something.

Image

I think I will have to put it down to Home Mechanicking and those extra spacers.

DuncanS
Posts: 143
Joined: Thu Aug 12, 2010 4:42 pm

by DuncanS

rbrtwyn: not sure about the facing but at this stage, seems an unlikely explanation.

BikeAnon: thanks for the suggestion, but with the likely cause established and full BB's going for about AUD35, I reckon I'll just order a new BB. And an installation tool so I can continue to live and learn as a Home Mechanic ;)

Sent from my GT-I9507 using Tapatalk

BikeAnon
Posts: 399
Joined: Sun Mar 02, 2014 6:36 pm
Location: NY USA

by BikeAnon

When you get the new BB kit. take the hammer to this one and expand on your home mechanic skills!

That's how I ended up learning I could replace just the bearings for 1/3 the cost of full shells.

DuncanS
Posts: 143
Joined: Thu Aug 12, 2010 4:42 pm

by DuncanS

I like your thinking.

Sent from my GT-I9507 using Tapatalk

DuncanS
Posts: 143
Joined: Thu Aug 12, 2010 4:42 pm

by DuncanS

At least I've learned that cadence magnets make for a good chain hanger.

Sent from my GT-I9507 using Tapatalk

eric
Posts: 2196
Joined: Tue Nov 11, 2003 9:47 pm
Location: Santa Cruz, California, USA
Contact:

by eric

GXP is not supposed to have spacers. Unlike other BB systems, bearing preload and crank lateral location is not set by spacers or wavy washers on the outside of both bearings. Instead, the location is provided by the NDS bearing. The crank spindle captures both sides of the bearing- there is a shoulder on the inner side where it necks down from 24mm to 22mm. The single deep groove ball bearing is sufficient for the small lateral forces it sees. The spindle floats in the DS bearing. This design is nice because there's no need to set the preload, something that is often done wrong.

I've found that the standard GXP bearings are really pretty good. At ~$25 a set I'm not sure it's worth making the fixture to remove and press new bearings into the cups.

Marin
Posts: 4035
Joined: Wed Jan 22, 2014 11:48 am
Location: Vienna Austria

by Marin

I dunno, I seem to have to replace my NDS GXP bearing after every 2nd wet ride. Switched to Shimano + adapter in 2 of 3 bikes already, saves 35g and lasts much longer. Black too!

BikeAnon
Posts: 399
Joined: Sun Mar 02, 2014 6:36 pm
Location: NY USA

by BikeAnon

Marin wrote:....Switched to Shimano + adapter ....
More details?

User avatar
Mr.Gib
Posts: 5577
Joined: Fri Mar 18, 2005 4:12 pm
Location: eh?

by Mr.Gib

For GXP (Sram) i think you have a seal over each end of the BB and a wavy washer on the drive side. Most of my bikes are press fit GXP and that's the way they are set up. My wife's rain bike however does have a threaded BB shell and uses the GXP team BB and I am pretty sure it is also set up that way. Trouble free for a few years. Even bought a another Team BB a couple of years ago expecting the original unit to fail and I am still waiting.
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

by Weenie


Visit starbike.com Online Retailer for HighEnd cycling components
Great Prices ✓    Broad Selection ✓    Worldwide Delivery ✓

www.starbike.com



DuncanS
Posts: 143
Joined: Thu Aug 12, 2010 4:42 pm

by DuncanS

The wavy washer is only for pressfit. As my little demo has highlighted, extra washers in there plus a bit too much torque can have fatal consequences for the bearings.

Sent from my GT-I9507 using Tapatalk

Post Reply