SRAM GXP in BB90

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Valbrona
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by Valbrona

Not done one of these before.

Do you fit an MR2437 bearing both DS and NDS, and then do you fit a shim to reduce the ID of the NDS bearing from 24 to 22?

If so, where do you get the shim from? Does it come with a 'SRAM GXP for BB90' bottom bracket, or do you make a shim from a fag packet or similar?

Thanks.

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Calnago
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by Calnago

Trek has “kits” that will allow you to do this. If you contact them they’ll be able to tell you the exact part number for the kit and you should be good. It’s not too expensive.
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alcatraz
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by alcatraz

MR2437 bearings are easy to find replacements but they aren't original GXP bearings.

You need a shimano to gxp conversion kit. Which essentially is a cylindrical spacer/sleeve for the NDS side and a wavey washer. The 2.5mm spacer sometimes supplied is for shorter shell widths and is not needed with bb90.

I have one of these conversion kits running on a bb90 domane and a sram red crank. It works fine. Depending on the thickness of your dust caps you will maybe have some difference in compression of the wavy washer. You need to observe the compression of that washer closely.

At first I thought the crank seized and that I had to change the order of the sleeve/dust caps. In the end I put it back the same way as it once appeared seized and it spun nice and free again. My tip is to make sure the bearings are pressed in fully and that the spindle is clean and goes through all the way.

Ideally the wavey washer should be nearly completely compressed. Otherwise you will have some side play which is bad for front shifting.

Make sure you have
1. bearings
2. dust caps
3. wavy washer (24mm ds)
4. reducer sleeve 24-22
5. patience

Then you should be good to go.

alcatraz
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by alcatraz

If you buy the bearings and conversion kit you will not have dust caps.

The crank will have more side play than with an original gxp bb, but your spindle and left bearing should last longer as they arent locked together.

/a

TobinHatesYou
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by TobinHatesYou

alcatraz wrote:
Sun Aug 19, 2018 5:22 am

Ideally the wavey washer should be nearly completely compressed. Otherwise you will have some side play which is bad for front shifting.
Play is bad for more than that. With Trek BB90 being more of a slip-fit system, play would probably result in the bearings backing out of the BB shell/bores.

IMO, the best thing to do would just be to get the appropriate 22x37x"8" bearing with the slightly wider inner race.

hambini
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by hambini

The method I have used in the past is to use a 6805 bearing on the top end of the tolerance spectrum, then machine POM for the interfaces.

SRAM manufacturing tolerances are very poor so after you have wound the taper on the non drive side crank arm in, you can have a gap that can vary by 2-3mm.

I try to avoid having a hardened steel bearing running against a relatively soft crank axle as it will eat it hence the POM
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by jlok

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alcatraz
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by alcatraz

TobinHatesYou wrote:
Sun Aug 19, 2018 6:38 am
alcatraz wrote:
Sun Aug 19, 2018 5:22 am

Ideally the wavey washer should be nearly completely compressed. Otherwise you will have some side play which is bad for front shifting.
Play is bad for more than that. With Trek BB90 being more of a slip-fit system, play would probably result in the bearings backing out of the BB shell/bores.

IMO, the best thing to do would just be to get the appropriate 22x37x"8" bearing with the slightly wider inner race.
I'd also recommend to just buy a gxp bb for bb90.

It just struck me though that what you said about conversion kit not being good because of the bearings backing out can't be any better with a gxp bb. The NDS bearing must be much easier to back out when the system relies solely on the one bearing holding the crank in place sideways.

If that doesn't happen I wouldn't worry about it happening with the conversion kit. I'd worry more about dropping chains. Luckily that hasn't been a problem after tuning the fd carefully.

Besides we always have a wide range of retaining compounds to use for bearings that won't stay put. Is the rider putting out 1500w sprints then it would probably require a different approach.

/a

Valbrona
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by Valbrona

Thanks folks. Great advice.

TobinHatesYou
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by TobinHatesYou

alcatraz wrote:
Sun Aug 19, 2018 11:40 am

It just struck me though that what you said about conversion kit not being good because of the bearings backing out can't be any better with a gxp bb. The NDS bearing must be much easier to back out when the system relies solely on the one bearing holding the crank in place sideways.
Essentially correct. The preload from the wave washer helps sandwich everything in place with press-fit GXP BBs...conversion or not. The only BBs that don't need the wave washer are external threaded BBs and conversion BBs which hold the bearings captive.

hambini
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by hambini

In my opinion GXP is the worst bottom bracket standard out there. Made to dodge some Shimano patents and they made a hash of it.
Hambini Aeronautical Engineer, Polluting YouTube since 2016 - views expressed are my own...

Valbrona
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by Valbrona

hambini wrote:
Sun Aug 19, 2018 4:40 pm
In my opinion GXP is the worst bottom bracket standard out there. Made to dodge some Shimano patents and they made a hash of it.
Not as bad a Stronglight ActivLink.

Visus
Posts: 179
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by Visus

Wanted to share some experiences I had with a Kogel BB90 Bottombracket:

I opted for Kogel as they supply a nicely machined aluminium spacer set (at least I thought that) for the GXP Kit and different seal options. I chose the green cross seals (higher friction than the standard blue road seals but better sealed) as I wanted to avoid water ingress specially on the badly shielded NDS. With these seals the bearing were really hard to turn from the beginning and thereby nullifying probably allready all advantages of a ceramic bearings. Cranks were hardly turning twice after install with these seals (with the blue ones the bearings were buttery smooth in hand but I already had them installed)

Everything worked fine for 1 year. I did a short service, regreasing everything in winter. At that point I already noticed that it was a lot more difficult to get the crank axle out of the BB (got it out with a few taps with the rubber mallet).

Few weeks ago the BB developped a click and I decided to regrease everything to see if it changes anything.
Now the problems began: I couldn't get the crank out. It was literally seized in the bearings. I had to use a lot (!!) of force with the rubber mallet to get it moving. Finally it budged but then it got stuck at the driveside bearing. I then realized the inner piece of the machined aluminium reducer (from 24mm to 22mm for the GXP stepdown) was still stuck on the axle. I had to use a wooden stick and again a lot of force to get it out at the driveside bearing (the reducer shim finally got unstuck.)

After inspection of the GXP Reducer I noticed it had developped a "lip" from the clamping force at the 24-22 stepdown (there's a little groove right after the stepdown) and that's why it stayed stuck on the axle
IMG_3710.jpeg
IMG_3711.jpeg
Now after thorough inspection of the removed axle I realized that the inner sleeve of the DS bearing (Kogel uses bearings with a ID of 25mm and then insert an aluminium sleeve to reduce them to 24mm) stayed put on the axle. You can see the wave washer beneath it. On the NDS bearing you can see the sleeve in place
IMG_3709.jpeg
IMG_3708.jpeg
At first I had no clue how to get it of. Cutting it with a powered tool would damage the spindle surface. Some kind of bearing puller might work but I had none. In the end I removed the spider and used a tap to hammer it off
IMG_3990.jpeg
The crank had some corrosion signs where the bearing made contact
IMG_3998.jpeg
Now I've installed a regular steel Trek GXP steel bearing kit with Wako's brake protector to prevent any future creaks. My bores are quite tight, more a pressfit application than slipfit, therefore I don't think the creaking BB, which led to this adventure, was even a moving bearing.

I'm quite unlucky with BB's and somehow often have really weird experiences with them. Did anyone experience something similar?
And to prevent this in future: what kind of grease is the best to prevent corrosion between unlike elements (in this case aluminium-steel). I have been using morgan blue's aquaproofpaste but I guess that's not optimal. At the moment im trying motorex 2000 grease (calcium based) in this bike. In another one I've tried white teflon grease (finish line) and I'll see which has better longevity/doesn't seize up my cranks :lol:

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wheelbuilder
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by wheelbuilder

I've heard several references to BB90 being more of a "slip fit" than press fit. While it may be true that some bearings can be removed from the bore by hand, this was the exact procedure we/I used to determine if the carbon bore was becoming oversized and required a "version 2 bearing" replacement.....next stop, back to Trek for re-surfacing. These bearings absolutely should require an extractor to remove, and a press to install. I've said it many times before, that even among Trek Certified Mechanics, these bearings have a tendency to not be pressed in fully. Contributing to a variety of problems including bore wear. Use a high quality press, and bring that thing to almost a hard stop.
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Methodical
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by Methodical

wheelbuilder wrote:
Fri Aug 23, 2019 3:52 am
I've heard several references to BB90 being more of a "slip fit" than press fit. While it may be true that some bearings can be removed from the bore by hand, this was the exact procedure we/I used to determine if the carbon bore was becoming oversized and required a "version 2 bearing" replacement.....next stop, back to Trek for re-surfacing. These bearings absolutely should require an extractor to remove, and a press to install. I've said it many times before, that even among Trek Certified Mechanics, these bearings have a tendency to not be pressed in fully. Contributing to a variety of problems including bore wear. Use a high quality press, and bring that thing to almost a hard stop.
Exactly. I've heard the same reference in other threads around here abouting BB90s being a slip fit (i.e. should be able to just push in by hand). This was never my experience until my BB starting creaking. Not sure why folks think they should be able to just push BB90 bearings in by hand. :noidea:

I've always needed to use a press to remove/install BB90 bearings on my Madone (and my fairly newly built Emonda) and one day I could litteraly remove/install by hand (i.e. my creaking problem) and had to go to the V2 sized bearings. I spoke to Trek about this prior to going through the LBS for warranty (i.e. required by Trek in case of the next step of sending in frame) and Trek admitted they were aware of problem and suggested the V2 bearings. Trek also stated that if the V2 doesn't work, I'd have to send in my frame to have the BB shell rebuilt.
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