Trek BB90 Problems Solved.

Trek BB90, and its mountain bike sibling BB95, are excellent bottom bracket systems. We get a lot of grief for saying things like this because there are legions of BB90 haters out there who are convinced it is the worst thing since unsliced bread. And they are vocal. Our answer to them is simple: You’re not doing it right. With Trek BB90 the setup is everything. Get it right and you’re riding on a dream. Get it wrong and you’re hating life because of mountain bike creaking.

Let’s talk about the two major reasons why Trek BB90 and BB95 bikes creak, and then I’m going to tell you how simple it is to make sure creaks don’t happen to you anymore. The first and most common reason for mountain bike creaking occurs when the bearings start moving around in the frame with each pedal stroke. This causes creaking, which is annoying, but the real danger here is that this loose condition leads to ovalization of the bearing bores in the carbon frame, and that ain’t good. Yes, every time you pedal a stroke and hear a creak from a loose bearing you are causing damage to your carbon frame. As long as you get on it right away there won’t be any lasting damage.

The fix is easy. We advocate bonding the bearings into the frame with a Loctite-style product. We prefer VibraTite530 or Loctite 609 for STANDARD frames where the bearings still require the use of press tool. If the frame is worn to the point that the bearing can be pushed in easily by hand or they basically fall out, you’ll need VibraTite538 or Loctite 638, which we package with our REPAIR kits.

A bonded-in bearing can’t move anymore. No movement, no creaking, no frame damage. Problem solved. There’s nothing to fear from bonding the bearings in the frame as long as you use the right retaining compounds such as the specific VibraTite and Loctite products I just mentioned. To ease your mind, here's a picture of the labels from a bottle of 609 and 638; note the depiction of a bearing being bonded into a rotating assembly and the description of what it does, "Augments Press Fits" and "Slip Fits":

 

 

The bearings can still be removed and serviced in the same manner over and over again using proper bonding practices. Loctite is not glue and its use does not violate your warranty.

The second reason for a creaking Trek BB90/BB95 bike is the typical steel on steel interface between spindle and bearings. We’re baffled by Trek’s insistence on using bearings with a 24mm inner diameter (ID). I'm sure the thought was, "Why not just slide the spindle right into the bearing, what could be easier". This causes creaking for obvious, common sense reasons, but it also causes corrosion problems that are exacerbated by water intrusion. Check out Figure 1 to see the most extreme case we’ve ever had in our shop.

 

It's dramatic, and obviously this disgusting rusty slime wasn't cause by the steel on steel interface per se, but the wear and corrosion at the bearing journals certainly was, and that's what we're concerned with here.

 Notice the irreparable damage to the spindle. We cleaned it up with ScotchBrite and acetone to prevent removing any more material, clearly seen in Figure 2 . The areas of concern are the bearing journals (the spots on the shaft where the bearings run) and not the non-critical, central portion of the spindle. A spindle with worn bearing journals means a loose fit, which means mountain bike creaking.

 

The fix is to use a standard 6805 bearing which features a 25mm ID inner race rather than a 24mm ID inner race. This gives us room to snap a polymer bushing into the inner race to reduce the ID to 24mm for a snug fit and to provide an all-important buffer between the steel components. This is the same strategy Shimano has employed since pioneering threaded, outboard-style bottom brackets decades ago. It’s a great idea that we ran with. Thanks Shimano.

Now that you know what’s causing all the BB90 and BB95 mountain bike creaking it’s time to fix it. Check out our Trek BB90 installation video below for detailed instructions on how to get the job done correctly.

If you have any questions please ask them. You can email us or call us. We’re here to help you.




Gary Mailhiot
Gary Mailhiot

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