The Yeti SB150 linkage has a design flaw - Here’s how to fix it!

I have about 1000km on my SB150 now, and one night about a week ago decided it was time to service my rear shock. Well, that project is still on-going. Upon disassembling the shock I found the rear linkage extremely notchy, and this report outlines my findings.

The part numbers are in reference to the Yeti SB150 manual.

Linkage overview

The Yeti linkage uses their proprietary Switch Infinity system as the main pivot, with a pair of F6902-EB bearings. The rear triangle is one piece, connected to a separate rocker that Yeti call the "SB150 link".  The rocker has 4 more 6902 bearings, 2 of which sit in the rocker and act as the secondary pivot point between the front and rear triangles, and 2 sit in the rear triangle. In addition there are 2 398 bearing, which sit at the ends of the dog bone links, or shock extenders, as Yeti calls them, making the total number of bearings 8.

The linkage itself works in a similar fashion to the Santa Cruz VPP and Pivot DW Link, but instead of a separate lower link there's the Switch Infinity, allowing the rear triangle to rotate around a virtual vertical axis. And ingenious system, albeit just a glorified single pivot system.

Main Pivot and Switch Infinity

The assembly consists of the following parts:
4.7 - 200020201 Switch Infinity G1 assembly
4.10 - 300040485 Collet axle 15mm
4.11- 300040454 Collet Wedge Sub-Assembly 15mm
4.12 - 300030285 Collet Nut M15x1.5

The SI glide rails are firmly attached to the frame, allowing the SI slider to vertically move on the rails. The swing arm then pivots around the SI slider on 2 bearings, and is attached to the SI with a collet axle 4.10. Note that the bearings here are not standard 6902s. They are listed as F6902-EB, so they have a flange on the outer race and are not the same 6902 MAX-e as the rest of the frame bearings. This assembly consists of the axle 4.10, nut on the drive side 4.12 and an expander bolt 4.11 to lock the shaft in place. Again, a very well thought out system. One of my problems turned out to be the collet shaft, which had seized to the drive side pivot bearing. It took considerable effort to break it loose, but luckily the bearings turned out to be OK. A good clean and lube and the unit is as good as new.

My strong recommendation is to grease the collet axle where it runs through the main pivot bearings and the SI slider to prevent seizure and future problems.

Secondary pivot and rocker arm

My main problem, and the design fault I will address here turned out to be the rocker arm bearing arrangement, but the bearing 4.20.2 on the shock extender 4.20.1 had also failed. This is a proprietary 398 bearing with an extended inner race so I had to order it, as your LBS, unless they are a Yeti dealer, is unlikely to carry this type. The 398 is a dual row ball bearing, which is a good bearing for this part of the frame. Even though the 398 with an extended inner race is not super rare or impossible to source aftermarket like the Industry Nine hub bearings, I just wish manufacturers would stop using proprietary bearings and stick with standard ones!

The assembly consists of the following parts:

4.1.1 - 300040501 S150 Link
4.1.2 - 300020052 Bearing 6902-2RS Extended, 15x28x7/10
4.16 - 300030298 Bolt Master, TI, Female, 8x41.0
4.17 - 300030069 Washer 8.5x12.5x0.5mm
4.18 - 300030151 Bolt, TI, Male, M6x12mm
4.19 - 300030062 Washer 6.5x12.5x0.5mm
4.2 - 200020326 Bolt, SS Pivot, Female
4.20.1 - 300040502 Shock Extended, Top (60mm)
4.20.2 - 300020032 Bearing 398 MAX DBL, 8x19x10/11
4.21.1 - 300040503 Shock Extender, Bottom (60mm)
4.21.2 - 300020032 Bearing 398 MAX DBL, 8x19x10/11
4.22 - 300040505 Shock Extender Bearing Extension
4.26 - 300020052 Bearing 6902-2RS Extended, 15x28x7/10
4.3 - 20002032 Link, Pivot Hardware, keyed, long
4.5 - 300030293 Link, Pivot Hardware, Male, 15mm
4.6 - 200020328 Stud, Link Bearing, Female, 15mm

Section view 1: Rocker arm to frame attachment

The sectional view above shows how the rocker arm is attached to the frame and references the part numbers. The problem I had was with bearing 4.1.2. The drive side had completely seized, despite being a full- compliment, ie. cageless, ie. "MAX" type bearing, which is generally regarded as the best option for pivot bearings if needle bearings cannot be used.

The design, its flaws and the remedy

The sectional view 1 shows the bearing arrangement in the rocker arm. This is your typical arrangement with the bearings pressed into the aluminum rocker, and aluminum insert in the carbon frame and a bolt that runs through the rocker arm bearings and the frame, holding the package together. Nothing new here and a proven design.

However, if this design is done correctly, dimension A should be the same on the frame and between the inner races of the bearings once they are mounted in the rocker. The distance between the bearings in the rocker is marked as C, and this should be designed so that there is only a very small clearance B between the bearing inner races and the frame to allow the rocker to be installed. This clearance is then closed to zero as the rocker bolt 4.6 is tightened with the end nut 4.5.

In the Yeti design this is not the case! If you install the rocker onto the frame, but don't tighten it down, clearance B is too large. This was pointed out to me by a member of the Facebook Yeti Bikes group, who had experienced a similar issue with breaking rocker bearings. I had to investigate!

 A clearly visible gap between the bearing inner race and frame

It turns out the frame width A in my frame was 32.9mm, and the distance between the bearing inner races, which, again, should be equal to A or just slightly bigger, was 33.25mm. This means a clearance of 0.3mm, which is far too much for such small bearings. As you tighten the rocker bolt 4.6, the bearing inner races are pressed closer to each other, which jams the balls into the outer races and effectively introduces so much preload on the bearing that it's not able to rotate freely. Now, preload is not uncommon in bearing arrangements and can be used to remove excess play or compensate for deflection, but such small bearings cannot handle more than maximum 0.01-0.05mm of preload, even in an application such as this one where the bearing doesn't actually rotate, but only reciprocates back and forth.

My conclusion is that Yeti have overlooked this when making the design and choosing the tolerances between the parts. A proper clearance B would be somewhere around 0.05mm, not 0.30mm.

To compensate for this I got some 0.1mm shim stock and cut 3 shims out of it. I fitted 2 shims on the drive side, and 1 on the non-drive side to bring clearance B closer to 0 when free. As I then tightened bolt 4.6 and nut 4.5 to the specified 15Nm torque, the rocker could move freely where as previously without the shims, it would seize completely or become very notchy. I will try and source some 0.30mm shim stock for the future, as fitting 3 shims between the frame and bearing is rather difficult, and having the linkage offset 0.3mm one way or the other is not likely going to make a difference in the overall functioning of the rear suspension.

Upon further investigation DIN988 bearing washers also work here, so if you can source them, they are a better and easier option. I bought a 10-pack off eBay for a few Euros in various thicknesses and meant for a 15mm shaft.

Custom 0.1mm shim. Id = 15mm, Od = ~19mm

The shims in place between the frame and the bearing inner race

Time will tell if this modification extends the lifetime of the bearings, but I would be surprised if it didn't. So the next time you're working on your linkage and find the rocker arm notchy or having seized bearings, this could be your problem!

DISCLAIMER: This problem may not be present on all frames! I'm only sharing information which I have found working on my personal bike.

UPDATE 23.07.2021: Small details updated and the correct shim type are now listed

UPDATE 08.10.2021: The 2021 frames MAY have had this issue partly resolved, as my new frame's dimensions only required a 0.1mm shim.