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MC How-To

Step by step: From general maintenance to complete restorations, we share tips and tricks for working on classic bikes.


BMW /5 Swingarm Bearing Service

BMW /5 Swingarm Bearing Service 

Last issue, we looked at servicing steering head bearings on BMW /5 machines, noting it as one of those jobs owners often put off until it's too late. If that's true of steering head bearings, it's doubly true of swingarm bearings, which owners often let go almost to the point of failure.

Bad swingarm bearings — or bushings — make themselves known by sometimes erratic and often sloppy handling. If you feel the back end of your bike wallowing through a turn instead of tracking through, you probably have worn out swingarm bearings/bushings and/or worn out rear shocks.

Owners are quicker to replace a set of shocks — typically just two bolts and they're out — with immediate improvements in handling following. Standard fitment shocks on many of our classics were pretty poor even when new; add in 40-odd years of use and most of them are pretty much junk.

 

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But swingarm bearing servicing is time-intensive and can require tools you may not have, like a good hydraulic press for pressing in new bushings. Yet while the average classic from Japan used bushings for swingarms, BMW's /5 series (and every air-cooled Beemer after) used tapered roller bearings.

 

Because they withstand high radial and axial loads while maintaining close tolerances, tapered roller bearings are an excellent choice in swingarm applications. But just as a steering head has a limited range of motion, a swingarm might only move through 45 degrees, describing that same arc again and again. As a result, the tapered roller bearings can take a set, visually identified in the bearing cup by radial lines called scalloping.

Scalloping results in a notchy motion in the swingarm, but chances are you'll never feel it because the combined weight of your body and the machine's on the swingarm tends to smooth out any roughness. And unless your swingarm bearings are trashed, you probably won't perceive any diminishment in performance. Yet that doesn't mean they shouldn't be inspected and cleaned, because even if they're perfectly serviceable, you'll feel safer and ride more confidently knowing their true condition.

You'll want to gather a few items before undertaking this project, including a new driveshaft housing-to-final-drive gasket, new swingarm seals — but not necessarily bearings — new driveshaft mounting bolts, and possibly a new driveshaft flex boot, the rubber bellow between the driveshaft housing and transmission.

You have to remove the driveshaft to replace the flex boot, so if it's at all suspect, now's the time. The seals have to be removed to service the bearings, and they'll be destroyed. But experience suggests it's rare to actually replace the swingarm bearings. Thanks to highly effective seals and the bearings' wear strength, they typically require only a thorough cleaning and regreasing to be put back in service.

Depending upon your level of skill, you'll want to budget a full weekend to give yourself plenty of time. Rushing is no fun, and often leads to distressing results. As always, a good shop manual is an essential aid and a necessary source for proper torque specs.

First, remove both mufflers, disconnect the rear brake rod and remove the rear wheel, followed by the complete rear fender assembly. 

First, remove both mufflers, disconnect the rear brake rod and remove the rear wheel, followed by the complete rear fender assembly. We removed the fender first, but you can do it either way. Next, remove the battery and battery box.

Drain the final drive unit gear oil; there are two drain plugs. 

Drain the final drive unit gear oil; there are two drain plugs. Remove the right shock, then remove the four 13mm nuts holding the final drive to the driveshaft/swingarm tube. Gently pull the final drive rearward and set it aside.

Remove the front clamp and pull back the driveshaft bellow. 

Remove the front clamp and pull back the driveshaft bellow. Wedge a screwdriver in the U-joint yoke to keep the driveshaft from turning and remove the four 12-point 10mm bolts securing the driveshaft to the output flange.

Next, remove the black plastic caps covering both swingarm pivots. 

Next, remove the black plastic caps covering both swingarm pivots. Using a thin-wall 27mm socket (we ground ours down to fit), loosen the pivot pin locknuts, then unscrew the pivot pins with a 6mm hex key.

Here's the left pivot pin being removed. 

Here's the left pivot pin being removed. The pins screw into the frame. Their machined ends protrude into and against the swingarm bearings, locating the swingarm to the frame.

Remove the left shock absorber and gently pull the swingarm assembly free of the frame. 

Remove the left shock absorber and gently pull the swingarm assembly free of the frame.

Remove the swingarm bearing spacer  

Remove the swingarm bearing spacer (not shown). Our swingarm seals were stuck tight. To remove them, we first cut mostly through the seal housing (it's soft metal; the swingarm's not) with a sharp chisel. Next, we folded the seal housing over using a punch. That released the seal enough to pry it free with a screwdriver.

Here's a swingarm bearing coming out, likely the first time it's been removed since it was installed way back in 1973 

Here's a swingarm bearing coming out, likely the first time it's been removed since it was installed way back in 1973! BMW's seals work well; although the bearing is somewhat dirty, it's mostly free of contamination from moisture.

Clean the swingarm and parts 

Clean the swingarm and parts. Drive out moisture from the bearings using compressed air (don't spin the bearing) followed by WD-40. This photo shows the cleaned pivot pins, bearings and bearing spacers (at left and right) along with our new swingarm seals.

The left bearing race in our cleaned swingarm 

The left bearing race in our cleaned swingarm. Although it shows signs of scalloping and/or staining, we opted to leave it alone. To be perfect it should be replaced, and probably will be in another 20,000 miles or so.

Next, repack the swingarm bearings with fresh grease and reinstall them. 

Next, repack the swingarm bearings with fresh grease and reinstall them. Note that we've already secured our new rubber swingarm bellow to the right or driveshaft side of the swingarm.

Using an appropriately sized socket or drift, drive the new seals in place 

Using an appropriately sized socket or drift, drive the new seals in place. You can tell when they've seated by the sound the socket makes when you hit it, changing from a somewhat hollow to a solid metallic "rap."

Install the bearing spacers 

Install the bearing spacers. One end of the spacer has a raised lip, which goes under the seal. The seals are quite pliable and you can gently roll the spacers into place even after the seals have been installed.

Set the swingarm in place and screw the pivot pins in evenly left and right 

Set the swingarm in place and screw the pivot pins in evenly left and right. The pivot pins press on the bearing spacers to locate the swingarm side-to-side. Don't tighten the pins or locknuts just yet. Reattach the driveshaft to the transmission flange using new bolts and blue thread-locker compound.

Using a caliper, measure the gap between the front swingarm pivot tube and the frame on both sides 

Using a caliper, measure the gap between the front swingarm pivot tube and the frame on both sides. It should be the same. If it's not, alternately loosen and tighten the pivot pins to adjust the swingarm until it's even.

Set initial bearing preload at each pivot at 13-15/ft-lb 

Set initial bearing preload at each pivot at 13-15/ft-lb. Turn the locknut finger tight, loosen the pivot pin, then re-torque to 6-9ft/lb. Check to make sure the swingarm to frame spacing is still equal on both sides. It can take a couple of tries to get it correctly set.

With a hex key to keep the pivot pin from turning, tighten the locknut using the 27mm socket with a Vise Grip firmly clamped to it 

With a hex key to keep the pivot pin from turning, tighten the locknut using the 27mm socket with a Vise Grip firmly clamped to it. This will set it enough to properly torque the locknut without fear of moving the pivot pin. Factory specs are 69-86ft/lb.

Torque the locknut, then check the swingarm movement 

Torque the locknut, then check the swingarm movement. It should be buttery smooth, with no binding. Clamp the driveshaft boot at the transmission, reinstall the final drive (with gasket), shocks, fender, battery box, battery, rear wheel and mufflers, hook up the brake rod, and refill the final drive and driveshaft oil. That's it, you're done!