33 BMW 1983 R80ST Remove Rear Drive, Swing Arm, Monoshock

The R80ST has a monoshock rear suspension and the associated redesigned swing arm from the R80 G/S model with a 37/11 ratio rear drive.

Rear Drive, Swing Arm & Rear Monoshock

Rear Drive, Swing Arm & Rear Monoshock

Rear Drive Gear Ratio 37/11

Rear Drive Gear Ratio 37/11

Tools

I use a 12 mm box end wrench that I ground down so it will fit in the tight clearance around the 12-sided nuts that attach the rear drive to the swing arm.

Grinding Down 12 mm Box End Wrench

Grinding Down 12 mm Box End Wrench

And I use a 10 mm box end wrench that I ground down so it fits better in the tight clearance around the bolts that secure the drive shaft to the transmission output flange.

I use a cut-down 27 mm socket I got from Cycle Works to fit inside the hole for the swing arm pivot bolt to remove its locking nut.

Cut Down 27 mm Socket For Swing Arm Pivot Bolt's Lock Nut

Cut Down 27 mm Socket For Swing Arm Pivot Bolt’s Lock Nut

Video

This is a short video summarizing how I do this work.

VIDEO: 1983 BMW R80ST Remove Rear Drive, Swing Arm & Monoshock

Remove Rear Monoshock

I start by removing the rear monoshock. It attaches at the top to the rear sub-frame and at the bottom to a bracket on the swing arm. The top of the shock will not rotate out of it’s bracket unless the top, right sub-frame bolt is removed, or at least unscrewed enough that the end of the bolt can’t interfere with the top of the shock. Both the top and bottom are secured with a bolt, two wave washers and a nut.

Shock Won't Clear Bottom Of Right Top Sub-Frame Bolt

Shock Won’t Clear Bottom Of Right Top Sub-Frame Bolt

Right Rear Sub-Frame Hardware Detail-Nut Is Welded To The Frame

Right Rear Sub-Frame Hardware Detail-Nut Is Welded To The Frame

Right Upper Sub-Frame Nut Is Welded To Sub-Frame

Right Upper Sub-Frame Nut Is Welded To Sub-Frame

Monoshock Top Bolt Hardware Detail

Monoshock Top Bolt Hardware Detail

Removing Lower Monoshock Bolt

Removing Lower Monoshock Bolt

Rear Monoshock Lower Mounting Hardware Detail

Rear Monoshock Lower Mounting Hardware Detail

Rear Monoshock Removed

Rear Monoshock Removed

Drain Swing Arm and Rear Drive Gear Lube

I drain the gear lube in the swing arm and rear drive. I found water in the swing arm. This makes sense as the rubber boot that goes between the swing arm and transmission is torn and rotted and this bike did spend some time outside.

Draining Swing Arm Gear Lube

Draining Swing Arm Gear Lube

Swing Arm Has Water In It

Swing Arm Has Water In It

I use a deep 17 mm socket to remove the rear drive fill plug. There is a breather cap at the top of the fill plug and the deep socket slides over it.

Removing Rear Drive Fill Bolt With Deep 17 mm Socket

Removing Rear Drive Fill Bolt With Deep 17 mm Socket

Remove Rear Drive

To take the pressure off the swing arm pivot bolt, I support the swing arm with a jack stand.

Supporting Swing Arm With Jack Stand Before Removing Rear Drive and Swing Arm

Supporting Swing Arm With Jack Stand Before Removing Rear Drive and Swing Arm

I use the ground down 12 mm box end wrench to remove the four 12-sided nuts that secure the rear drive to the swing arm.

Rear Drive Is Secured To Swing Arm With Four 12-Sided Nuts

Rear Drive Is Secured To Swing Arm With Four 12-Sided Nuts

The top outside nut won’t come off the stud as it interferes with the lower monoshock bracket. So I remove all the other nuts and then slide the rear drive backward to remove that nut.

Lower Monoshock Mount Bracket Is Very Close To Top, Outside Nut

Lower Monoshock Mount Bracket Is Very Close To Top, Outside Nut

Removing Swing Arm To Rear Drive 12-Sided Nut

Removing Swing Arm To Rear Drive 12-Sided Nut

Top, Outside Swing Arm Nut Interferes With Lower Monoshock Bracket

Top, Outside Swing Arm Nut Interferes With Lower Monoshock Bracket

Swing Arm 12-Sided Nut Detail and Rear Drive Stud Detail

Swing Arm 12-Sided Nut Detail and Rear Drive Stud Detail

The rear drive is stuck to the swing arm so I use a plastic mallet, aka, my “fine persuader :-), to get it loose.

NOTE:
On the twin shock models, there is a paper gasket between the rear drive and swing arm flanges. The gasket is not used on the monoshock swing arm models.

Persuading Rear Drive To Separate From Swing Arm

Persuading Rear Drive To Separate From Swing Arm

Swing Arm To Rear Drive Nuts

Swing Arm To Rear Drive Nuts

The drive shaft coupling has interior splines that mate with a gear on the rear drive to power the rear drive.

Drive Shaft Coupling Has Interior Splines

Drive Shaft Coupling Has Interior Splines

Rear Drive Gear Engages With Interior Splines On Drive Shaft Coupling

Rear Drive Gear Engages With Interior Splines On Drive Shaft Coupling

Remove Swing Arm

There is a rubber boot between the front of the swing arm and the rear of the transmission that encloses the drive shaft flange and transmission output flange tunnel. Mine is torn and rotted. The boot is secured with two straps that screw together. I remove them and cut off the rotted boot.

NOTE:
If the boot is in good shape, you can push it to one end so you can access the four 12-sided bolts that secure the drive shaft flange to the transmission output flange.

Swing Arm To Transmission Rubber Boot Secured With Two Straps

Swing Arm To Transmission Rubber Boot Secured With Two Straps

Removing Drive Shaft To Transmission Boot Clamps With Screw Driver

Removing Drive Shaft To Transmission Boot Clamps With Screw Driver

Drive Shaft To Transmission Boot Strap Detail

Drive Shaft To Transmission Boot Strap Detail

Drive Shaft To Transmission Boot & Straps Removed

Drive Shaft To Transmission Boot & Straps Removed

I remove the four 12-sided bolts that secure the drive shaft flange to the transmission output flange using a ground down 10 mm box end wrench. To do this, I rotate the drive shaft so a bolt is at the 3:00 position. Then I put the transmission in first gear and remove the bolt. I put the transmission in neutral and rotate the drive shaft to bring the next bolt to the 3:00 position and repeat until I remove all four bolts.

NOTE:
Be careful when removing the bolts that you don’t drop them into the swing arm tunnel. If you do, and the rear drive is attached, use a magnet on an expandable stalk to fish it out.

Four Drive Shaft 12-Sided Bolts

Four Drive Shaft 12-Sided Bolts

Removing Drive Shaft 12-Sided Bolt With Ground Down 10 mm Box End Wrench

Removing Drive Shaft 12-Sided Bolt With Ground Down 10 mm Box End Wrench

Drive Shaft 12-Sided Bolt

Drive Shaft 12-Sided Bolt

Drive Shaft 12-Sided Bolts Detail

Drive Shaft 12-Sided Bolts Detail

NOTE:
I replace these four bolts whenever I remove them as they receive a lot of stress.

There is a black plastic dust cap the fits over the hole in the frame that the swing arm pivot bolt and and locking nut are inside of. I remove the cap.

Swing Arm Pivot Bolt Dust Cover

Swing Arm Pivot Bolt Dust Cover

I use a cut-down 27 mm socket to slip inside the hole to remove the locking nuts. Mine were very tight so I braced my leg against the foot peg to get leverage on the nut. I use an Allen to remove the pivot bolts that fit inside the swing arm bearings. Then I slip the swing arm out of the frame.

Cut Down 27 mm Socket For Removing Swing Arm Pivot Bolt Lock Nut

Cut Down 27 mm Socket For Removing Swing Arm Pivot Bolt Lock Nut

 

Bracing A Foot On Foot Peg To Get Leverage To Remove Swing Arm Pivot Bolt Lock Nut

Bracing A Foot On Foot Peg To Get Leverage To Remove Swing Arm Pivot Bolt Lock Nut

Swing Arm Pivot Bolt Lock Nut Detail

Swing Arm Pivot Bolt Lock Nut Detail

Swing Arm Pivot Bolt Detail

Swing Arm Pivot Bolt Detail

Removing Swing Arm From The Frame

Removing Swing Arm From The Frame

Swing Arm Hardware Detail: (L to R) Drive Shaft 12-Sided Nuts, Swing Arm Pivot Bolts, Swing Pivot Bolt Lock Nuts

Swing Arm Hardware Detail: (L to R) Drive Shaft 12-Sided Nuts, Swing Arm Pivot Bolts, Swing Pivot Bolt Lock Nuts

Here are the rear drive, monoshock and swing arm removed from the frame.

Rear Drive, Monoshock & Swing Arm Removed

Rear Drive, Monoshock & Swing Arm Removed

And, here is what the bike looks like now. The remaining work includes removing the air box, transmission and the engine.

Down To The Air Box, Transmission, Engine and Frame

Down To The Air Box, Transmission, Engine and Frame

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