Swingarm Upgrade

[TCHLFXVT]

I have a 74 R75 that I am converting in to a cafe bike for a Winter project .
I want to upgrade the swing arm to a newer stronger model , I remember hearing that these are better than a CC brace job.
I would like to know what are best year replacements to seek that will fit my old /6
Thanks ,Tom

[Polarbear]

Take yours off and to a fine machinist shop for such. Tell'em what you wish and its easier this way, maybe cheaper too. A simple hardened steel rod welded around the bottom of the housing is all thats required. Good luck with your project, sounds cool. Randy:dance

[20774]

I understand that in '79, they added the cushioned driveshaft which made shifting smoother. Beginning in '81, the swingarm is a beefier unit through the '84 models. That might provide some added stiffness without having to go the route of external bracing, etc. I tmight require some modifications in terms of the brake light switch, though.

[rinty]

I used to have an '82 RS, and with the stock swingarm, the bike would squirm in corners at higher speeds (the rest of the chassis had had all the usual upgrades done to it).

Bracing the swingarm settled the bike right down; it was one of the best mods I had done.

[toooldtocare]

My bike (78RS Motorsport) has the CC swing arm (actually San Jose when it was installed in 85), Progressive springs, Koni shocks, San Jose fork brace, and San Jose billet triple clamp. I am very satisified with the handling. It is very stable in the turns and rock steady at high speeds, not that loose feeling like my old R90S had

Other mods you might want to consider are SS brake lines, floating rotators, and ceramic brake pads if you have not done those yet. With these, my bike also stops with the best.

Enjoy your project.

[bmweuro]

How do you weld hardened steel to mild steel without something cracking at some point? Use a 80-84 swingarm and your driveshaft. Under the rear foot peg mount weld a triangular piece(3/16 thick) between the cross brace under the battery/footpeg mount/main frame. This is the only place the frames flex. Swing arms do not flex. This has been tested on the track with a 73 HP /5 @ 385 pounds and a 215 pound rider.


Take yours off and to a fine machinist shop for such. Tell'em what you wish and its easier this way, maybe cheaper too. A simple hardened steel rod welded around the bottom of the housing is all thats required. Good luck with your project, sounds cool. Randy:dance

[AnnapolisAirhead]

I read someplace that there was a fat R65 swingarm that could be used. Might wanna research it. Sorry, I didn't bookmark the posts.

Anton? I think he had some info on that...but memory is the second thing to go with age...can't recall the first! :scratch

[bmweuro]

To short

I read someplace that there was a fat R65 swingarm that could be used. Might wanna research it. Sorry, I didn't bookmark the posts.

Anton? I think he had some info on that...but memory is the second thing to go with age...can't recall the first! :scratch

[TCHLFXVT]

How do you weld hardened steel to mild steel without something cracking at some point? Use a 80-84 swingarm and your driveshaft. Under the rear foot peg mount weld a triangular piece(3/16 thick) between the cross brace under the battery/footpeg mount/main frame. This is the only place the frames flex. Swing arms do not flex. This has been tested on the track with a 73 HP /5 @ 385 pounds and a 215 pound rider.

I just took a look at the frame ,I'm not sure where you need the reinforcement .... Under the battery mount cross brace there is another lower cross brace , is this the brace you say to weld the triangular piece of steel ?
Do you have any pictures of this operation you could share , That would really help,I'm not good with directions ,much better with pictures ..

If swingarms don't flex is there a real need to replace mine with a 80-84 unit ?

I presume the answer is yes ,then why use my old driveshaft ?is that more desirable than the cushioned one from the later models ?

Thanks for your help to everyone,
Tom

[rinty]

I'm not sure where you need the reinforcement...TCHXXXX

Tom:

Here's some details from HPN's site:

http://www.hpn.de/pdf/hpn7.pdf

Some owners make their own gussets, or arrange to have them made, and welded in. But if you just install a thicker upper triple tree, quality suspension components, and braced swingarm, the chassis will be plenty stiff.

Have fun. :)

[bmweuro]

I just took a look at the frame ,I'm not sure where you need the reinforcement .... Under the battery mount cross brace there is another lower cross brace , is this the brace you say to weld the triangular piece of steel ?
Do you have any pictures of this operation you could share , That would really help,I'm not good with directions ,much better with pictures ..

If swingarms don't flex is there a real need to replace mine with a 80-84 unit ?

I presume the answer is yes ,then why use my old driveshaft ?is that more desirable than the cushioned one from the later models ?

Thanks for your help to everyone,
Tom

Sorry I do not have any pictures. You really do not need to replace the swing arm. Under the frame where the cross bar attaches to the left and right side of the frame(under the battery). You will see a piece of the passenger footpeg plate welded to it. This is horizontal to the ground and has about a 6mm welded piece. On a lot of the older bikes that had saddlebags this part is cracked. Weld a 3/6 to 1/4 triangle in that corner. The triangle should be about one inch per side.

[rinty]

Tom:

Here's another link: see post 60:

http://www.bmwmoa.org/forum/showthread.php?t=39894&highlight=hpn&page=4

[jforgo]

I understand that in '79, they added the cushioned driveshaft which made shifting smoother. Beginning in '81, the swingarm is a beefier unit through the '84 models. That might provide some added stiffness without having to go the route of external bracing, etc. I tmight require some modifications in terms of the brake light switch, though.

I would verify whether or not a later swingarm transplant also requires the driveshaft be the later cush configuration. I am suspecting it does.