R100 Big Tube swingarm questions

[xavier296]

I bought a good looking "big tube" swingarm, from the 81-84 model year, to install on my 79. You can immediately see why this would make a difference in handling on the rear. Max bmw microfiche makes it look like the pivot pins are a different length, does anyone know if I need the shorter pivots to run this swingarm?

Or maybe I can put earlier style bearings and seals and use the original pins? I was expecting to change the bearings anyway, and would prefer to avoid buying 70 dollars worth of pivot pins.

I know I have to mod the rear brake switch also, but unfortunately, the instructions on this forum have lost all the pics that used to be there.

[DoktorT]

[QUOTE=xavier296;16867404]I bought a good looking "big tube" swingarm, from the 81-84 model year, to install on my 79. You can immediately see why this would make a difference in handling on the rear. Max bmw microfiche makes it look like the pivot pins are a different length, does anyone know if I need the shorter pivots to run this swingarm?

I cannot be specific as I have not done this. Check the fiche and see if the part no.s are different for the 79 and 81 piviot pins. I was under the impression this was a straight forward swap.

I know I have to mod the rear brake switch also,

News to me. I would think any 81+ RS/RT would have the disk brake and others would have drum, so there may be some difference if you use a disk swingarm with a drum setup or vice versa. Switch is same but mounting varies?? Again, you can compare part no.s, but the parts blowups are marginally usefull for assembly, and some are just flat wrong. That is why many of us try to confirm these things before throwing time/money at swaps and such.

Anyway, hold the phone because expect someone with direct experience will be along to confirm. Or you could spend a few days at the Snobum site where likely this type of info is available.

Do submit this to the Airheads list for quick response and likely from the Bum himself. Cutter is there daily as well and he would know.

[bmweuro]

Screw the original ones in and see if they bottom out and you can still get the jamb nut on. If you can then use them

[wirewrkr]

You can use the bearing and seal and spacer setup from the earlier style if you want.
Especially since those late model bearings will set you back around $130.00!!
Don't forget the grease retainer on the one side.
For the brake light setup, you'll have to get creative.

[Max Headroom]

As it happens, I've just about finished installing a big-tube swingarm on my R90S, and it appears to me that the earlier pins will work with the later bearings. I haven't adjusted and tightened them yet, but they seem to fit OK at this stage.

The brake light switch is a bit more of a fiddle. I trimmed about 10mm (or 3/8" in the old currency) off the mounting bracket with a Dremel to clear the new swingarm, and then re-mounted the switch as close to the muffler bracket as it would go. I was fortunate to have a matching foot brake pedal, as It has a deliberate kink at the "switch end" where it strikes the switch when compared to the earlier style which is straight. If you're stuck with the earlier brake pedal, you'll probably need to fit a little tab to meet up with the switch. There's probably several ways of dealing with this issue, hence the advice to "get creative" from Wirewrkr!

I didn't take any photos. sorry. I could take some later today if it helps, but everything is assembled and I'm not sure if the photos would reveal anything meaningful.

[bmweuro]

I too am installing a big tube swing arm on an R90S. I have it loosely fitted. I'll take pictures as I go.



BTW- Use the early drive shaft. The spring breaks in the later ones.

[xavier296]

Thanks for the timely input gentlemen! I am trying to be a good little builder and install everything now before I have everything painted and powdercoated, so I think I have enough info to just try to install the new swingarm with the parts I have. I took a good look at the brake light switch earlier, and can see that cutting the mount and reinstalling the switch closer to the ear would be the answer. I have an earlier pedal, so I will have to make up something to push the switch closed.

I am hesitant to install my solid driveshaft into the new swingarm as I hear it is quite a pain to install. Don't you need a special press?

[bmweuro]

I had someone with the proper tools swap it out.

[SOLO LOBO]

Originally Posted by bmweuro

I had someone with the proper tools swap it out.

"Proper tools" Pffft...... (not that I would advise anyone else to use the method below

[bmweuro]

Got the rear brake switch figured out today using a BMW brake switch. I'll do a full tutorial soon.

[bmweuro]

Here is the how to deal with the rear brake switch tech article http://boxermetal.com/?p=248

[xavier296]

Thanks for the great article euro. What type pivot pins did you end up using?

My new swingarm is waiting patiently:

[bmweuro]

You're welcome. The early pivots appear to work fine.

[Jon-Lars]

This setup works best with the use of the later, wider-race bearings that are specified for the later swingarm.
The wider race puts the load closer to the frame, reducing flex.

[bmweuro]

Originally Posted by Jon-Lars

This setup works best with the use of the later, wider-race bearings that are specified for the later swingarm.
The wider race puts the load closer to the frame, reducing flex.

Do you know what the width difference is between the 2 bearing? Since either bearing race bottoms out in the swing arm I am curious.