Changing Final Drive on an LS

[steek]

Hello,

I've got a Siebenrock 860 kit installed and wanted to change the standard final drive ratio to something taller.  There seems to quite a few airhead final drives available at the moment on that "popular online auction site" (OK one or three) but until now I hadn't yet realised that the LS has a 220mm rear drum, not a 200mm like all the others.  Any suggestions?

Cheers,
Keith

[Barry]

Yes, due to the LS using a different wheel, the drum brake is both different in diameter and in width. 

Someone will need to confirm this but I think the final drive is the same and you can just transfer the brake components.  In  your search for a replacement, remember there are two types out there, the smooth case up to 1980 and the ribbed case final drive from 81. I'm guessing yours will be the ribbed case.

you will ideally also need to change the speedo with one that matches the ratio of the new drive.

[steek]

Hello Barry,

Thanks very much for the reply.

I've currently got a ribbed final drive, and would like to keep the same style, but from looking what's available on that "popular on-line auction site" as Adam Hills puts it on Spicks'n'Specks, it looks like the older-style final drives are more numerous.

And then there's the problem with the rear brake drum being 220mm instead of the more common 200mm.  I haven't got my head round how to make use of the smaller-brake-drum type without something like transferring the internals of the final drive to my larger case if that's possible).

Anyway, the problem of the speedo seems less of a worry in some ways.

Cheers,
Keith

[georgesgiralt]

Hello,
Using RealOem web site, I searched the part number for a R65 LS rear drive (bike made in February 82) and got one. Then I searched what bikes had the same rear drive and found this :
https://www.realoem.com/bmw/enUS/part?id=0365-USA-02-1982-248-BMW-R65LS&mg=33&sg=74&diagId=33_0615&q=33111241093
It looks like the drum brake make no difference. and if I'm not mistaken this is because only the shoes are different to accommodate the bigger drum.
But now we live in an environment where camera speeding system are very common and I think that it will be wise to adjust the meter to be somewhat accurate.... Just my 2 ¢

[Barry]

Airhead speedos typically over read by 10 % or more, so depending on the final drive ratio you choose, the speed indication might possibly end up more accurate. However the odometer is quite accurate, so unless you change the speedo ratio the odometer will under read. 

What I've done with my speedo is to make it read spot on at 30MPH for the reason Georges stated.

[Burt]

I just used to run the car and bike past the speed camera and ask them to make a note of my speed whilst noting what my speedo was reading.  Usually done at my indicated speed limit and then make a mental note of the percentage difference and use that across the range.  A variance of 7-8% is what I remember.  Quite useful after a change of tyres. 

A bit more user friendly than using the LIDAR 

[georgesgiralt]

Hello,
I use a GPS based speed app for my phone. I choose one with a big numerical display in order to be legible when the phone is on a tank bag.
My new phone can see around 80 positioning satellites from various countries (USA, Russia, Europe, China and India). This way I expect the indicated speed to be darn accurate.
And I recorded the speeds at the RPM I use most. My speedo is not that bad (10%) and the odometer is spot on.
I do not like having my picture taken when I wear motorcycle gear. They do not do justice to my Apollo body..... Hence I try to have speedos as precise as I can get ...

[steek]

Hello,

Thanks very much for the replies and especially for the link.  Sorry to be a bit thick, but can I get away with a 200mm rear drum attached to a different final drive if I change my existing brake shoes to the more standard (200mm) sized ones, or do I still have a problem with the drum diameter?

Cheers,
Keith

[georgesgiralt]

Yes you will have a problem. The brake shoes must match the drum they are made for.
So if you change the final drive of your bike, keep your existing shoes for your existing drum. And put them on the "new" final drive. They should fit perfectly.

[steek]

Hello George (I'm guessing from your profile name),

OK, got that.  But will a "new" final drive fit my wheel if it came from a bike with a 200mm drum?

Cheers,
Keith

[dogshome]

Hiya, this is the part number for an LS FD:
Final drive drum brake   I=32:9=3,56   1   09/1980      33111241093
From here:
https://www.realoem.com/bmw/enUS/showparts?id=0365-USA-10-1983-248-BMW-R65LS&diagId=33_0615

The number for 'vin ordinaire' R65:
Final drive drum brake   I=32:9=3,56   1   09/1980      33111241093
From here:
https://www.realoem.com/bmw/enUS/showparts?id=0364-USA-06-1983-248-BMW-R65&diagId=33_0615

If you search LS shoes, you will see they are extended compared to the regular type. See pics below.

So, yes it will fit 

[steek]

Hello dogshome,

Thanks for that, just what I wanted to know.  Now to pick a ratio and something affordable, of course not always availale at the same time, unfortunately.

Cheers,
Keith

[dogshome]

I dropped on a 33:11 which suits the 850 where I live - not many hills and always solo. I think Tony here prefers something slightly lower.

The original ratios were fun away from the lights on 860, but a pain as soon as you got out of town. Now I've swapped, it seems no slower to me on the higher ratios as I'm not having to swap cogs at low speeds. First was always a bit too low for small islands and second too high. First is now a driving gear and second isn't buzzing at 30.

Oh, when you find one, don't be put off by gunk and minor leaks from the main seal. The acid test is to spin the gears using an electric gun drill on low speed. If it's quiet, all is well. Out of spec backlash is normal and don't worry. Any vibration or howling - forget it.

Stripped plugs are also normal. The filler, level and drain on the body can easily be done. The two on the driveshaft end needs special tools, the bearing retainer has to come out to get a decent helicoil tap in. Leaks on the brake pivot are easily fixed.

30% wear on the splines is ok, if they are half gone, don't bother.

[steek]

Hello All,

Well, I've just bought a kilometer per hour speedometer from BMW Meyer, w=715 and a 34/11 3.09 final drive from MotoGo Dojo from that popular on-line auction site.  The listing for the diff says the bike it came off only had 12000 miles on it, and the photos of the splines looked OK to me, but what do I know (not much).  BMW Meyer certainly had a few speedometers for sale, nice to have some choice.  Their web-site say they've been disassembled and cleaned.

I got the 715 speedo for several reasons, one being that BMW Meyer confirms the speedo is for a 34/11 diff so I suppose that's something.  That handy little JPEG table suggests the W number should be 711, but I'm not sure a difference of 4 is going to cause too much trouble.  The 711 speedos that BMW Meyer did have didn't appeal for various reasons.

Cost about $1200 Aus (with postage), give or take, split roughly equally between the diff and the speedo, or about $800 US.

Cheers,
Keith

[steek]

Hello,

I'm a bit of a dill, the German company is called BMW Bayer, not what I typed.

https://www.bmwbayer.de/en/second-hand-parts/62-instruments-measuring-systems][url]https://www.bmwbayer.de/en/second-hand-parts/62-instruments-measuring-systems[/url]

Keith