Here is a photo essay of sorts detailing the disassembly of a 1973 BMW Final drive. The same applies to all 1970’s era BMW’s (R90 R100 R75 R80 /5 /6 /7 S etc). The seals were shot inside causing leaks. The splines are decent so no need to weld on a new set of splines. I plan to have the drive blasted and powder coated to match the rest of the bike for an upcoming build.
The image descriptions have notes on the disassembly.
I had a wonderful opportunity of installing a Kat Dash /5 LED kit on my customized California blue 1973 R100/5 (yes, it is a /5 with a R100 engine) .
I had the headlight apart already to tighten up the custom key assembly that started turning inside the headlight bucket when I turned the key.
A nice small, tidy box containing the kit arrived in the mail.
The bulbs are labeled nicely in baggies with stickers that indicate the bulb color. I wasn’t sure what the wiring was for and then read the directions and figured it out.
Side note – This bike has the custom key seen here (not a typical /5 nail style key) and LED turn signals that required I wire in resistors to create more load to activate the turn signal relay. And, I decided to adapt all the wiring to a /6 style relay board. It all makes sense to me…
But here is what the headlight bucket looked like when I opened it up (spaghetti anybody?).
The gold things are resistors I had that were wired along with the LED turn signals.
One lead of the resister was wired with the positive lead of the turn signal and the other lead of the resistor was wired with the same ground as the turn signal.
R75/5 headlight wiring with /6 Relay board
The Kat Dash kit is pretty easy.
Follow the directions.
BE CAREFUL not to twist the LED’s in the bulb housings too much. They will come ripped out of the bulb base if you do.
A few things to realize – There are additional wires with resistors added to allow the Generator/Voltage light to activate with the LED bulb.
The same goes for the Turn Signal indicator Light.
I got half way through my install when I hit a major problem – one of the LED lights popped out INTO my speedometer! Yikes! This was not any fault of the LEDs. It had to do with the bulb base being worn/bent too much to hold the bulb in place correctly. I had to take everything apart, remove the speedometer, and spend about 10 minutes with a tiny magnet until I was able to fish the light out of the speedometer’s rear bulb housing area.
If the bulb sits crooked in the wired base, FIX it before you install it into the speedometer. With my 4yr old’s fingers to help me with the photo, I was able to fix it with a dental pick and bend that lip out to catch the bulb better, and hold it straight in the housing… and most importantly, not eject the light into the speedometer housing!
I continued my assembly, and to my surprise, after I wired in the relay to allow for the new LED turn signal indicator bulb to work, I no longer needed my big gold resistors in my wiring scheme.
Kat had sold me an electronic turn signal relay that works with LED bulbs and I ended up not needing it.
Here is the bike off:
Bike with the LED running light on:
Bike with the LED lights on – So bright the gamut of the camera could not capture them:
A 1978 BMW R100s fixed up and released back into the wild.
This bike is an absolute dream to ride. It runs amazingly smooth.
I had to go through some serious DMV hoops to get the salvaged title status back on the road with a deadline of 5 months until I incurred DMV penalty fees. I made it to the registration day with 2 days to spare.
I cleaned, restored, replaced, rebuilt whatever it needed to get it back on the road. The front end is from a spare R90/6 that I had lying around.
This is one of those things I try to do to every BMW motorcycle I rebuild.
This area is cracked on nearly every frame I tear down. It is the rear foot brake area which also is the muffler / silencer hanger, and where the passenger foot pegs attach. This frame is a 1978 BMW R100s. If you are considering rear sets on your bike that attach to this section, then I HIGHLY RECOMMEND doing this procedure.
cracked tab near rear foot brake pivot hole on BMW airhead framecracked tab near rear foot brake pivot hole
cracked tab near rear foot brake pivot hole on BMW airhead frame
New piece of metal to weld onto the old cracked section to reinforce the area making it MUCH stronger and no longer prone to cracking.
Welded metal onto the rear foot brake section of a BMW R100S
Finished powder coated frame with the welded metal. This area is out of sight to most people unless they take the rear tire off.
This makes bike #4 I have gotten out in the Desert. Three R75/5 models and one R90/6.
Just the way I like them too… cheap and dead. I can’t allow myself to chop up a good condition BMW motorcycle but when they come to me like this, I can get creative. Luckily it came with a good condition toaster tank.
This one is going to be restored for a guy who spent the last 6 years building hospitals in Saudi Arabia. He wanted to treat himself to a BMW or two when he returned so here we go!
We’ll probably upgrade this engine a bit, go to a 5 Speed kick start, and get this ready to tackle the roads and hills in Michigan.