Won't start, unless

[22600]

I have heard of this problem before but can't remember the fix. Some one please jump start my memory.

My ride ( 1978 R100rs) just started this today when I told her we were going to Sedalia. She must be getting old and barn sour.

With tranny in neutral, my key in on position, kill switch off, all normal lights lit, I hit the start button and nothing. I'm on center stand with side stand up as this is the way I have started it forever.

Still in neutral, I pull in the clutch and hit the start button and she comes to life and purrs like a kitten.

Before I realized it would start with the clutch pulled in, I took apart the right throttle control and start switch and took a look at it all...took me awhile to get it all back right. Glad that part is over.


I took tank off and looked at all the connections I could see from bars on and found nothing unusual. Everything looks clean.

Whats up? Before I take the whole bike apart.:

[jimwjarmour]

hi rs beemer check the neutral switch or wiring there should be a connection just above the left footrest you could link it out to test hope this assists hope you enjoy the rally ,Jimmy

[PGlaves]

The logic is the starter will engage if and only if: the bike is in neutral, or the clutch is pulled. Your bike doesn't know when it is in neutral so you must pull in the clutch to start it.

The clutch switch is working. The neutral switch is not working, or the wiring to/from the neutral switch is faulty.

I don't have a wiring diagram but I'm sure somebody can jump in here. The switch is at a very awkward spot at the rear of the transmission.

[22600]

I will check it out in the morning....I did think about a/the switch at the back of transmission but could not find it....I will look closer...either way it won't stop me from riding. I think I had a problem like this about 30 years ago but not sure....I slept a couple times since then.....thanks again.

[PeoriaMac]

The neutral sending switch is under the transmission and behind the spacer through which the rear motor mount bolt goes. Clear? Probably not from that description . It was designed as some sort of revenge by a German engineer still unhappy with the provisions of the 1917 Treaty of Versailles.

According to the microfisch at MAXBMW the sending unit can be accessed by the following method:

Part # 13 61 31 1 243 097 SWITCH 0.04 1 $35.09

"To replace the transmission switch, we suggest the following technique. Remove rear engine stud #7. Then using a long aluminum drift (wooden dowel would work) drive the ÔÇ£engine rear shelf spacerÔÇØ back (towards the rear wheel) about ?¢ inch. You will be working on the left side of the engine, using a hammer and drift. DonÔÇÖt forget to use a new aluminum washer on the new neutral switch".


Others will tell you to remove the transmission, remove the spacer, put the spacer in a freezer, replace the sending switch, replace the transmission and the chilled-slightly-smaller spacer.

I've never tried the MAXBMW method. I have removed the transmission to replace the neutral sending switch and I do know for sure that you do need to make sure you replace the aluminum washer. Otherwise, your bike won't go out of 1st gear. Mine didn't anyway.

Or...

You could just remember to pull in the clutch every time you start the bike.


Mac

[boxermaf]

Also, be sure to get the CORRECT switch - there are (2) basic versions based on the model year of the bike/transmission you have installed. If you pick the wrong one-it won't work. Rusty the parts guy at MAXBMW can get you the proper one.

You can replace it without removing the transmission, but you DO have to remove that rear engine mounting bolt/spacer and put a jack under the thing to keep it in position.

And, the new washer bit is also important - one of the versions of the switch has a thicker spacer/washer between it and the transmission too - this is necessary to make sure it works properly and doesn't interfere with gear changes. You'll be disappointed if you get it wrong.

Hopefully you've just got a loose wire, or maybe the wire connector has pulled off the switch terminal - that would be a simple and quick fix!

[wecm31]

I had a leaky neutral switch on my recently acquired used gear box and changed it out a few weeks ago during a Tech Day I was hosting.

Much easier on a lift, but you can do it on the ground.

We didn't support the rear of the engine, with the swing arm in place and the drive shaft connected, I don't see how the engine could move in the frame. I guess it wouldn't hurt to block up the back of the engine though....

The trickiest bit was knocking that spacer rearward and then reinstalling it again.
That took a few minutes of tapping from both sides to get it out and back in place . All in all, took about half an hour, much better than pulling the gear box.

And personally, I coat the entire plastic molding around the terminals with JB weld. I find the switch always leaks through the body, not the threaded connection to the bike. Hopefully the JB weld will give an additional barrier to the gear oil.

[dbrick]

Or...

You could just remember to pull in the clutch every time you start the bike.

That'll work, but if the clutch switch or its wiring fails, then the starter won't work at all.

Do you feel lucky?

[Stan_R80/7]

If the neutral light goes out when the gears are shifted out of neutral - and back on when put in neutral - but the starter does not work, then that is very peculiar. Per the wiring diagram: http://www.omnilex.com/public/bmw78/78r100wire.jpg the transmission neutral switch provides a ground. That same ground causes the neutral light to glow. The wiring diagram shows a diode in the connector board that may be bad or loose - which would explain the lights but no starter relay ground from the neutral switch.

The clutch switch, which allows the starter to work, is part of the same circuit as the neutral switch per the diagram but does not turn any lights on. If the neutral light goes off when in gear and will come back on when back in neutral - that indicates the neutral switch is working based on the wiring diagram. I would try checking the (85b) terminal connections in the headlight connector board per the wiring diagram. Good luck!

[mneblett]

If the neutral light goes out when the gears are shifted out of neutral - and back on when put in neutral - but the starter does not work, then that is very peculiar. Per the wiring diagram: http://www.omnilex.com/public/bmw78/78r100wire.jpg the transmission neutral switch provides a ground. That same ground causes the neutral light to glow. The wiring diagram shows a diode in the connector board that may be bad or loose - which would explain the lights but no starter relay ground from the neutral switch.

Just came on this thread, and that's where I was going in the thought process -- that diode is known to occassionally die. If the neutral light is working, you can jump the diode to see wheether the bike will start in neutral with the clutch out.

If it is a dead diode, the problem is it's a pita to get to -- it is on the *back* of the connection board in the headlight shell. If it were me, I would ignore the issue until back from Sedalia -- it will be a lot of tedious work getting access to replace the diode. Remember to disconect the battery before starting to maneuver around all those wires in the headlight shell!

[lmo1131]

I did think about a/the switch at the back of transmission but could not find it....I will look closer

pretty good chance that wire to the switch has broken, or very nearly. And as PG says, it's in an awkward spot, and has a black rubber plug over it, or should (which doesn't make spotting it any easier)

the plug is removed here

[22600]

for all the info and pics....After looking at the 10 day weather forecast and seeing that there was lots of rain and thunderstorms for my route from Tex to mo....I decided maybe I wouldn't go. I went out and told old Goldie we might not go and she started right up in neutral without pulling in the clutch.

So, maybe I do have a loose wire or bad connection near the tranny. I will get my big glasses on and investigate more closely.

Thanks again...

DW

[22600]

pretty good chance that wire to the switch has broken, or very nearly. And as PG says, it's in an awkward spot, and has a black rubber plug over it, or should (which doesn't make spotting it any easier)

the plug is removed here

Call me blind , but I can't see what we are talking about here. This pic doesn't look like its under the tranny. Or we talking about two different switches? What I have found is under the trannny itself....which is a very tight space. The wires that go to that area are very greasy...I think I will first try and clean that area to see what I'm looking at.

I did find this on the web....http://bmwmotorcycletech.info/neutralswitch.htm by
R. Fleischer....

I think that I will wait till I get back from Sedalia before I do anything. I
am afraid if I start now I will run into some problems or not get part back in time to make the repair...anyway....she seems to be working fine again...and I can always just pull in the clutch, " in a clutch".

Lots of fine info from all you wrenches....thanks again....

DW

[mneblett]

That's the neutral switch on a /5 4-sp box. A '78 RS 5-sp will have a switch on the bottom -- looks like an oil pressure switch on the outside.

[PeoriaMac]

Rsbeemer,
If you haven't found the neutral sending switch yet...here's where it's at.
Unless your garage is brighted than mine, and you've got a lift...get a flashlight.
On the left hand side of the bike, find the rear motor mount.
The motor mount bolt is covered by a "spacer" --a hollow tube --as it runs
below the transmission.
In front of the spacer - sticking out of the transmission --is the neutral switch.
If it's like mine, it's dark and oily and hard to see.
Two wires should be seen coming out of it. That's the switch.

Item 13 on this diagram:
http://www.maxbmwmotorcycles.com/fic...7&rnd=05012012