How does reverse gear system work? - BMW Luxury Touring Community
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post #1 of 21 Old Sep 1st, 2008, 12:39 pm Thread Starter
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How does reverse gear system work?

K1200LT wanna-be here, who wonders how the reverse gear works.

Searched the forum, found lots of "how-to-fix-it" posts, but I'm still fuzzy about how the system is designed and operated.

Would someone provide an overview?

Thanks,

Bob Allred
Riverton, Utah
'03 K1200LT
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post #2 of 21 Old Sep 1st, 2008, 12:43 pm
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Re: How does reverse gear system work?

It basically works off of the starter motor.



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post #3 of 21 Old Sep 1st, 2008, 5:10 pm
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Re: How does reverse gear system work?

Not sure how technical you want it....

on the left side of the bike there is a nob you turn to reverse ...with that engaged..you press the start button and it will "creep in reverse" the bike needs to be in neutral to do this,


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post #4 of 21 Old Sep 1st, 2008, 9:23 pm
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Re: How does reverse gear system work?

The front shaft of the starter motor drives a gear train in the engine, which has a "sprag" (one way) clutch in the last gear. When the motor is used to start the engine, the sprag clutch grabs, locking the starter motor action to the gear which in turn spins the crankshaft.

The other end of the starter motor shaft drives a gear in the transmission. When the knob on the side of the bike is turned to engage the reverse gear in the transmission, the starter motor then turns the transmission gears when it is run. This only works when the engine is running, and the sprag clutch on the engine side will then not lock up, because the engine is running faster than the starter gear.

Rather clever arrangement to use the same motor for dual purpose. The sprag clutch however is a real witch to replace if it gets gummed up with carbon and no longer grabs when you try to start the engine! DAMHIK!
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post #5 of 21 Old Mar 18th, 2013, 2:40 am
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Re: How does reverse gear system work?

"I have a BMW K1200 LT 2001 model, when i switch the reverse gear its starts flashing R and when pressing the starter button RPM revs but the bike doesn't move. can you help?"

QUOTE=dshealey]The front shaft of the starter motor drives a gear train in the engine, which has a "sprag" (one way) clutch in the last gear. When the motor is used to start the engine, the sprag clutch grabs, locking the starter motor action to the gear which in turn spins the crankshaft.

The other end of the starter motor shaft drives a gear in the transmission. When the knob on the side of the bike is turned to engage the reverse gear in the transmission, the starter motor then turns the transmission gears when it is run. This only works when the engine is running, and the sprag clutch on the engine side will then not lock up, because the engine is running faster than the starter gear.

Rather clever arrangement to use the same motor for dual purpose. The sprag clutch however is a real witch to replace if it gets gummed up with carbon and no longer grabs when you try to start the engine! DAMHIK![/QUOTE]
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post #6 of 21 Old Mar 18th, 2013, 4:25 am
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Re: How does reverse gear system work?

A technically acurate description by David Shealey, and whilst not wishing to commence or incite an oil change debate or any other oil thread for that matter, his mention of carbon (and sludge) build-up is indeed the killer of any sprag (overrun) clutch unit. This is one of those subtle things that can happen over a long period of time, till one day the starter clutch just refuses to grip due to the sprags being gummed up. My solution - keep the oil changed at a level where soot (carbon) saturation levels are not an issue. No short runs for my K12 (30 minutes minimum from cold), engine oil out at 5,000 Kms intervals. No problem with the gearbox side as no carbon contamination in the gearbox. Cheap and convenient compared to problems with the sprag units. My strategy, others may disagree.

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post #7 of 21 Old Mar 18th, 2013, 5:25 am
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Re: How does reverse gear system work?

Thank you for the reply.

My LT engages in R and the dash flashes R and the starter revs but the bike wont move. And if I push it back it feels as if I have handbrakes on.


Quote:
Originally Posted by K100Dennis
A technically acurate description by David Shealey, and whilst not wishing to commence or incite an oil change debate or any other oil thread for that matter, his mention of carbon (and sludge) build-up is indeed the killer of any sprag (overrun) clutch unit. This is one of those subtle things that can happen over a long period of time, till one day the starter clutch just refuses to grip due to the sprags being gummed up. My solution - keep the oil changed at a level where soot (carbon) saturation levels are not an issue. No short runs for my K12 (30 minutes minimum from cold), engine oil out at 5,000 Kms intervals. No problem with the gearbox side as no carbon contamination in the gearbox. Cheap and convenient compared to problems with the sprag units. My strategy, others may disagree.
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post #8 of 21 Old Mar 18th, 2013, 9:27 am
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Re: How does reverse gear system work?

Seems like this thread has wandered a bit.....

Occasionally my 02 LT would not move if switched to reverse, but a tiny bike movement or jiggle got everything engaged. Probably not either problem/solution. Seemed like it took the slight movement to get all of the gears lined up from time to time.

Dano
Tampa, Fl.

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post #9 of 21 Old Mar 18th, 2013, 9:47 am
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Re: How does reverse gear system work?

Yes i have tried to do that, but like i said, it felt like i have the hands break on and it would not move. its strange, i looked at all the threads here, nothing is similar to my issue.


Quote:
Originally Posted by DanDiver
Seems like this thread has wandered a bit.....

Occasionally my 02 LT would not move if switched to reverse, but a tiny bike movement or jiggle got everything engaged. Probably not either problem/solution. Seemed like it took the slight movement to get all of the gears lined up from time to time.
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post #10 of 21 Old Mar 18th, 2013, 12:20 pm
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Re: How does reverse gear system work?

At times I've had to roll just a bit one way or the other to get the knob to turn. Other than that the only times it hasn't worked was when I pressed the trip computer button instead of the starter button.

Chris Ehlbeck
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post #11 of 21 Old Mar 18th, 2013, 1:02 pm
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Re: How does reverse gear system work?

If you are getting the "R" you have the gear train engaged. The problem lies in the reverser controller as it feeds the starter motor with current at a reduced rate from the starter relay. One simple cause involves the power feed to the controller. The sprag clutch is not involved in reverse as the engine is already running and turning if faster than the starter can.

There are three heavy Black/Yellow wires coming from the controller. One has a black sleeve on the eyelet and it goes to the starter tie point behind the battery on the left side. One has a brown sleeve and that goes to the ground tiepoint behind the battery on the right side. The third (and offten misplaced) has a red sleeve and that goes to the battery positive terminal. This gets left off during battery changes as it is a Black wire. I would check that first.

Normal operation is once you have the lever in R you get a steady "R" on the dash and when you press the starter button the engine revs go up a bit and she moves backwards until you release the button.
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post #12 of 21 Old Mar 13th, 2018, 9:27 am
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Re: How does reverse gear system work?

Is it common for the reverse controller to have issues?

What I've noticed is that my reverse doesn't like to work when temperatures are below about 70F.

Mechanically, the starter motor is engaging properly in the gearbox, and a get the "R" on the dash, but I don't hear the starter motor engage when I press the start button.

Are these reverse controllers basically black box? Can they be repaired? I see them on eBay used for around $80.

-Steve
Titusville, FL
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post #13 of 21 Old Mar 13th, 2018, 11:19 am
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Re: How does reverse gear system work?

Quote:
Originally Posted by dshealey View Post
The front shaft of the starter motor...when you try to start the engine! DAMHIK!
It's the stuff in the dots that makes the difference in answering this question! This was a great reply, Mr. Shealey.Thanks!!

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Last edited by Billyjoe Jimbob; Mar 13th, 2018 at 11:22 am. Reason: Misspelled Mr. Shealey's name...I'm a klutz.
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post #14 of 21 Old Mar 13th, 2018, 12:00 pm
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Re: How does reverse gear system work?

Quote:
Originally Posted by kayedd View Post
"I have a BMW K1200 LT 2001 model, when i switch the reverse gear its starts flashing R and when pressing the starter button RPM revs but the bike doesn't move. can you help?"

QUOTE=dshealey]
The sprag clutch however is a real witch to replace if it gets gummed up with carbon and no longer grabs when you try to start the engine! DAMHIK!
[/QUOTE]

As is the starter since the "sandwich design" precludes replacement without separating the bread.

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post #15 of 21 Old Mar 13th, 2018, 12:35 pm
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Re: How does reverse gear system work?

Quote:
Originally Posted by anarchosteff View Post
Is it common for the reverse controller to have issues?
Mechanically, the starter motor is engaging properly in the gearbox, and a get the "R" on the dash, but I don't hear the starter motor engage when I press the start button.
Try looking a these posts to see if that helps you in troubleshooting:

http://www.bmwlt.com/forums/k1200lt/...-not-work.html

http://www.bmwlt.com/forums/k1200lt/...osed-work.html

http://www.bmwlt.com/forums/k1200lt/...t-working.html

http://www.bmwlt.com/forums/k1200lt/...e-problem.html

http://www.bmwlt.com/forums/k1200lt/...noperable.html

Mike Trevelino
Williamsburg, VA
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2000 LT - Totaled at 99,960 miles


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post #16 of 21 Old Mar 13th, 2018, 1:05 pm
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Re: How does reverse gear system work?

Reverse working only when warm is a new one.

There are two switches that come into play when you go from F to R on the knob. One removes the starter signal from the starter relay and the other is what illuminates the "R" on the dash and puts it into reverse mode. The starter signal always goes to the reverser controller but it does not act on it unless the bike is in "R" mode. I do know that one failure mode of the controller is a fiery meltdown as we have seen several of those on this board.

John
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post #17 of 21 Old Mar 15th, 2018, 11:24 pm
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Re: How does reverse gear system work?

Quote:
Originally Posted by jzeiler View Post
There are two switches that come into play when you go from F to R on the knob.
My F & R stickers are worn off........ how do I know whether I'm going forward or reverse.......














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post #18 of 21 Old Mar 16th, 2018, 7:10 am
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Re: How does reverse gear system work?

Quote:
Originally Posted by cws View Post
My F & R stickers are worn off........ how do I know whether I'm going forward or reverse.......
If your knob is pointing straight up you are in drive.
If your knob is pointing backwards you are in reverse.
When I say knob I am only referring to the one on the side of your bike.
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post #19 of 21 Old Mar 16th, 2018, 10:23 am
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Re: How does reverse gear system work?

Quote:
Originally Posted by Wazza View Post
If your knob is pointing straight up you are in drive.
If your knob is pointing backwards you are in reverse.
When I say knob I am only referring to the one on the side of your bike.
Some people have snagged a pant cuff on the knob and mount it upside down...

So if its pointing forward you are in reverse.
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But lack DE, MA, RI and CT with the 2005 LT

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post #20 of 21 Old Jun 27th, 2018, 6:36 pm
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Re: How does reverse gear system work?

There are two micro switches mounted at the end of the reverse selector shaft these sometimes gum up with dirt and may need cleaning or replacing.
1 operates the dash light and the other allows the starter switch to power the reverse unit.
I hope that helps.
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post #21 of 21 Old Jun 28th, 2018, 7:40 pm
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Re: How does reverse gear system work?

Quote:
Originally Posted by peterj View Post
There are two micro switches mounted at the end of the reverse selector shaft these sometimes gum up with dirt and may need cleaning or replacing.
1 operates the dash light and the other allows the starter switch to power the reverse unit.
I hope that helps.
Actually one interrupts the starter button signal coming out of the reverser controller from the starter relay and the the other puts the reverser controller into operation (turns it on). The light is controlled by the reverser controller from a signal on pin 5.

If you break those the bike will not start.

John
2009 K1300GT Red Rocket
2009 R1200GS (Gone)
2005 K1200LT Ocean Blue Blue Wizard 110 K and counting...
2006 Bushtec Turbo+2 Spell
2004 330 Ci Convertable
K4AN

Have ridden a Motorcycle in all 48
But lack DE, MA, RI and CT with the 2005 LT

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