Author Topic: neutral light stays on every gear 1978 cb750f (3?)  (Read 1351 times)

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Offline sohcphreek

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neutral light stays on every gear 1978 cb750f (3?)
« on: September 20, 2007, 10:28:53 am »
I have never removed a neutral switch before and would like some input from a experienced sohc pro! Does the oil leak out? can the switch be cleaned or should i have a new 1 in hand?  thanks for any help. sohcphreek :-[

Offline Jonesy

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Re: neutral light stays on every gear 1978 cb750f (3?)
« Reply #1 on: September 20, 2007, 10:36:39 am »
Before you pull the switch, check the wire. The switch completes the ground side of the neutral light circuit, so if the wire going to the switch is chafed or pinched anywhere, the light will come on.

If the wire checks out OK, the switch might not be fully seated in the bottom of the crankcase. This can happen if the O-ring on the switch is the wrong size. If you have to pull the switch, a few drops of oil might come out, but nothing major. Some people have been able to take the switch apart and clean it.
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Offline sohcphreek

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Re: neutral light stays on every gear 1978 cb750f (3?)
« Reply #2 on: September 20, 2007, 10:41:11 am »
I think wires are fine and it's never been apart. It just started this on my last ride. all of a sudden the shifts didn't seem as crisp and clean as they have been for the last 15 years. I changed the oil and filter but this didn't help either. sohcphreek

Offline spitfire

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Re: neutral light stays on every gear 1978 cb750f (3?)
« Reply #3 on: September 20, 2007, 10:42:29 am »
Had problems with the neutral light on my 76 750F1, staying on 2 years after I bought the bike (1978), I changed the switch and it still would not go out, so I taped over the light on the console.
When I removed the engine last year at the start of the rebuild I found the real problem, the cable to the switch was grounding out under the engine where the cable had chafed.
The light started playing up again recently so I removed the switch and tested it on the bench, it was fine, but I had put the retaining clip on the wrong way and the switch was not seated properly, with the clip in the correct position all is well.
No oil came out, if however your bike has been sitting for a while there may be some oil in your bottom end and you may get some leakage.

Cheers

Den
Wirral UK
1976 CB750F1 bought new in 76
1977 CB750F2: Restoration started
1964 BSA A65R: Waiting restoration
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Offline sohcphreek

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Re: neutral light stays on every gear 1978 cb750f (3?)
« Reply #4 on: September 20, 2007, 10:51:50 am »
Thanks for the info. I should not assume the the wires are good!! you know what they say about assuming!
Going to the garage now to trace the wires  oh theres a fridge full of sierra nevada ale. i'll get through this!
thanks again

Offline Steve F

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Re: neutral light stays on every gear 1978 cb750f (3?)
« Reply #5 on: September 20, 2007, 01:09:29 pm »
Thanks for the info. I should not assume the the wires are good!! you know what they say about assuming!
Going to the garage now to trace the wires  oh theres a fridge full of sierra nevada ale. i'll get through this!
thanks again
Before you make it any harder than it needs to be, just disconnect the wire from the switch, and let it hang while the key is on.  If the light stays lit, THEN start tracing back through the circuit.  If the light goes out, it's the switch.

Offline Canada

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Re: neutral light stays on every gear 1978 cb750f (3?)
« Reply #6 on: September 23, 2007, 12:23:04 am »
I was also having the problem too. I removed the switch and it tested fine. I was having the problem where the light would be on all the time but when in neutral it would get a hair brighter. The best that I can tell is that the little ball that activates the light is partially pushed in due to the the "little wheely thing" that it fits into when the transmission is in neutral. I could be way off base with this theory! When not in neutral the ball stay partially depressed so the light stays on. Or is it the other way around? I can't remember! I was lucky and it has seemed to work itself out. Not sure if this helps???
Does clinching your teeth slow you down in the corners?

Offline KB02

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Re: neutral light stays on every gear 1978 cb750f (3?)
« Reply #7 on: September 23, 2007, 06:13:50 am »
What if the switch doesn't want to seat all the way in? I'm having the same problem. When I had the engine out and put the switch back in, it didn't want to seat all the way in. I was afraid (rightly so?) to pound on it with any kid of hammer.
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Offline jtb

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Re: neutral light stays on every gear 1978 cb750f (3?)
« Reply #8 on: September 23, 2007, 07:41:22 am »
Have someone push on the switch, while you shift up and down through the gears.  All of a sudden it will seat correctly.  If it is not all of the way in, the light will stay on all the time.  (I knew a girl like that... ::) ;D)
1977 CB750F
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Offline Impi

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Re: neutral light stays on every gear 1978 cb750f (3?)
« Reply #9 on: January 08, 2019, 03:25:37 pm »
jtb... I am frustrated with the same issue but reading your last comment (Knew a girl like that) and it just turned my frustration into a really good laugh and ready to fight it some more!

Offline madmtnmotors

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Re: neutral light stays on every gear 1978 cb750f (3?)
« Reply #10 on: January 08, 2019, 03:48:42 pm »
Test the diode (not the rectifier) before replacing anything. I've replaced three of them lately. A bad diode will "backfeed" and turn on the neutral light.
TAMTF...


Wilbur



My most recent project "Evolution": http://forums.sohc4.net/index.php?topic=100352.0
F2/F3 O-rings: http://forums.sohc4.net/index.php?topic=113672.msg1300721#msg1300721
Cam Tower Studs: https://www.mcmaster.com/#93210a017/=t19sgp
Clean up that nasty harness: http://forums.sohc4.net/index.php?topic=137351.msg1549191#msg1549191
                                           http://forums.sohc4.net/index.php/topic,148188.msg1688494.html#msg1688494
                                           http://forums.sohc4.net/index.php/topic,139544.msg1579364.html#msg1579364
                                           http://oldmanhonda.com/MC/wiring750K1.html
Charging system diagnosis: http://forums.sohc4.net/index.php?topic=1012.msg8345#msg8345
Get the manuals: http://manuals.sohc4.net/cb750k/
The Dragon: http://forums.sohc4.net/index.php?topic=45183.msg1571675#msg1571675
Headlight Switch: http://forums.sohc4.net/index.php?topic=113986.msg1283236#msg1283236
Branden's leak free top end thread: http://forums.sohc4.net/index.php?topic=107040.0
Engine Lifting Made Easy: http://forums.sohc4.net/index.php/topic,58210.msg1684742.html#msg1684742
                                      http://forums.sohc4.net/index.php/topic,100352.msg1675840.html#msg1675840
Static and Dynamic Timing: http://www.hondachopper.com/garage/carb_info/timing/timing1.html
Airbox Gasket Replacement: http://forums.sohc4.net/index.php/topic,114485.msg1290000.html#msg1290000
"Café" : http://forums.sohc4.net/index.php/topic,84697.msg953814.html#msg953814
PD Carb Choke Linkage: http://forums.sohc4.net/index.php/topic,100352.msg1669248.html#msg1669248
                                    http://forums.sohc4.net/index.php/topic,110931.msg1248354.html#msg1248354
Follow up on your damn posts: http://forums.sohc4.net/index.php/topic,144305.msg1791605.html#msg1791605
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Gumtwo Seat Cover: http://forums.sohc4.net/index.php/topic,164440.msg1897366.html#msg1897366
Primary Drive: http://forums.sohc4.net/index.php/topic,166063.msg1919278.html#msg1919278
Tank Latch: http://forums.sohc4.net/index.php/topic,165975.msg1919495.html#msg1919495
Shorten your forks: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-shorten-forks-td4042465.html DO NOT CUT THE SPRINGS!
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Offline 70CB750

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Re: neutral light stays on every gear 1978 cb750f (3?)
« Reply #11 on: January 08, 2019, 03:50:31 pm »
Most of the Neutral lights problems are related to switch seating - like wrong o-ring size.

Offline madmtnmotors

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Re: neutral light stays on every gear 1978 cb750f (3?)
« Reply #12 on: January 08, 2019, 04:02:50 pm »
Most of the Neutral lights problems are related to switch seating - like wrong o-ring size.

Except that this has suddenly appeared after 15 years without ever having removed the switch...


I think wires are fine and it's never been apart. It just started this on my last ride. all of a sudden the shifts didn't seem as crisp and clean as they have been for the last 15 years. I changed the oil and filter but this didn't help either. sohcphreek

Testing the diode doesn't cost any money and can be done with a continuity tester in about 30 seconds to rule it out.  8)
« Last Edit: January 08, 2019, 04:05:06 pm by madmtnmotors »
TAMTF...


Wilbur



My most recent project "Evolution": http://forums.sohc4.net/index.php?topic=100352.0
F2/F3 O-rings: http://forums.sohc4.net/index.php?topic=113672.msg1300721#msg1300721
Cam Tower Studs: https://www.mcmaster.com/#93210a017/=t19sgp
Clean up that nasty harness: http://forums.sohc4.net/index.php?topic=137351.msg1549191#msg1549191
                                           http://forums.sohc4.net/index.php/topic,148188.msg1688494.html#msg1688494
                                           http://forums.sohc4.net/index.php/topic,139544.msg1579364.html#msg1579364
                                           http://oldmanhonda.com/MC/wiring750K1.html
Charging system diagnosis: http://forums.sohc4.net/index.php?topic=1012.msg8345#msg8345
Get the manuals: http://manuals.sohc4.net/cb750k/
The Dragon: http://forums.sohc4.net/index.php?topic=45183.msg1571675#msg1571675
Headlight Switch: http://forums.sohc4.net/index.php?topic=113986.msg1283236#msg1283236
Branden's leak free top end thread: http://forums.sohc4.net/index.php?topic=107040.0
Engine Lifting Made Easy: http://forums.sohc4.net/index.php/topic,58210.msg1684742.html#msg1684742
                                      http://forums.sohc4.net/index.php/topic,100352.msg1675840.html#msg1675840
Static and Dynamic Timing: http://www.hondachopper.com/garage/carb_info/timing/timing1.html
Airbox Gasket Replacement: http://forums.sohc4.net/index.php/topic,114485.msg1290000.html#msg1290000
"Café" : http://forums.sohc4.net/index.php/topic,84697.msg953814.html#msg953814
PD Carb Choke Linkage: http://forums.sohc4.net/index.php/topic,100352.msg1669248.html#msg1669248
                                    http://forums.sohc4.net/index.php/topic,110931.msg1248354.html#msg1248354
Follow up on your damn posts: http://forums.sohc4.net/index.php/topic,144305.msg1791605.html#msg1791605
Taiwanese Cam Chain Tensioners:  http://forums.sohc4.net/index.php/topic,155043.msg1774841.html#msg1774841
Gumtwo Seat Cover: http://forums.sohc4.net/index.php/topic,164440.msg1897366.html#msg1897366
Primary Drive: http://forums.sohc4.net/index.php/topic,166063.msg1919278.html#msg1919278
Tank Latch: http://forums.sohc4.net/index.php/topic,165975.msg1919495.html#msg1919495
Shorten your forks: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-shorten-forks-td4042465.html DO NOT CUT THE SPRINGS!
Clutch How To: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-change-and-adjust-a-clutch-SOHC-td4040391.html
Sent from my Tandy TRS-80!

Offline flybox1

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Re: neutral light stays on every gear 1978 cb750f (3?)
« Reply #13 on: January 08, 2019, 04:19:45 pm »
Thanks for the info. I should not assume the the wires are good!! you know what they say about assuming!
Going to the garage now to trace the wires  oh theres a fridge full of sierra nevada ale. i'll get through this!
thanks again
Before you make it any harder than it needs to be, just disconnect the wire from the switch, and let it hang while the key is on.  If the light stays lit, THEN start tracing back through the circuit.  If the light goes out, it's the switch.

^^ this
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