Topic: ouch, my transmission!

[nobody]

So I'll start by saying "Yes, I'm an idiot, I know"

I have a 74 cb750, I was out riding around with a friend of mine, having a little fun. I was coming out of a sharp right turn, went to kick it into second at about 6000rpms and missed. I reapplied the clutch and kicked it up again. To my dismay there was a pretty horrid grinding that I hadn't heard before. I must have damaged something internally because now it shifts kind of hard and the neutral light no longer functions.

So is there anything I can do, short of rebuilding the transmission, to smooth operation and get my neutral light back on???

please help!!!

[Terry in Australia]

Well it looks like you'll need to strip the engine down regardless, just to make sure you don't have little bits of gear or shift dogs floating around in your oil. (which lubricates your engine, as well as your gearbox)

You can start by dropping off the sump pan and see what bits of metal are resting there, and you might be able to diagnose what you've broken, but my advice is to not ride it anywhere until you know what you've done, and you've changed the oil and filter to stop it doing even more damage to the rest of your engine. 

If you want to fix it without stripping the engine, I suggest you go to your local magic shop and buy yourself a good quality wand............... 

[nobody]

Why would the neutral light suddenly stop working though? That part confuses me.

[martino1972]

Why would the neutral light suddenly stop working though? That part confuses me.

the neutral light works off of the shift drum.....

[CB750F2]

As well as taking the sump off for an inspection I suggest that you take off the transmission cover on the LH side of the motor. There you will see the shift linkage and see what drives the drum. There is an indent in the drum that operates the neutral switch. You may be lucky that something has dropped or bent in the linkage that can be fixed without taking the motor out. I would not run the motor until you know the reason for the hard shifting and has been repaired. Listen to what Terry has told you.
Pat

[nobody]

Ugh, that's not what I was hoping to hear. 

I'll leave it in the garage today and do a little tear down tomorrow I suppose. Wish me luck.

I've never taken a transmission apart so any tips one might have of what exactly I need to look at (pictures maybe?) would be helpful. I'm working out of the Haynes manual.

[MCRider]

Ugh, that's not what I was hoping to hear. 

I'll leave it in the garage today and do a little tear down tomorrow I suppose. Wish me luck.

I've never taken a transmission apart so any tips one might have of what exactly I need to look at (pictures maybe?) would be helpful. I'm working out of the Haynes manual.

Everything talked about so far is short of "taking the transmission apart" by a long sight. You're just touching on the outsides. Removing warts.

To take the transmission apart involves pulling the engine, flipping it over and removing the bottom crankcase. Equivalent to open heart surgery.

Lets hope its a wart.

[754]

Got spare parts waiting?

 The take the motor out, strip off trans & clutch cover, and flip it over and split the cases..& change the bad stuff..
 can be done in a long evening if you are motivated.

 Just proceed carefully and dont try taking shortcuts.

 look for rounded dogs, bent or scored  shift fork, damaged shift drum, bad teeth, etc

[Alan F.]

And download every manual you can get your hands on.

Run a search for the words manual and download together, you'll get tons of links.

Most will be .PDF files, you can print the pages you need and bring them out to your bike, make notes on them, get fingerprints on them......

Best of luck, and don't worry.
-A

[nobody]

Got spare parts waiting?

I do not, I saw some spare engines on craigslist a little while back for pretty cheap and thought "I should get one" followed immediately by "Eh, my bike is running great, I don't need one"... I now regret that self contained conversation. I can't find any spare engines or any parts 750s on craigslist right now. Any ideas where I should look for transmission parts???

[OldSchool_IsCool]

Do a search for local motorcycle boneyards. 

[754]

Ther was some problems in 72 with 4th gear, I remember swapping a good trans to a guy once for his & $.

 So if you find one of those you might have the parts you need.
 There used to be lots parted out on ebay, often going cheap.

 If you read the manual on trans removal a few times, and it not making complete sense.... might be better to find someone to do it for you..

[fuzzybutt]

it will be rare if you find a tranny by itself... having said that, i did find a perfectly usable tranny on ebay for my 400f and snatched it up.
cheap too!

+1 i just got one for 4.95. shipping was more than the part at 5 dollars.

[nobody]

So I got the oil pan off and couldn't find any little bits of metal in there. The oil filter Looked pretty clean as well. I removed the left rear cover and looked at the gear shift mechanism and couldn't find anything visibly damaged in there. I've attached a picture of what I saw, if anybody could point me towards what specifically I should be inspecting I would appreciate it.

[martino1972]

okay,let's re trace our steps abit here before you take it way to far apart.....

-releasing clutch kills the engine....and with killing it i mean,it just can't keep running,as if your bike is against a wall...
-it does that in neutral as well as in gear..
-if you put it on the center stand and you rotate the rear tire...is that possible or doesn't it move..
-does it do the last one in neutral AND in gear or just in gear..
-if rear wheel DOES move in gear,does it rotate the engine...


okay,what I would do is take the clutch apart first...remove the plates,basket etc.... this will leave you with just the shaft that comes out of the tranny.....
rotate that shaft,what happens,is it stuck or does it rotate freely in neutral.
then put it in gear and see if it moves the rear wheel when you turn that shaft.....

this will tell ya if the tranny is seized up or not....

[nobody]

I think you're thinking of a different thread man... The only symptoms my bike has right now are hard shifting and a nonfunctioning neutral light. It still runs, rides, shifts and such. It just isn't shifting smoothly anymore.

[mystic_1]

Quick and easy test for the neutral light:

Under the bike on the left side, find the single wire that connects to teh screw in the center of the neutral switch.  Disconnect this and ground it to the engine somewhere.  The light should come on.

If it does not, you have a problem in the wiring or the bulb.  If it comes on, there's a problem in the neutral switch itself.

mystic_1

[martino1972]

I think you're thinking of a different thread man...

      your so right......duh........sorry.......you can put it back together....

[CB750F2]

The picture that you have shown of the shift mechanism shows that nothing is obviously out of place there. The neutral switch is located just underneath the shift drum. If you look from underneath the bike you will see where a wire is connected to the centre of the switch. Turn the ignition switch ON and then using a short bit of wire short out the neutral switch terminal to earth. The neutral light should come ON. If it doesn't the bulb is probably blown. Assuming that the light comes ON refit the gear lever and try and step through the gears - you will probably have to rock the rear wheel to allow the gears to mesh. At each gear pull the clutch in and rotate the rear wheel. There will be some drag because of oil between the clutch plates. This drag will decrease in the higher gears. Watch the neutral light as you shift from 1st to 2nd and from 2nd to 1st in case you see a flicker. If there is a flicker but does not come ON when in neutral you could try replaceing this switch. This switch also locates the shift drum so have a spare available when you remove it. There is also an O ring to stop oil leaking.
Also check that the shaft that the shift forks pivot on has not been forced outwards and so falling out of its internal support. This shaft is located at about 2 o'clock from the shift drum and is about 1/2" in diameter. The end should be flush with the transmission housing and held in by a bracket.
So that's a few ideas. They are "long shots" but are worth checking. Pat

[nobody]

So I just went out there and fiddled a little bit more, tried earthing the neutral switch like you mentioned. No luck, the light stays off, I highly doubt it's just a bulb that went out because the bulb worked five minutes before my missed shift incident. I also looked at the shift fork pivot shaft thing that you mentioned, not pushed out or loose in any way...

So at this point it looks like whatever is happening is internal. Does anybody have any idea what the culprit may be now? What did I break on the inside that would be affecting the changing of gears? Should I try to find a parts bike or a spare engine to have whatever extra parts I need? How difficult is this transmission to work on? I've taken two car transmissions apart and replaced bits before but never a motorcycle transmission... should I just fork over the money (I don't even know how much one would charge) and pay somebody to fix it?

[mystic_1]

Regardless of what's going on inside your tranny, grounding the neutral switch should have 100% caused the light to go on.  The fact that it didn't says there's a wiring or bulb problem.  Your transmission could be ground completely into powder but grounding the neutral switch wire would still cause the light to come on.

Getting into the transmission requires dropping the motor and splitting the cases.  I agree with Heffay's assessment.

I'm thinking the most likely culprit at this point is a bent or broken shift fork, that would cause the symptoms you describe, except for the light thing.

mystic_1

[nobody]

Hmm, maybe I grounded it wrong? I touched the wire to the screw there and then touched it against various other bolts and frame mounts...

I guess I'll wait for the bike shops to open on Tuesday and get some estimates. Would it be safe to drive it to a shop or would it be advised to get a truck?

[mystic_1]

Oh, should have said that the key should be on for the neutral light test, of course.

Most prudent would be to truck it in, but if it's just shifting hard, you might be able to get away with babying it in.  I'd call around first though, most shops turn up their noses at working on bikes this old (read: they have no experience and don't want to take the chance).

mystic_1

[754]

Realisticaly if you ride it in for them to re & re, even if its just a shift fork(5 min job once apart) they are going to have to charge at least 6-8 hrs.. so 400 -600 or more. They cant give a low estimate on it.


so at least pull the motor & sidecovers off, now its a 1/2hr labour to get an estimate.

 Pretend you have a final exam, subject Tranny Re & Re, start cramming, it can pay off..

[MJL]

Next time try to match rps with speed, it won't be so hard on your transmission.