Something snapped! A diagnosis.

[mesmeridicus]

I had just pulled out of my parent's neighborhood today on my way home when, accelerating in first gear, I felt a violent "snap" of some sort. I pulled over to the curb and turned off the bike. After taking a moment to compose myself, I started the bike back up. The engine runs fine, which was a relief. However, whenever I put the bike in gear (I tried first and second), I'd hear a grinding noise accompanied by a decided lack of power. By that I mean that the bike would not move at all. It stuttered forward a bit, but applying any throttle at all in gear would result in that grinding noise, a burning smell, and severe distress on my part.

I'm hoping it's just my clutch, but violence of the "snap" I felt has me worried. Unfortunately, I had music playing in my helmet so I was unable to hear whatever noise followed the break.

Help me out here and tell me it's just my clutch.

[mack]

Drive train

Put the bike on the center stand and make sure it's in neutral. with the motor off, try to rotate the back tire by hand. This should tell if the drive train is intact up to the middle drive. If it won't rotate w/o grinding then slip the rubber boot off and remove the four bolts securing the drive shaft to the middle drive then try to rotate the rear wheel again. Could be the U joint by the sounds of it, but the middle drives do fail once in a while. The smell of burning rubber has me puzzled. Clutches don't usually fail that abruptly unless there is a catastophic event, but in that case it most likely wouldn't be spinning the disc's.

[mack]

more

This will be a process of testing and elimination. Starting with the easy to get at stuff first. If the drive train is intact up to and including the middle drive then you need to have a look inside the clutch cover. This can be done by placing the bike on the side stand, that way you don't have to drain the oil, but at this point I would probably leave it on the center stand and drain the oil anyway just so I could rotate the rear tire while in gear to help find the source of the grinding. If it's coming from the bottom end then it's tranny trouble and the fix will be a bit more complex and time consuming. But don't panic yet, we aren't at that bridge yet. I'm stll betting on the U joint.

[James England]

Personally, I doubt that it's the clutch. There isn't really anything to 'snap' like that on them. As has been said already, you need to start at the rear wheel and work forward, eliminating each possible reason. You have the bevel gearbox at the rear wheel...does it have oil in it? Then the UJ joint..... Is it in good shape? ..the middle gearbox could cause crunching if no oil in there, so have a look at that....

If all is fine as far as the bike gearbox, then it's the transmission inside the bike somewhere.

UJ joint does sound a strong suspect in this inquiry!

[TopCatGr58]

Well,

This was way early in the morning when he posted, and hasn't posted a followup, so hopefully he's busy performing diagnostics. He was actually riding it in 1st when the snap happened, the pulled over to the curb, so the rear wheel didn't LOCK UP, I would assume he was able to pull in the clutch and coast to the curb...so the middle drive wasn't totally locked up.

However, a burning smell....he didn't say RUBBER, just a burning smell, could be the rear brake locking/dragging?? The snap could have been a SKIP of the 1st gear dogs/slots? It could also have been a skipping of the final driveshaft splines with the final drive? We don't know how long he's had the bike, if he's ever serviced/lubed the final drive/splines junction??

Then trying to drive it, just stutters in 1st or 2nd, lots of grinding noise, but bike wouldn't move much at all. Jerry experienced a driveshaft failure a while back...splines broken/worn down.

My bet is the driveshaft splines/final drive junction. Will be curious to hear what he finds as the real culprit!?

T.C.

[James England]

Yes, it will be intriguing to know the autopsy report. If it is, as you say, the shaft and final drive, it's an easy enough repair with cheap parts readily available, so let's hope it's that rather than the gearbox dogs......

[mesmeridicus]

Thank you gentlemen for all your help.

Actually, I've been at work all day. The bike is at my parent's house, currently, and I'll be headed over tomorrow to try out your suggestions.

Some background information:

I've had the bike since August of 2013. It's a 1979 Special. Upon purchase, the bike had about 9,000 miles on it and was in great condition. As of yesterday's disaster, it had about 14-15,000 miles total. I've replaced the oil several times, but I have not replaced the driveshaft oil nor have I had it serviced.

As far as I could tell, the bike hadn't shown any symptoms of an impending failure or problem. The oil pressure/brake check light would come on sporadically, and switch off whenever I activated either front or rear brake. It definitely has enough oil (20w-50, I believe), so I'm inclined to believe that the wiring connection is faulty and triggering the light.

The engine runs like normal when I start the bike. The burning smell was not caused by the rear brake locking -- I pushed the bike back to my parent's house in neutral and did not experience any unusual resistance.

I would like to clarify that something may not have "snapped," as I could not hear over the music. I just felt a jolt which felt like something snapping, and proceeded to coast to the side of the road in neutral.

Once I check it out tomorrow I'll post and let you guys know what I've found.

And, again, I'd like to thank you all for your help. The knowledgeable advice and friendly interest in my predicament is impressive and, I think, rarely found on such forums. I started riding three years ago at 21 and I am immensely grateful for all the help I've found here since.

I'll update tomorrow.

[LoHo]

Mes, this is the place for help...many of these guys know more than the manual tells us. If you take it to a shop, the guys there will look at you like you just rode a horse in and they'll have to scan their online manual muttering that you should just buy a modern bike. Plus, the listers have broken these bikes in a vast variety of ways and have fixed anything you can break. Don't be afraid to get into it and try things out. It will be your bike even more than it is now after you get her going again.

[James England]

Don't panic

As LoHo has said, there's a lot of knowledge here on the forum. Also, everyone wants to help everyone else and it's usually done without any ego-flexing or unpleasantness.

So, why not report back once you've done your initial investigation of the bike? Keep asking questions and you'll always get a response and the problem you have experienced will soon be identified.

[WMarshy]

Thank you gentlemen for all your help.

Actually, I've been at work all day. The bike is at my parent's house, currently, and I'll be headed over tomorrow to try out your suggestions.

Some background information:

I've had the bike since August of 2013. It's a 1979 Special. Upon purchase, the bike had about 9,000 miles on it and was in great condition. As of yesterday's disaster, it had about 14-15,000 miles total. I've replaced the oil several times, but I have not replaced the driveshaft oil nor have I had it serviced.

As far as I could tell, the bike hadn't shown any symptoms of an impending failure or problem. The oil pressure/brake check light would come on sporadically, and switch off whenever I activated either front or rear brake. It definitely has enough oil (20w-50, I believe), so I'm inclined to believe that the wiring connection is faulty and triggering the light.

The engine runs like normal when I start the bike. The burning smell was not caused by the rear brake locking -- I pushed the bike back to my parent's house in neutral and did not experience any unusual resistance.

I would like to clarify that something may not have "snapped," as I could not hear over the music. I just felt a jolt which felt like something snapping, and proceeded to coast to the side of the road in neutral.

Once I check it out tomorrow I'll post and let you guys know what I've found.

And, again, I'd like to thank you all for your help. The knowledgeable advice and friendly interest in my predicament is impressive and, I think, rarely found on such forums. I started riding three years ago at 21 and I am immensely grateful for all the help I've found here since.

I'll update tomorrow.

What gear were you in when this happened?

What was your throttle position, were you accelerating hard or moderately hard or crusing steady state?

Might have been second gear dogs jumping if you were accelerating moderately hard... More info would help make a conclusion... might be an ignition issue..?

[mesmeridicus]

What gear were you in when this happened?

What was your throttle position, were you accelerating hard or moderately hard or crusing steady state?

Might have been second gear dogs jumping if you were accelerating moderately hard... More info would help make a conclusion... might be an ignition issue..?

Accelerating moderately hard in first gear into second.

Put bike on centerstand, rear wheel will move in first gear without much resistance (there is some), and I hear a clunking sound when I turn it in gear.

Headed back out to garage to open her up.

[mesmeridicus]

This will be a process of testing and elimination. Starting with the easy to get at stuff first. If the drive train is intact up to and including the middle drive then you need to have a look inside the clutch cover. This can be done by placing the bike on the side stand, that way you don't have to drain the oil, but at this point I would probably leave it on the center stand and drain the oil anyway just so I could rotate the rear tire while in gear to help find the source of the grinding. If it's coming from the bottom end then it's tranny trouble and the fix will be a bit more complex and time consuming. But don't panic yet, we aren't at that bridge yet. I'm stll betting on the U joint.

Rear tire rotates like normal, without grinding, in neutral. Clunking/grinding sound when rotated in first gear.

Following your advice, I'll be removing the clutch cover to have a look.

[mesmeridicus]

Clutch cover is off, I'm staring at the innards.

Nothing seems broken or problematic. No metal chips, shavings, et cetera. Everything rotates as far as I can tell. I made the mistake of putting the bike in neutral prior to removing the clutch cover, however, so it's not in gear.

Next step?

[BA80]

You can still put it in gear with the clutch cover off, you just can't release the clutch.

[mesmeridicus]

You can still put it in gear with the clutch cover off, you just can't release the clutch.

Yeah I put it in gear, don't know what I was thinking.