New member with some drivetrain questions

[TitanNeil]

Good day fellow GS worshippers...

I have recently acquired an '83 GS1100GK that I am right now tearing into so it will be ready by spring. I have a few questions, so sorry in advance for the long post (and possibly obvious questions - although I did check the FAQ's).

The bike has been off the road for 2 years. It sat under a tarp at my friends 'salvage' yard - basically a farm field. He offered it to me for a low price, and I could have my pick of any parts I needed for it from whatever I could find on other bikes (so far, 3 GS850's and others yet to examine).

The bike had been repainted (2 tone brown), looked reasonably presentable, and I had an '82 GS1100G for 7 years in my mid-20's so I was already bonded with the bike in heart and soul. I took it.

Upon closer inspection at my shop, the bike has a few problems. Number one: something in the drivetrain had stripped, that is why it went to the boneyard. Someone had removed the clutch assembly to check it and it came with the bike, but I can find no problem with it at all. I pulled the rear wheel off to check the splines - again no problem that I can see.
Now, I can attempt to slide out the primary bevel drive gear from the side of the transmission case to check it, but it is going to be a bear, I can see that. Does anyone have any ideas before I go any further? I'm torn between pulling the motor (and repainting it while its out) and just fixing the problem in situ.

I guess my main question is this: how can I find the fault in the drivetrain? Do I have to put the clutch back in and the wheel on and run the bike to find out? Or is there some other way?

Thanks in advance!

Oh, the bike has 92k Kms on it.

[TheCafeKid]

Good day fellow GS worshippers...

I have recently acquired an '83 GS1100GK that I am right now tearing into so it will be ready by spring. I have a few questions, so sorry in advance for the long post (and possibly obvious questions - although I did check the FAQ's).

The bike has been off the road for 2 years. It sat under a tarp at my friends 'salvage' yard - basically a farm field. He offered it to me for a low price, and I could have my pick of any parts I needed for it from whatever I could find on other bikes (so far, 3 GS850's and others yet to examine).

The bike had been repainted (2 tone brown), looked reasonably presentable, and I had an '82 GS1100G for 7 years in my mid-20's so I was already bonded with the bike in heart and soul. I took it.

Upon closer inspection at my shop, the bike has a few problems. Number one: something in the drivetrain had stripped, that is why it went to the boneyard. Someone had removed the clutch assembly to check it and it came with the bike, but I can find no problem with it at all. I pulled the rear wheel off to check the splines - again no problem that I can see.
Now, I can attempt to slide out the primary bevel drive gear from the side of the transmission case to check it, but it is going to be a bear, I can see that. Does anyone have any ideas before I go any further? I'm torn between pulling the motor (and repainting it while its out) and just fixing the problem in situ.

I guess my main question is this: how can I find the fault in the drivetrain? Do I have to put the clutch back in and the wheel on and run the bike to find out? Or is there some other way?

Thanks in advance!

Oh, the bike has 92k Kms on it.

Did you pull the splines out of the hub of the rear wheel and actually inspect them? They will appear to be ok if you just pull the wheel and dont look CLOSELY, because the backside of the spline, which is what you are looking at when you have the wheel off, never actually contacts the drive spline in the pumpkin. So there will be about an eighth inch or so that is perfectly ok. Just behind that however, they could be flat as a pancake. I have pics if youd like to see. this is a COMMON problem on the mid 81 shafties and on.

[49er]

Did you pull the splines out of the hub of the rear wheel and actually inspect them? They will appear to be ok if you just pull the wheel and dont look CLOSELY, because the backside of the spline, which is what you are looking at when you have the wheel off, never actually contacts the drive spline in the pumpkin. So there will be about an eighth inch or so that is perfectly ok. Just behind that however, they could be flat as a pancake. I have pics if youd like to see. this is a COMMON problem on the mid 81 shafties and on.

This is quite likely the problem.

But if not, you should investigate the condition of the secondary drive assy that connects to the drive shaft. The 1100G's have a history of shearing the threaded part on the secondary gear. This doesn't happen to the 850's. I think it's caused by the design of the thread cut on the later assemblies. I have repaired the pinion on a late model, higher ratio '83 diff which was also broken in the same area. I drilled and tapped a new threaded spigot and have been running it on my 850 for the last 12 months with good results.

[TheCafeKid]

This is quite likely the problem.

But if not, you should investigate the condition of the secondary drive assy that connects to the drive shaft. The 1100G's have a history of shearing the threaded part on the secondary gear. This doesn't happen to the 850's. I think it's caused by the design of the thread cut on the later assemblies. I have repaired the pinion on a late model, higher ratio '83 diff which was also broken in the same area. I drilled and tapped a new threaded spigot and have been running it on my 850 for the last 12 months with good results.

The 850 and 1100s also do not share the same drive and driven gear sets. They are not interchangeable from what ive read.

[TitanNeil]

Thanks for the responses - you're right, I didn't check the splines closely. I'll clean the goop out of them tomorrow and see whats really going on.
If they check out o.k, should I disassemble the pumpkin? Pull the primary bevel? Pull out my hair?

[TitanNeil]

Sorry, I should have added the question: is it the gearing in the transmission or in the pumpkin that is different in the later 1100? I pulled an extra rear wheel and pumpkin off of a parts bike in the boneyard, just in case that was the problem, but I don't know what GS the donor bike was - the parts looked identical. If it was an 850, would the pumpkin be different somehow?

[TheCafeKid]

Thanks for the responses - you're right, I didn't check the splines closely. I'll clean the goop out of them tomorrow and see whats really going on.
If they check out o.k, should I disassemble the pumpkin? Pull the primary bevel? Pull out my hair?

Dealing with the pumpkin and bevel gears is a bit tricky from what ive read. Especially the pumpkin, as there is alot of lash to play with. If it turns out your pumpkin is bad, I have one you can have for cheap, as well as the driven gear.

[BassCliff]

Greetings and Salutations!

Hi Mr. TitanNeil,

I'm glad you found a GS and I'm glad you found us. Please click here to receive your mega-welcome, chock full of suggestions and links to vendors and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. If you look on page 12 of the Rear Wheel Removal guide, you'll see what a bad spline gear looks like. Check this page for GS shaft drive gear ratios.

We'd appreciate some pictures too. Not you, your bike!


Thank you for your indulgence,

BassCliff

[49er]

Sorry, I should have added the question: is it the gearing in the transmission or in the pumpkin that is different in the later 1100? I pulled an extra rear wheel and pumpkin off of a parts bike in the boneyard, just in case that was the problem, but I don't know what GS the donor bike was - the parts looked identical. If it was an 850, would the pumpkin be different somehow?

Not sure if the transmission secondary gear sets are different between the models. The diffs are the same from the '79 850's up to the late '82 model 1100G's. They are 34/11. In '83 they produced a 32/11 diff and fitted it to both G and GK models. Yours should have the higher ratio!

[Nessism]

The 850 rear end is a direct bolt-in for the 1100. I know because I have an 1100 rear end in my 850. The 850 gear ratio is slightly higher than the '83 1100 rear end but not enough to worry about. Honestly though, the rear ends are bullet proof and not likely the problem. In fact, I've never heard of a rear end failing so most likely yours is fine.

[TitanNeil]

O.k, I pulled the driven gear out of the rear wheel to check the splines. They appear to be worn to a fine point, but are not rounded over or flattened. Damn!~ I have a spare wheel and pumpkin here, it would have made things a lot easier...

[SqDancerLynn1]

Check & see if one of those 850's is a 79 & get the splines from it they are all the same. You might even get a spare while at the yard

[TitanNeil]

I have a spare here, and I am going to swap since the one I have is nearly worn out. Unfortunately it ISN'T worn out, that would have explained the 'lack of forward propulsion' that took the bike off the road in the first place. There must be damage further up the drivetrain...

[49er]

I have a spare here, and I am going to swap since the one I have is nearly worn out. Unfortunately it ISN'T worn out, that would have explained the 'lack of forward propulsion' that took the bike off the road in the first place. There must be damage further up the drivetrain...

Since you've already checked out the clutch, it's now time to slide the dust cover back at the engine end of the torque tube to check the condition of the secondary drive assy flange and universal joint at the top of the drive shaft. My bet is that the driven gear threaded spigot that holds the drive flange has failed/sheered.

[TitanNeil]

Next step...

Thanks to all for the replies. I think (guess?) the secondary drive must be sheared at the thread. If so, can this repair be done with the engine in place, or do I REALLY have something messy to do this winter?