HELP: Drivetrain Thud?

[southoxs1100]

All,

I have an XS1100SF and when I accelerate hard in first gear there is a slight thud coming from the rear-end. At first I thought it was clutch slip, but after new friction discs, steel plates, and HD springs I do not believe that is the case. This only happens in first gear under heavy acceleration. Has anyone else had this issue? Possibly U Joint? Teeth broken? Any tips for taking apart the middle and final gear? Any other possible causes of such a noise/instance?

I would appreciate any insight, advice, or tech tips.

Thanks!

[DGXSER]

Are you a Tranny type?

Ok...sorry....Are you certain it is not the 1st gear Transmission slipping out of gear? Is it a repetitive thud? or just one thud and then fine?

Repetitive thuds could mean your first gear is slipping out under the heavy load.

[southoxs1100]

DGXSER,

If I stay in the throttle it will keep accelerating. Is it possible that it could pop out and then pop back in? how hard is it to inspect the gear drive, i.e., do I need to pull the motor?

Thanks.

[trbig]

It's hard to describe a sound on here. What USUALLY happens if it's the typical gear problem, is the edges of the gears get rounded. Under pressure from hard acceleration, this pushes the gears apart for a split second, then they grab at the next landing. If still accelerating, it will slip by that one and keep doing in quick succession. Mine started it a while back and only did it once... then again.. another time. It will get worse each time it does this until it won't hold the gear at all.. just grind against each other. I tested mine by putting a 2nd person on and getting on it in 1st. With the extra weight, there was no doubt about the gear. As it gets worse, it will resemble sitting on a machine gun.

It seems like 2nd gear is what goes on the XS and 1st on the XJ. I have no clue why since they are the same motor from below the cylinders on back. There are many articles you'll find if you do a search for "2nd (or second) gear fix". Some pull the motor and split the cases, but you can do it with the motor in the bike still.

Have you checked the fluids in the middle and final gear.. drained the oil in them recently to make sure you don't see any metal bits in there? Does the gear oil smell really burnt?


I would avoid the hard accels until you figure out what the problem is. You'll probably have to actually pull the gears out to be able to inspect them.

Tod

[joebus]

I remember the first time I drove a shaft driven bike and it does make a kind of a thud sound when changing gears compared to the belt driven i was used to ridding. Maybe it is just that?

[TopCatGr58]

Hey South,

Tod's given you a great deal of info. My 81XS lost 1st first, and then 2nd went a few months later. My theory is that many folks don't use 1st very much or for very long, or for much rpm, but once they shift into 2nd, they use it longer and under more throttle!? But it could also be that having to shift THRU neutral allows more banging of the dogs and slots??

Anyways, sorry to hear that have already done the clutch work, because to fix this, you have to go back into it, you were actually half way there with the clutch work. You don't have to pull the engine, different approaches are recommended, I prefer flipping the bike upside down. You can take a look at the tech tips...repairs, transmission section, you'll find several on the 1st and 2nd gear dremmel fix.

Aside from the chance of damage to the final drive....a few folks have torn up the splines where the driveshaft mates with the FD due to the fact that the ZERK/grease fitting on the final drive/driveshaft junction does NOTHING to direct or put grease where it's needed. You have to take the FD off of the swingarm to inspect and clean/regrease the splines and such there.

So..from what you have described, my bets are on the 1st gear dogs/slots wearing...so that they DO jump out and then back into gear depending on the amount of throttle you put into it!!

You don't have to waste your summer IF you want to just ride it, just don't put so much throttle into 1st gear, and then shift into 2nd and above. Just be aware that IF you start experiencing the same symptoms in 2nd, then you know the repair is emminent!!
T.C.

[Axel]

Clunk

My bike does this too if I really rev it out in first . It makes a clunk and then continues normally

[DGXSER]

I would consider myself a shadetree mechanic at best. Never had a bike open before, torn down car engines, but never a bike. and I got the repair done with the help of all the great folks here on the site.

So you guys can surely do it in less than one week including working the day job.

[79XS11F]

Could be drive line lash or perhaps the crush rubbers in the drive hub are toast.
Rob

[southoxs1100]

Thanks for all the advice and tips,

I checked and changed my middle and final gear oil last night and did not see any shavings and gear oil was good and clean.

I recently put tires on it so, I pulled the final drive off and greased the splines, so I am thinking these are in good shape.

A friend of mine who has had KZ1000's and a couple of these bike said to check the ignition and carbs for a miss. I check vacuum lines and made certain the advance was do its job and it is, timing is in good shape. I noticed some gas coming out of the boot on the airbox side of the number two carb. Could a miss cause this reaction, i.e., the jerking feeling?

I have read the tech tips sections on the tranny (which is incredibly informative and so is this site) and downloaded a manual. Luckily I have a 82' XJ650 that is my everyday cruiser to ride this summer, so I will probably tear it down this summer...It will be a learning experience.

Thanks again!

-Mark

[TopCatGr58]

Thanks for all the advice and tips,

I noticed some gas coming out of the boot on the airbox side of the number two carb. Could a miss cause this reaction, i.e., the jerking feeling?

Thanks again!

-Mark

Aha, the plot thickens! With a leaking carb #2 most likely due to a sticking float needle valve or float, it's flooding that carb, and will NOT respond properly to low rpm throttle input. Once you get the rpms up and into the mains, it can smooth out some. I had a broken float post that wasn't properly repaired(slightly slanted) causing a similar situation, was running at a rally in the mountains, was either essentially WOT or not, fun trying to keep it running in the twisties! However, I don't recall any actual THUDDING type activity, just wouldn't respond well to throttle input. But a flooded carb/cylinder could cause intermittent firing etc., might be possible. Would suggest you tear back into your carb and check, fix your float problem, and then when it's running right and no leaking, then you can test again for the THUD/SKIP, and if it's still present in 1st, then you can probably be assured that it's the tranny and not the other situations which sounds like you've pretty well eliminated!
T.C.

[Ivan]

I keep thinking swing arm bushings... Not sure though.

[southoxs1100]

All, Thanks for all the tips. I changed the oil from 15-40 to 20-50 this weekend. In addition, I cleaned and rebuilt the carbs and took care of the leaking issue. Bike runs good and no more leaking. Regarding first gear, only when i get after it if feels like clutch slip (I am almost certain that it is not the clutch). I thought it may be the tire but I am running Dunlop GT 501's. I am not ruling out the first gear issue, but wouldn't I hear transmission noise? Thanks.

-Mark