Better XS11 u-joint for 750 final drive

[3Phase]

The XS1100 u-joint yokes are made out of cast iron. Basically, I didn't like the feel and fit of the drive shaft in the output yoke while doing the 750 final drive mod with a copper bushing as a spacer.

My XS1100 drive shaft could move a full tenth of an inch from side to side with the copper spacer. I cut the output spline tube from a spare XS1100 u-joint assembly to use instead of a copper spacer.

To my dismay, the spacer fit the end of the drive shaft perfectly and no wobble was possible but it would not fit through the swingarm tube up to the yoke!




The swingarm will have to be removed for this mod and now is an exellent time to adjust/grease the swingarm bearings and check the integrity of the rubber u-joint boot anyway.

Obtain a copper bushing for a spacer.

Cut and trim the copper spacer until you find the correct fit for the XS1100 drive shaft to the 750 final drive input coupler.




Cut the output splines from a spare XS1100 u-joint using the copper spacer as a template.






For a solid fit and to use the spacer splines to power the shaft under load, drill two opposing, matching holes in the spacer and the output yoke with a 1/16" drill bit.

Use broken 1/16" drill bit shanks as hardened locator pins to hold the two pieces together and then bond them with JB Weld so the spacer cannot slip off of the cold pins.




The u-joint output yoke can now engage the drive shaft splines almost their entire length.

There is no wobble or any other undesireable movement at all.














Check the fit of the u-joint and drive shaft on the bike before installing the swingarm.







Clean and install the swingarm tube and install the drive shaft.













Measure from the swingarm flange face to the drive shaft gear face to ensure the correct fit in the 750 final drive input coupler splines.





Until I actually bought a 750 final drive, I was wondering about the differences between the XS1100 and XS750 final drive couplers.

For those that are wondering why you can't put the 1100 coupler on a 750/850 final drive, here they are!

Side view, 1100 on left, 750 on right.



Top view, 750 on left, 1100 on right



Bottom view, 750 on left, 1100 on right





Regards,

Scott

[xschop]

.10"

You should really check your universal joint wear....splined spacer will not make up for a worn u-joint and keep you from hitting the pavement if it were to fail....Good job on showing the spline differences on the 750/1100 FD couplers too.....A custom machined and splined product of the two couplers would be the perfect solution besides a custom shaft.......$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

[3Phase]

You should really check your universal joint wear....splined spacer will not make up for a worn u-joint and keep you from hitting the pavement if it were to fail....Good job on showing the spline differences on the 750/1100 FD couplers too.....A custom machined and splined product of the two couplers would be the perfect solution besides a custom shaft.......$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

Oh, you know it!

The entire reason I found this site in the first place was because I wanted to change the gear ratio. I was thinking about the transmission, originally, but I found your final drive mod and xs11.com during a Google search.

It's been a battle just to keep this bike running and I wasn't thrilled with the idea of a copper/bronze spacer so I put the whole thing on the back burner until I found an inexpensive 750 drive to play with.


According to the seller I am the proud new owner of a 1979 XS750 final drive.

I had to replace the XS1100 drive shaft when I first bought this bike because the lower drive shaft splines were out of round, with an uneven wear pattern.

Because of that I checked the coupler, new drive shaft, u-joint and yoke wear, lash, runout, engine mounts, and all contact points and wear patterns with a dial indicator and calipers. I also removed, cleaned, inspected, greased, and reassembled the u-joint cross. That was all a lot of fun.

With the u-joint output yoke clamped in a vise, the drive shaft fully inserted with no spacer, stock, and held by the c-clip, I had about 0.020" total 'wobble, or 0.010" runout at the far end of the drive shaft and 0.002" or 0.003" lash.

With the copper spacer, shaft 'wobble' increased to about a tenth of an inch total or 0.050" runout at the far end and 0.002" or 0.003" lash.

A 0.050" runout isn't too bad ~ten inches from the yoke with the shaft only inserted ~2/3 of the stock distance but after removing, cleaning, and inspecting the XS1100 final drive input coupler I found some lower side wear from rubbing against the aluminum pinion bearing housing under some monstrous torque load at some time in the past; probably the same load that ovaled the old drive shaft so badly that it had to be replaced.




The new XS750 final drive pinion shaft diameter is smaller than the XS1100 pinion shaft. The rub mark on the coupler extends about half way around the coupler base and forced me re-examine the shaft, spacer, yoke, u-joint cross, lash and runout (and a bunch of other things I can't remember right now) with a fresh set of eyes.

My XS1100 final drive is clean and pristine. The lash, pinion bearing preload and gear contact pattern is exactly where it's supposed to be and nothing rubs anywhere. The u-joint assembly is tight with no appreciably wear.
So, at some point in the past, someone popped at least one humongous wheelie or did something that made the input coupler rub, briefly, against the aluminum pinion bearing housing.


I considered welding the spacer to the yoke, but it's cast iron. Welding/brazing could harm more than help and it's not easily reversible.

So, I dressed the spacer and yoke contact faces with a ultra-fine finishing file and got the fit under 0.001" of an inch. I then drilled four holes and used two 1/16" drill bit shanks to pin the yoke and spacer together and epoxied it to keep the spacer from falling into the swingarm when the drive shaft is removed/inserted. The resulting assembly now has less than 0.0035 total 'wobble, or less than 0.002" runout, 0.002" or 0.003" lash, and it can be disassembled to restore the XS1100 final drive.

The new crush washer is supposed to be here tomorrow so I'll let you know how it works after I lace it all up tomorrow. This is going to be a lot of fun with no seat!



Regards,

Scott

[xschop]

Solutions

There is another "solution"....not expensive if you have welding/jig skills.....shorten the swingarm by 5/8"

[Ivan]

I really don't think welding would cause any harm if it were done right.

Automotive driveshafts have the yokes welded to the tube, so I would bet you could get it done. Especially if it were preheated and used a good tig a little at a time to minimise heat distortion. I would strongly consider taking it to a drive shaft shop and asking about getting it welded. You would increase the strength of the spline as well. From my hot rodding days, shortening a drive shaft was fairly inexpensive, cutting the end off, shortening the tube then re-welding the end back on was only about $35, but that was 10 years ago.

[3Phase]

Yeah, but... but.... y'all already have me cutting up the swingarm and getting a custom yoke made and I haven't even had a chance to fire it up and ride it, yet! <laughing>

I mean, I may not like it (doubtful, from what I've read) or the drive shaft and yoke break and the whole bike could s'plode and I'd be stuck with my rain gear riding a tricycle this winter like that guy on Laugh-In!



Regards,

Scott

[Ivan]

I did the drive mod and my feelings are mixed. I used to do 5k at 80 now I do about 4400. At a cruise in 5th it works great, but it is like starting out in third all the time, I have to slip the clutch a lot on take off.

As for the mileage, I can't say yet about that. At Talimena, while hotrodding around through the hills I pulled 40-43 mpg, but on the way home, nice flat straight roads, going down wind, I was back to 32-34. I am going to do some more tuning work on the carbs, check the cam timing and ignition timing before I jump to any conclusions.

One thing's for sure, I won't win any street races with the higher rear drive ratio.

[3Phase]

The U-Joint Works

I quite literally went by the seat of my pants to test the u-joint and final drive.
Tomorrow I'll try it on the freeway with a better temporary seat.






So far there is no sign of cracking, leaking, vibration, wibbling, wittering, wobbling, or anything else out of the ordinary; just smooth, effortless power in every gear.

I like it!


Regards,

Scott

[James England]

Wouldn't it be nice to be able to talk to one of the original Yamaha designers about this? I mean, I bet some of them are still around and I bet Yamaha know where they are.......

[3Phase]

Well, aside from having to learn Japanese, yes, it would be a lot of fun!