Variation of the 750/850 final drive mod

[3Phase]

The spacer for the XS750 mod' is not a loaded part of the drive train and will have very little if any wear after tens of thousands of miles.
It doesn't matter if it's the original copper spacer shown in the mod' or the splined spacer I cut from another u-joint yoke -- a spacer is just a spacer.

The drive shaft is tougher than the u-joint yoke and almost doesn't wear at all but the yoke splines do.







The drive shaft position in the Final Drive coupler is a little close to the edge of the coupler splines.

When I make a new u-joiint assembly and have it welded I'll add
some extra length to put the drive shaft a little further back and
deeper in coupler.

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[BA80]

Have you got any pics of yokes that have failed?

[3Phase]

Have you got any pics of yokes that have failed?

No, just this one that I caught before it got too bad to save. I'd put pretty close to the same miles more or less on it that you did when you checked the copper spacer. I don't even remember now why I pulled the u-joint but the spacer and drive shaft were in fantastic shape and the yoke was getting hammered so I welded it up. The 1/8" drill bit pins hadn't really done anything useful except keep the spacer from falling off and following the drive shaft down the swing arm when I cleaned and greased it.

The wear doesn't really show 3D in the pictures but if I put machinist blue on the splines, the drive/coast face contact would mostly be at the upper/front of the original yoke splines and the relatively unworn spacer splines. The 'middle' of the splines doesn't really make full contact except when I do stupid stuff that seriously loads the drive train.

The assembly has been in use since however many thousand miles ago but I had to pull it this morning to start prepping the swing arm and the frame. The drive shaft and yoke splines have begun to re-seat themselves to each other but you can still see most of the taper, stepping, and wallowing. It's basically running-trash but the yokes are strong as all get out so after I put the engine back in it'll probably let me do launches and ride the stupid thing like a unicycle until I can get another assembly cut and welded.

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[BA80]

Scott, Tod and I and anyone else are not trying to say that this isn't a good idea. It's an excellent idea. However, taking in to account live on the road testing from those of us who have put more miles on a single bike than most do on multiple rides, with the exception of Brent of course , that have been running the original mod have had no type of failure directly due to the mod itself, it is mechanically unnecessary.

Your mod idea is great if you don't plan on swapping back or if you just need peace of mind but according to stats on real world miles and use, it's completely unnecessary, mechanically and financially.

No need to argue over facts that are there. No need to argue the facts you have presented either.

Sorry if I have offended in any way. Facts are facts.

[dbeardslee]

I don't doubt that the original mod would probably last forever the way I ride. But I'm a sucker for a nice mod, and I do like the way the yoke looks with the welded extension. That being the case I found a couple u-joints on flea-bay and snapped 'em up. I figure I'll get my local welding shop to fab it up for me, and this winter I'll swap the modded u-joint for the one I've been running. It'll give me something to do.

One of the u-joints is off a 78, and the other is off an 81. But a u-joint is a u-joint... right?

[3Phase]

Wow, AT&T's auth server got cooked in the heat and we lost Internet for a while.

Greg, I'm not in the least bothered and I hope I didn't really upset anyone while I was having fun! If so, I apologize. I woke up again today not lookin' at roots. It's a great day!

Yamaha seems to have used harder and softer materials at various places in he drive train to save the more expensive parts:

The u-joint yoke is softer than the drive shaft and will wear out or strip before the drive shaft.

The drive shaft is softer than the final drive coupler and will wear out or strip before the coupler.

The rear wheel hub is softer than the final drive hub and will wear out or strip before the final drive hub.

It's pretty good engineering.

Checking the u-joint is mostly like checking any driveline, you grab hold of it and shake. If it wobbles there's something wrong, check it out and make it not do that. If it's good, grease it up and give the nice people their car back!

The u-joint wasn't a clapped out part, before I did the mod' I found a new one with a matching drive shaft. The drive shaft/yoke wobble was almost non-existent and was definitely way less than 'Chop's recommended 1/10". So I have my one example yoke that had just started to wear out when I caught it and had it welded. I was extra hard on it because I was trying to break the 'joint, the Final Drive, anything. You can imagine my complete surprise when the u-joint splines wore out and the drive ate the pinion and side bearings and had to be replaced.


Doug, the '78 to '82 (maybe up to '84 in Canada?) all use the same assembly, if it's good just bolt it in and ride it!

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[dbeardslee]

Doug, the '78 to '82 (maybe up to '84 in Canada?) all use the same assembly, if it's good just bolt it in and ride it!

I think I'll use the whole assembly on whichever one has the best u-joint, and cut the end of the yoke off the other one and have it welded on. Then I can just swap out the lengthened assembly for the one that's currently installed.

The seller claims the one from the 81 came off a bike with 31K miles and says it has no play in it. It looks good in the pics, but you know what they say - caveat emptor.

Which brings up another question - is there any place where you can get the actual u-joint part of the assembly new? Is it even possible to press in a new u-joint in the old housing?

[3Phase]

I've changed the u-joint cross before and it's not difficult, just a little finicky. There's a thread around here somewhere about how to change it and how to make the special tool so you don't bend the yoke.

Yes, the u-joint cross is available. I haven't actually bought one yet because then I'd have to change it.

Post 15

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[dbeardslee]

I've changed the u-joint cross before and it's not difficult, just a little finicky. There's a thread around here somewhere about how to change it and how to make the special tool so you don't bend the yoke.

Yes, the u-joint cross is available. I haven't actually bought one yet because then I'd have to change it.

Post 15

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Cool. And it looks like it's a greasable u-joint. All things being equal I much prefer greasable u-joints. And this is why - u-joint lubrication path

[BA80]

From that image shown the zerk is in the end of the bearing cap. Not sure there would be enough clearance so it wouldn't wipe out the boot.

[dbeardslee]

From that image shown the zerk is in the end of the bearing cap. Not sure there would be enough clearance so it wouldn't wipe out the boot.

There's little caps you can use to plug the zerk fitting hole. Then you just take the cap off when you want to grease it. My cherokee has u-joints like that on the front axle. I've got a grease gun with a big rubber tip, and when I want to grease 'em I remove the caps and just hold the rubber tip firmly in the hole. I'm thinkin' something like that might work for these.

[motoman]

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There's little caps you can use to plug the zerk fitting hole. Then you just take the cap off when you want to grease it. My cherokee has u-joints like that on the front axle. I've got a grease gun with a big rubber tip, and when I want to grease 'em I remove the caps and just hold the rubber tip firmly in the hole. I'm thinkin' something like that might work for these.

Yeppers........and thirty pumps from the nomal size grease gun WILL get splines and suxh lubed up just fine,,,,,every other oil change.That equals the 1oz. required from original yellow owners manual. For what its worth, my final has NEVER been removed from new, and lube will squeeze out around 4bolt flange mount.......I'd call that good to go. Has worked for me 34yrs, following original yellow owners manual that dame with bike when new., and bike is at 83K original miles at this point. No reason to EVER remove those four flange bolts unless your interested in a final drive change to the higher geared 850 tripple drive Can easily prove the splines get lube when properly done. CZ will even back me up o that.

[dbeardslee]

No reason to EVER remove those four flange bolts unless your interested in a final drive change to the higher geared 850 tripple drive

Already got a type 2 750 final drive in it. It's a thing of beauty, but I can't stop tinkering. Hi. My name is Doug, and I'm a tinkerholic.

[Prisoner6]

I've changed the u-joint cross before and it's not difficult, just a little finicky. There's a thread around here somewhere about how to change it and how to make the special tool so you don't bend the yoke.

Here is a great U-Joint tutorial thread:

How to Change/Lube Driveshaft U-Joint

[3Phase]

I love it! Spicer made a fantasy video!

If the grease won't come out you can try loosening the cap(s) but you still have to find the whatever-it-was that blocked it in the first place or the 'joint will fail. In big trucks, heavy equipment, combat engineering and recovery vehicles they like to explode. That's highly unlikely to happen to an XS11 if the u-joint fails but Peterbilt got sued and lost because it burned up a bridge:-

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Big-rig, big-money fingerpointing over Montebello bridge explosion
Posted by Hillary Jackson on July 14, 2015 in Crime

A 2011 tanker explosion that destroyed a freeway bridge in Montebello occurred because Peterbilt Motors Co. manufactured a defective part deep within the chassis of the big rig, an attorney for a transportation company told a jury Tuesday, but a defense blamed the accident on the truck’s mechanics.

Greg,

You're right, if it's in the end cap it'd rip the boot but you could change it out and use one of those flush mount fittings. You have to grease those with an adapter that's like airing up a basketball with a hypodermic needle but it'd work. If the fitting's in the body you wouldn't be able to get to it or it'd just break off unless it was in the 'side' between the trunnion arms.

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