Rear Differential issue

I bought a new Rear differential for my bike and I opened it to inspect the inside of the unit. It looked clean so I put it back together and torqued down the bolts. The unit will not turn freely now. I took it apart again and made sure that the gears were aligned and they were. I hand tightened the bolts down and they were restricting the rotation of the gear. My question is- when you take it apart, what happens to the unit? Will the differential slide back into position when engine torque is applied or does further maintenance need be required?

 

Engine torque isn't supposed to move anything in the final drive (it's not a differential). If you can't turn it by hand something is wrong.

There are stacks of shims on both the ring and pinion gear. They set the appropriate gear lash and contact area of the gear teeth. If you've left out a shim or installed one in the wrong place you could lock it up.

Setting one up properly is an art.

It's also possible it wasn't right when you bought it and the seller "solved" the problem by not tightening the fasteners.

 

That's why Dog created exploding parts diagrams.

 

My advice to all novice mechanics, learn well from the experience of SKYLRK62. Final drives are not to be trifled with; if it ain't broke, don' fix it!

 

Sadly I have to agree on that point, it's easy enough to get an idea of a final drive's health looking through the oil filler at the gear teeth & by turning/attempting to wobble the pinion shaft...

Now it's done though, I guess the next thing is to ask how far it was stripped & is it possible any shims got moved around?

 

The Final Drive Gears need to be aligned with great precision.

The process is done by measuring the very close tolerances with a Dial Gauge Indicator.

You might be better-off acquiring a replacement Final Drive off Ebay or form a Salvage Yard.

http://www.ebay.com/itm/1980-Yamaha-XJ6 ... f4&vxp=mtr

 

I haven't driven it. The unit is good, nothing stripped. As soon as I realized it was wrong I went on here. You guys are right, I'm a novice when it comes to this stuff. I'm am on a fast learning curve though. What should I do? Do I need to totally reassemble the unit?

 

What you have now is called a "learning opportunity" in my profession. If you decide that you have the time you can re-fit the gears. You'll want both gears to be squeaky clean. You'll need either prussian blue or gear paint. You won't need a dial gauge (though that speeds the process greatly, and you'll need the factory manual for your bike). The end result you're looking for is an even mesh of the gears at the center of each tooth face.

Process: Pull out one shim, paint one gear, reassemble and check for easy rotation. Disassemble and check the contact pattern on the unpainted gear. Clean the paint off of the gears. (now for the fun part) Spend somewhere between several minutes to several days repeating the process until all of the shims are in the case AND the contact pattern is perfectly centered on the adjacent gear face. You'll be swapping shims around, so you need to measure and mark each shim so you can identify how much you are moving the gears every time you swap a shim This is where a dial indicator comes in handy). What complicates this is you don't know if you moved one shim from one gearshaft to the other when you disassembled/reassembled the box, or if it was two shims (or more).

There is no way to reassemble a 90º gearbox by following a parts diagram alone. The shim placement and thicknesses will be unique to each gearbox due to differences in the final dimensions of each individual part. It's a good skill-set to have, but it's one that you will rarely use as a hobbiest.

Here is a guide to how the paint should look. It's for an automotive application, but the gear mesh works the same.

 

throw the dis-assembled one out, get a replacement...install it and then get a bottle of Crown to celebrate doing something the easy way...

 

Thanks! I made a mistake, but like you said, turn it into a learning experience.

 

Personally, that's the option that I'd choose, except for the throwing out of a good part. Either sell/ trade it on, or use it as a learning tool.

 

how far did you take this poor thing apart?
the book kind of says if you didn't replace any bearings or housings the shim that was in it should work. it looks to be one big round shim that takes a lot of measurements and reading markings to figure out but if you didn't change anything it should just go back.
you didn't wiggle jiggle enough

 

All I did was open it up.

 

I wonder if it was already bad then, & the seller left the bolts loose to make it appear to work?

 

OK now I wonder if the bearings were free to begin with. The only thing that would keep the gears from moving are bad bearings, improper gear alignment, or a FUBAR'd case) Grab your camera...it's movie time (or pictures if that's all you can do). I'd like to see the innards, and an external movie of the output shaft as you spin the input with the case closed.

 

I'll make a a YouTube vid and post it tomorrow.

 

I figured it out! I was being too ginger with it. Before, i was gently mating the two together and tightening the bolts to draw it the rest of the way. I took Polock's advice and mated the two, then whacked the hell out of it with a rubber mallet. It now spins freely and no drag. I guess it got off place when doing it the other way. Sometimes a good hammer will fix anything, haha! Thanks guys for all the input. Looks like I saved myself a ton of work. Whew!

 

Forty dollars on a complete unit! (2nd hand)! Try getting that on a modern bike!

 

i have 1 in my shed would have given it to you if you were close by. Got it off my later model virago parts bike. Internal ratio is supposto be a bit lower figured 1 day i would try it on my maxim x

 

You could check it out by turning the splines until the pinion has turned say 10 times & recording how many times the splines turn compared to how many turns of the back wheel on the bike to turn the shaft 10 times to compare the ratio, would save fitting it if it turned out to be the same?