final drive complete strip

monkeyboy

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I know the crown wheel replacement has been covered loads but if you could just please indulge me on a few questions regards the other bearings replacement I would appreciate some advice. I'm preparing my old GSA for another long trip later this year and I've got the final drive apart. The bike has done 105k and the crown wheel was changed at about 70. The bike did some hard rough miles between then and now.

The small taper bearing on the crown wheel looks/feels very worn and I can pull it maybe 1-2mm laterally in its cage - I'm guessing that's not normal - and there is some fluid seepage through to the UJ. Only a bit and it's probably been there for a while. I've certainly run my others like that but I reckon I might as well change the lot when I'm here.

So - looking at the pdf manual, the big crown and taper bearings look simple enough - I'm going to get myself a good puller set like this cos I'm sure it will be useful - especially for dismantling the input bevel.

So - my question is.... is the dismantling/assembly of the input bevel straightforward (if you have the right tools) and is it worth the investment? I'm guessing I'd replace all the bearings and seals at the same time. Any advice welcome. This trip is about 12-14k with quite a bit of rough so it would almost certainly make it but I can do without titting about enroute, even though I'll carry a spare crown/seal. I don't think I've ever heard of a input bearing fail - except didn't someone have one that machined its way through the casing?

ta
 
I can see how you can get the bearings off the crown and pinion with that bearing puller set, but I doubt you will be able to remove the tapered bearing seat from the casing.

I would be interested about the play in the tapered roller bearing on the crown gear as mine has way more play than yours, yet it is smooth running and there are no edges on the running faces.

The job is pretty straight forward. it is only bearings and seals after all. Provided your preload is correct from the last overhaul, and your replace like for like, you shouldn't need to reshim.

As to whether it is worth the investment. You will never know the answer to that.

:thumb2
 
Thanks Ian. I know what you mean, but my investment is probably just in peace of mind. My taper bearing shows no edges either. The case looks like it should allow that much movement with the holes as big as they are but if it's only a few quid and easy to change then I might as well. See what a new one feels like.

I know I'll need to get the pin wrench to remove the input bearing (unless anyone has one I can borrow!) but that puller should then help dismantle the bearing set on the shaft according to the BM manual. I've always shied away from doing gearboxes and final drives but this one looks reasonably straight forward and I'd like to know what to do in case it goes tits up on the road anyway.
 
Tapered roller bearings out of their race will always have a lot more play in them than their ball race brethren, you can't really tell if its excessive once the rollers are out of the fixed race, you can visually inspect the rollers for wear or damage, or just change the bearing and race, I haven't looked too closely at the race postion on the FD but in the past the road to enlightenment has gone past a suitably sized chisel and a large hammer :D quite probably with a diversion for some heat therapy :D
edit, Hmm just had a look at a picture of my FD in bits, looks like the hammer and chisel are out, and heat and an internal bearing puller may be in order
 
That's a 1200 - mine's an 1150 but it's interesting none the less.

As for the taper bearing - looks straight forward to change with a good puller at hand. I don't want to break out the hammer if I don't have to. Bad/expensive/painful things usually happen!

Just as long as I don't have to re shim! The more I think about it the more I might just leave the input bearing. I'll just ride carefully:)
 
You need a special tool for the input side and the torque is very high so you need a decent bench with a good vice. Personally I just sent mine to Scriminger Engineering. That was Easter 2012 and they rebuilt the unit for me prior to an Alaska trip. About £200 then, including shipping it back to me in Scotland. It's still going strong, strongly recommended.
 
You Do Need to Re-shim

Ian J Hartley
I can see how you can get the bearings off the crown and pinion with that bearing puller set, but I doubt you will be able to remove the tapered bearing seat from the casing.

I would be interested about the play in the tapered roller bearing on the crown gear as mine has way more play than yours, yet it is smooth running and there are no edges on the running faces.

The job is pretty straight forward. it is only bearings and seals after all. Provided your preload is correct from the last overhaul, and your replace like for like, you shouldn't need to reshim.

As to whether it is worth the investment. You will never know the answer to that.
Click to expand...

If you change the taper bearing you WILL need to re-shim! You can change the large crown wheel bearing and use the existing shim ok -but, of course, that's only true if it was shimmed correctly at the factory or previously - which is not always the case:eek:
If you change the small taper bearing you MUST re-shim to achieve the correct tooth clearance/backlash - I know this from personal experience:rolleyes:
If you have to shim a new taper bearing then it would be sensible to also check if the pre-load shimming at the large bearing is still correct - If it ever was correct!
To extract the taper outer ring I had to make a slide hammer with an expanding lipped end boss to engage behind ring and also heat casing area - worked fine, but not easy.

Cheers......................Grizzly:beerjug:
 
Got the bench and a good vice:) I know it would be easier to send it away - and probably initially cheaper too as I'm going to buy a good puller. Thing is that I want to know how to do it myself. Part of this trip is right across China and I want to know how to sort it out if I have to, just in case. The old girl is in bits at the moment going through an extreme makeover and this is just one part of it. I just like to know how things work:)

Who knows - I might feck it all up and send it away in the end anyway:)
 
So how hard is re-shimming without anything offical to measure the backlash? The shiming itself is easy - but how did you measure it?

Extracting the taper should be easy with the puller - I've got a slide hammer and blind bearing puller too so should be ok
 
monkeyboy said:
As for the taper bearing - looks straight forward to change with a good puller at hand. I don't want to break out the hammer if I don't have to. Bad/expensive/painful things usually happen!

Just as long as I don't have to re shim! The more I think about it the more I might just leave the input bearing. I'll just ride carefully:)
Click to expand...

You only need a two legged puller, or just a bit of heat, the bearing just falls off. In fact i've removed one on the raid with molegrips carefully placed behind the bearing and hit the grips with a hammer.
And you do need to shim if replacing the taper bearing. Otherwise you'll have a knock-on effect and cause problems elsewhere in the unit. But it won't show up for a few thousand miles.


Grizzly said:
If you change the taper bearing you WILL need to re-shim! You can change the large crown wheel bearing and use the existing shim ok -but, of course, that's only true if it was shimmed correctly at the factory or previously - which is not always the case:eek:
If you change the small taper bearing you MUST re-shim to achieve the correct tooth clearance/backlash - I know this from personal experience:rolleyes:
If you have to shim a new taper bearing then it would be sensible to also check if the pre-load shimming at the large bearing is still correct - If it ever was correct!
To extract the taper outer ring I had to make a slide hammer with an expanding lipped end boss to engage behind ring and also heat casing area - worked fine, but not easy.

Cheers......................Grizzly:beerjug:
Click to expand...

:thumb2
 
Understood, thanks. So how do I measure the backlash without the BM tool. Just use a ruler?
 
Thanks Ian - I found that just now. I'll check it out. I've ordered a tapered bearing anyway - just to physically compare a new one with the one in situ, then I'll decide whether to bite the bullet and change it
 
hi, just a question on this, im after replacing both bearings the large output and the tapered bearing, there was shims behind the large bearing which I turned around and reused, but there wasn't any shims on the smaller tapered bearing should there have been? ive it back together now and theres a ting bit of movement in it, any ideas?
 
Must Be a Shim

There will be a shim for the taper bearing - its fitted under the inner part of the taper bearing where it fits on the crownwheel. The shim can vary from about 2.00mm to 2.80mm - but I would say there should ALWAYS be a shim.
It's Item 4 in the diagram.
Cheers....................Grizzly:beerjug:
 

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Just an opinion, having just replaced an input shaft taper roller bearing on a BMW car diff, taper roller bearings like any other kind are made to be EXACTLY the same size including the assembled height. Unless you are changing the input shaft and pinion, or the crown gear itself, or there is very significant wear on either gear, if I can't you should not need to reshim.
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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