Deep Rumblings:

Hi,

I suspect I know the answer to this but I'd like the benefit of your experience before I go throwing more money at the 100GS.

I replaced the clutch and propshaft recently and the bevel drive seemed fine. Likewise the swing arm and paralever joint bearings were OK and were just greased and re-set.

Yesterday was the first proper outing since the work was done (305 miles).

I was on the Northern Section's "Wheels Across the Wall" run, which involved a lot of single track roads & off-road tracks, including the Keilder Forrest trails. I was having to apply some brisk acceleration in the lower gears to keep up with the 1200Gs'.

During the day I was aware of some vibration when under load and this got worse on my way home. I think I can hear a rumble as well as feel vibration now (I'll need to take it out without my earplugs in !).

Looking at it today, the rear end seems tight. If I hold the top UJ through the rubber boot that covers the gearbox output flange there is minimal backlash between the UJ and the rear wheel movement.

Running it on the stand, in second, at tickover produces a fair amount of clonking - but most shaft drive gearboxes do, you should hear my Land Rover.

I haven't peeled the boot back, but I am pretty sure that the stretch bolts are still tight.

I think the problem is in the gearbox - probably the final drive bearing.

Has anyone had one go - and can you describe the symptoms ?

I don't want to re-build the gearbox, only to find that it is the bevel box after all.

Its a 1989 100GS with 50,700 miles on the clock (and 10 previous owners !).

Thanks.

Bob.

Get yourself a coffee and have a read http://home.jps.net/~snowbum/transmission.htm

Out of three Airheads I've got two with gearbox problems. I've been doing plenty of reading and I think I'd better get saving. It looks like I'm going to have to buy a whole new layshaft, A helical input gear and a new 5th gear as well as fit new bearings and seals on one and a new endcover and reshim on the other

What to do.....

Drain your oil.

On the drain plug there is a magnet. Normal wear produces a bit of fine metallic sludge around the magnet, the consistancy of toothpaste--no discernable chunks of metal when rubbed between the thumb and forefinger.

If you feel bits of metal in the sludge, your output shaft bearing is likely digesting itself. Time to pull the transmission (a bit of a chore, but real straightforward).

The late airhead transmissions (1988-1996?) suffered from a factory cost-cutting measure. They eliminated a circlip on the output shaft to keep the shaft from drifting axially. This drift is what causes early output shaft bearing failure.

Whoever does your transmission, make sure you have the shaft machined and circlip installed, if it hasn't had it done already.

Tom, the left coast of Amerika

Rob Farmer said:

Get yourself a coffee and have a read http://home.jps.net/~snowbum/transmission.htm

Out of three Airheads I've got two with gearbox problems. I've been doing plenty of reading and I think I'd better get saving. It looks like I'm going to have to buy a whole new layshaft, A helical input gear and a new 5th gear as well as fit new bearings and seals on one and a new endcover and reshim on the other

Click to expand...

Rob,

Thanks; I've suspected for a while that the box needs some attention and actually bought a set of springs and oil seals in anticipation. Cowardice got the better of me though as I was 'relieved' to find some play in the front propshaft UJ and put the vibration down to that.

I guess your flange puller arrived - where did you get it from (and how much - if you don't mind me asking) ?

I took a rubbing of the flange when the box was on the bench recently and was intending to get a puller made - but a ready-made one would be a lot simpler.

I recently bought a Sykes bearing splitter with hydraulic puller that will fit the oilhead output bevel/wheel bearing (125mm dia). It cost just under £300 ! The Sykes puller is enormous and I suspect all I need for this application is a very heavy steel disc with four flange bolt holes plus a central hole for the socket / extractor shaft. I'd be interested in a picture of your flange puller.


When I drained the gearbox oil recently there was just a small amount of grey 'fuzz' on the magnet and no obvious hard bits (though I wasn't really checking for them).


Do you fancy taking on my gearbox re-build as well as your own (as you are obviously heavily into shimming, from other posts I have seen) ????


I will be leaving for Spain / Morocco in under two weeks time (1150 GSA, fortunately) so I doubt if I will start serious work on the 100GS until end October. I might get the box out though, as I can now do that in a couple of hours.

Thanks for the info, I suspect we will be corresponding again on this topic.

Bob.

chiefrider said:

Drain your oil.

On the drain plug there is a magnet. Normal wear produces a bit of fine metallic sludge around the magnet, the consistancy of toothpaste--no discernable chunks of metal when rubbed between the thumb and forefinger.

If you feel bits of metal in the sludge, your output shaft bearing is likely digesting itself. Time to pull the transmission (a bit of a chore, but real straightforward).

The late airhead transmissions (1988-1996?) suffered from a factory cost-cutting measure. They eliminated a circlip on the output shaft to keep the shaft from drifting axially. This drift is what causes early output shaft bearing failure.

Whoever does your transmission, make sure you have the shaft machined and circlip installed, if it hasn't had it done already.

Tom, the left coast of Amerika

Click to expand...

Tom,

Thanks.

I drained the gearbox recently and the oil was OK (just a small amount of soft grey sludge). I'll drain it again after yesterday's 300 mile run and see if it is worse.

Rob Farmer gave me a link to a useful site so I'll remove the box and start checking for worn bearings and existance of circlips.

Bob.

Bob,

I bought the flange puller from Ed Korn in the states http://www.cycleworks.net/

It cost $78 + $11 for postage. The $11 postage was cheap but took a long while to arrive. UPS quoted $78 for a two day delivery.

Eds a mine of information and makes excellent tools - he's also very patient with Englishmen flapping when their tools don't arrive in double quick time and they only paid $11 for postage .

I've had a few of his other tools off him in the past and they work great.

Gary H (on this site) has a brilliant engineering setup and really knows what he's doing with it, I'm sure he would machine you a groove in your output shaft for a few pounds.

Rob Farmer said:

Bob,

I bought the flange puller from Ed Korn in the states http://www.cycleworks.net/

Click to expand...

Thanks again.

Bob.

Any chance of a three for one offer Garry

Thought not

My new (second hand) box is now in....and I can hear all sorts of noises, that may, or may not, have been there all along.

Reliable...BMW...that's as near as the two words get these days

Voyager said:

I suspect all I need for this application is a very heavy steel disc with four flange bolt holes plus a central hole for the socket / extractor shaft. I'd be interested in a picture of your flange puller.

Thanks for the info, I suspect we will be corresponding again on this topic.

Bob.

Click to expand...

Bob that is exactly what you need, I will have a look in the garage as my Dad machined me one when I had the airhead over here. We used a thin plate with a few holes just to get a puller to grip on the sides and gave it an almighty wack which prompted the flange to pop off. Once the flange is off piece of piss really.

You are more than welcome to use my flange puller disc as long as you return it after use

maverick said:

Bob that is exactly what you need, I will have a look in the garage as my Dad machined me one when I had the airhead over here. We used a thin plate with a few holes just to get a puller to grip on the sides and gave it an almighty wack which prompted the flange to pop off. Once the flange is off piece of piss really.

You are more than welcome to use my flange puller disc as long as you return it after use

Click to expand...

Maverick,

That's a very kind offer - I accept.

I will certainly return it after use.

I am a bit concerned about your description of it as a "thin plate", I was thinking of sometinng around 15mm thickness or more as Rob Farmer has had trouble getting his flange off the taper.

I am hoping to use a bearing separator behind the plate in order to give it an even pull (without bending the plate).

I'll PM you with my address.

Bob.

when my gearbox blew 5th gear it was an output shaft bearing that caused the damage after pricing up the repair doing the work myself the parts came to 450.00 a recon box was 400.00 so before you do the work price the spares you might be surprised