Crunch time with my gearbox

[bangpaul]

This slipping into neutral problem is getting worse. It seems to happen more often when I'm going down the gears, which is dangerous because I'm relying on the gears to help with braking. Gear changes seem to be getting crunchier too.

I found the filler hole, and the level seems fine, but the oil is that milky-brown iced-coffee colour. Viscosity doesn't seem too bad, I suppose, although I've never encountered gearbox oil before.

I'm getting a bit concerned. Any advice? I was going to just replace the oil and hope things improve. Seems like the only option within my capabilities.

Any tips for the oil change? First time I've done it but I can't imagine it's much different to changing the engine oil.

Thanks, as always.

[Barry]

Changing the oil is very straightforward. Same principle as changing engine oil - do it hot and leave to drain well.

By your description of the colour it sounds like you might have water in the oil. It can get in past the speedo drive rubber boot which may need replacement or better sealing. With regular maintenance and a sound gearbox, gear oil should always look much the same colour when you drain it out as when you put it in. Having said that you are always going to find some fuzz on the magnetic drain plug. If it feels like smooth grey paste then that's normal. Any gritty fragments or slivers of metal suggests a problem needing investigation. If the oil is a really bad colour you might consider a 2nd oil change soon after to make sure all the crap has been flushed out.  

Slipping into neutral can indicate gearbox problems. There was a gear selector modification kit available back in the day but it's no longer available and the parts needed to make it up now amount to such serious money you might be better going for an exchange or 2nd hand gearbox. Before condemning your box though make sure after the oil change that you are using appropriate shifting techniques. Lightly pre-load  the shift lever before pulling in the clutch and the change will be easier and make sure to follow through till the shift lever hit it 's stop.  

[bangpaul]

Thanks Barry. You've got a knack for explaining things well to people who don't have much experience with these things. I hope your career made use of your teaching skills. I do have a couple of further questions though.

The speedo drive rubber boot is the rubber cap thing that's at the top of the gearbox on the right hand side where a cable goes in right? If so, this is old and cracked and could very well be allowing water in.

The big rubber boot on the driveshaft is also worn and needs replacing. It seems to be leaking a bit. Has anyone ever tried shoo goo as a temporary measure? I'm not up to dismantling the rear end yet.

Also, I may have not expressed myself very well when I described it as "slipping into neutral." The bike doesn't slip out of gear into neutral. I seem to get it into gear, the shift lever hitting it's stop, but when I let the clutch out I find I'm in neutral. But I'll try the technique you mentioned as I haven't heard or tried that before.

Lastly, what sort of gear oil is best for these old bikes? Is there much difference between them?

Thanks again. I'd never have the confidence to attempt these things without this site. It's becoming a real education.

I'm starting to get the impression this bike wasn't as well maintained as I was lead to believe. But it might just be it's been used continuously, and the harsh sun here would be pretty unforgiving on those rubber parts.

[Barry]

The speedo drive rubber boot is the rubber cap thing that's at the top of the gearbox on the right hand side where a cable goes in right? If so, this is old and cracked and could very well be allowing water in.
 

Yes that's it. Mine was old and cracked and didn't seal well around the cable so had to be replaced.

The big rubber boot on the driveshaft is also worn and needs replacing. It seems to be leaking a bit. Has anyone ever tried shoo goo as a temporary measure? I'm not up to dismantling the rear end yet.
 

Unless the boot is actually split you maybe abe to adjust the clamp to re-seal it. Fiddly job though.

he bike doesn't slip out of gear into neutral. I seem to get it into gear, the shift lever hitting it's stop, but when I let the clutch out I find I'm in neutral. But I'll try the technique you mentioned as I haven't heard or tried that before.

This technique is not my idea. It's a commonly used method mentioned on all the Airheads forums. Finding the odd neutral between gears is not unheard of but shouldn't be a common experience.

Lastly, what sort of gear oil is best for these old bikes? Is there much difference between them?
 

Any decent 80W/90 gear oil to GL4 or GL5 spec will be fine.

[bangpaul]

Thanks again Barry.

The boot is actually split it seems. Or it has lots of little splits. Seems like quite a task replacing it. Do you think a polyurethane-based adhesive would work alright for a while? As long as I gave it a good clean of course. Far from ideal I know.

[Bob_Roller]

It's a quite easy job to replace the rubber boot, remove the speedometer cable from the transmission, remove the old boot, lube the new boot, install it over the end of the cable .

Believe it or not, the boot goes over the fitting at the end of the cable, doesn't look like it should, but it does .

[bangpaul]

Sorry Bob. Probably didn't make it clear that we'd veered off the topic and begun talking about the big driveshaft boot. That's the one I'm thinking of shoe gooing.

The other one doesn't look to hard, but I'm sure I'll manage to complicate things. As long as the parts guy has one on hand....

[montmil]

Replacing the speedometer boot is no biggie. A little oil or silicone lube will assist the boot over the speedo drive.
   Do Not strip the threads in the gearbox case by over-torquing the bolt securing both the battery negative cable terminal and the speedometer drive! Just snug it up with a short wrench.

The driveshaft boot replacement is much more complicated.
   Besides a new boot- which has a "top and bottom" installation position- you will need new driveshaft U-joint attach bolts to refit after going through the swingarm removal and transmission detach. The correct BMW bolts are now shorter than the OEMs and do not utilize lock washers.
   As the swingarm will be loose, you may as well use this opportunity to clean, inspect and re-grease the swingarm tapered roller bearings. A transmission spline lube would also be in order.

Do you have either a Clymer or Haynes shop manual? Will be very helpful should you consider undertaking the driveshaft boot replacement chore. All straight forward but often fiddly.

The driveshaft boot will flex with every movement of the rear suspension; I would not place any large bets on the success of trying to use an adhesive to "fix" splits.

Charlie Mike. Let us know what you need by way of assistance.

Monte

[Matt Chapter]

Any tips for the oil change? First time I've done it but I can't imagine it's much different to changing the engine oil.

Thanks, as always.

I just did my transmission oil for the first time and would really, really have liked to use a 19 mm socket to undo the drain bolt, instead of trying to use the box wrench in the standard toolkit.  Next time I'll have one for sure.

[Rob Valdez 79 R65]

A 19mm socket has many uses on these bikes.  (engine mounts, for one other).

Replacing the swing-arm boot can be frustrating for anyone, especially so for a first timer.
Get all your cuss-words lined up beforehand.  A new boot does not have the flexibility that re-installing the old one would have.

I created a hook tool for this job by taking a small screwdriver and heating the tip cherry red and bending it 90°.

[montmil]

... I created a hook tool for this job by taking a small screwdriver and heating the tip cherry red and bending it 90°.

Now you share this little gem of wisdom. I'm going to make up my own bendy screwdriver just so I'll have one for "next time".

I think I tore off three fingernails getting that freakin" boot fitted. [smiley=wall.gif]

Monte

[Rob Valdez 79 R65]

... I created a hook tool for this job by taking a small screwdriver and heating the tip cherry red and bending it 90°.

Now you share this little gem of wisdom. I'm going to make up my own bendy screwdriver just so I'll have one for "next time".

I think I tore off three fingernails getting that freakin" boot fitted. [smiley=wall.gif]

Monte

Trust me - the special tool only makes you think the job is going to go easier.

[Rob Valdez 79 R65]

And some of the boots are marked with both a "upper" (ober).

Look closely, you should see that one end of the boot is "squarish" and the other end round.

According to this guy's blog, the square end attached to the swing-arm and the round end attaches to the gearbox.  http://type247.wordpress.com/page/2/

[bangpaul]

It's a quite easy job to replace the rubber boot, remove the speedometer cable from the transmission,

Let's start with the basics then: how do I get the speedo cable detached from the gearbox?

[montmil]

It's a quite easy job to replace the rubber boot, remove the speedometer cable from the transmission,

Let's start with the basics then: how do I get the speedo cable detached from the gearbox?

Remove the small bolt on the trans box just below the rubber bootie. 10mm wrench req'd.

Withdraw the bolt.

Withdraw speedometer cable. Done, done and done.

Look closely at the bolt. It is rifle drilled, ie: hollow in the longitudinal axis. It is a vent for the transmission. Make sure it's clear.

Exercise caution when refitting the bolt. DO NOT over tighten and strip the threads in the gearbox case! Just snug it up and be happy.

Monte