Warren’s final drive after refurb


If you plan on taking the final drive to bits, beware. It isn’t as straight forward as you think.

At least consider reading the shaft drive manual first. If you want to just replace the seals, then I’m covering that further down.

Click below to download a PDF version of the manual.

Firstly, if the drive works, and it doesn’t leak, then don’t take it apart. Leave well alone.

If you take the drain plug out and there are a small amount of metal filings in the oil, this is normal. If you have pieces of gear and larger chunks of metal in the oil, then you’re in doodoo. It’d probably be easier to buy a second hand final drive.

Still reading? Oh dear. Well here goes. I do not recommend that you attempt to remove any of the bearings, unless you really need to change them. This will upset the gear lash (the way the gears mesh) in either case. So first read the final drive service book to best understand how to service this unit.

There are two types of drive, which we will call types 1 and 2. The rear drive, driveshaft and middle gearbox are all matched to the type of final drive.

Type 1 doesn’t have the small drilling shown below. Part 3 is next to the drilling. This write-up concerns type 1.

Type 2 final drive showing extra hole

Now back to the task at hand.

The first step is to get the bike on the centre stand, drain the oil as per the Haynes or Clymer manual recommendations, and then get the back wheel and bottom shock absorber on the drive side removed. Take careful note of the spacers and seals on the back wheel. Place them back on the spindle/axle and put it through the wheel for safe keeping. Tie the brakes out of the way.

Replacing The Shaft Drive Oil Seal

Undo the 4 nuts holding it onto the swinging arm, and slide it away from the exposed gear. Lay it on something soft. You’ll probably (definitely) get some more oil out of it. You will get some oil out of the end coupling also. Don’t worry, this is normal. There is bleed through from the final drive to lubricate this gear. Therefore the seal condition in this area is very important. That’s what we will cover first.

The coupling is sealed around the outer by a lip oil seal (Yamaha Part No. 93101-38086-00, see below), and there is a seal on the gear itself (Yamaha Part Number 93108-27006) to stop the oil filling into the swing arm.

In order to remove the drive shaft itself from the swing arm, and middle gear box, use two suitable drifts behind the gear and lever it out using the swing arm as a pivot point. (A clip holds it into the middle gearbox). Lay it out on a soft cloth and check the condition of the gear, splined shaft and seal. If the seal (93108-27006) needs replaced, you’re stuffed. Yamaha discontinued it.

You may be lucky to find someone with old stock, but it will cost you. Alternatively, there is a Honda part which I found is a perfect fit. (This took me hours of research and hard work and comes from a 2005 Honda shaft drive). The Honda part number is 91261-ME9-005.

The seal sizes of the original Yamaha one are 27 x 43.6 x 7. The Honda seal is 27 x 43 x 7. When I received it, I checked it with a vernier calliper as 26.8 x 44.3 x 6.9. To cut a long story short, it was tight on the shaft, and fit inside the coupling nicely.


Since Warren wrote the original article. I (Captain Sensible) followed his instructions and took some pictures as I went along.

My seal looked like this – nasty:

Here’s a picture of the old seal taken off and the new one ready to go on. I have de-rusted and zinc plated one of the retaining washers because it was badly corroded:

And here’s what it looks like when it’s all back together:

The unusual thing about this oil seal (apart from the fact that it’s made by Honda) is that it rotates with the shaft and the coupling. So in theory it should last a long time.

Replacing The Drive Unit Oil Seals

The other seal in the coupling must never be re-used.

Update: the seal is Yamaha part number 93101-38086, but since Warren wrote this article it has become very hard to find. Fortunately it’s a standard size, easily available from many suppliers. The dimensions are:

  • Outside diameter: 50mm
  • Inside diameter: 38mm
  • Depth: 7mm

I got mine from Simply Bearings.

To remove this oil seal, you’ll need to take the 22mm coupling retaining nut off the centre shaft. This leaves you with a problem. As soon as you try to loosen the nut, the drive spins round. Yamaha recommend a special tool for this. There are 2 ways to solve this if you don’t have the special tool.

Option 1 – Make A Special Tool (Warren’s Method)

All you need is a jubilee hose clip that can open up to 70mm and an old 13mm spanner (check the final drive back plate retaining nut size first). Cut the spanner leaving the ring key end with 60mm from the end to the cut end, and then weld this end on to the clip end on. You will need to weld it at a slight angle so that the ring end spanner will fit on the retaining nuts while the clip goes round the rear wheel drive gear on the back of the final drive. It should look like an overgrown ring spanner when you’ve finished.

You can then use this to hold the gear while you remove the coupling shaft nut.

Option 2 – Use An Impact Gun

The title says it all really. If you have an air impact gun (or one of the electric equivalents) then the coupling retaining nut will come off easily and you can use the same technique to put it back on when you are finished. Obviously not everyone has access to an impact gun, but on the other hand Warren’s technique needs a welder and not everyone has one of those either.

Take note of the order the washer and spacers come out. They must go back in the same order. This is what “preloads the bearing”. In other words, it puts pressure on the bearing to its journal, so they wear correctly with no free movement.

If you give the coupling a wiggle, then it’ll come away. A gentle tap with a rubber or hide mallet should do it. This will expose the outer seal which can be picked out with a hook, or carefully stabbed with a screwdriver, avoiding the landing area behind it.

This landing area will need to be spotless, so be very careful to remove any excess rust with a 1200 silicon wet and dry paper, and a little soap. Don’t press too hard though as this will create hi-low spots.

It would be crazy not to check the bearing condition at this point, and a gentle tap on the centre of the coupling shaft with a copper or rubber mallet. If you hit the centre too hard, and then it’ll put pressure on the centre race and cause damage to the journals.

Gently push the new seal home using the old seal to protect it and a drift, like a large sized socket or similar. It looks odd when it’s in place – like it’s high – so watch for this. A little smear of Petroleum Jelly will help. It’d be an idea to mark round the rim of the old seal before you take it out so you know it’s all the way home.

Replace the shaft and bearings and check that it seats against the seal nicely. Replace the back o-ring on the drive coupling. Renew the prevailing torque nut, and torque as per manual recommendations and insert back into the drive with the original shims and two nuts to hold it. Put the drive on the back wheel and jam it with a suitable soft drift to get the torque needed.

Replacing the back seal

Remove the rear cover plate using a 13mm socket or spanner and very carefully prise out the back plate.

It’s quite tight, and the aluminium is easily damaged, so take great care. There is a seal on the back plate which is easy enough to replace, and only costs about £2 from bearing seal manufacturers. Hook the seal with a hook and pull it out, or stab it with a screwdriver. Be careful again not to damage the seating area as this will affect its ability to prevent oil loss.

Once this seal has been renewed, lay the plate aside and inspect the inside of the drive unit for damage. There is a guide to acceptable gear wear patterns in the final drive book. Check this out before you go any further. Now carefully lift the main gear out of the drive. BEWARE. There are shims at the back of the pinion.

It is important that they go back the same way round that they came off as the pinion bears on this so it’ll be worn in.

Very carefully lay this on a soft cloth. Check the condition of the rear bearing shaft. If there’s any damage to this, you need to consider a second hand drive.

You can have it welded and reground, but you are in danger of destroying the case hardening on the gear and shaft.

Now look into the bearing itself. The rollers should be totally unmarked and matted at worst, but better shiny. If it’s pitted, blued, brown, or anything else, it needs to be replaced. If it does, there’s a long convoluted procedure for re-shimming the drive unit. You need to hope that it’s fine. The bearing is attached to a sleeve that appears to be pressed into the drive casting from the opposite side. It is.

Drive sleeve with bearing pushed up:

This sleeve also holds the back seal and bearing in place. It is actually easier to get this out than you think. I used a deep reach ½ inch drive 13mm socket, with an old extension bar in it and a rubber hammer. It needs to be knocked into the drive. With the sleeve, will come more shims, the bearing and the seal at the back of the shaft.

Normally you wouldn’t attempt to re-use a bearing that you’d knocked out, but this one will come out with the pressure on the OUTER race. Damage to most bearings will occur if the inner race is struck at all. It’s a parallel roller bearing where the others are tapered roller bearings.

Replace this seal and clean out the area behind the bearing with a lint free cloth. Gently tap the seal into place using the sleeve and the bearing until it’s all the way home.

Bearing removed:

Put everything back together rubbing a small amount of petroleum jelly on the new seals, and replace the o-ring on the back plate. Be very careful to put back all the shims exactly as you found them. If you renew anything other than a seal, you will have to set up gear lash as per the shaft drive manual.

If you don’t, the drive will whine, and wear prematurely. You have been warned!

Renew the oil with the recommended grade, the best you can afford. Hopefully what you have done is given the drive another 30 years of life.

Once you’ve renewed all the seals, it’s a good idea to paint the unit, so it looks as good as it performs. Always makes you feel better if something is shiny. You feel like you have achieved something.

I used Hammerite, smooth silver, which doesn’t need a primer apparently. However, I would recommend that you at least clean the whole drive with cellulose thinners. That way the paint will take much better.