90 Speedo failure

[albervin]

My speedo "died" on Sunday. 12,568 miles. I was attempting the longest ride on the 90 Deluxe in the 18 years I have owned it. One really big hill and several smaller ones. Max of 54 mph was obtained, briefly. Anyway, the worm drive is sheared and there are nasty marks on the drive gear. The cable also sheared at the speedo head.  IF I can obtain a new worm drive (suggestions please) how do I extract the old one? I see a tiny grub screw but I couldn't pull out the gear using the cable. So, I need to remove old worm gear and buy new inner cable, worm gear and possibly drive gear. The bike is virtually original from new and I hate it when these things happen 

[slawsonb]

Can't help with the parts, but wanted to offer condolences. My '68 GTR has had several original parts fail. Just wish we could make them last forever.
...bert

[disc_valve]

   REPLACEMENT OF BRIDGESTONE SPEEDO DRIVE GEARS

   One weak point on Bridgestone singles is the speedometer drive in the front brake plate, which has been known to strip gear teeth at quite low mileages. Bridgestone originally only listed the large speedo gear as a spare part, which was pretty useless by itself since the smaller pinion in the brake plate was usually damaged at the same time.

   In recognition of this, Bridgestone did produce a speedo drive repair kit for a short period, consisting of the small pinion, bearing bush and thrust washer to fit the brake plate. Unfortunately this kit was never produced in large quantities and is, to the best of my knowledge, unobtainable now.

   There is, however, an alternative to searching for another BS brake plate   which may not have a good speedo pinion in it anyway. Instead, you need a set of speedo gears from an early Honda lightweight. I have used Honda C100 and early C50/C70/C90 speedo gears to fix my own bikes, so I know that they will fit. Honda step-through models built after the late 1970s, however, used a much longer pinion which will definitely not fit the BS brake plate.

   Suitable used Honda brake plates are, however, still quite common and are almost certain to contain a good speedo pinion, but if you can’t find a large speedo gear to go with it you may have to order this from Honda. If you use a C70/C90 speedo pinion (with 8 teeth) the matching large gear is Honda part number “44804 096 000”. (Note, however, that some other small Hondas use speedo pinions of identical dimensions but with 9 teeth, These will need a different matching gear for which I don’t know the part number).


   Once you have obtained a suitable pair of Honda speedo gears, the transplanting process is quite straightforward. The small pinion will lift out of the Honda brake plate once the outer bush/cable union has been removed. The union is, however, cast into the alloy brake plate during manufacture and you will probably have to destroy the donor brake plate to remove it. Once the Honda pinion is out, put away the hammer and chisel and turn your attention to the Bridgestone brake plate.

   First, remove the small 3mm grub screw which holds the brass outer pinion bush into the BS brake plate, and pull the bush out of the brake plate. The bush may be tight, but it is only a push fit and you should be able to gently drift it part way out from inside the brake plate. Once the bush has started to move, an old speedo cable end screwed onto the cable union end will give something to grip on and pull. The small pinion will now lift out along with a small thrust washer. Temporarily replace the outer pinion bush and check that the large Honda gear drops onto the spigot in the centre of the brake plate and revolves freely without fouling the brass pinion bushes. The problem here is that the Honda gear is slightly larger in outside diameter than the Bridgestone gear, and it may be necessary to relieve the edge of the brass bushes in the brake plate to provide clearance. Once you are satisfied that the large speedo gear fits properly and rotates freely, remove it and the outer pinion bush from the brake plate. Now transfer the small thrust washer from the old pinion onto the new Honda pinion, then grease the pinion and fit it to the brake plate along with the BS outer pinion bush (not forgetting to replace the 3mm grub screw to lock the bush in place).

   Now we turn our attention to the large Honda gear. This gear comes complete with a connector plate pressed onto it, which needs a little adjustment to allow it to work with the Bridgestone hub. The ears on the connector are slightly too wide apart and need to be bent inwards slightly until they match the drive slots in the wheel hub. Once the gear connector plate has been modified, push the large Honda speedo gear into place on its spigot in the brake plate. If the gear pushes fully home at this stage, meshes correctly with the pinion and rotates freely, all that remains is to liberally grease the speedo gear and pinion and refit the wheel.
 

   You will, however, probably find that the large gear cannot be pushed fully home yet, even though you are certain that it fitted properly before the small pinion was in place. If so, you should prepare yourself for some unusual engineering. The next part sounds like a bodge, but I can assure you it does work (although I wouldn’t recommend trying it in a more highly loaded gear application). You will need a small glass container with enough battery acid to fully immerse the large gear.



   REMEMBER:  BATTERY ACID IS NASTY STUFF!

   DO NOT allow it to come into contact with your mouth, eyes
   or clothing.

   Wash your hands thoroughly after handling the acid.

   After use, dispose of the old acid properly.


   Lever off the connector plate from the large Honda gear, mask up the gear by covering it in grease all over except for the actual gear teeth, and then drop it into the acid bath. The acid will slowly etch away material from the exposed surface of the teeth. Remove the gear after 10 minutes, rinse it thoroughly under the tap and try it for fit. If the gear and pinion still won't mesh, drop the gear back into the acid for another 10 minutes. On my BS90 it took about 40 minutes in the acid bath before the gear would fit properly. If the gear will not push fully home with finger pressure, it is too tight and you must continue with the acid etch.

   Once the gear has been etched away sufficiently to fit, wash off all traces of the acid and dry it thoroughly. Then refit the connector plate and liberally grease both the large gear and the speedo pinion. Push the large gear fully home in the brake plate and refit the wheel to the bike. Don't worry if the wheel still feels a little stiff to turn at this stage. As long as the wheel can be spun by hand the gears should bed in after a few miles and then run smoothly.


   Depending on which set you choose, the Honda speedo gears may have a slightly different reduction ratio to the original Bridgestone parts. In the worst case, the speedometer will read about 5% slower after the repair, but this is barely noticeable on the road and may mean that the reading is actually closer to the true road speed. On the plus side, the Honda gears are far more robust, with the added benefit that replacements are more easily available should the speedo drive eventually fail again. I have used a set of C100 gears in my BS90 now for over 15,000 miles with no problems, and have have just fitted a set of C90 gears to the front wheel of my BS100 after an “in flight” failure of the original Speedo drive.

[disc_valve]

Hi, Albervin,

My previous post is a copy of a note I made some whhile back about replacing speedo geasr on the BS90. I'm not sure if original BS90 speedo gears are still available (check with Richsrd - site owner), but if you can track down one of the old Honda C50/C70 or C90 brake panels, then that's a way out of your problem. Note that the later model small Hondas from 1980 onwards used different set of speedo gears, and these  definitely won't fit.

You are right that the little grub screw hiolds everything into the brake panel. You need to remove the screw completely, not just loosen it - it goes into a small hole in the brass cable fitting. If the brass bit won't pull out easily, it's probably rusted in place. You could fit an old cable end to the brake plate fitting, grab it in a vice, and pull on the brake plate until the veins stand out on your forehead. If that fails, try tapping a small wedge into the gap between the cable fitting and the small speedo pinion, inside the brake plate.

I used this repair method years ogo on both my 90 Deluxe and my 100TMX. and it's lasted well.

   
Hope that helps,

Graham


 

[CL-100]

Would this work as a replacement?

[albervin]

Thanks for the great replies. I have already wrecked a speedo cable trying to pull out the old unit. Those speedo gears look the business CL-100, are they for sale? I am in NSW, Australia. It would be nice to get the bike back to full working order as I hate having things nearly right.

[CL-100]

It's for sale on ebay in the US.  The seller is in Taiwan and will ship anywhere.  All I did to find it was to open ebay and type into the search box:  Bridgestone 90 100 speedometer pinion gear

It was the first thing that came up and there were a few used items there also.  There were 2 sets of the new item for sale.

Good Luck.  Let me know if you need help to locate it.  I can send you a link in regular email if that's easier.   

[CL-100]

Actually, the seller is in Thailand, not Taiwan.  My mistake.

[albervin]

Thank you. One way or another I think I may have the problem licked. Much appreciated.