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Author Topic: Are the speedometer gearboxes rebuildable?  (Read 3430 times)
markb
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« on: January 16, 2012, 12:13:09 PM »

I'd like to take one apart and clean and regrease it.  Has anyone ever done this?  It looks like there is a set screw that holds a cap on the end opposite where the cable goes in.  Also are the seals obtainable?
Mark
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Mark B
1969 CB750 sandcast #97 current project Restoration thread link
1969 CB750 sandcaxt #576 next project
1969 CB750 sandcast #1553 next project after that
1969 CB750 sandcast #1990 next project after that
1969 CB750 sandcast #5383 Sold Restoration thread link
1970 CB750 K0 restored
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Steve Swan
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« Reply #1 on: January 16, 2012, 01:07:11 PM »

Yes, the speedo drives are rebuildable.  First, remove the large circlip to remove the main ring gear and thin thrust shims.  Remove the tiny (brittle brass) set screw to remove the (tiny splined) end cap/plug.  The length of these splines on this cap is about 12mm, sometimes the cap can be pretty stubborn to get out.   I made (in the lathe) a small tool from a piece of rod acting as a combination drift/guide that slips over the drive spade that i use to gently tap out the drive gear.  You'll have to drill a hole in this piece of rod you're making the tool from.  Drill the hole a little longer than than the length of the spade so the tool can go "home" against the main part of the drive gear.  (The o.d. of this tool will slip down past the seal, against the drive gear.  To remove the cap, i clamp the drive in my brass jawed vise.  Then i mildly-moderately heat the end where the cap is, and genty tap the end of my tool, which will drive out the end cap, followed by the gear.  A word of caution, the drive spade is long and can be easily broken, without using some sort of tool to act as a drift/guide.  I don't suggest tapping on the spade nor do i suggest trying to remove the end cap with pliers (you can figure out how i know this..!)  A SPECIAL NOTE:  **all end caps are not the same!!**  Earlier end caps are a different diameter than later end caps.  I don't know what vin these end cap diamters were changed.  IF i recall correctly, both the visible part of the end cap and the splined part that slips in the drive are different diameters.  I source the seal from our local bearing store.

If you have a spare drive of a later model, you might familiarize yourself with the above procedure on a drive box you don't have as much affection for as the drive box on #97.... !
« Last Edit: January 16, 2012, 03:58:24 PM by Steve Swan » Logged

Steve Swan
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« Reply #2 on: January 23, 2012, 03:13:30 PM »

Mark, did you get your drive apart ?
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« Reply #2 on: January 23, 2012, 03:13:30 PM »

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markb
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« Reply #3 on: January 23, 2012, 03:43:16 PM »

I haven't yet.  I was waiting for your reply.  Wink  Cheesy Actually I'm still trying to get all my plating ready but I have picked up the gearbox a couple of times and looked at it.  I was halfway there with a procedure and your excellent description should get me all the way.  I do have a spare drive that I will practise on plus I've got the ones of 97 and 1553.  Both of them feel pretty stiff which is why I was thinking of at least trying to regrease them.  When I work on them I'll take some pics and note any differences. 
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Mark B
1969 CB750 sandcast #97 current project Restoration thread link
1969 CB750 sandcaxt #576 next project
1969 CB750 sandcast #1553 next project after that
1969 CB750 sandcast #1990 next project after that
1969 CB750 sandcast #5383 Sold Restoration thread link
1970 CB750 K0 restored
2010 H-D Tri Glide Ultra Classic (Huh?)
markb
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« Reply #4 on: May 14, 2015, 04:06:50 PM »

I canít believe itís been over three years since I was looking at my speedo gearboxes.  Shocked  With a little prodding from Steve I finally tore into them and yes, they are re-buildable.  I have four and figured I might as well rebuild all four at the same time.  I could hardly move two of them, including the one from #97.  Hereís the one from #97 all apart.


First I removed the big seal.  Then there is a retaining ring.  This was a little tricky since itís only a wire.  I held against one end of the ring with a small screwdriver and got under the other end with a dentist pick and carefully worked it out.  Then I removed the gear.  There is a washer on top and two shim washers on the bottom.  Next I removed the set screw that holds the cap in.  Itís an M4 and itís only about 4mm long so not very big.  Of course the screws came out easy except on #97.  I think it was recessed a bit more than the others and because there was a slight taper on the sides of the screwdriver it didnít engage completely and stripped out the slot. 

Time to get creative again.  I picked up a 1/16Ē diameter left hand drill.  Plan A was that it would bite into the screw enough to back it out.  Iíve had that work on screws that werenít in very tight but not this time.  Plan B was to tap a little square end driver into the hole and back it out.  Fortunately that worked.

Now to get the end cap off and remove the worm.  The diameter of the flange on the end cap was just under 11/16Ē so I drilled an 11/16Ē hole in a piece of bar stock so I could support the housing while I tapped out the worm and cap.  Against Steveís advice I did pound on the end of the tang.  Partly I was feeling lazy and partly I wasnít sure what Steve did.  I used a piece of 9/16Ē diameter stock which is just under the diameter of the hole so it helped me keep the force centered on the shaft.  Plus I was careful and didnít hit very hard. 


Hereís a picture of my support ring and a removed end cap.


With the knurling on the cap they definitely werenít go to fall out and it almost seems like the set screw is overkill.  Make sure if youíre rebuilding more than one gearbox that you keep the caps with the housings they came from, because of the knurling, so that the holes line up.


So once the end cap is off the worm can be removed.  There is a washer that goes between the worm and the end cap.  To remove the small seals I just drilled a small hole in them and screwed in a small sheet rock screw and they pulled right out. 

Now for the good part.  There are differences in the early and later gearboxes.  Stay tuned for my next post.  Wink
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Mark B
1969 CB750 sandcast #97 current project Restoration thread link
1969 CB750 sandcaxt #576 next project
1969 CB750 sandcast #1553 next project after that
1969 CB750 sandcast #1990 next project after that
1969 CB750 sandcast #5383 Sold Restoration thread link
1970 CB750 K0 restored
2010 H-D Tri Glide Ultra Classic (Huh?)
Steve Swan
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« Reply #5 on: May 14, 2015, 04:22:08 PM »

COOL !

I knew i remembered differences in the gear boxes ! 

Now i can hardly wait to hear what they are !
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markb
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« Reply #6 on: May 18, 2015, 01:32:18 PM »

Sorry for the delay but here are the differences between early and later gearboxes.  I have four to compare: 97, 576, 1553 and an unknown (possibly diecast).  All of the later units appear to be identical except for the numbers stamped on the housing.  In the pictures below the #97 parts are on the left.

One difference I was able to find on the outside (besides different stamped numbers) was the rib at the 6:00 oíclock position as shown in this picture.  The rib is wider on #97.


Internally the housings are not the same.  The hole in the cable input end is the same but it is different on the cap plug end.  The #97 cap hole is 13mm diameter and the later ones are 15mm diameter.  The diameter of the head on the plug is the same at 17mm.  Also notice the flat area near the cap end on what would be the inside of the housing on #97.


Hereís where it getís interesting.  Even though the hole in the #97 housing is smaller, the worm is bigger.  The worm on #97 is 12mm outside diameter and on later units it is 10mm diameter.  This means that there isnít as much clearance between the inside diameter of the housing and the outside diameter of the worm.  Maybe it was changed to allow for more room for grease.


Since the worm is bigger it makes sense that the gear would be smaller since the centerline to centerline dimension appears to be the same.  The #97 gear is approximately 39.6mm diameter and later ones are 40.8mm.  Notice the little slot on one of the tangs on the later gears.


The teeth on the gear look very similar.  I thought there may be a different ratio but both early and late gears have 26 teeth.

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Mark B
1969 CB750 sandcast #97 current project Restoration thread link
1969 CB750 sandcaxt #576 next project
1969 CB750 sandcast #1553 next project after that
1969 CB750 sandcast #1990 next project after that
1969 CB750 sandcast #5383 Sold Restoration thread link
1970 CB750 K0 restored
2010 H-D Tri Glide Ultra Classic (Huh?)
Steve Swan
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« Reply #7 on: May 18, 2015, 09:31:09 PM »

Great stuff !!!!  BRAVISSIMO !!!!  232 has this very same drive.  these early vins are chock full of neat stuff.
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Steve Swan
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« Reply #8 on: May 18, 2015, 11:56:49 PM »

Definitely one that can go in to "Distinctions."
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markb
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« Reply #9 on: May 19, 2015, 07:21:54 AM »

Another observation I made is that there doesn't appear to be any kind of finish on the housing.  No paint or clear coat - just polished.  Has anyone seen anything else?
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Mark B
1969 CB750 sandcast #97 current project Restoration thread link
1969 CB750 sandcaxt #576 next project
1969 CB750 sandcast #1553 next project after that
1969 CB750 sandcast #1990 next project after that
1969 CB750 sandcast #5383 Sold Restoration thread link
1970 CB750 K0 restored
2010 H-D Tri Glide Ultra Classic (Huh?)
markb
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« Reply #10 on: June 08, 2015, 04:05:44 PM »

I forgot to mention the seals. 

I found a Honda replacement for the small one.  It is part number 91256-623-003.  The dimensions are 4.8 x 15 x 4.  At first I thought it was the same as the seal for the tach cable in the valve cover.  That one is 4.8 x 14.5 x 4.

I couldn't find a Honda replacement for the big one.  It is an NOK seal part number TC 34 48 7 Y1.  It is a double lip seal with dimensions 34 x 48 x 7.  I couldn't find a place to buy the NOK domestically but found an equivalent.
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Mark B
1969 CB750 sandcast #97 current project Restoration thread link
1969 CB750 sandcaxt #576 next project
1969 CB750 sandcast #1553 next project after that
1969 CB750 sandcast #1990 next project after that
1969 CB750 sandcast #5383 Sold Restoration thread link
1970 CB750 K0 restored
2010 H-D Tri Glide Ultra Classic (Huh?)
markb
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« Reply #11 on: June 09, 2015, 04:41:17 PM »

Seal update:
I tried order the small seal using that Honda number and it is NLA.  When I find a valid number I will post it.
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Mark B
1969 CB750 sandcast #97 current project Restoration thread link
1969 CB750 sandcaxt #576 next project
1969 CB750 sandcast #1553 next project after that
1969 CB750 sandcast #1990 next project after that
1969 CB750 sandcast #5383 Sold Restoration thread link
1970 CB750 K0 restored
2010 H-D Tri Glide Ultra Classic (Huh?)
Steve Swan
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« Reply #12 on: June 09, 2015, 05:55:25 PM »

thanks Mark.  i know i replaced 232's seal, i can't remember where i got it, had to be through our local machine supply store.  shoulda written this stuff down...
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markb
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« Reply #13 on: June 10, 2015, 07:45:22 AM »

91256-240-003 should be a good Honda number for the small seal.  If that doesn't work you should be able to find an equivalent using the dimensions of 4.8 x 15 x 5.
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Mark B
1969 CB750 sandcast #97 current project Restoration thread link
1969 CB750 sandcaxt #576 next project
1969 CB750 sandcast #1553 next project after that
1969 CB750 sandcast #1990 next project after that
1969 CB750 sandcast #5383 Sold Restoration thread link
1970 CB750 K0 restored
2010 H-D Tri Glide Ultra Classic (Huh?)
Sgt.Pinback
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« Reply #14 on: October 03, 2017, 05:22:36 AM »

In first parts list (04-1969) there is a srew on the speedo gearbox.

Are those the very fist gearboxes and if so, until which VIN was it used?
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Cheers, Uli (Leonberg, Germany)
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