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TR2/3/3A TR3a spedo drive

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ekamm

ekamm

Jedi Warrior
Offline
I've been planning my winter projects for some time now and one of the items is to get my speedo working. When I got the car in July '09 the speedo cable was not attached to the tail housing and in the place where it would attach was a blanking plug of sorts.
tach001.jpg

At that time I asked everyone what the deal was and got some different responses. Someone offered me the speedometer drive piece that is missing. At that time I didn't pursue it as I wasn't in the position or knowledgeable enough to feel confident to tackle it. I now am ready to take it on and wonder if anyone has an extra drive from an old tranny that they could part with? I still won't know about the drive gear that I assume is on the transmission. I've looked at the parts breakout but can't identify the gear that drives the speedo drive gear.(if that makes sense)
 
Sorry, no speedo drive, but as far as what drives it, it's a worm gear cut into the main shaft. If you look here, part #11. A little to the left of where number 11 is pointing to, is the worm gear.
 
So then the # 72 screw is a part of the speedo setup?
 
Not anymore than the rest of the tranny. You must also look at the external gearbox page, parts 70->75. Art is showing what actually drives the gear.
 
I see that, and I've looked at the external gearbox breakout. That is what I need and have none of. most of which is N/A according to the catalog. The worm that I assume you are talking about is in the center of the mainshaft in this drawing, and as far as I can tell the cable attaches at the tailhousing? Anyone have a pic of yours attached?
 
What are the chances of the worm gear being damaged. The deal is, that this was my dad's car and I don't know why the drive gear is missing. But he always used some shade tree guy that did some work on lbc's, and I have to assume that there was a problem that he either didn't want to pay a lot for or the part wasn't available at the time. How will I know other than installing and drive it?
 
ekamm said:
What are the chances of the worm gear being damaged. ... How will I know other than installing and drive it?
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Well, that, of course, would be the proof... But, the worm gear on the shaft would be the most robust part. Odds are more likely that the drive gear is the part that broke years ago. I'd say that it's worth snagging an eBay drive gear assembly and installing it. Then turn things over by hand for a few revolutions. If you encounter any terrible resistance while doing that, stop. Then you'll need to go into the tranny and see what's going on with your mainshaft. If, as I think is more likely, it works -- then you're good to go. You need the part anyway, so get one. Just try not to break it...

There's more to speedo problems than the stuff you're looking at now. If the speedo hasn't been driven in years, it may have some problems, too. Before you put in a cable and run it, try the speedo by hand, too.
 
Seems unlikely to me that it would be damaged as the shaft is both larger and harder metal than the driven gear; but I find that plug puzzling. I'm wondering if that gearbox didn't come from some other application, that had the speedo takeoff somewhere else (not that I know of any such application).

Is the hole for the setscrew there?

You might be able to look down the hole while shining a light in there, but I'm guessing the only way to really tell is to poke a driven gear in, and see if turning the shaft also turns the gear. Or just remove the tail housing.
 
martx-5 said:
Edit: BTW, there's one on e-bay right now.
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Phew! Lotta money for that, especially since the description is not accurate. TR3/4 never had a 3.89 ratio, it was 3.90 (10 teeth on the pinion, 39 teeth on ring gear). Plus, even when the optional 4.1 was fitted, the driven gear for the speedo did not change. Any adjustments for diff ratio, tire size, etc. were taken at the speedo head. The speedo cable always turned at 2/5 of the output shaft speed (until 73 TR6).
 
I am pretty sure that there as never a change in the housing or gearbox. I have looked at and compared the tailhousing to a friends 3 and they are identical. Where is the set screw hole supposed to be. I have spun the cable end (after cleaning and lubing) and the speedo moved easily so I'm hoping that that part is good.
 
Ya seemed like a fair amount of money to me as well. That's why I thought some one might have a spare.
 
ekamm said:
Where is the set screw hole supposed to be.
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Here is a shot that shows (barely) the head of the set screw. You can see the speedo drive sticking out below it.

DSCF0004.jpg


I could probably part with one, but the way things are going, it would probably be Thanksgiving before I could dig it out and get it shipped. If that works for you, drop me an email.
 
Mine is non-OD, I should have said that to start with. I assume that that would make a difference.
 
Yes, I realize you don't have OD. In spite of the switches visible, the above photo is a non-OD box as well. It just has an OD top cover for some odd reason.

The speedo takeoff with OD is similar, but mounted on the other side and at the rear of the OD. You can see it in this shot from the Buckeye Triumphs site

TestStand.JPG
 
I don't see any setscrew like the one you show but I will have to look at the car later. I assume that the screw hole will be perpendicular to the drive gear shaft, and it's purpose is just to ensure that the assembly doesn't come loose.
 
Ok I crawled back under today and took a few more pics after cleaning up a bit. There is no sign of any set screw and as I look at what is a thin metal cap I wonder how I'm gonna get this sucker out. There isn't any lip that I can see.
Picture006.jpg

Picture011.jpg
 
Here is another.
Picture013.jpg


The second is a pic of a club members 3a tailhousing. it looks very similar to mine but he has an O.D.
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Hard to really tell anything from those shots, as the hole for the setscrew would be on the other side of the protrusion above the hole with the plug.

To remove that type of plug normally involves destroying it. One way is to drive a screwdriver or punch through and pry it out; or I have seen purpose-made pullers that use a big screw through the center of the plug. If you Google for "Freeze plug removal", you'll find lots of suggestions.

BTW, not sure if the wrong photo got posted or what, but that second shot is NOT of an overdrive. The body of the overdrive replaces the entire rear housing of the non-OD transmission; that is clearly the non-OD housing. The OD sticks out beyond the body of the gearbox, that location would be covered by the solenoid bracket/accumulator cover. As I mentioned before, with OD the speedo drive moves to the other side (and back about a foot to the output of the OD).
 
I could have been wrong about the O.D. The gearbox housing was different I was thinking he said it was O.D. The car was on a lift and I too the shot to see his setup for the speedo drive. I have the pics on my home computer and I'll poke around a little more this evening. So the set screw hole should be facing up to ward the floor of the car?
 
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