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#612839 - 08/13/15 11:23 pm Gearbox Conversion Longshot (don't flame) or???  
Joined: Sep 2008
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Mike Cornwall Offline
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Los Angeles, CA
I started having trouble with the gearbox on the 1978 T140V, got it open and found that the needle bearing at the back of the layshaft (?) spilled its guts and ate up a lot.

I'm trying to stay upbeat, anyways looking around for a new set of gears I can see this will cost plenty. I always liked the feel of the 4-speed better, and I might just go that way but....

Looking online it's impossible not to see perfect gear clusters from modern Triumphs at very low prices, for what looks like good equipment. The crazy idea started to work its way into my head, "could a unit twin gearbox be modified to run a newer set of gears?"

I know already this sounds totally absurd and I expect to catch some grief about it, but I think it's a fair question, if a bit naive-sounding. Has anyone ever tried it?


1972 Tiger 650
1978 Bonneville 750
1968 Victor 441
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#613008 - 08/15/15 8:42 am Re: Gearbox Conversion Longshot (don't flame) or??? [Re: Mike Cornwall]  
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bon Online content
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I think the possibility of a hinkley triumph gearbox fitting a meriden triumph is probably nil. Bloor wanted as much clear water between his products and their meriden predecessors.

#613086 - 08/15/15 8:19 pm Re: Gearbox Conversion Longshot (don't flame) or??? [Re: Mike Cornwall]  
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NickL Online content
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Power in - Power out positions for a start........ It may be worth while buying a complete engine/g'box assembly, robbing the box and selling the motor on.



#613091 - 08/15/15 9:21 pm Re: Gearbox Conversion Longshot (don't flame) or??? [Re: Mike Cornwall]  
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Zombie Offline
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It's time to step to the plate, and swing open that wallet.

I've been looking to upgrade a T120 4 speed to a late model T140 gearbox. 500.00 bucks seems to be the "magic" number.

It might be less expensive to find a blown engine at a salvage yard, and part out what you do not need. I'm pursing this right now. However the salvage guys know what time it is, and are pretty stiff on their prices...

My next big idea will be searching dormant volcanoes for a sacrificial T140 to calm the gods.
I can't find any volcanoes in Florida tho... Maybe Georgia has a few? (volcanoes)

#613112 - 08/16/15 5:05 am Re: Gearbox Conversion Longshot (don't flame) or??? [Re: Mike Cornwall]  
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Stein Roger Online content
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If distance between shafts are equal I'd be more than surprised. You're looking at a major re-engineering if they're not. Besides, the bearings are much bigger in the new box, there won't be material enough in the gearbox cover to fit them, so at new cover would have to be designed. At the clutch side you're basically screwed. Etc Etc.
Should you, by some extreme effort,make everything fit in there, you'd have to be prepared to change to RH side chain drive...
With that problem solved, you'd have to find a way to convert the primary from chain to gear drive, otherwise you'd have to deal with a 5 speed reverse. This is a modern cross over box, remember...
I suppose making a non-unit box might be feasible, but you'd still have to contend with the direction of rotation...
Verdict: NOT possible unless you really want to sink money into a bottomless pit.

Hth

#613214 - 08/16/15 5:20 pm Re: Gearbox Conversion Longshot (don't flame) or??? [Re: Stein Roger]  
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Mike Cornwall Offline
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Los Angeles, CA
Thanks Stein Roger, it was really just a question out of curiousity more than anything practical so your explanation is appreciated. We will see how things go.


1972 Tiger 650
1978 Bonneville 750
1968 Victor 441
#613280 - 08/17/15 2:57 am Re: Gearbox Conversion Longshot (don't flame) or??? [Re: Mike Cornwall]  
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Stein Roger Online content
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I know Mike, and I only answered since I've looked at it myself earlier! ;-)

#617393 - 09/14/15 4:12 am Re: Gearbox Conversion Longshot (don't flame) or??? [Re: Mike Cornwall]  
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Mike Cornwall Offline
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I ended up getting a set of '74 gears on a bidding site. They came with an inner gearbox cover for a right side shift, and I had an outer cover off a T120 so it was just a matter of changing the gear change quadrant over. I haven't put the primary together but I'm not 100% sure the indexing is right, will have to fight that again, I suspect. And plug up the crossover on the primary side.

In the meantime, I need to figure out how I'm going to move the brake to the left side. I think I have most of the parts to just make a mirror-reversed left side brake mechanism along the lines of the stock setup, use a T120 brake lever and weld a nut on the back of a hole in the drive side engine plate for the shaft to pass through. Mount the master cylinder to a tab welded to the passenger peg tubes, and run a long brake line (maybe add a brake light switch in that line) across and back to the caliper on the timing side. The only thing I can't picture with this setup is what the brake spring will catch on?

The other thought I had was to hook up the brake lever on the primary side in a similar way but run a steel bar from there to the stock location of that shaft and sprung hanger that actuates the master cylinder, leaving the MC where it was with the timing side brak. I thought maybe the bar could be tapped to thread onto the male threads on the inner end of the shaft. Does that make any sense?

My question is, has anyone seen good examples of the disc brake to primary side conversion? I'm open to cutting up a forward control kit, using all the stock stuff to make a new setup, whatever works. The bike is not stock looking, I'm just thinking about what will work well. Any advice is welcome, I searched the site and the web for photos but I couldn't find anything. TIA for any help!

Last edited by Mike Cornwall; 09/14/15 4:23 am.

1972 Tiger 650
1978 Bonneville 750
1968 Victor 441
#617442 - 09/14/15 11:42 am Re: Gearbox Conversion Longshot (don't flame) or??? [Re: Mike Cornwall]  
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AngloBike Online content
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UK Berks
I took a some images a year or so ago.
I found them on my computer but need to bung them onto a photo sharing site

The bike was a triumph - I think!

The cylinder was a nissin

#617454 - 09/14/15 12:53 pm Re: Gearbox Conversion Longshot (don't flame) or??? [Re: AngloBike]  
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Mike Cornwall Offline
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I'd really appreciate it, the one I'm using is a Brembo.


1972 Tiger 650
1978 Bonneville 750
1968 Victor 441
#617487 - 09/14/15 3:00 pm Re: Gearbox Conversion Longshot (don't flame) or??? [Re: Mike Cornwall]  
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DMadigan Online content
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For my R3 OIF I made rearset plates. The drive side has the master mounted behind the plate with a hard line running to the timing side.

If you want the disc on the left side, someone makes a caliper that fits over the sprocket that the chopped bikers like. As long as you do not lube the chain it should work well enough.

#617488 - 09/14/15 3:07 pm Re: Gearbox Conversion Longshot (don't flame) or??? [Re: DMadigan]  
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Mike Cornwall Offline
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Thanks DMadigan, that looks trick. Did you fabricate that linkage?


1972 Tiger 650
1978 Bonneville 750
1968 Victor 441
#617491 - 09/14/15 4:00 pm Re: Gearbox Conversion Longshot (don't flame) or??? [Re: Mike Cornwall]  
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DMadigan Online content
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Yes, I used a T150 shift lever for the brake lever and modified shift shaft to mount the lever onto. The inner arm has a keyway to lock it to the shaft.

#617518 - 09/14/15 7:20 pm Re: Gearbox Conversion Longshot (don't flame) or??? [Re: DMadigan]  
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Mike Cornwall Offline
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Mike Cornwall  Offline
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Shift lever/shaft is a great idea! so obvious!


1972 Tiger 650
1978 Bonneville 750
1968 Victor 441
#617564 - 09/15/15 6:58 am Re: Gearbox Conversion Longshot (don't flame) or??? [Re: Mike Cornwall]  
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AngloBike Online content
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#617597 - 09/15/15 11:22 am Re: Gearbox Conversion Longshot (don't flame) or??? [Re: Mike Cornwall]  
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Mike Cornwall Offline
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Anglo, thanks for those. I'm going to see about plagiarizing that for the brembo MC. Does having the reservoir tube on the bottom help bleeding or hinder it? I must admit, I can't tell from the Nissin logo if that MC is rightside up or not!!! LOL


1972 Tiger 650
1978 Bonneville 750
1968 Victor 441
#617599 - 09/15/15 11:29 am Re: Gearbox Conversion Longshot (don't flame) or??? [Re: Mike Cornwall]  
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DMadigan Online content
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The Nissin is upside down. Actually, they are more typically used vertical or nearly so. To bleed the cylinder will have to be rotated 180 so the reservoir pipe faces up.
This is an AP cylinder with integrated reservoir:

#617671 - 09/15/15 8:26 pm Re: Gearbox Conversion Longshot (don't flame) or??? [Re: DMadigan]  
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Mike Cornwall Offline
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That makes sense, thanks. I actually have a Honda enduro with that vertically mounted Nissin MC.

Let me ask, when I put the inner trans cover from the timing-side shifter on, I noticed this machined area and it occurred to me I might need something there. I'm talking about the oval area with the two tapped holes next to the shifter.





1972 Tiger 650
1978 Bonneville 750
1968 Victor 441
#617698 - 09/16/15 12:18 am Re: Gearbox Conversion Longshot (don't flame) or??? [Re: Mike Cornwall]  
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DMadigan Online content
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That is for the cam holding leaf spring used on '71?-'73? instead of the plunger in the bottom of the case. Some people have problems with it and replace it with the plunger.

#617699 - 09/16/15 12:23 am Re: Gearbox Conversion Longshot (don't flame) or??? [Re: DMadigan]  
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Mike Cornwall Offline
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I was like 95% sure it was for the leaf spring but I didn't want to not ask.


1972 Tiger 650
1978 Bonneville 750
1968 Victor 441
#618300 - 09/20/15 2:44 pm Re: Gearbox Conversion Longshot (don't flame) or??? [Re: Mike Cornwall]  
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Mike Cornwall Offline
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Mike Cornwall  Offline
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Los Angeles, CA
Expanding plug or freeze plug to block off the crossover passage?


1972 Tiger 650
1978 Bonneville 750
1968 Victor 441
#618325 - 09/20/15 6:17 pm Re: Gearbox Conversion Longshot (don't flame) or??? [Re: Mike Cornwall]  
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Stein Roger Online content
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Originally Posted By Mike Cornwall
Expanding plug or freeze plug to block off the crossover passage?


Not to be flippant Mike, but ? What passage?

We're still talking about the 78? Seems you have an earlier inner cover fitted, as the milled recess was indeed to fit the leaf spring. This was discontinued for the 73 season as I assume it didn't provide many benefits and proved a little troublesome on assembly and in service compared to the very sound original plunger design.

#618691 - 09/22/15 9:51 pm Re: Gearbox Conversion Longshot (don't flame) or??? [Re: Stein Roger]  
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Mike Cornwall Offline
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Mike Cornwall  Offline
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Los Angeles, CA
From my post 9.14.2015:

"I ended up getting a set of '74 gears on a bidding site. They came with an inner gearbox cover for a right side shift, and I had an outer cover off a T120 so it was just a matter of changing the gear change quadrant over. I haven't put the primary together but I'm not 100% sure the indexing is right, will have to fight that again, I suspect. And plug up the crossover on the primary side."

That's what I was referring to regarding an expanding plug or a freeze plug.


1972 Tiger 650
1978 Bonneville 750
1968 Victor 441
#618717 - 09/23/15 5:30 am Re: Gearbox Conversion Longshot (don't flame) or??? [Re: Mike Cornwall]  
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Stein Roger Online content
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Ah Mike, I get it now. Sorry I didn't catch that. Yes I guess a plug here would be needed.

Have fun, SR


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