Five Speed Gearbox Conundrum

[Old Jock]

So I wrote a little write up on stripping and rebuilding the 5 speeder.

Now I'm asked a question that's got me stumped and need some help

On the end of the output shaft after the double row bearing but before the speedo worm drive in my box I had (in order from bearing to worm drive) thin washer or shim, O ring, support washer

So I get asked about the thin washer and see as was pointed out to me that its not in the parts book.

Can anybody enlighten me with an answer to 2 questions

1) For those that have stripped their boxes, was the thin washer there or was mine a one off

2) For the Gbx Gnus, what does it do and how critical is it?

John

[JoeW]

In the V7 Sport parts book it shows part number 14 21 73 00 "shim" just in front of the speedo drive gear. I'm sure it controls placement of the speedo gear. Not sure what would happen without it. It only comes in one size so, there is no adjustment.

[mtiberio]

I don't recall the thin washer, perhaps someone was doing some custom shimming to tighten up a box.

[sib]

Perhaps you can all be a bit more helpful by indicating the year and model of the bikes you are talking about.  Maybe some year/model combos had a shim and some didn't.  FWIW, I also have a "V7", but it doesn't have a shim or a speedometer drive in the 5-speed gearbox, since it has an electronic speedometer that gets its signal from the rear wheel.

[Dick]

The shim and o-ring were an update to the five speed, but I don't know the year of the update? The thin washer basically keeps the 0-ring trapped in place. That's my thought, anyhow.

[Old Jock]

The 5 speeder boxes were pretty generic, but to answer your question Sib, this particular box was on an LM 1000 or 5 as its known, the LM 4's were I believe identical. My bike was a 92.

I think that JoeW is referring to the original V7 that is the bike produced from 72 onwards

https://www.youtube.com/watch?v=SIVItTmetrI

Dick

That is very useful thank-you

John

[charlydaytona]

Thanks for posting this up John. I have just realised that I have a login. I emailed you.

Just some background as to why I ask the question.

I have rebuilt the gearbox for a T3 from 1979. Everything is in order but got a bit confused about this little washer. I have stripped this box before back in the mid 80s when the large spring on the input shaft decided to crack..anyway..I only ever remember the 'o'ring between the worm wheel support washer and the big double race bearing.

Now I have also got a gearbox from a 1984 LeMans 1000 (IV)..this also does not have the washer.

I did have a thought a bit along the lines of the shimming idea mentioned above..the actual worm wheel sits pretty deep in the oil seal on the output shaft..perhaps adding a thin washer has allowed the worm wheel to sit a bit better against the oil seal? Just thought and a pretty wild guess to be honest.

Also just as an added piece of interest when I stripped the LeMans 1000 box down I discovered that someone had actually removed the large shock (belleville spring) from the input shaft and welded the gear and the hose (as they're  referred to in the parts list) to the shaft, so that in effect it was one solid piece. Maybe this is what has been causing all sorts of issues with pinion wear and maybe extremely harsh clutch engagement? Dunno..just another thought really.

Charlie

[Vasco DG]

The thin shim is purely a register to help crush the o-ring and help it seal. Like many things that occur in the design/upgrade timeline with Guzzis it shows a degree of prescience for upcoming models as in reality it is fairly redundant on the Tonti and Loop framed bikes. It was installed on the five speed on the last of the machines before the introduction of the spineframe.

On these earlier models if there is a slight weepage up the shaft it is of little or no consequence as any oil lost will simply go into the UJ cavity where it will help keep the seals on the trunnions moist and pliable. Loss will be negligible as the gearbox isn't pressurised, in fact up until the 850Tvi don't think there was an o-ring even!

With the advent of the Spineys with their exposed driveshaft any leakage would lead to unsightly dribbles down the back of the box. Hence the need to ensure better sealing and the addition of the register shim. With it in place the o-ring gets squeezed uniformly rather than only in segments by the 5th gear engagement splines on the output shaft.

Pete

[Old Jock]

Many thanks Pete

I was hoping you or Charlie would chime in giving the chapter and verse.

That pretty much puts it to bed

Thank you to all who were kind enough to reply

John

[Kiwi_Roy]

John,
       I just pulled mine apart with your tutorial in hand (thanks for that), I see that washer
Is it just there to fling the oil off rather than have it creep along the shaft?

[Old Jock]

Its not an essential Roy

Think from Pete's description it just helps seat the O Ring that's all

Glad to have been of some use  ;)

John