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PostPosted: Thu Sep 28, 2017 11:37 pm 
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Make sure you have the right parts as all looks the same but is not. Count the teeth of your reverse gear and compare. There are for the 1850 single rail two ratios.

Jeroen

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PostPosted: Sat Sep 30, 2017 2:51 pm 
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Yes you can fit a 1500 dolly bell housing to an 1850 box but the input shaft would need to be modified to allow use with the
1500 engine. Its not the correct length as is...

There are also 2 flavours of 1500 bell housing....one goes with the scroll type of seal and the other for the sprung rubber conventional seal.
They also have an input shaft to match accordingly.

This is a very useful bit of kit for us spitfire 1500 owners as it means you can use the close ratio dolomite gears with the Spit 1500 engine and make a much nicer spit.

On the dolly 1850 internals the reverse ratio goes with the layshaft and must match. 1500 one is different but would work with a TR7 4 speed layshaft which have the same ratios as an 1850 but the different reverse. Ive built up a few boxes with TR7 layshafts like this as the dolly one is about 3 times the price.

That may explain some of the things you have been finding.

Jonners

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PostPosted: Mon Oct 02, 2017 5:19 pm 
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Hi All,
Thanks for all your advice. I counted the teeth on the reverse gear and I went for the 21 teeth one as being the same. So it looks like I have an early overdrive with a later box of cogs. Running this cog with the newer layshaft in the open it seems to mesh O.K.
So far so good !

When in comes to the layshaft I would like to replace the existing one with an alleged 1850 one in much better condition. I have compared them for number of teeth and they are both identical: 15 ;15 ;20 ;24 ;26, but I read in the Haynes manual that the "helix angle" is different between early and late layshafts on 2nd gear and are not swappable.

Helix angle : Is this the angle between the long axis of the shaft and the angle of the tooth profile ? It is difficult to measure because the teeth are curved.
Does this mean the teeth just won't mesh properly, so the various bits won't fit ?
Is there any other way of telling if I have the correct laygear ?

Thanks All,
Tony.


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PostPosted: Tue Oct 03, 2017 10:55 am 
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If the gear angle is different it will not mesh...

You wont find out until you try and assemble it and find the layshaft wont drop in to mesh...which would be annoying.

Do you still have the gears and layshaft that were known to work together?

Jonners

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PostPosted: Tue Oct 03, 2017 5:55 pm 
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Hi Jon, Thanks for that. Yes I do still have the old gears. One input shaft and one layshaft. Both in poor condition.

As a matter of interest the Haynes manual gives figures on measuring the individual gears endfloat on the bushes. Is this how it is done please ? See photo. The new reverse gear shaft is in the plastic jaws of the Workmate with a magnetic dial gauge on the end of the shaft . I can then push the gear upwards and get a reading of 0.05 mm = 2thou ?

Thanks very much,
Cheers for now,
Tony.


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rev gear end float.jpg
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PostPosted: Tue Oct 03, 2017 6:51 pm 
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Looks like you are measuring up and down?

End float I take to be along the shaft. In the case of the revers cog its just located by the selector so it cant touch bits it shouldnt
when the whole lot is spinning.

If you keep the gears with their original bushes you should be fine. They would have been measured at the factory. I only check if I need a new
gear as the old one has teeth missing. Even then I have never found one out of limits.

Jonners

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PostPosted: Fri Oct 06, 2017 11:24 am 
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Yes, thats right; I was measuring the up-and-down movement of the gear on the shaft.
I shall stick to left/ right endfloat checks.
Now that I'm starting to re-assemble it, what is the word on the street about using that pink engine-assembly compound in an overdrive gearbox ? I read that super slippery gearbox additives are a no-no for instance.
Or just use EP90 ?
Thanks,
Tony.


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PostPosted: Fri Oct 06, 2017 11:30 am 
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Quality mineral oil is all you need for assembly.

That and some patience, good circlip pliers and a nice long tubular drift to get the new bearings down the shaft and then in to the case.
Make sure you put the bearing on the right way....circlip groove outermost.

Jonners

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PostPosted: Thu Oct 12, 2017 1:01 pm 
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I've started the re-assembly and got the reverse gear idler in so far.
Now looking at the rest of the bits do I assume correctly that the reverse gear power path is from the input shaft --> down to the laygear --->along to the straight cut gear through the reverse gear idler and onto the outer " gear "cut into the item called the "1st /2nd synchro-hub" . This appears locked to the mainshaft ?
Thanks,
Tony.


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PostPosted: Thu Oct 12, 2017 7:32 pm 
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Quote:
I've started the re-assembly and got the reverse gear idler in so far.
Now looking at the rest of the bits do I assume correctly that the reverse gear power path is from the input shaft --> down to the laygear --->along to the straight cut gear through the reverse gear idler and onto the outer " gear "cut into the item called the "1st /2nd synchro-hub" . This appears locked to the mainshaft ?
Thanks,
Tony.
Correct!

Steve

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PostPosted: Fri Oct 13, 2017 11:26 am 
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Yes but be careful as without the selector mechanism in place and operating as it should you can bring the reverse idler into mesh with the
reverse cog on the synchro hub while another gear is selected on the front synchro hub and lock the mainshaft.

This can be useful while fitting some bits but dont leave it like that. You can push synchro hubs into mesh with a screwdriver in the selector fork groves.

Jonners

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PostPosted: Fri Oct 13, 2017 2:38 pm 
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Hi All, Thanks for that Jon & Steve. I think my understanding of how an 1850 gearbox works is rather lacking. For instance I couldn't work out why there was nothing listed as a "4th gear". However I found a Wikipedia page on constant mesh gearboxes and that indicates that the input shaft is locked to the mainshaft to get the 1 : 1 top-gear ratio and seems to be something to do with these synchro; cones . So no actual 4th gear. It also explains why the cogs are locked to the mainshaft. I guess I'll understand better as it goes back together.
Thanks All,
Tony.


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PostPosted: Sat Oct 14, 2017 6:01 pm 
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I've got 1st gear in after working out how those split collars work.
But the Haynes manual now says " check the synchro rings for wear. ( I think they are all the same as they have the same part no;)
What am I looking for please ?
The inner bores of each of them have a number of fine concentric rings cut in them, the 3 locating lugs are all there and the teeth around the outside are all there.
Is it O.K. to re-use them ?
Thanks,
Tony.


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PostPosted: Sun Oct 15, 2017 8:26 pm 
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Compare them with the one on first gear at the very back end of the box. This in most cases gets the least wear as few Sprint users would ever change down in to first.

The tough job is the second gear synchro, which gets a hammering in both directions.

Jonners

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PostPosted: Wed Oct 18, 2017 9:54 am 
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Thanks Jon ! I think I'll have 4 new synchro rings on that basis.
However as Jeroen mentioned not all parts are the same !
I need a new 1st / 2nd synchro-hub. UKC 8748.
I located a "UKC 8748 WO". Now I compared the new with old and the central bit with the springs and ball bearings fits perfectly but the number of teeth around the circumference should be 33 ; in fact it was only 27.
So to use this do I need to change the reverse idler and the layshaft ?
Which parts should I be looking at please ?
Thanks,
Tony.


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