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Gearbox Rebuild


Darren Groves
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Just wanted to say a big thanks to Pete Lewis who I've been messaging over the last few days about this rebuild, always so willing to help and the advice is always spot on, so once again thank you! To give him a break from my endless questions, I thought I'd throw this one out to the wider community.

 

After my gearbox failure a week or so ago, finally got an opportunity to strip it down to see what went wrong. Didn't take much to find the remains of the needle roller bearing in the case and in the output shaft.

 

2nd & 3rd synchros have been on the weak side since I fitted it 2-3 years ago, so will change those from my selection that I acquired over the last couple of years. The 3 held together by string in the photo were advertised an NOS, so favourites to use I guess, the remainder are a selection of original items advertised as good usable items.

 

Are there any recommended methods to test the synchros whilst fitting, rather than discovering they weren't so good after refitting the gearbox?

 

Cheers

Darren 

 

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Well the new cat has me up far too early, a pm siesta seems iminent so j

here's some clues

 

the brass bronze rings were the std of the day ( mostly made by companies like Otto Fuchs)

you can see the slot relief to drain the oil, the more iron looking dont have these, iron rings are a different

grip may not need the relief, but are a different generation to the brass type or even for a different oil specification , not used on small chassis 3 rail boxes

 

you have the wring the ring onto the cone witha twisting action, it should grip easiliy and have a good gap between the dog teeth face and the gear dog teeth, if its close to bottoming out its worn out

There should be a well defined flat tooth chamfer on the ring and the dog teeth , this is where all the work

Is done, any chimbled teeth means lost baulking action and gear changes can clash during a change

 

 

 

 

without any clues the black rings are from either earlier or later design they may not have the same cone or tooth chamfer angles as the Brass ones , dont use these without some carefull measuring

 

many aftermarket baulk rings were machined in lathe chuck which produced a lobed cone due to the pressure on the chuck jaws, these will not wring on properly and are useless, they must be turned on a mandrill to keep them really round.

 

synchro is driven from the mainshaft , any wear or angle mismatch on the rings or incorrect tooth chamfer angles >< can make it baulk for ever or let go half way through a change,

its these chamfer teeth that work hard to spin up or slow down the clutch disc in the blink of an eye

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Well the new cat has me up far too early, a pm siesta seems iminent so j

here's some clues

 

the brass bronze rings were the std of the day ( mostly made by companies like Otto Fuchs)

you can see the slot relief to drain the oil, the more iron looking dont have these, iron rings are a different

grip may not need the relief, but are a different generation to the brass type or even for a different oil specification , not used on small chassis 3 rail boxes

 

you have the wring the ring onto the cone witha twisting action, it should grip easiliy and have a good gap between the dog teeth face and the gear dog teeth, if its close to bottoming out its worn out

There should be a well defined flat tooth chamfer on the ring and the dog teeth , this is where all the work

Is done, any chimbled teeth means lost baulking action and gear changes can clash during a change

 

 

 

 

without any clues the black rings are from either earlier or later design they may not have the same cone or tooth chamfer angles as the Brass ones , dont use these without some carefull measuring

 

many aftermarket baulk rings were machined in lathe chuck which produced a lobed cone due to the pressure on the chuck jaws, these will not wring on properly and are useless, they must be turned on a mandrill to keep them really round.

 

synchro is driven from the mainshaft , any wear or angle mismatch on the rings or incorrect tooth chamfer angles >< can make it baulk for ever or let go half way through a change,

its these chamfer teeth that work hard to spin up or slow down the clutch disc in the blink of an eye

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Thanks Pete, the ones that look like steel were in fact bronze but tarnished, found three that looked and feel the best.

 

I assembled the mainshaft and refitted it, then decided that the 1st/2nd hub wasn't right so removed it again, but now I'm thinking it was right so another question.

 

The 1st/2nd hub has a pin/ball bearing that locates it onto the mainshaft, this is in line with the 3 spring/ball bearings for the outer hub. When the outer part of the hub is pulled rearward the whole hub assembly is locked onto the mainshaft and there's little movement, but with the outer part of the hub forward there's a lot of movement.

 

Probably not explained that very well, so here's a couple of very short videos:

 

Outer hub rearward: https://youtu.be/sDjQyNi6JMo

Outer hub forward: https://youtu.be/kha4NqKtTzU

 

Is this correct? 

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Think you find this gives gives 2nd its initial ring load before the sleeve starts to

pressure the baulk ringe, as theres no shifter plates , its only for 2nd gear synchro.

Big of an odd design but that movement is correct

if any more pops out the memory bank I will revise the idea.

 

pete

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Thanks Pete. So it's looking like it could be correct, that's a bonus as I'm pretty sure its assembled correctly. Have checked the exploded diagram several times just in case I'm doing my usual of missing the bloody obvious!  ;)

 

Have posted the question elsewhere also, if nothing received to the contrary I'll go with that.

 

Had to take the output shaft to a local engineer, could remove the remains of the roller needle bearing case, hopefully will be ready tomorrow.

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Dont forget to fit the reverse idler spacer tube, or the woodruff key for the OD pump cam

 

wjen fitting the od keep the cam at its lowest so the pump roller rides up ot easy

 

two good levers to pry open the piston plates so the clutch is free to align the innards

 

and keep the small etched or dot marks aligned on the planets it easy for them to move around when your not looking

 

pete

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Spotted the woodruff key, that's definitely done. Reverse Idler Spacer Tube? Not sure what that is, is it on this diagram: http://canleyclassics.com/images/diagrams/herald1360_plate_m.jpg

 

I haven't touched the OD, was planning to leave that for another day. Do I still have to align it or can I just pop it back on?

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Ah ha the reverse spacer is on 4synchro boxes sorry, its easy for it to fall out while you fiddle about

 

the 1st 2nd hub float up down the shaft is definitley Correct

 

the od if un touched may drop on easy, you wont know till you try to drop it on , if its not been turned it could be clunk click and its on, if it decides to be stuborn then through the gap between adaptor hsg and the main unit nudge a pair of good bladed screwdrivers through and pry the two piston bars to open a little this releases the cone and allows the internal splines to align and the mainshaft to drop through the hubs inside

 

the book tells you to peer down inside and twiddle with a long driver to align the hubs, it dark its deep

its darn near impossible.

 

if you have an old OD mainshaft you can grind a lead on the tail splines to use as a mandrill before you fit

the OD. You still have to open the piston bars but its on a bench not sitting ontop of the gearbox

 

always best to fit the OD to a vertical gearbox, not horizontal in a vice

 

keep fingers out the way , it can drop with surprise.

 

pete

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From what Darrens found the plastic caged spigot rollers do need a different stem gear

having looked up the sizesin the WSM the cased needles need a 0.6875" stemwheel bore ,

the plastic caged spaced needles needs 0.75" so you cant upgrade from the cased needles to caged needles without a change of the input(stemwheel) gear

the main shaft spigots are all 0.5" across the small chassis cars untill later dolly tr7 with 18mm spigots

 

pete

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All back together now with the original type needle roller, shame I couldn't use the plastic caged type, but seems it's the 4 Synch output shaft that's needed. Just need a spare moment to get it back into the car.

 

I spent the whole day thinking I had a washer over, but couldn't work out where it was from. I was convinced the young lad at the workshop planted it in with the others parts just to confuse me. As I went to fit the rear flange on the back of the OD it all made sense.... :-)

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