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Advice on 3 synchro gearbox rebuild
https://www.ausmini.com/forums/viewtopic.php?f=2&t=100227		 Page 1 of 2
Author:  Morbo28 [ Sun Jul 26, 2020 7:56 pm ]
Post subject:  Advice on 3 synchro gearbox rebuild
Hi brains trust. I'm rebuilding 3 synchro remote change box (from 67 Deluxe, assuming it was original with the car). What else would you do when you get 130mm of rain in a day?!

I have a few questions if you don't mind.

This layshaft - do you think it is serviceable? Internal bearing surfaces are good, but what do you think of the gears - specifically first?

Image

Image

Also, Minispares reckon "A new Baulk ring should ideally sit at about 45 thou above gear with 40-60 being the usual range. anything below 30 thou and the gear should be examined for replacement."

The OLD baulk rings have about 35 thou gap...would I be correct in assuming that NEW baulk rings should open that gap up a little and therefore be more comfortably within spec?

Advice appreciated :)
Author:  Morbo28 [ Sun Jul 26, 2020 8:24 pm ]
Post subject:  Re: Advice on 3 synchro gearbox rebuild
One more thing - I have the 3 synchro which used idler bearing with OD of 25.4mm and due to damage I want to get a machine shop to take it out to accept the 4 synchro idler bearing with OD 26.9mm.

What ID of the idler bearing hole should I get the machine shop to enlarge it to in the case? I assume a slight interference fit? If there is a dimension you could give I'd be grateful thanks.
Author:  drmini in aust [ Sun Jul 26, 2020 10:13 pm ]
Post subject:  Re: Advice on 3 synchro gearbox rebuild
I have a bare MK 2 S case here I will measure it tomorrow.
With a micrometer and telescopic gauge.
Author:  Morbo28 [ Sun Jul 26, 2020 10:41 pm ]
Post subject:  Re: Advice on 3 synchro gearbox rebuild
drmini in aust wrote:
I have a bare MK 2 S case here I will measure it tomorrow.
With a micrometer and telescopic gauge.

That would be very kind thankyou!
Author:  drmini in aust [ Mon Jul 27, 2020 12:24 pm ]
Post subject:  Re: Advice on 3 synchro gearbox rebuild
It measures dead on size for 1-1/16".
1.0625".
Your cluster's 1st gear doesn't look bad, the inner end gets chewed a bit when selecting 1st from neutral. And the flanks don't look bad either.
When these get too worn it can jump out of gear.
Author:  Morbo28 [ Mon Jul 27, 2020 2:51 pm ]
Post subject:  Re: Advice on 3 synchro gearbox rebuild
You've mentioned in the past that if you take any material off the face of the box around the idler gear hole, that the same amount of material should also be taken off the housing too.

I'm wondering why this is? I would think I could just use a thicker washer on the box side and it would bring it all back in spec? And therefore I thought I could keep the housing as is. I think I must be missing something.

And thanks, the measurement and the opinion on the gear condition are both appreciated!


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Author:  drmini in aust [ Mon Jul 27, 2020 6:31 pm ]
Post subject:  Re: Advice on 3 synchro gearbox rebuild
There was a very limited range of hardened thrust washers. Most used were 133-134 thou.
I bought all Mini Suzuki spares' used stock and my thickest one is only a 136 thou.
Minisport SA have a 22 thou 'blue' gasket, this is around 10 thou thinner than stock. I've used these a few times.
I find it easier to mill the flange... because I have a mill. ;)
Author:  Morbo28 [ Mon Jul 27, 2020 7:26 pm ]
Post subject:  Re: Advice on 3 synchro gearbox rebuild
Informative and helpful as always, thanks Doc :)
Author:  drmini in aust [ Mon Jul 27, 2020 7:43 pm ]
Post subject:  Re: Advice on 3 synchro gearbox rebuild
Don't be tempted to mill the gearbox casing flange because it then won't be level with the block face.
Mill the flywheel housing flange.
Author:  Nicho [ Mon Jul 27, 2020 9:01 pm ]
Post subject:  Re: Advice on 3 synchro gearbox rebuild
I have 2 x 3sp syncro boxes i can check out the layshafts and see if they are servicable.
What is the part number and I'll check they are the same.
Author:  Morbo28 [ Mon Jul 27, 2020 9:13 pm ]
Post subject:  Re: Advice on 3 synchro gearbox rebuild
Nicho wrote:
I have 2 x 3sp syncro boxes i can check out the layshafts and see if they are servicable.
What is the part number and I'll check they are the same.
Part number is 22G231 for the laygear thanks Nicho.

If first gear on the main shaft is any good, I'd consider that too. And any idler thrust washers you might have hanging around. If you're willing to part with them for a price of course.

I am on a tight budget for this build so for some parts I'm hunting second hand to try to reduce costs.

:)



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Author:  Bill B [ Tue Jul 28, 2020 3:17 pm ]
Post subject:  Re: Advice on 3 synchro gearbox rebuild
Years ago I built a 3 speed synchro box with a used cluster gear because new gears were unavailable. Teeth on 1st were worse than yours and it whined a lot in first, but you don't use 1st a lot.
Have recently rebuilt that box with a new cluster gear and first gear whines a lot! But you don't use 1st a lot.
Also fitted Mini Spares latest baulk rings which gave at least 0.050" gaps and so far work really well.
Author:  drmini in aust [ Tue Jul 28, 2020 6:36 pm ]
Post subject:  Re: Advice on 3 synchro gearbox rebuild
Re the baulk rings, their quality varies lately. A mate had his 4th gear one break recently, rebuilt 2 years ago. No synchro at all on it now.
We need to pull the 1st motion shaft out and replace the ring.
With a good S/H one, 0.020" ground off its inner face for more life.
Author:  Bill B [ Tue Jul 28, 2020 7:17 pm ]
Post subject:  Re: Advice on 3 synchro gearbox rebuild
drmini in aust wrote:
Re the baulk rings, their quality varies lately. A mate had his 4th gear one break recently, rebuilt 2 years ago. No synchro at all on it now.
We need to pull the 1st motion shaft out and replace the ring.
With a good S/H one, 0.020" ground off its inner face for more life.


It's always in the back of your mind when you fix something these days.... all we can do is hope for the best.
Author:  Nicho [ Sun Aug 02, 2020 7:34 pm ]
Post subject:  Re: Advice on 3 synchro gearbox rebuild
Forgot to check the part number, but got one out today. I'll give it a close inspection tomorrow and let you know.

Morbo28 wrote:
Nicho wrote:
I have 2 x 3sp syncro boxes i can check out the layshafts and see if they are servicable.
What is the part number and I'll check they are the same.
Part number is 22G231 for the laygear thanks Nicho.

If first gear on the main shaft is any good, I'd consider that too. And any idler thrust washers you might have hanging around. If you're willing to part with them for a price of course.

I am on a tight budget for this build so for some parts I'm hunting second hand to try to reduce costs.

:)



Sent from my Pixel 3 XL using Tapatalk
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