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Anyone know of an Gearbox inspection guide
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Author:  69k1100 [ Sun Apr 12, 2015 8:36 pm ]
Post subject:  Anyone know of an Gearbox inspection guide
Greetings,

I am looking to rebuild my gearbox at some point of time, using a few unknown ones to make a good one, problem is I have kno idea what a knackered gear/layshaft/baulk ring looks or feels like in terms of back lash or surface wear.

Is there a guide available? Or any pointers? The box I will be building will be a remote, unstressed weekender.

Any tips would be appreciated, thanks.
Author:  timmy201 [ Mon Apr 13, 2015 1:18 pm ]
Post subject:  Re: Anyone know of an Gearbox inspection guide
Minimania have a rebuild video series
http://www.minimania.com/Classic_Mini_G ... ania_Video
And so does guessworks
http://www.guess-works.com/Tech/Rebuild/
And some photos
http://www.theminiforum.co.uk/forums/to ... x-rebuild/
Author:  Irish Yobbo [ Mon Apr 13, 2015 3:39 pm ]
Post subject:  Re: Anyone know of an Gearbox inspection guide
I followed the minimania rebuild videos, and they cover things quite well. The only thing that isn't covered by any is the disassembly - which is actually harder than the assembly!

None of them do seem to cover inspection though. Get a repair manual, as they should cover tolerances there.Off the top of my head, the most important ones should be:

- Inspect all bearings for wear or cage damage
- Inspect the layshaft for wear - tolerances should be in the manual
- Inspect the clearance of the laygear thrust washers
- Inspect the clearance of the selector forks on the gears
- Inspect the dog teeth of each gear, and also each gear selector hub. It's also a good idea to replace the selector hub springs, which aren't covered in the videos
- Inspect the syncro to gear-cone clearance, and make sure they grip on the cone (this is very important!). Clearance should be about 45 thou when new if memory serves.
- Inspect the idler gear clearance when re-fitting. Too loose and it'll get noisy, too tight and very bad things happen.

Be sure to do a search about each of your replacement parts as well - there are good and bad replacements for each (some are cheap Chinese rubbish). Don't skimp on the layshaft, diff pin or double-row bearing, if they need replacing get good ones. But also, don't replace just for the sake of replacing. The original parts were of decent quality, in many cases good-condition second hand is better than a poor quality new part.
Author:  timmy201 [ Mon Apr 13, 2015 4:33 pm ]
Post subject:  Re: Anyone know of an Gearbox inspection guide
Here is a strip down guide..

http://www.theminiforum.co.uk/forums/to ... with-pics/
Author:  69k1100 [ Wed Apr 15, 2015 12:21 pm ]
Post subject:  Re: Anyone know of an Gearbox inspection guide
Thanks Guys, I will dig out the Haynes manual and see what it says .
Author:  drmini in aust [ Wed Apr 15, 2015 2:27 pm ]
Post subject:  Re: Anyone know of an Gearbox inspection guide
re the layshaft, they all wear at the 1st gear end. If there is any wear there at all (you can see and feel it) bin the shaft. Fit a new one.
I would replace every ball & roller bearing in the box, except the tiny needle rollers inside 1st, 2nd & 3rd gears. These hardly ever wear, replace if damaged or rusted.

re the mainshaft (aka 3rd motion shaft), inspect the `nose' journal that goes into the 1st motion shaft. If worn through the case, don't use it.
Either find a better shaft, or else I can do you exchange on a reconditioned one with a hard bearing inner ring press fitted.
Author:  69k1100 [ Thu Apr 16, 2015 3:43 pm ]
Post subject:  Re: Anyone know of an Gearbox inspection guide
Cheers Doc,

Already binned a couple of layshafts, I guess since the shaft is static and loaded mainly on one side the surface always breaks down in the same place, at least this is what I observed with the few shafts I removed.

Binned is a strong word though, they make bullet proof steel drifts.
Author:  low n blown [ Sat Apr 18, 2015 7:08 am ]
Post subject:  Re: Anyone know of an Gearbox inspection guide
I tried to cover some of it in the last issue of BMC Experience. If you get stuck happy for you to give me a call or pm me. I should be able to talk you through what you are looking at.
G.
Author:  69k1100 [ Mon Apr 27, 2015 3:00 pm ]
Post subject:  Re: Anyone know of an Gearbox inspection guide
Well I've taken the gears off the main shaft, the gears themselves are OK but the dogs look done for

Image
Image
Image
Mainshaft
Image
3rd Gear
Image
2nd Gear

1st gear the dogs are in better condition, but still a couple of them are chipped. It should be noted I have another gear set but unfortunately this one was washed out and sat in the open air for some years so its got surface rust. Interestingly the set with the surface rust has the races drilled to aid oil flow to the main shaft bearings.

Both the main shafts are in similar condition, however they also both have slight bluing on the output end, although i am responsible for the bluing on one of the shafts the other one I didn't have to heat, yet the bluing is present? Is there any way to check the integrity of the shaft for possible heat damage?

I have two more boxed I can tear down but honesty I'm expecting more of the same. Is there a possibility to re-use these gears or am I looking at digging deeper into the parts bin?

Thanks for your help.
Author:  Irish Yobbo [ Mon Apr 27, 2015 3:26 pm ]
Post subject:  Re: Anyone know of an Gearbox inspection guide
I'm no expert, but the bluing may be due to the factory heat treatment.

Your 2nd gear is cactus, but just from those pics your mainshaft doesn't look bad. It would be best to check for wear with a micrometer on the bearing journals to be sure.

I think that 3rd gear looks OK. You can expect a couple of chipped teeth, not ideal but workable so long as there aren't many. I bought a refurbished 2nd gear from guessworks UK - mainly because they re-surface the gear cone, and I was having syncro issues. Be sure to check the teeth of your selector hub too - I'm pretty sure that's where mine is giving me grief.

Also, for each gear get a good syncro - one that grips, and that when pushed onto the gear cone as far as possible, has a decent gap. Factory gap was about 45thou or so. But do make sure they grip! You don't necessarily need new ones.
Author:  69k1100 [ Mon Apr 27, 2015 9:52 pm ]
Post subject:  Re: Anyone know of an Gearbox inspection guide
I was pretty sure 2nd gear was done for, seems 1st gets off lightly due to the car being stationary during engagement, 4th is the next least abused for some reason, 3rd gets lightly abused but 2nd cops it the most. I have the other three gears covered but 2nd will be the killer. Lucky I have two boxes to go through yet, might find something tasty inside.
Author:  drmini in aust [ Tue Apr 28, 2015 8:57 am ]
Post subject:  Re: Anyone know of an Gearbox inspection guide
The problem is when the dogs wear like this (and the synchro outer sleeve too) there is less and less dog engagement length. Ultimately the dog flanks of both wear to an angle, and this causes jumping out of gear (2nd in particular).
I went through this recently on a Mk2S box that did this. New 2nd gear was NLA, luckily a mate had a gear and its matching synchro hub that was near mint, so I fitted that.
Author:  Irish Yobbo [ Tue Apr 28, 2015 9:09 am ]
Post subject:  Re: Anyone know of an Gearbox inspection guide
69k1100 wrote:
I was pretty sure 2nd gear was done for, seems 1st gets off lightly due to the car being stationary during engagement, 4th is the next least abused for some reason, 3rd gets lightly abused but 2nd cops it the most. I have the other three gears covered but 2nd will be the killer. Lucky I have two boxes to go through yet, might find something tasty inside.


It's changing down that wears the most. When you change up, you take your foot off the accelerator - the revs drop and are close to that of your next gear. Changing down is the opposite, the revs drop, but the next gear has higher revs.

So 4th to 3rd will wear the gear a bit, but 3rd to 2nd has a bigger gap in ratio. Also, many people will change to 2nd early to slow the car down. It's always the 2nd gear that wears on a mini.
Author:  Phil 850 [ Sat May 02, 2015 4:19 pm ]
Post subject:  Re: Anyone know of an Gearbox inspection guide
Irish Yobbo wrote:
69k1100 wrote:
I was pretty sure 2nd gear was done for, seems 1st gets off lightly due to the car being stationary during engagement, 4th is the next least abused for some reason, 3rd gets lightly abused but 2nd cops it the most. I have the other three gears covered but 2nd will be the killer. Lucky I have two boxes to go through yet, might find something tasty inside.


It's changing down that wears the most. When you change up, you take your foot off the accelerator - the revs drop and are close to that of your next gear. Changing down is the opposite, the revs drop, but the next gear has higher revs.

So 4th to 3rd will wear the gear a bit, but 3rd to 2nd has a bigger gap in ratio. Also, many people will change to 2nd early to slow the car down. It's always the 2nd gear that wears on a mini.


I was taught by my father to "heal toe" when changing down so you have control of the speed of the car and match the engine speed to the gear you are going in to 8)
Less wear on the clutch and gearbox :D
I still do this even with modern cars including the wife's STI.
Author:  69k1100 [ Sat May 02, 2015 7:01 pm ]
Post subject:  Re: Anyone know of an Gearbox inspection guide
I rev match too but the reality is the best method, provided you're not racing, is to take the car out of gear and use the brakes.
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