Gear inspection

FastFred · Jun 28, 2013

I have got hold of a pretty decent second hand gearbox cluster with a main and layshaft that both clock true within a couple of thou. I was just checking the driving faces of the gears and wondered why on so many of the gears there is what is best described as pitting? You can see the same on the gears on the old britts site (how the box works bit) although similarly the driving faces look good. Is this anything to worry about and is it seen on some new gears at all? The pitting looks like cardides to me exposed by corrosion perhaps?

JohnTy · Jun 28, 2013

Hi Fred
the pitting you describe is usually on the driving faces and is what causes the "old bus sound" (sorry American cousins as most of your buses seem to be automatic or semi auto you would not hear this) have another look at the gears and make sure you are getting the driving faces correct!
I replaced 5 gears in mine last year and bearings, bushes plus kickstart shaft. I reckon it cost me about £600. But it is quiet now and does the things it should do.

Not all pitting needs replacement but, it all adds noise.
Cheers
JohnT

FastFred · Jun 28, 2013

Think I got it right. All maingears drive one way and laygears the other?

JohnTy · Jun 28, 2013

gears 1-3 drive from the mainshaft onto the layshaft, and drive from the fixed gear on the end of the layshaft to the sleeve gear. This gives two opposite drives (wear on different sides)
4th gear basically locks the mainshaft to the sleeve gear output, so effectively no gears are driving.
I would suggest when you think this through you will find the driving faces of the teeth are the side that are pitted and worn. The clean faces with little or no wear are the overrun side that are not exposed the high forces of acceleration.
Hope this makes sense!
JohnT

FastFred · Jun 29, 2013

Thanks JohnTy, I was meshing the gears and rotating them thro the sequence but got in a kerfuffle it seems..

FastFred · Jun 29, 2013

Checked that JohnTy. Basically the drive faces on 1-3 main are opposite on the lay gears and the 4th gear laygear drives the sleeve gear on gears 1-3 (you know this). Interesting but they are more pitted on the other faces, I'll take that as a positive. Going to renew 2nd main and rebush all. Some small line wear but acceptable.Thanks.

AntrimMan · Jun 29, 2013

JohnTy said:
Not all pitting needs replacement but, it all adds noise.
Cheers
JohnT

Very true.
In a previous thread this pitting was discussed along with some images of the gear teeth, I think it was Windy who stated that the pitting is evident to varying degrees in all the Nortons. Also that newly replaced gear sets will look pitted very shortly once put into service. The statements were not contradicted. I do apologize if I have incorrectly identified the author.

These gear boxes do work as intended.
They do also suffer from a host of oversights.
Replacement parts are readily available because they quickly sell.
All the Best.

JohnTy · Jun 29, 2013

Hi Fred
did you manage to get a new gearbox case?
I guess you have as you are rebuilding!
Cheers
JohnT

FastFred · Jun 29, 2013

See other post today. I am rebuilding, the Yorkshire way..

concours · Jun 29, 2013

JohnTy said:
Hi Fred
the pitting you describe is usually on the driving faces and is what causes the "old bus sound" (sorry American cousins as most of your buses seem to be automatic or semi auto you would not hear this) have another look at the gears and make sure you are getting the driving faces correct!
I replaced 5 gears in mine last year and bearings, bushes plus kickstart shaft. I reckon it cost me about £600. But it is quiet now and does the things it should do.

Not all pitting needs replacement but, it all adds noise.
Cheers
JohnT

Lol, no, not now, but as a kid the howl from old school bus rear diff was loud! (I am young enough that straight cut transmission gears had been phased out) Now it's just a neck snap from mis-operated Allison or ZF autos.

JohnTy · Jun 29, 2013

FastFred said:
See other post today. I am rebuilding, the Yorkshire way..

Seeing where you live, you had best be very careful, you are likely to get sent back t'north for such skinflint ways

Glad it is coming together.
When you finally get your head round the gears I think you will find the sleeve gear and corresponding layshaft gears are pitted on the drive side

Cheers
JohnT

JohnTy · Jun 29, 2013

concours said:
JohnTy said:

Hi Fred
the pitting you describe is usually on the driving faces and is what causes the "old bus sound" (sorry American cousins as most of your buses seem to be automatic or semi auto you would not hear this) have another look at the gears and make sure you are getting the driving faces correct!
I replaced 5 gears in mine last year and bearings, bushes plus kickstart shaft. I reckon it cost me about £600. But it is quiet now and does the things it should do.

Not all pitting needs replacement but, it all adds noise.
Cheers
JohnT

Click to expand...

Lol, no, not now, but as a kid the howl from old school bus rear diff was loud! (I am young enough that straight cut transmission gears had been phased out) Now it's just a neck snap from mis-operated Allison or ZF autos.

A local vintage bus company runs tours around the Lake District, god bless em. Manual crash gearboxes (no syncro on any gears) and having to double de clutch to change gear makes for an interesting drive! As soon as they get up enough speed going up hill to need the next gear, by the time time they have double de clutched and found the next gear it has slowed down so much they have to go back down a gear! and the noise is very nostalgic, whining transmissions

Cheers
JohnT

Hortons Norton · Jun 29, 2013

I remember asking about those type of wear marks and was told "son those small pits hold oil and are good" :wink: And the box is still working great with many miles on her now. And I have also a bike that has all new gears, Really can tell no difference in the two. Ride safe!!

Gear inspection

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