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How Does My Gearbox Look?


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#1 pakgorgor

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Posted 27 October 2019 - 11:57 PM

My gearbox was starting to develop a whine and was constantly dropping out of 3rd gear. I'm starting my rebuild now and took some pics before I strip it all apart. There are some marks on two of the gears and I'm not sure if it's normal? How does everything else look to you?

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Edited by pakgorgor, 28 October 2019 - 12:15 AM.


#2 Moke Spider

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Posted 28 October 2019 - 12:34 AM

The marks on the teeth are to identify what type of gear set it is. It's done at manufacture. In your case, this is what's often referred to as a 'Single Line' set. They are sorta 'middle of the road' in terms of wide or close ratios.

 

Nothing I can see pokes me in the eye from those photos.

 

Strip it down, then lets have a look.



#3 pakgorgor

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Posted 01 November 2019 - 08:13 PM

I've stripped it down further and found the source of the whining. The double bearing was missing a few balls!! Some of the needle bearings inside the main shaft were also falling apart. The plastic cages fell apart and bits of the plastic were laying at the bottom.

 

I'm still unsure as to the cause of the gearbox dropping out of 3rd. Any ideas?

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Edited by pakgorgor, 01 November 2019 - 08:14 PM.


#4 mini-mad-mark

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Posted 01 November 2019 - 08:49 PM

I'm no gearbox expert but I would guess that the misalignment seen by the shafts due to the missing/damaged bearings allows the gears to get out of mesh or drop out



#5 Swift_General

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Posted 01 November 2019 - 09:00 PM

Very often worn selector forks. Put the 3rd/4th synchro in the fork and measure the clearance. Could also be weak synchro springs, but probably less likely. Given that your main bearing is knackered, I am wondering if this was allowing axial play of the main shaft due to the helical final drive on drive/overun causing it to drop out of gear and accelerate wear of the fork due to constant thrust loading. Also check the dog teeth and teeth on the synchro outer ring which may have been damaged as a result.

#6 cal844

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Posted 01 November 2019 - 09:02 PM

It could be that your engine stabilizer bushes are worn so the engine is moving too much, or it could be that synchro hub or fork is worn

#7 alex-95

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Posted 01 November 2019 - 09:03 PM

The whining was probably due to the double roller bearing cages breaking up and falling out (makes it look like there are balls missing).

 

I had the same problem but with 4th gear popping out. I think this can be a few problems, the crank levers (steel bits that go into the selector forks) are worn or have too much slack between the top washer and the levers and spacers. could be worn selector forks and could be weak springs on the synchro hubs.



#8 pakgorgor

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Posted 01 November 2019 - 10:06 PM

It could be that your engine stabilizer bushes are worn so the engine is moving too much, or it could be that synchro hub or fork is worn

 

I've changed the stabiliser bushes before, it didn't fix it and hence the strip down of the gearbox.


Edited by pakgorgor, 01 November 2019 - 10:09 PM.


#9 pakgorgor

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Posted 01 November 2019 - 10:10 PM

Very often worn selector forks. Put the 3rd/4th synchro in the fork and measure the clearance. Could also be weak synchro springs, but probably less likely. Given that your main bearing is knackered, I am wondering if this was allowing axial play of the main shaft due to the helical final drive on drive/overun causing it to drop out of gear and accelerate wear of the fork due to constant thrust loading. Also check the dog teeth and teeth on the synchro outer ring which may have been damaged as a result.

 

In addition to the double roller bearing, it was the 1st gear needle roller which completely deteriorated.

 

Where do I measure the clearance between the synchro and fork? What should the clearance be?



#10 pakgorgor

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Posted 02 November 2019 - 01:15 AM

Here's a close up of the 3/4 synchro hub. I can't find a picture of a new one to compare. Does it look really worn?

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#11 Moke Spider

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Posted 03 November 2019 - 08:14 PM

The whining will have come from the gears not running parallel to each other, which is usually form worn bearings, or with the drop gears, from misalignment. They will usually only do it when loaded up, so if it was only doing it in say 2nd gear, I'd be looking closer at this gear and how it's mounted. If it does it in all gears, then it's either the Drop Gears and / or the Final Drive.

 

As Alex mentioned, there's no balls missing from the Mainshaft Bearing, it's only that the cage has gone that makes it look this way. This would almost be certainly the issue with it dropping out of gear.

 

None the less, all checks should be made while it's in bits, replacing all bearings, Layshaft and what ever else is worn or damaged. The maximum allowable clearance in the Shift Forks is 0.015", however, when buying a new one (if it's needed) take your hubs with you and check them on the counter. Many I find are out of spec, right out of the bag.

 

What I can see of the Dog Teeth on 3rd Gear still look OK. These heed to be 'sharp' in shape, and not rounded off on the lead in side. Same goes for the Outer Track of the Hub. I have had the best look I can at your photos, sorry I find them not quite clear enough, they appear to have a good shape, but I think they are chipped ??

 

This is about the best photo (as in clearest) I have;-

 

aGDmJar.jpg

 

While these are not chipped, they are well worn and right on about the limit of what will still - just - work, though, personally, I wouldn't refit it



#12 pakgorgor

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Posted 04 November 2019 - 05:46 AM

Thanks for all the infomation! I will be ordering the rebuild kit from minispares so all the bearings and layshaft will be replaced. I've attached some better pics of the synchro hub, I guess it does look pretty worn and might be worth replacing?

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#13 Moke Spider

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Posted 04 November 2019 - 07:39 AM

In the last of your 3 pics here, I feel that the 'teeth' on the lower side look a bit too rounded off for my liking, I think while it's in bits, replacing at least the outer track of the hub would be a good idea.



#14 Ethel

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Posted 04 November 2019 - 03:27 PM

I thought we were looking at the better side too. I'd say the ones on top in the centre of the frame are serviceable, if it's just the camera angle with the rest.

 

You can always compare them with a set  of gnashers that were working well, 2nd gear usually gets the worst hammer. 






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