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Syncro On 4th Is Not Happy

NickR33
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NickR33 Grand Master

NickR33

Posted
Posted

Hi guys, I had a problem with 4th gear at Sandown on the weekend... when shifting from 3rd to 4th, close to redline say above 6,000rpm, I was getting a nasty crunching sound... now it would still go into gear fine and it was only happening when I was trying to shift quickly (if I eased it in there was no sound, but it meant for a fairly slow change)

...so my question is, do I need to get the box out asap and fix it or can I get away with a few more trackdays/drags etc without losing 4th gear altogether? Am I stupid for not worrying about it? (Maybe I can smash the whole lot so I am forced to go out and by an OS giken gearset hehe)

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https://www.sau.com.au/forums/topic/130510-syncro-on-4th-is-not-happy/
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saliya Rising Star

saliya

Posted
Posted

Hey,

When the gear is crunching you are doing damage to the sleeve that actually does the job of engaging the gear.

Yep, your 4th synchro is most probably worn.

Do this enough and even without breaking anything else you'll burr the front of the teeth on the sleeve - which

will probably make it difficult to get it into gear and then keep it there.

Getting replacement sleeves for some boxes is hard (e.g. I can't get one for my 32GTR box; I have to

upgrade the entire 1st-3rd train in order to be able to use a different 4th sleeve). Your box might be different.

Don't know your box; but on mine 1st, 4th and 5th synchros are 1-piece; 2nd and 3rd are 3-piece.

This is probably why 4th seems to go first on GTR boxes :)

The long and the short of it - I would fix the synchro before you do more damage. They are wearing parts

and should be relatively cheap to replace - the hardened sleeves and/or gears are _not_ cheap

to replace assuming they are even available. You probably want to do 3rd and 4th synchros.

Do a bearing set while you're in there and you'll probably get another 10-15 years of motoring out of the box :)

Regards,

Saliya

MANWHORE Grand Master

MANWHORE

Posted
Posted

Redline themselves say that the shockproof is not to be used in synchro boxes.

I know that everyone on here thinks it's the bees knees. they put it in their box and it shifts like new. I totally agree there.

My issue lies with box longevity. Basically, a thinner oil allows you to shift smoother. e.g. if you put atf in the box. But also, it's a catch 22, it'll shift smoother for a dieing box, but it'll wear out much quicker too.

Lets just say that my box is notchy too. I just live with it. I'd prefer to kill it by notching it occassionally, rather than it dieing from redline shockproof.

NickR33 Grand Master

NickR33

Posted
  • Author
Posted
Hey,

When the gear is crunching you are doing damage to the sleeve that actually does the job of engaging the gear.

Yep, your 4th synchro is most probably worn.

Do this enough and even without breaking anything else you'll burr the front of the teeth on the sleeve - which

will probably make it difficult to get it into gear and then keep it there.

Getting replacement sleeves for some boxes is hard (e.g. I can't get one for my 32GTR box; I have to

upgrade the entire 1st-3rd train in order to be able to use a different 4th sleeve). Your box might be different.

Don't know your box; but on mine 1st, 4th and 5th synchros are 1-piece; 2nd and 3rd are 3-piece.

This is probably why 4th seems to go first on GTR boxes :mad:

The long and the short of it - I would fix the synchro before you do more damage. They are wearing parts

and should be relatively cheap to replace - the hardened sleeves and/or gears are _not_ cheap

to replace assuming they are even available. You probably want to do 3rd and 4th synchros.

Do a bearing set while you're in there and you'll probably get another 10-15 years of motoring out of the box :stupid:

Regards,

Saliya

I am pretty sure the 32GTR and 33GTSt boxes are very similar and I am now seriously considering a freshen up before I do damage to more than just the synchro, thanks for your help

Munna1 Proficient

Munna1

Posted
Posted
Hey,

When the gear is crunching you are doing damage to the sleeve that actually does the job of engaging the gear.

Yep, your 4th synchro is most probably worn.

Do this enough and even without breaking anything else you'll burr the front of the teeth on the sleeve - which

will probably make it difficult to get it into gear and then keep it there.

Getting replacement sleeves for some boxes is hard (e.g. I can't get one for my 32GTR box; I have to

upgrade the entire 1st-3rd train in order to be able to use a different 4th sleeve). Your box might be different.

Don't know your box; but on mine 1st, 4th and 5th synchros are 1-piece; 2nd and 3rd are 3-piece.

This is probably why 4th seems to go first on GTR boxes :D

The long and the short of it - I would fix the synchro before you do more damage. They are wearing parts

and should be relatively cheap to replace - the hardened sleeves and/or gears are _not_ cheap

to replace assuming they are even available. You probably want to do 3rd and 4th synchros.

Do a bearing set while you're in there and you'll probably get another 10-15 years of motoring out of the box ;)

Regards,

Saliya

The syncro may be cheap but getting it installed isnt thats for sure I had mine done 3 years ago costs a bloody fortune.

cheers

saliya Rising Star

saliya

Posted
Posted
The syncro may be cheap but getting it installed isnt thats for sure I had mine done 3 years ago costs a bloody fortune.

cheers

Put it this way: the labour cost is going to be roughly the same whether you do 4th gear synchro only, or an entire

rebuild on the internals of the box (getting to the 4th gear synchro probably requires complete disassembly).

So it might be 'a fortune' now; but when a sleeve is burred or smashed and it's not replaceable, it's 'a fortune' plus

another few large :)

(Yes, you can buy secondhand drop-in boxes of similar vintage - but aside from the 'you haven't seen it running

and/or disassembled, so how do you know it's any good' factor, any box that's of roughly the same mileage will

probably have roughly the same problems...

Regards,

Saliya

  • 2 weeks later...
Doobs Proficient

Doobs

Posted
Posted

Got the exact same problem with my 'line last nite.

Shifted up from 3rd to 4th at about 5000rpm, nasty crunch.

Looks like the box will be comin out to replace teh synchro's. fun! :huh:

izataskyrine? Collaborator

izataskyrine?

Posted
Posted

dont feel to bad mate.. i was shifting from second to third in my 34 gtt and ripped every single tooth off third. the box was like new up to this point and showed no signs of wear (even had perfect syncro on reverse which is almost unheard of)

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