What makes my AXM/ASZ gearbox crunch into third?

[Bowie69]

Long time no see, but when the CQ has been running mostly OK there's not much to post about!

But recently, overnight, my gearbox started to make horrid crunching sounds when going up into third. Quite disappointing given I swapped the gearbox out (detailed in the linked thread) 5-6 years ago for the same problem.

So a couple of questions:

1) What causes the crunch up into third? It is not a problem with a cold box, but once slightly warm it crunches badly. I assume synchro parts of some sort, maybe a spring or something? But does any one know what needs changing? I'd prefer to repair rather than change this time.

2) What am I doing wrong that means my gearboxes fail like this? This is the third box in the car, first one failed through abuse, second and now third went the same way.

Thanks for your help people.... looking forard to knowing all

[rynaqui]

May be a bad synchro, could be the boxes you have were given the incorrect type of oil or not serviced at all which could have eaten these kinds of metals, I certainly recall a GL4 vs GL5 gearbox oil discussion on the board a few years ago. I have been using Redline 75W90 with good results in my O1E (once warm). Third gear isn't happy when cold but Flawless when warm.

On an old accord with a similair issue, I would simulate a 2nd into 4th into 3rd which would avoid crunching, not ideal but better than nothing.

[Bowie69]

Yeah I'd assumed bad syncro, but it literally started happening overnight, almost like something broke.

I've run miller oils mostly, their 75x90 semi synth, as this apparently does NOT eat bronze/whatever in the gearbox according to their blurb/FAQ. They have been serviced, more than almost anyone I would think.

Has anyone repaired a box like this? I can't imagine the rest of it being in a poor state (I had it apart for checking before), just this annoying issue.

[K Simmonds]

That does sound like an issue with the second to third syncro, it's pretty bad luck to have it happen to three gearboxes in a row though strange coincidence's do happen. Do you shift from second to third very aggressively?

Totally different car but I had two boxes do this in row with my first G60 Corrado many years ago, both failed inside a month which I put down to the car being chipped to 180bhp and my driving style. However, I fitted a very old, high mileage third gearbox from a dead Passat which I pulled out the scrap bin as I was skint and never had it happen again and I didn't adjust my driving, though the shift points changed road speed considerably due the ratios being very different.

I've never really delved into gearboxes but the guy I worked with does and it's just a case of being really methodical, you may need to either fabricate or purchase pullers for some boxes but I don't know if that's the case with our cars.

Someone on here has posted the entire Bently manual, that should detail all that's required to do a gearbox strip and rebuild.

https://www.s2forum.com/forum/member...al#post2158239

[Bowie69]

Thanks Kit,

Yeah not very aggressively tbh, 1-2 yes, probably, but by the time third is needed you are at the speed limit (60mph), so by then I am often slotting it into 4th or 5th....

For clarity, first box just went bang totally, not syncro related (don't ask....).

Thanks for bentley link, I will take a look, there' snot much on rebuilding these boxes online sadly, 01e yes, but that's quite different.

Unless someone has an AXM box floating about they know is good? This one was was probably on 160K.

[newsh]

Is the clutch fully disengaging? If not it can overwork the synchros and wear them out.

I've got a 6 speed here if you want to convert ?

[Bowie69]

Yeah, pretty sure newsh , disengages maybe a third of the way down.

Perhaps I am just asking too much of the poor old thing, are these boxes known for wearing like this?

I'm not convinced a 6-speed is the way forward, are there any real benefits over the 5?

[K Simmonds]

The six speed would only give you a couple of advantage's in a 7A, those being a wider gear selection that helps with slightly with fuel economy, they're also known for being close to indestructible even at very serious power levels.

However there are a couple of disadvantages one being the hassle of making it fit.... Shorter prop from an ABY required as well as a now very hard to find hence expensive gear linkage and a subframe spacer for one of the gearbox mounts. They're also not as nice to use as a five speed, they all seem to be slightly notchy from first to second and generally not as smooth between gears.

The five speed should take all a 7A can throw at it, they seem to hold up in 3B S2's fine even when running RS2+ spec, It's pretty much the same box just with slightly different ratio's and 110mm driveshaflt flanges. Their limit is generally considered to be around 420bhp and 550NM, mine was fine running a very aggressively mapped RS2 set up and I used to change rapidly from second to third in a straight line pretty often at the top of the rev range to overtake on short straights.