How much will your average 085 box handle? How can it be made stronger? And other than the different ratios, how does the ATV differ?

I've found various factors. I learnt to stop breaking them, and my tips are:

Use the right clutch plate - if the springs bottom-out it sends an impact into the box.. I used a 200mm Golf TDi plate to discover this, then complete 6n2 GTi kits since.

Torque. The 1.6 8v AEE's had the most and broke the most. 1.6 16v AFH was more powerful and quicker, but being that bit softer low end it didn't break half the boxes anywhere near as quickly.

5th gear - make sure it's adjusted correctly. Otherwise it only has half the strength at best. This is in the FAQ.

1st and 2nd are weak, so don't snatch them, and if you have really big torque, wait until you're in 3rd before really laying it down.

Bear in mind my experience is with hi-torque long stroke engines. Some have ran compressed engines with far greater peak bhp with them.

Thanks mikey. The engine is unlikely to have quite as much low speed torque as you have described with the 1.6s you've done.

When you say have 5th adjusted, how do you mean? Having the correct size?

Where these 085s you broke? I was hoping they were 6n boxes

The weight difference between a mk1 to a mk4 must make these AEE's behave totally differently haha, I'm lucky to get any wheel spin etc, not sure on load on the box

AEEs shouldn't be braking gearboxes all the time, not unless it's boosted or they're 6N 'boxes - but then it's difficult to know the providence of a secondhand 'box when you're fitting it to a car.

I think Yoof's about on the limit of the 085 with his GT2554R turbo now, in its current guise its circa 230bhp and 220lb/ft and he lost some teeth from 2nd gear last time out on track - though this was on cut slicks and the 'box has been run down the 1/4 mile with proper drag slicks too.

With a K03 I've yet (touch wood) to have a gearbox failure, though it's not seen the same amount of drag slick 1/4 mile action that Yoof's has, so might not be a fair comparison - and it was a freshly rebuilt 'box 3k before the turbo went on.

When I ran a G-lader I did hold the Club G40 record for number of dead gearboxes, points of note (for 86C era 085s, not 6N ones) are:

- Pinion gears can fail due to wear at higher mileages, if you're unlucky when they fail the diff may make a bid for freedom out the 'box casing.

- Kerb impacts damaging driveshafts can fracture pinion gears, also breaking the diff. (My G40 donor had been written-off by kerb impacts - guess what happened to the 'box?!)

- 1st and 2nd gear synchros can take a hammering, especially if your linkage is badly adjusted and/or you're an animal with the shifter.

- 5th gear synchro/dog teeth vulnerable if the parts are mis-aligned. (Check Mikey's guide - though I've only experienced this once on a 'box I'd had in bits and done a pikey rebuild on using various secondhand parts.)

- 5th gear outright failure on high torque cars, especially if torque is delivered quickly rather than progressively. Not helped by limited oil flow (and hencing cooling) to 5th gear. You can mitigate against this one by ensuring that your 'box oil level is correct, and that if you're running an aggressive but strong torque profile not mashing the throttle at low rpm in 5th.

6N 085s seem to have some additional weaknesses with some of the bearings, and the diff bearing design is different to the earlier type of 'box. I have a DXH that I'm intending to do a post-mortem on at some stage when I finish scrapping off my old gearbox graveyard!

This dyno plot from a healthy higher-spec G40 gives you an idea of why they can give 'boxes a hard time. Dyno operator mashes the throttle just before 2,000rpm, and around 5-600rpm later it's jumped from 40-140lb/ft.

The first one was the original 8p from the '88 coupe, lost 5th. Knew nothing about them so i scrapped it.

Second was an 80s Golf 4-speed, lost 1st. Didn't bother to look into it. There was another 4-speed from a MK2F which i took straight back out, engine was a 1.3 but it was horribly short geared.

The rest were 6n/6k/Seat boxes (i think five, could be six, lost count), looked into them and why they were failing. Broken link's and sync's typically, no broken actual gear teeth though - but Yoof running double the power my carb'd AEE was proves it's not just absolute power that kills them, but the way it's delivered. And this seems to affect what parts break.

After all, 6n2 GTi's seem to kill diffs.

Some blame the box design and materials but i'm not so sure it's down to that. Maybe partially, but i can't see VW making changes to aggravate the problem some cars were already having by the '90s.

One thing's for sure - the magnet isn't big enough! But i've found some serious quantities of iron filings and broken bits of metal in some, lots of bearing damage to both rollers and tapered shells, so that may be unfair. It shouldn't be loosing that much metal..

Current one is now in the 6n (the old one in the 6n had too short a final drive for the commute), it's a parts bin special made mainly of 6k and 6n parts. Happy with the ratios and it did well for several thousand with the 1.6 AFH in it's highest state of tune (12.3:1 and CBR900's 38mm carbs). Again, GTi clutch.

MK2 has a GTi unit which i know isn't right, yet to investigate what's wrong with it, haven't ran it yet.

Thanks andy for the graph. Doubt I'll be making anything above 200bhp, if that. Will be a KO3, but not for the strip.

Any way to strenghten the chocolate 6n boxes? Whats the rivet to bolt mod?

The rest were 6n/6k/Seat boxes (i think five, could be six, lost count), looked into them and why they were failing. Broken link's and sync's typically, no broken actual gear teeth though - but Yoof running double the power my carb'd AEE was proves it's not just absolute power that kills them, but the way it's delivered. And this seems to affect what parts break.

Too much torque is typically signified by lost gear teeth, but as we've both said, the way that torque is applied is key to what level you can get away with.

In my experience, 170lb/ft delivered in an instant by a G-lader seems to be on the limit, whereas with the more progressive transient torque response of a turbo 200-210lb/ft is okay. Graph posted above wasn't from my car, but G-lader torque curve was similar albeit with a higher peak.

Synchros failing isn't usually down to power/torque - that's either linkage, animal shifter usage, or in the case of the 6N 'boxes shite bearings allowing gears to move on the shafts. Had the 'box on one of my Saabs rebuilt, and the local gearbox guy had piles of 6N 085s in the corner - he reckoned the bearings on the ends of the gear shafts were shite, in turn causing all sorts of selector/synchro issues as misaligned teeth attempted to mesh. Diff to crownwheel rivets failing seems to be a common affliction of late '90s early '00s VW gearboxes in general.

Would be really interested to know what drove VW's design changes from 86C > 6N 085 transmission, and whether the apparent weaknesses introduced in the 6N variant are material, design, oil or vehicle platform related.

That all makes sense. t will be mated to a turbo, and I doubt I'll get near 210ft/lbs torque, so mine should be ok (old 085). Also, I'm a pretty considerate driver!

Anyone know where to find the tallest 5th gear from? Also, will putting a 6n 5th affect life time (i.e. are they weaker?)

Tallest is 51/36 teeth which i found in a 6n diesel, next is a 50/37 which i found in a 6n 1.4 8v.

MY 1.6 gearbox had like a 47/40 with longer final drive, so with the diesel set it's like i have a 6th gear but 5th is missing!

I'm sure that only the design causes them to shear, they're a bit small and the linkage was literally an afterthought with 5th gear basically on the outside of the 4-speed derived gearbox.

Which 1.6 box did you have? I have one in the 'loon which should hopefully be matched nicely to the 1600 engine.

Did you put the diesel one in then? What was that like to drive?

Was out of a '98 4dr 6K saloon which had the short block 75bhp 1.6 8v AEE engine, i don't know the gearbox code.

4th only just gets it over the ton so that's fairly short, but 5th has it sitting 2700rpm @ 70mph.

I used the 50/37 to enable me to use 5th in 40mph zones.