5 speed gearbox tips and tricks

[gav t]

hi guys i was wondering if anyone had any info on strengthening the mk1 5spd gearbox
it has been a long time since i have delt with these boxs and memory tells me 5th gear was prone to breaking

cheers gav

[gldgti]

what are you doing with it?

might be cheaper and easier to go to an 02a instead.

the 020 will shear the rivets in the ring gear of the differential first (happened to me) so the first thing to do is usually a HT bolt kit for that.

you'd probably need to have a LOT of power and be doing some interesting weekend activitied to break 5th gear. I think its very unlikely.

What is (relatively) common is for (I think its a bolt) to break that holds the 5th cog in the right place on the shaft... it can then move along on the shaft a bit. and cause some other problems.

[roccodingo]

MOST prone problem with 5th gear is low oil, overheats the gear and leading to failure ...

Bolt kit is a good idea if you intend rebuilding the box.

[Peter Jones]

I've broken an input shaft due to a clutch failure and gotten the box stuck in third due to aggressive shifting.

Apart from that the 020 is standing up well. Mind you my races are rolling starts.

My box is also a hybrid of parts.

4K gear cluster (close ratio)
3.94 Ring and Pinion
ARP diff bolts
Wavetrac diff
CHB casing

engine speed up to 8K and road speeds just under 200km/hr

Penrite synthetic gearbox oil to VW spec.
2.0 litres through the speedo hole.

[gav t]

thanks guys it has the bolt kit and a new bolt holding the fifth gear on

it is in a track car i have been building on again off again for about a decade now

this gear box has a close ratio gemini gear set in it so i want to look after it and dont realy want to aim for more power than it will handle

i have another gear box that has an extra bearing in the end housing for 5th gear (not sure if this is the 02a)
im sure this would be better but not sure if my internals will fit from memory one of the shafts are different

[gav t]

thanks peter

what size wheels and tyres are you using to achieve those speeds

[Peter Jones]

Wheels are 14 x 6

Tyres are 185/60/14 Toyo R888

Wreck to Race thread in my sig below has all the details.

[dubmc]

Wheels are 14 x 6

Tyres are 185/60/14 Toyo R888

Wreck to Race thread in my sig below has all the details.

sorry to hijack, but pete i'm looking at some Toyo R888 how do you find them? i've been getting qoutes around $1k

[Peter Jones]

They've been great for me. Biggest performance upgrade on the whole car.

I think I paid about $218 per corner.

[roccodingo]

i have another gear box that has an extra bearing in the end housing for 5th gear

This is just a latter version of the 020, yes the pinion shaft is longer for the additional bearing.

[Bora Sport]

FYI From personal experience O2A boxes can also suffer the dreaded diff rivet failure with catastrophic results.

[gav t]

thanks for the info guys appreciate it

[Preen59]

Bottom line, fit diff bolts. Most LSDs come with diff bolts, so if you're fitting one of them, happy days.

They can break first gear on hard launches, but the way around that is to pre-load the clutch before you launch. This takes the slack out of the 'box and removes the shock loading.

Tim B's Mk1 Kjet Turbo has done a heap of drag strip passes (ran a best of 12.99, so it wasn't slow) with sticky tyres, 2-step burnouts etc etc and had a real hard time without breaking anything. But it was running a Diesel 4spd with a welded diff and ARP diff bolts.