I am trying to make up a little bit of a store of data for all of you who have sadly killed their c64 box
Could you be so kind as to detail
Year of car
Power of car
Original box?
Box fluid changed before failure ( time ? Day / week / month before ? )
LSD? Factory or aftermarket?
Speed when failed ( approx )
Thanks!
Being one of the earliest to kill the gearbox
Year of car 2006
Power of car 300hp 200lb/ft
Original box? Yes
Box fluid changed before failure ( time ? Day / week / month before ? ) Nope completely original
LSD? Factory or aftermarket? No
Speed when failed ( approx ) 6,000rpm ish in 3rd
Failed 2009
It is on youtube…
Exige Gearbox Failure - YouTube
After that it got,
New gearbox (I drove it home from Spa 350 miles with no 3rd gear and the old box was completely destroyed inside)
Quaiffe LSD
Jubu semi helical 3rd and 4th
JDS laminova gearbox oil cooler
Redline MT90 oil
R1Brizz from Seloc
2008, Komotec 320S, factory fitted box, Redline Oil every 2 years, No LSD, entry to corner changing down into 3rd at around 40mph - instant grinding and box locked.
WillB from Seloc
2006 Exige S 220
Approx 58,000m, majority road use, no heavy track use.
Original box, failed at low road speed. No diff
Diff broke in the gearbox, so no drive at all.
535Dboy from Seloc
2008 S - tuned to 280Bhp
c30k miles
3rd gear went pop at slow speed. Managed to get it home as about 2 miles away !
Open diff
Heavy track use and had just come back from Spa having been driven hard by an ex F1 drivers son around there which was fast and I forgot to put the Go-pro on!
What’s your goal here Andy.? We all know that there have been issues with the gearbox particularly on heavily tracked or modified cars. I find that these type of threads can be bad for the brand if it makes it seem like there is a bigger issue. You aren’t going to get people jumping on to balance the thread and explain how rare the issue is on stock cars.
Advice to anyone with a concern would be to upgrade 3rd 4th and final drive. Decision is just whether to do this proactively or whether to be optimistic and keep fingers crossed and then upgrade if and when it goes.
My goal is to understand what kills the box.
4 out of 4 so far had no diff. Is that a pattern?
It’s not track use that kills them exclusively , and it certainly doesn’t appear to be power related as 2 were standard cars.
I don’t think it’s bad for the brand if we understand it. There are pockets of information but no one appears to have taken the time to correlate results.
Just trying to understand patterns.
Box was designed for 190 hp in Celica. Little wonder there are some (not many) failures when pushed beyond that in Lotus application. Led to believe that’s why the series production cars didn’t go above 260hp.
For the record I pulled 5 teeth out of std final drive on mine with Quaife LSD. That was with around 300hp and 220 lbft. Bad luck (Or served me right) as only 2nd track day after removing a straight cut final drive as it was too noisy. Now running semi-helical. And also now running gearbox oil cooler.
As far as I’m concerned it was torque and track use that killed it, hence the upgrades to cover as many bases as possible.
I understand where you are coming from. I am just trying to work out if there is a pattern, I wholeheartedly agree that a box that was designed for a whole 133ibft and then asked to do 32% increase is stretching it a bit!
I’m with Will here, the main issue is the design of the box was for a car with no torque, my first torque related failure came on the dyno as we hit 260hp and it literally spun out the clutch just on power as there wasn’t enough clamping force.
The design of the box allows for slight de-meshing of 3rd and 4th at the box gets hot and is under load, also the gears are skinny for 3rd and 4th. Add it getting very hot on track extra torque and it will break! Add in shock loading on track over curbing and that just makes it more likely to break. Therefore;
put in stronger 3rd and 4th, consider the final drive as well
add in a cooler, using a laser temp gauge the casing was over the operating temp of the oil, that means the oil probably was as well, I’m not sure but I think running my cooler took out 30 or 40 degrees of temperature from the gearbox case
What box fluid were you guys running?
I am aware of the narrow 3rd and 4th gears - thats just built for purpose.
I found it interesting so far that the standard boxes that let go were open diff boxes. I wonder if the axle tramp doesnt help either?
Interesting on the temps Ade,
Im now running a C64 with Kaaz close ratio kit, LSD and the 4.3 Final drive. Surprisingly the temps never go above about 85 degrees C, This is measured with a temp sensor wired into the dash along with engine oil temp and pressure sensors (No Cooler fitted)
The Kaaz gears have a lower tooth angle than the Toyota gears (They are very slightly wider also) so I assume this puts less stress on them, and hence lower oil temps . I went for the 4.3 final drive for two reason
1 To get the overall gearing i wanted
2 The 4.3 had a MUCH bigger tooth pattern than the standard 4.53
Without too much scientific input I figure its torque spikes that kill gears, ie
No LSD = spinning wheel that suddenly regains grip
Changing into third from second is the most popular gear change on road and track at high revs (again a torque spike)
Add to this the hi angle helical cut of the gears and we get massive temp rises in the oil (past its operating window??)
Hi temps allows the casing to expand and twist = less tooth contact= Hi loads at the tooth tips
One area never mentioned is mechanical sympathy! Our very own Tarmac Terrorists raced for thousands of miles with a standard C64 and NEVER broke it. I not suggesting that’s a fix but should also be a consideration as ramming it through the gears introduces more toque spikes
I hope im in the right area for the fix as I have addressed all of the above with the Kaaz kit,LSD and final drive
For info the car has the 2-11 GT4 270 kit fitted (but not checked by me so far)
It’s about time somebody logged this properly for the sake of science! I’d love to compare Dave’s data with a standard 260 car (for example) and then something that’s been tuned a bit further (such as Andy’s) to see if there’s some sort of exponential increase over a certain torque level.
I’m sure the C64 issues are just a load of smaller factors added together, fixing one is not going to make the box bullet proof but may give you years of happy motoring. I know the Celica guys blow these up at stock NA power (and it always seems to be third gear) so power/torque alone isn’t the killer. If the added heat of track work + significantly higher torque levels is a contributing factor then this can be heavily mitigated by just having sensible stint lengths which may explain why some people ‘get away with it’ for years and years whereas others blow up straight after a dyno run.
[mention]seriouslylotus[/mention] I see you recommend Datum on SELOC, do you know any indicative costs for stripping/rebuilding a C64? I have vested interest in this thread because I want to put an LSD in my car, and once I go down that route it would appear reckless to not consider 3rd/4th/FD with clutch/flywheel all at the same time - which suddenly becomes a VERY expensive bit of insurance for something that might not go wrong. 
Sadly I never did any proper logging, just user a laser probe on the top of the case, I remember it being over well 100degees C and most gearbox oils don’t want to be that hot, maybe 80 tops
Very useful info [mention]seriouslylotus[/mention] . Thank you for your input.
Strip / inspect/ reassemble is £330.00 plus vat Any parts required are extra £££
Fitting a diff adds a few ££ more than just the parts as the new LSD will need shimming to spec
Tom also offers a vapour blast and re-plating of the bolts for those that want a’new’ looking box
Cheers Dave, not half as bad as I expected (don’t tell Datum I said that ). I did the dangerous thing of watching a Youtube video of a C60 stripdown and all I could see was $$$$$ flying past as we got onto removing the 19th circlip and checking thrust clearance for the 14th time.
TJScott - Seloc
turbocharged s2 exige
320hp
factory box, open diff
fluid changed a few months before failure, changing from 3rd to 2nd on entry to a corner on the warmup lap for a track day, box grinding in every gear, still able to crawl onto a trailer. suspected minced final drive.
car was then pinned back to 290 ( if i recall ) and boost by gear set up with a few more mapping tweaks to preserve the replacement box.
If you have power then the gearbox is a consumable.
I had SSC 3rd 4th and FD, gearbox cooler running off a Stack gauge with the sender in the bottom of the box. The syncros would last 7k or so?? The gears were fine.
The temps ( at Spa for instance) could go to 120+ or so without the cooler and 100 with ( set to come on at 95)
I’ve decided to fit an oil temp gauge into my (totally stock) gearbox before my next track outing to see what’s going on in there. I’ve already got a SPA design oil temp gauge plumbed into the sump, so I’m going to buy a spare 1/8NPT sensor and get an M18x1.5 - 1/8NPT adaptor for the gearbox drain plug (I think M18x1.5 is correct 
) then temporarily plug that into my existing gauge, rather than coughing up (and making space in the dashboard!) for a second gauge.
Will see how track temps differ from road temps, and see what impact stint time has on it. As Andy will testify my stint lengths are restricted by biological restrictions rather than automotive ones so I might not be able to put in any endurance tests
If I see high temps after just a couple of laps, I’ll look to at the very least setup some provisions for oil cooling - should be a fun mini project to keep me busy, and doesn’t rely on the intrusive steps of gearbox removal etc.
The big step for me (in both effort and cost) will be when my gearbox has to come out of the car, expecting the OEM clutch to fail me at some point in the near future (if 3rd gear doesn’t go first) so once that box is out and sat on my garage floor it’ll be time to have a long hard think about how far I go to ‘future proof’ vs just throwing in boxes and viewing them as consumables.