C64 box killers - post in here

Topics relating to the Lotus Exige S2 (series 2)
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andybond
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TOK from Seloc

C64 gearbox 5th gear syncro failure / selector issue - no more 5th and 6th gear for this gearbox.

2005 S2 na exige with some fast road cams- and a lotus sport LSD.
johnfishcurtis
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If I read this thread anymore, I'll end up driving like my grandma :lol:
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matt447
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johnfishcurtis wrote: Tue Jul 21, 2020 11:56 am If I read this thread anymore, I'll end up driving like my grandma :lol:
Yeah, I must admit I thought I was sitting pretty here in my NA, sub-220bhp version, safe from this problem - but if I read too many more of these I'm going to end up replacing my gearbox with a stronger version! (or am I just trying to justify the KAAZ close ratio gear set to myself... ahem...) :angel:
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andybond
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matt447 wrote: Tue Jul 21, 2020 12:08 pm
johnfishcurtis wrote: Tue Jul 21, 2020 11:56 am If I read this thread anymore, I'll end up driving like my grandma :lol:
Yeah, I must admit I thought I was sitting pretty here in my NA, sub-220bhp version, safe from this problem - but if I read too many more of these I'm going to end up replacing my gearbox with a stronger version! (or am I just trying to justify the KAAZ close ratio gear set to myself... ahem...) :angel:
Dave @seriouslylotus groupbuy!
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matt447
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andybond wrote: Tue Jul 21, 2020 12:22 pm
matt447 wrote: Tue Jul 21, 2020 12:08 pm
johnfishcurtis wrote: Tue Jul 21, 2020 11:56 am If I read this thread anymore, I'll end up driving like my grandma :lol:
Yeah, I must admit I thought I was sitting pretty here in my NA, sub-220bhp version, safe from this problem - but if I read too many more of these I'm going to end up replacing my gearbox with a stronger version! (or am I just trying to justify the KAAZ close ratio gear set to myself... ahem...) :angel:
Dave @seriouslylotus groupbuy!
If we can get a group buy going at a sensible price, I'd be totally up for it... :)
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Fonzey
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This thread encouraged me to dig through loads of archived posts from this forum and others from back in the late 00's when S2 tuning was probably a bit more of an "in" thing to discuss.

It was quite amusing to keep reading stuff like "The jubu gears are a fine mitigation until someone comes up with a proper solution", but various abandoned projects to look at Honda and/or Audi box conversions etc all fell flat.

There's a great thread on exiges.com (here if interested: viewtopic.php?f=12&t=13991&hilit=jubu) where many of these topics are discussed. At that time Jubu gears (and Kaaz) were new solutions and nobody was really sure how robust they had been. Perhaps the fact that many of these projects fell flat over the years is because the Jubu/Kaaz solutions actually worked out to be pretty dependable.
ade
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I have to say, from 2009 till when I sold my car in 2016 the gearbox was fine, I know Lee who bought it off me has not had any issues since either but he doesn't really track it.
I probably did 20 or 30 track days after fitting the Jubu gears and the cooler. I am also quite nice to my cars and was always careful not to run curbs on full power so I didn't shock load the transmission
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andybond
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From Darkslide over on SELOC

Year of car - 2008
Power of car - 240BHP
Original box? - Yes
Box fluid changed before failure ( time ? Day / week / month before ? ) - About a month before failure (recommended upgraded oil)
LSD? Factory or aftermarket? - Open standard diff
Speed when failed ( approx ) - 40mph ish

Went when changing from 2nd to 3rd at fairly high revs but not on the red line. No user error that I remember and all seemed fine until the fatal gear change. Was able to drive home but with 3rd gear missing and some interesting noises coming from the box. Not entirely sure what failed as managed to source a replacement with the broken one now in my shed awaiting stripping.

Also worth mentioning that the box didn't grind at all even when cold and never gave any hint of the impending failure.

I've heard of loads going, I think every specialist in the land has a little pile of broken gearboxes sitting in a corner somewhere
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Fonzey
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Not sure how relevant this is, but thanks to my new ECU and gearbox temp probe I've got a bit of data.

My motorway cruising temp seems to settle at 80degrees celsius, recovery time is very slow so it will retain heat for a long time after parking up too compared to engine oil which I guess is dispersed over a wider surface area so can cool quicker.

On track I saw a peak temp of 103 degrees C. Not as high as I expected, but I do keep my sessions short at around 15 mins max. At time of cooling down laps, my temp was still steadily climbing up so I've got no reason to doubt that temps would continue going up and up had I stayed out on circuit longer.

I can't find any details for what temps we should aim for in a gearbox, gearbox oil doesn't need to worry about burning off/evaporating moisture like engine oil does as it's a closed system on the C64, but I guess you should still aim for a minimum temperature so that the oil is at its best. MT90 which most people (incl. myself) use don't seem to advertise any optimum temperatures, at least not that I can find. The only temp related data I can find on their datasheet is:

Vis @ 100°C, cSt 15.6
Vis @ 40°C, cSt 86.2

That means absolutely nothing to me :lol: Should we infer from this that 40 degrees is the minimum operating/load temp we should aim for and 100 is the highest? Or are they just two arbitrary measurements?

Based on pretty much nothing other than guess work, I think I'd aim for a gearbox cooler that kicks in (via electric pump) at 85degrees so that it's not on the go constantly under normal/cruise driving in an attempt to keep the temps under 100 degrees.

Oh, and to add balance to the thread I survived a trackday with ~ 195ft/lbs on standard gears and no cooler. Let's see if I can get it to survive another one :mrgreen:
winthattt
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cSt is the units for the viscosity, centi Stokes. It shows the oil is much less viscose as it gets hot. They are not limits, just points on the curve. I think good synthetic oils can go to 150C before they start to break down. At about -40C they are like treacle so starting an engine is tricky.

True story, in parts of the USA where it gets very cold truck drivers would warm there engine with a small bonfire under the sump. Unfortunately, the new engine we were working on has a plastic sump, for a while!
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