Rate my gearbox

The Oily Bits S2 Specific Topics
1

Since I bought this car I’ve been rattling around trying to figure out how far I’d like to take it, what I want from it, etc. I think I’m rounding in on a decision and much of the back and forth has been gearbox related.

I don’t want to rehash the C64 issues in this thread as they’re discussed in pretty good detail here: Exiges.com - Exiges.com - Lotus exige club but I do want to gain some critique on what I plan to do about it, as I know a few here have gone for upgraded boxes either preventatively or as a response to a failure.

I’ve been flip flopping between leaving it until it blows up and taking it out pre-emptively and being sensible. Due to the costs of the proactive measures I’ve even questioned whether I have a long term future with the car, and whether selling now and getting the next project is the right move but I’m really struggling to identify a car that ticks all the boxes I get from the S2 currently so I’m now intending to plough on with preventative measures, I think.

I don’t have much ambition to raise the power further, so at 280bhp the box may well be safe for the foreseeable but the car is becoming used more and more for track and less and less for road, so if it is going to go pop - I’d rather it didn’t ruin a trackday or European trip or whatever. That said, once the box is toughened up a bit, the temptation to push a little more power may be overwhelming :mrgreen:

Anyway, here’s the plan:

  • Fit Toyota/MR2 LSD, the same that Lotus supplied as an option to some later S2s.
  • Fit uprated clutch and lightweight flywheel
  • SSC 3rd/4th gear replacements, “semi helical” to try and retain some sensible levels of NHV from the box.
  • Komotec or Jubu 5.0 final drive. Komotec is cheaper, so will probably come down to that :mrgreen:
  • Toyota C60 Sixth gear

I’ve done some maths on ratios etc with the different FD, and I’ve calculated the following:

OEM:
1st 43mph
2nd 67mph
3rd 92mph
4th 117mph
5th 149mph
6th 167mph

Proposed:
1st 40mph
2nd 62mph
3rd 85mph
4th 108mph
5th 138mph
6th 175mph

So the summary being that acceleration through the gears should be marginally quicker, but by adding the C60 6th gear I retain road manners when cruising in sixth, RPM at national speed limit should actually be a couple hundred lower than it is OEM. There are a few circuits now where I’m brushing the limiter in 4th at the end of the straights so these will become much earlier changes into 5th which I guess could be considered a down side - but as I get better as a driver I’d like to think I’ll be carrying more speed at that point anyway so the extra shift would become inevitable.

Another alternative which would give very similar gear speeds 1-5 (if my maths are right) would be to emulate seriouslylotus with the Kaaz gear set and 'yota 4.3 FD but it’s a bit more expensive and it’s a little more ‘racey’ at the top end which is better for a dedicated track car, but I do want to retain some road manners.

As for gearbox cooling, I’m still on the fence. I’ve been logging gearbox oil temps in the second half of this year and I’ve not seen anywhere near the temps quoted elsewhere on ‘gearbox failure’ threads so I’m tempted to run without and log my first couple of trackdays with the new gears and make sure the temps have not ramped up drastically. I am only ever going to do short sessions on track which probably keeps things in check. I have priced up the bits needed and it’s not a massive expense in the grand scheme, but it’s adding more plumbing/weight/complexity which are just additional points of failure - so I don’t yet view it as a no brainer cheap insurance.

Let me know what you think, I’ve not bought anything yet other than the differential, that’s going in this winter regardless but everything else is open to adjustment. I’m mainly looking for some glaring problems with my gear ratio maths that may lead to a car that feels awkward to drive at pace, or some alternative products that I’ve not yet considered.

Hell, even try to talk me out of it if you want and go down the road of treating C64’s as consumable parts… the thought has crossed my mind!

2

Not worth the expense in my opinion of the preventative work.
Especially as the preventative work hasnt been proven as bullet proof.

3

Yep I agree on both fronts, not particularly good value for money for the non-quantifiable level of reliability that it grants.

That said, I’m (obviously) still not ruling it out. I think it’s a given that with the 3rd/4th and FD addressed that the weakness just moves along the chain a bit but the fact is, it HAS moved the weakness on a bit which might mean buying me another season/year/decade of trackdaying.

It’s about doing what I can with a budget I’m comfortable spending. If I don’t spend it on the gearbox, I’ll only spend it on something stupid like carbon fibre or worse, my pension :laughing:

It sounds insane to type it, but having my third gear go pop at a trackday would actually make my life easier… as it would justify the decision :unamused:

4

You = me

I am not even convinced that the 3rd/4th gears will shift the problem, if you read long enough there are reports of these failing.

5

This Kyle.

6

No gearbox oil cooler fitted to my car, It doesnt need it.
The different ratios and helical angles in the Kaaz box means it creates MUCH less heat (Less friction I assume)
Heat and driver abuse are the worst for failures IMHO, Then torque.

7

Sticking the LSD in is 100% worth it. Interested to know which lsd you’re going for.

Mine ( S2 S) frequently spins up an inside wheel on track.

I guess whilst the box is in bits changing the 3rd 4th would be a good option.

8

Any idea on what temp figures are considered dangerous seriouslylotus ?

9

SSC/Holinger claim they’ve never had a 3rd/4th gear failure, at least not reported to them. Final Drive, Synchro and input shaft failures are all next in line from what I can gather and I’m not aware of any cost effective mitigations for the synchros and input shaft.

This isn’t about making the box bullet proof, as I don’t think that’s possible - it’s about deciding how much I’m comfortable spending and then getting the most robust box that I can out of it. The temptation to run my OEM till it pops is still lurking in the background, but I really don’t want to aggro, cost and drama of it failing in style at a trackday - because knowing my luck it’ll be on a sighting lap of a Spa weekend or something like that :unamused:

Yep I’ve found the same, the open diff is really struggling at this power. I spent a bit of time at Croft altering my approach a bit and I’ve got to be honest I did manage to ‘drive around the problem’ by the end of the day and I could now make an argument to say that the differential probably wasn’t losing me too much time (if any) BUT it felt like it was sapping the fun out of a couple of corners, so I’m still very much intending to lob the LSD in, regardless of what I do with other components.

I picked up a second hand Toyota LSD, they came in the UK spec Mk3 MR2s and it’s the same unit that Lotus offered as an option on later S2 cars. They come up fairly regularly on eBay for £250-£300.

1 Like
10

My SSC 3/4th had plenty of abuse from 340hp and were absolutely fine. The syncros and bearings need replacement.
The FD was also SSC.
Friends have said that the thing that gets the car to come alive is a very close ratio gearbox. I didn’t do that
I agree with the celica 6th. More manners driving to the track
I never needed 6th on track. At the end of the Kemmel straight I was just about to hit the rev limiter in 5th, same at the end of Lavant at Goodwood. I read that as 154 on the speedo, so your 149 OEM estimate is probably right.
Ultimately you chase speed and the journey is fun. Many of us have done it, then you run out of love for the car as it is so altered from the road car you bought.

11

Good info, thanks for that. Did you upgrade to the SSC stuff after a failure on your stock box?

The gearbox man I’ve spoken with about doing this work has said he’ll give all the synchro’s a going over for me (whatever that means) but the replacement don’t seem to be that expensive from Toyota so I’d just get them replaced if needed.

I’ve been there/done that with “ruining a car for the road”, I hope I’ve learned from it and I do keep that in mind when choosing parts etc. I’m under no illusion though, once I’ve run out of sensible mods to do to a car I quickly lose my attention span and look towards something else. I could do with a cheaper hobby, Class A drugs for example.

12

I hadn’t had a failure but it was only a matter of time that 3rd or 4th went. So I did those as i increased the power. Strengthen those and it’s the next weakest link, which to my mind was the FD, so repalced that too.
The sychro and bearings are cheap and you just need to consider them consumables. The expecnse is the gearbox removal and relacement. I can’t recall but 7-9 hours rings a bell.
I recommend Competition Transmission Services for the rebuild stuff.

13

Also , I note Dave’s comment about the cooler, but I needed one. At Spa gearbox oil was soon up to 110deg and continuing to rise without switching on the cooler, which kept it at just over 100.

14

My gear box has not been above 80 degrees so far with the Kaaz gears kit (No cooler installed)

15

Cheers Gents, all good info.

I’ve got monitoring for the gearbox temps so the car will initially run without a cooler, and I’ll see what happens when I get it on track next year. I’ve got data to compare against from an OEM gearbox and there’s every chance that running chunkier gears with finer tolerances will generate more heat so I’ll keep an eye on it. I’ve got a cooler install all planned out, pretty sure I know exactly what parts I’ll buy to make it up and it’s not that expensive in the grand scheme of things… I just don’t want to be adding a lump of weight and complexity until I know it’s needed.

This has been a pleasant surprise, spoken with a couple of specialists and the rebuild costs are actually pretty low and that’s the only part I’ll be outsourcing. Removing the box from the car and reinstallation will all just cost me my own time so that should help.

If I wasn’t so set on having an LSD fitted, I’d probably just leave the whole lot alone (until it blows up, if it ever does) but since I’ll be going to that effort to get the box out/dismantled - I’ve talked myself into doing the upgrades at the same time.

16

Agrreed , the cost was OK once the box was out. Something in the order of £600-700

17

I’ve decided to go ahead with most of this plan, though it’s hit a hiccup already.

The Komotec FD that I’d chosen from their website doesn’t actually exist when I’ve made an effort to actually buy it. They have another offering in the pipeline, but we know how those pipelines can stretch. I’m keen not to drop my gearbox until I have parts in my hand in fear of being stuck without a car in Spring.

I’ll keep an eye on it, but alternatives in the market seem to be thin on the ground. The Jubu one is straight cut and quite a bit more expensive than the imaginary KT one was. I know SSC used to do one (I plan to use SSC gears for 3rd/4th) but I can’t find it listed anywhere anymore, so perhaps it got discontinued.

Other options are:

  • Rebuild box and retain stock FD and chance it
  • Rebuild box with the lower ratio Toyota FD which is more readily available and is stronger due to fewer teeth… but that would mess up my ratio plans

Hmmm :question:

18

My car is still going strong with the original FD and jubu 3/4 gears, to be fair, it is not my original box as that was so ruined when I drove it 330miles back from Spa with no third gear it was only useful as scrap, but I did buy another box from a 2006 car and that is still on it’s original FD and is still running with 300hp, personally I’d chance it. 3/4 are chocolate whereas the FD is made of tough cheese :wink:

19

I ended up going for a Kaaz FD. The Komotec leadtime stretched out again and I wanted to get a move on, the Kaaz was also much, much cheaper than either the KT or Jubu options - hopefully not because it’s another variety of cheese :laughing:

It did mean going 4.8 rather than 5.0, so not quite as aggressive on the ratios as my initial plan but should still be a nice step up from stock and the improved acceleration I get will hopefully go some way to justifying all of the cost/effort.

20

Hope you are putting in the taller Celica 6th gear?