patibbitts Posted July 21, 2019 Share Posted July 21, 2019 My K Series 1600 Supersport is fitted with a CC 6 speed box, cruising is not very comfortable as the revs are quite high, higher than that of the type 9 five speed due to the 'overdrive ' nature of the fifth gear of the type 9 box, I believe? My question is:- Q: what is entailed swapping the 6 speed out, for a type 9? Q: if a basic type 9 is sourced from say ebay, would the first motion shafts' splines be compatible I,.e. a straight swap - Ford box to Rover clutch splines? Q: clutch cable connection set up? Q:which Bell housing is used? Q: gear lever position the same? Q: any trick bits required? Q: does anyone have a 5 speed they are not using?? (Pls)! Assistance greatfully accepted, Link to comment Share on other sites More sharing options...
sjl1 Posted July 21, 2019 Share Posted July 21, 2019 The six speed box is paired with a 3.6 rear diff. 6th is 1:1 so final drive is 3.62 compared with .82(5th) times 3.92(rear diff ration for a 5 speeder) = 3.21 so a bit lower by 12% but not hugelyi think the cc 6 speed is loosely based on the ford box and they are a straight swap (good news) but you do need to change the rear diff ratio (bad news). You should be able to cheaply source a 5 speed box but consider upgrading with a BGH gear kit which raises 1st gear to make it more useful (standard 5 speed 1st gear is quite low)You will recover a decent amount for the 6 speed box and diff to cover the costs good lucksimon Link to comment Share on other sites More sharing options...
patibbitts Posted July 21, 2019 Author Share Posted July 21, 2019 Great info Simon, thanks very much. Link to comment Share on other sites More sharing options...
p.mole1 Posted July 21, 2019 Share Posted July 21, 2019 Check your diff ratio, some came with a 3.9 ratio which gives a very low top gear. I changed to a 3.6 ratio, much better. If you have a Supersport the standard 5 speed ratios are totally unsuitable for a Caterham, also the higher ratio of the 5 speed will kill your top gear acceleration with a Supersport 1.6, the 1.8 is much better as it is less peaky.The 6 speed box was specially designed for the 1.4 Supersport, do you have 13 inch wheels? this will give very low gearing with 60 profile tyres. I am running 14 inch wheels 60 profile tyres a 3.6 diff and a 1.8 this gives around 18mph per 1000rpm and around 16 mph with the 3.9 diff. The 1.6 Supersport is quite a peaky engine and you may find the 5 speed box will ruin the character of the car Link to comment Share on other sites More sharing options...
Englishmaninwales Posted July 21, 2019 Share Posted July 21, 2019 ....and to add you’ll devalue it too. Link to comment Share on other sites More sharing options...
Wrightpayne Posted July 21, 2019 Share Posted July 21, 2019 Dont do it - check you have a 3.6 diff first (sure another post intimated it wasn’t). The 6 speed and supersport cams are a perfect combination.I read elsewhere caterham have stopped making the 6 speed so if you do remove it maybe worth storing for a few years as bound to go up in value (as the 5 speeds seem to be doing)Also, the standard 5 speed is a compromise as the first gear ratio is wrong for the car so will ideally need changing and before you know it you’ll be into a £2k rebuild with quaiffe or Tracsport semi helical gear kit!Keep the six and sort the diff out! Ian Link to comment Share on other sites More sharing options...
patibbitts Posted July 21, 2019 Author Share Posted July 21, 2019 Gents, Points noted with thanks. Link to comment Share on other sites More sharing options...
Mark Durrant Posted July 22, 2019 Share Posted July 22, 2019 A cheaper alternative would be to change to a 3.38 diff. I have a 3.38 CWP for sale (£150) that you can have fitted to your existing diff. Link to comment Share on other sites More sharing options...
Seabea23 Posted July 22, 2019 Share Posted July 22, 2019 How does one check a diff ratio? Does one have to drop the diff off the car and open it up or is there an easy way. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 22, 2019 Member Share Posted July 22, 2019 Jack up a rear wheel or two and turn the propshaft or wheel and count the relative number of turns. It's easier to count the turns if you mark the wheel and shaft.It's slightly different between open and locking diffs, and you need to remember the factor of two if only one wheel is turning.Jonathan Link to comment Share on other sites More sharing options...
SM25T Posted July 22, 2019 Share Posted July 22, 2019 Sometimes fitted with a tag showing the ratio. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 22, 2019 Member Share Posted July 22, 2019 I'd check the current ratio as above, and I'd also like to know the circumference of the rear tyres.Jonathan Link to comment Share on other sites More sharing options...
Seabea23 Posted July 22, 2019 Share Posted July 22, 2019 Interesting, I will give it a go next time I have it up in the air. Thanks. Link to comment Share on other sites More sharing options...
anthonym Posted July 22, 2019 Share Posted July 22, 2019 Quaiffe do/did a type 9 seven speed replacement, so a 6 with an overdrive 5th type gear. Was expensive, not looked lately. Or indeed change the car? For those longe motorway/arterial roads I use a trailer.I’m planning a 6 speed with open 4:1 diff in my BDR, (if that’s ever finished.) So that should be fun. However,, I am keeping the 5 speed and LSD for when the fun stops.Anthony Link to comment Share on other sites More sharing options...
Rex Posted July 22, 2019 Share Posted July 22, 2019 If you change from a 3.92 to a 3.62 won't that also change the speedometer reading? Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 22, 2019 Member Share Posted July 22, 2019 If it's driven from the gearbox it will. But solutions are trivial for electronic instruments and available for mechanical.Edited: Or used to be!Jonathan Link to comment Share on other sites More sharing options...
p.mole1 Posted July 22, 2019 Share Posted July 22, 2019 Yes I changed from a 3.9 to a 3.6 and my speedo reads low by about 10% of the acurate speed! so I have to be careful not to speed. You can alter the the speedo drive ratio or have the speedo re- calibrated or just leave it and remember it reads low. Link to comment Share on other sites More sharing options...
Alastair B Posted July 23, 2019 Share Posted July 23, 2019 I run a 1999 1.6k with a 5 speed box but with DVA work to the head, verniers and 633 cams, kit 13A if I recall. I got my car from another buyer then got the performance mods done. I did not know till later it had a 3.62 ratio differential, whereas the 3.92 is normal. With the performance mods. and a powerspeed 4-2-1 exhaust the car is still quite quick for road work, 60mph comes up in 5.5 seconds but the higher speed cruising has the lower revs. This works for me, but is not usual. I guess I am losing a bit of sprinting capability for the trade of lower revolutions, each to their own. Link to comment Share on other sites More sharing options...
anthonym Posted July 23, 2019 Share Posted July 23, 2019 each to their ownso true. Link to comment Share on other sites More sharing options...
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