Crown wheel and pinion options

[Weavie]

I am rebuilding a 1997 Caterham 1700 Crossflow Series 3LC and I want it to be a good road/touring car, not necessarily for track days. Before the rebuild started, the engine would rev to 6000 rpm but, with the standard 4-speed gearbox, I always wanted to change up to give a better cruising speed on dual carriageways, etc. It has a Marina live axle which I have to take apart to determine the final ratio on the diff, but I am led to believe it might be a 3.6 to 1.
Fitting a 5-speed box means carving the body about which I am reluctant to do so can anyone please advise me on alternative diffs that might give the car "longer legs" at the top end? It is also fitted with a Quaife unit which will be serviced, although Quaife have said there is nothing that they can do to help me with my challenge.
Many thanks

[downsman]

With crossflow power and 4 speed box I think 3.6 is your best bet. If you go for a longer final drive, you will lose acceleration.

The great thing with the 5 speed is you can go for a shorter diff like 3.9 to get better low gear acceleration, but still have sensible cruising revs.

[Weavie]

Have you fitted a 5-speed box into a narrow body Caterham? How easy/difficult is it and what gearbox would you use?
Steve

[AdamIndy]

Are you not just better off changing to a type 9 5 speed box? It will bolt straight up to your engine. I believe the gearbox mounts are further back than the 4 speed(type 3?). Depending on your current gearbox you may also need to shorten the propshaft.

As said above, you could then change the crown wheel and pinion to a 3.9.

In my car(MK indy) I run a 140bhp Xflow with a type 9 box and 3.62 rear diff. 60mph is around 2500rpm in 5th on 15" wheels.

[Weavie]

Please excuse my ignorance but what is a type 9 5-speed box? How would I know it if i saw it?
Thanks

[AdamIndy]

Haha no problem at all.

The type 9 gearbox was originally found in the Sierra/Capri. It is the go-to box for the majority of kit cars.

Think of it as the newer version of yours(assuming yours in a type 3 or "rocket" gearbox). It's a 5 speed with fairly "spaced out " ratios. Ideal for a road/touring car. They can be picked up in decent condition somewhere in the region of £200-£400.

1st gear is short(around 30mph), mine will wheelspin right through 1st from tick over in the dry if that's your thing. The other 4 are less frantic.

This website will give you all the information you may need.

http://www.type9gearbox.co.uk

[Weavie]

Brilliant! I am on a steep learning curve with the Caterham so any help or advice is much appreciated. My last experience of taking cars to pieces and rebuilding them was a Mini Cooper 998cc that I used for restricted rallies in sunny Wales back in the 60s!
Thanks very much.
Steve

[downsman]

My Sigma Roadsport 125 has the type 9 5 speed with 3.9 crown wheel and it's great. If you have some spare cash, it is worth getting at least a higher first gear installed from what people tell me. I'm too tight, and will live with it until it needs rebuilding

[Weavie]

Hi Downsman

Thanks for the advice. As you say, better to do it while it's being rebuilt
Steve

[bcr5784]

Weavie said:

Hi Downsman

Thanks for the advice. As you say, better to do it while it's being rebuilt
Steve

Also bear in mind with the T9 you can get a fairly wide variety of ratios. Not that cheap for more radical changes but worth a thought to raise first gear for instance. eg http://www.s262612653.websitehome.co.uk/DVAndrews/... Lots of other suppliers too.

[Tango7]

HI, you mention having to carve the car about to get a 5 speed in but what makes you think that? 5 speed boxes were a fairly common fitting in cars of that age and I would expect it to be a straight fit in

[Weavie]

I was told that by an ex-Caterham employee when I asked him some time ago. It would be great if it was a direct replacement. I am going to First Transmissions tomorrow with my current gearbox to put it alongside a Type 9 5-speed to spot the differences. I'll let you know how it goes.

[Weavie]

Sorry, the company is called First Motion Transmissions.