Gearbox speed sensor leak

[Eriedor]

Had my gearbox rebuilt over the summer, just returned to the car after it's sat for 2 months and found a ~8 inch oil stain under the gearbox sensor.

Is this just a matter of putting some silicon or other sealant around the sensor joint? Or something more serious to fix?

 

You can see a small drop forming, left, 2/3rds down below where the sensor meets the gearbox

[Jonathan Kay]

I still find this assembly confusing. Previous discussion, including use of threadlocker.

You can remove and reinstall the sensor (and the cap on the other side) with the gearbox in place. Slackening the gearbox and engine mounting bolts allows the tail of the gearbox to be shoved from side to side.

Please let me know if you'd like an Assembly Guide.

Jonathan

[John Vine]

I suspect the small oil seal on the drive spindle is leaking.  You'll be able to see it once you remove the circlip and top-hat.

It would have been inserted with a gentle tap from a drift or suitable socket.  But I don't know how easy it is to replace in situ as I've never had to do it.  You may have to prise out the retaining cap on the opposite side of the tail shaft in order to extract the spindle and then knock out the seal.

No doubt someone who knows will be along in a minute.

JV

[Wrightpayne]

Seal is relatively easy to change - I've done mine 3 or 4 times to try and resolve a leak. Its all from underneath and only needs the sensor / circlip / tophat removing. The seal is a normal oil seal - I posted the spec on the forum some time ago (three numbers which give overall dia, depth and inner bore)

I've also changed the speedo drive with the box in situ, which is a lot more challenging. Still didn't cure the leak.

I have a belief that the speedo drives are tapped to knock their retaining plug out, however, this affects the integrity of the metal ferrule on the plastic speedo drive which I suspect then passes oil.

I'll have another go at the leak this winter.

[Graham Howard]

I never managed to cure the leak on mine, changed to a wheel sensor. Have a look at this thread.

https://www.caterhamlotus7.club/forum/techtalk/change-gearbox-speed-sensor-wheel-speed-sensor-k-series

[ECR]

Not tried it, but according to Steve perks, it's possible to fit two seals, one behind the other. Maybe this will double the leak time? :)

[Jonathan Kay]

"Seal is relatively easy to change - I've done mine 3 or 4 times to try and resolve a leak. Its all from underneath and only needs the sensor / circlip / tophat removing. The seal is a normal oil seal - I posted the spec on the forum some time ago (three numbers which give overall dia, depth and inner bore)

"I've also changed the speedo drive with the box in situ, which is a lot more challenging. Still didn't cure the leak.

"I have a belief that the speedo drives are tapped to knock their retaining plug out, however, this affects the integrity of the metal ferrule on the plastic speedo drive which I suspect then passes oil.

"I'll have another go at the leak this winter."

I've never seen a decent set of assembly notes and photos of the components.

Please, Ian...

Jonathan

[Eriedor]

I'd love some notes on changing it, I'm quite the amateur! Irony is it never leaked before the rebuild and was loose, after rebuild the sensor is nice and tight and leaks!

[Eriedor]

Spoke to R&R, sounds like blanking and using a wheel speed sensor makes the most sense, I don't want to keep chasing down this leak.

Has anyone got experience doing that? Can I buy the blanking plate or does it need fabricating? Same for bracket for the wheel speed sensor?

https://caterhamparts.co.uk/senders/6707-rear-wheel-speed-sensor-kit-de-dion-cars.html

[John Vine]

Re a conversion, the link in #5 is a good starting point. 

What year is your car, and what speedo do you have at the moment?  (If you can post the Caerbont part number, that would help.)  Fully programmable (sensor pulses per mile) electronic speedos didn't appear until around 2004/5.  If yours is the previous electronic model, you might have a problem getting it to interpret sensor pulses properly.

Sensor-wise, I think you have two choices: one driven by a driveshaft-mounted reluctor ring (the set-up on current models) or one that detects (say) propshaft or hub disc bolts.  But I don't know whether these will talk to your existing speedo.

JV

[Eriedor]

Ah yes I missed that link. Mine is a 2001 so will need to upgrade my speedo it would seem. 

Hub disc bolts sounds like a simple solution. 

Found this guide which suggests blanking the existing sensor on the gearbox is a gearbox out job which is annoying. Interested to understand how I blank it too.

https://www.caterhamlotus7.club/guides/technical-guides/speedometers