email me

james [at]
[dot] com

Site updated
20 March 2011

Speedo Cable

by James Mather

MG Midget 1500 5 Speed Conversion. Speedo Drive cable

The bottom end of the Midget 1500 Speedo cable, left and Sierra (hacked off end) on right. Difference appears to be the thickness of the flange.

Speedo cable both
Speedoc cable modded

Hey presto, 2 minutes in the lathe and the MG outer cable fits the Sierra gearbox. The nylon bush which used to be inside the MG flanged bit is removed. The flange is soft zinc so take care with it.
The problem now is that the MG inner cable square end is too big for the Sierra gearbox. See “A final word”, below, for how to solve this.

..and a final word (or two) on speedo cables I ended up using the standard MG midget cable! The MG inner is too fat for the Ford gearbox so strip back the outer strands of the inner for the bottom 1” of the cable. You will find that the inner cable is actually several cores. The inner core will still be square and will fit inside the Ford speedo drive thingummy. I found the best way to remove the outer strands was to file through them on two opposite sides and gently remove them. Avoid unwinding the strands as you won’t get the final bit to lay flat again. To stop the rest of the cable unwinding, I ran soft solder into the cable, where my new thin bit became the original size again 1” from the bottom end. I believe that some Sierra drive pinions are plastic and that it is possible to heat the end of the MG cable and use it to melt a new square hole in the cable driver. I don’t know because I have never done it. Let me know.

I removed the little right angle gearbox from the speed head. The cable comes through the RH side (as you sit in the car) of the tranny tunnel. The hole needs to be 4” to the rear of the cross member and the bottom edge needs to touch the floor. I made mine about 1” dia to allow for movement of the transmission. It then sneaks under the carpet in front of the drivers seat (in RH drive cars) behind the X-member. It then curves forward over the X-member. I didn’t want to drill the X-member, but a 13mm hole would let the top end of the cable through. You need to avoid sharp curves. Alternatively you could drill another hole in the floor and take the cable under the car and into the engine compartment and through the original hole. It will need to be as long as the Simplon Tunnel and you will have to buy it! I like my idea:-) The cable then disappears behind the RH footwell RH side trim panel. It emerges from the front of the trim panel, curves back towards the driver and straight into the back of the speedo. A “P clip” holds the cable up to the scuttle. The standard length is perfect.

The circlip is awkward to fit into the gearbox to retain the bottom flange so it may be an idea to fit it before the rear mounting is finally in place.

Speedo Calibration:

The standard speedo now reads 70 mph at 4,000 RPM in 4th (1:1 ratio same as the old 4 speeder). Popping into 5th drops the revs to 3,200. I have yet to check it but I think I have been lucky with calibration as that seems not too far out. I am told that new speedo gears are cheap from Ford but I know nothing about them I am sorry. I will check the speed over a measured mile on the motorway. 1 mile in 60 secs = 60 MPH!

You can of course use GPS to check accuracy.


Fit a computer?
If you want computer functions and accuracy you to can do what i a pushbike speedo too. Cost me £10. Pics of the hub sender here...

Speedo bracket1

Bare bracket fitted to brake backplate. Magnet fixed to drum with epoxy is under white silicone. stuff.

Sender mounted with supplied O rings onto my bracket.

Speedo bracket