The speedometer cable on the MGF is made up of three sections. The first runs from the back of the instrument panel, through the bulkhead and connects to the second section underneath that black plastic panel in the bonnet. The second section runs under the floor and connects to the third section roughly just under the seats. The third section then goes up into the engine bay, across the top of the engine, and then down to the top of the gearbox.
The sections are separated from each other by simply pushing back a retainer clip and then pulling the sections apart.
Perhaps the most awkward section to replace is the first, since you have to get access to the back of the instruments panel. For details on doing this, see
Replacing the tachometer.
The second section is a lot more accessible, but you need to raise the car on ramps or axle-stands so as to be able to remove the under floor belly panel.
Fitting new under floor heater pipes.
The third section is even more accessible, but you will still need to raise the car on ramps or axle-stands.
A significant point of speedometer cable failure is that when the speedometer no longer registers movement, the power steering EPAS also registers no movement, but if the car is actually moving and therefore the engine at high revs, the EPAS will cut out the power steering after 30 seconds, and the red dashboard EPAS warning light will come on. It will then remain on every time the ignition is switched on, until the cable is repaired. There is no reason why the car cannot still be driven, though you will experience very heavy steering at slow speeds and when parking, but once you get over about 30 mph, its hardly noticeable. There should be no damage done to the EPAS during this time, but you can remove the power steering 40A fuse from under the bonnet if you so wish. Replacing the speedometer cable automatically correctd this EPAS fault condition
Replacing the third section:
Raise the rear of car on ramps or axle-stands.
Release the speedometer cable from the 2 under-floor clips 'A'.
The cable will simply pull down out of the rear clip, but the clip next to the cable joint is of a different design. The lower section of the clip effectively hinges at the end next to the speedometer cable, and is held in place by central toothed edge. When released, it simply swings down.
Separate the rear cable from the middle section by pushing back the outer retainer 'B', and then withdraw the rear cable.
From inside the boot, remove the engine grill cover.
Looking straight down the rear engine compartment wall, you will see the speedometer cable 'C' entering the gearbox 'D'. .
Note the path that the speedometer cable passes through the engine compartment. It needs to be as smooth a curve as possible.
Here you have an option: you can disconnect the cable from the cable union gear assembly, or undo the bolt that that holds the assembly keep-plate. I preferred the latter, since it allows you to undo and then refit the new the cable to the union away from the engine bay, with less chance of damaging the thread. Either way, once undone, raise that end of the cable, and withdraw the whole cable.
If you have opted to remove the whole assembly, then note that there is a rubber seal on the gear assembly. Be careful not to damage it.
Undo the cable from the gear assembly and screw on the new cable, ensuring it is tightened to 10 Nm.
Here you can see the cable disconnected from the gear assembly, and also the state of my broken inner cable.
Feed the new cable down through the engine compartment, making sure it follows the same route.
Refit the assembly, lining up the hole in the assembly keep-plate and refit the retaining bolt.
Underneath the car, refit the two cable to each other and pull the outer retainer over the connection, making sure that it has clipped home.
Refit the cable to the two retaining clips
The following is an extract from TECHNICAL BULLETIN NO: 0005 ISSUE: 1 issued 02 July 1997
SPEEDOMETER NEEDLE FLUCTUATION - CABLE
Needle fluctuates particularly at speeds between 40 and 50 mph. May also be accompanied by slight ticking or rattling noise which has been transmitted through to the instrument panel area.
Speedometer inner cable drive connections poorly matched.
Confirm condition reported by road testing vehicle.
The following action should only be applied if speedometer needle fluctuation is greater than 2 mph (3 kph). If fluctuation is less than this, explain to the customer that condition should be regarded as normal and cannot be improved.
In order to reduce fluctuation it will be necessary to follow a process of elimination.
Starting with the under bonnet connection (illustration 1), separate both halves of the cable joint, turn inner cable 1 flat clockwise and re-connect.
Carry out further road test to assess improvement. If no change, continue the same action with the remaining connections in the order listed, re-testing vehicle after each action. Cease rectification process when road test result is satisfactory:
If the above actions fail to improve condition, repeat the sequence in the same order, i.e. turn the inner cable a further flat.
It will not normally be necessary to replace any parts to rectify this condition.