speedo jump in 1971 2+2 V12 Auto

[club3999]

Help Please
I am a new e type owner, always a dream car for me and living the Tampa USA
My new (to me) e type has speedo jump or swing at about 60 mph to 80 mph
Can anyone help me diagnose?
I would hope, and think, its the speedo cable that needs replacing?
If so are originals still available and are they easy to fit.
Thanks for any advice
Mark
:D

[christopher storey]

The good news is that all relevant parts are available . What is slightly more difficult is that determining the cause of this type of problem is not always that easy. You are right to start by replacing the cable . This is a messy but not difficult job that can be done from under the car at the gearbox end , and from under the dash at the instrument end . However, it can also result from a fault in the speedo itself ( in which case there are a number of people in the US who overhaul them - look at various threads on Jag-lovers) or from problems with the right-angle drive gear at the gearbox end. If this gets stiff or sticky it can produce your symptoms. However, as you suggest, start with the obvious first i.e. the cable

[Heuer]

I agree with Christopher that the cable is the most likely culprit but even a new one can cause problems. This is because it is the curvature of the cable as it routes back to the gearbox. Check the routing as a previous owner may have fitted a replacement poorly and ensure it has the gentlest curves possible. One fix I know of is to use the speedo cable from the 2+2 as it is longer (108" I seem to recall) so this allows much gentler curves.

[Woolfi]

May be there is a more simple way, how to cure the "jumping". Separate the speedo-cable from the speedometer and put some oil inside the end of the cable. If the oil is reaching the end of the cable at the gearbox, MAYBE the jumping will reduce or stop. If you blwo pressed air inside the cable, after you have put some oil, the oil will reach the end much quicker. Maybe you have toe drive some days, until the oil is reaching the end and the jumping will reduce.
When the jumping has reduced bot not stoped, you can put some grease into the cable. Grease is working like a "turn-absorber".
The older the cable (rust, dirt, lack of oil) is or the sharper the curves are, that bigger is the power you need at the beginning of the cable gerabox, to turn the cable at the end at the speedo. The inside of the cable is doing "longline-turn swinging". The movement of the beginning at the gearbox and the movement of the end at the speedo is not steady / equal. If you can reduce the force to turn the cable, that "longline-turn swinging" is reduced. I had such a problem at my car. After putting oil and grease (motorcycle chain grease) inside the cable, the swinging has reduced a lot, but doesn't diappear completely.
Also the speedometer can cause the problems. This problem to cure can be more difficult.
You have to excuse me simple und and little bit crazy english, but I am german.
Never forget: oil is the "soul" of every turning-machine.
Regards Wolfgang Gatza