Speedo hunting at lowspeed, and under-reading

jp928

Well-Known Member
#1
74 S2 4 speed. Speedo fluctuates badly under 40kph, from almost zero to 40. Once past 60 its almost steady, but under-reads badly, based on a GPS display. Have partly pulled, cleaned and oiled the cable, no change. Whats the most likely cause - speedo head, cable, gearbox drive?
thanks.
 

colnerov

Well-Known Member
#2
Hi, Usually it the oil in the cable working its way up into the head, cause it to drag and affecting the influence of the magnet on the needle's drum.

Colin
 

jp928

Well-Known Member
#3
And the fix is - remove head, open, then - wash oil out with ? The oil finds its way through the angle drive into the head? I have swapped in a brand new angle drive with no change in behaviour, but I guess if the oil is already in the head a new angle drive wont cure it. If its an oil problem there should be some in the old angle drive?
 
#4
What about some degreaser on a cotton bud or maybe even a drop of diesel?
On the P4/P5 speedo's it's often the odometer that stiffens up causing a drag on the cable so that could be a possible source of your problem.
 

DAK

Active Member
#5
I had exactly the same issue with the speedometer in my '68 TC and tried all of the ideas mentioned above. I even swapped the speedo unit out with the one from my '65 SC and the problem persisted. The issue turned out to be that the nut on the coupling flange on the output of the 4 speed gearbox was not torqued properly. The speedometer worm gear is not keyed to the shaft and is only held in place by the friction provided by the pressure of the output flange assembly against the end of the worm gear. In the workshop manual there is a warning about the need to ensure the nut is torqued to 75 ft-lbs and Loctite is used on the main shaft splines in order to avoid fluctuations in the speedometer.
I retorqued the nut on my gearbox and the speedometer is very steady and fairly accurate now.
 
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jp928

Well-Known Member
#6
No sign of oil on the original angle drive. Have seen issues on a TC re the drive flange not being done up correctly, but that affected the gear change, not the speedo. Checking that area will have to wait until i have to put it up on the quickjacks again.
thanks
 

jp928

Well-Known Member
#8
Pulled the cable inner today, no sign of issues at the end. Fitted a spare speedo head (in MPH, instead of KPH) just to isolate that as a cause. I had thought to replace the inner with a spare I have, but its 90mm too long. I hope I am not alone in not enjoying refitting the dash - those big philips head screws at the left end are a real pain , and why does it keep pushing back when you try to get the right end close enough to get the screws started???
Next I will check the cable is properly held into the gearbox - which, due to the new carpets and underlay, will mean I need to remove the pass seat. If nothing wrong there then I will have to jack it up again and check the output flange!
 

jp928

Well-Known Member
#9
Test drive - no wild swings anywhere, but small oscillations while accelerating, and a small overread at steady speeds. I think that means the problem is in the original speedo head, not the cable or the gearbox drive! Might also get the clock serviced when I get the speedo head looked at.
 
#10
The springback is often caused by either the speedo cable being not quite free where it goes over the ledge OR the Trip meter zeroing cable hitting something at the back. sometimes the plastic surround can also get caught on the foam bit between it and the dash cover (though these days its often gone completely missing).

The speedo repair guys normally ask for the whole panel as bending it can alter all the printed circuit connections, so you fix your speedo but then the tacho or a guage stops working...

M
 

SydneyRoverP6B

Well-Known Member
Staff member
#11
When my Rover's speedo flickers somewhat more than usual, removing, cleaning, then regreasing the cable with graphite grease also delivered improvements. I have had the speedo instrument seize resulting in the angle drive on the back being broken. That was way back in circa 1987. It was making a clicking sound beforehand and the needle was flickering far more than usual. Then it went bang and the needle fell to zero o_O I removed the gauge and took it to an instrument repair place in Marrickville, Sydney. Wonderful job, totally silent upon refitting, no flickering, and beautiful ever since. Subsequently when the needle has started to dance a little, removing the cable, clean, and regrease with the trusty graphite grease has always done the trick.

Ron.
 
#12
Due to repeated faulty senders I drove my daily truck for 2 years without a speedo. Did wonders for my mileage lol. My Rover speedo (ribbon type) bounces around more than Pamela.... :LOL:
 

Peterv

Active Member
#13
As well as a jumping needle, I had a weird fault where the indicated speed didn't change when accelerating and only showed the new speed when you lifted off. (getting a surprise at how fast I was going sometimes) Cleaned the cable with wax and grease remover and a fresh dose of lithium grease fixed the jumping but after several attempts at fixing it I ended up replacing it with a NOS speedo. This one was reading about 20 mph slow so did the re-magnetising trick now it's spot on.
 

jp928

Well-Known Member
#14
Getting the clock serviced was a bad idea. Took it to an instrument place I had used before on a couple of things from the Rover 9 without issue or complaint. A$395, with a minimum of A$330. Wont be going back there. No notices about minimum charges at the counter or their web site. Guess I am stuck with it now, but it will outlast me an its next few owners.
 
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