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My 69 does 5mph in park.

4K views 32 replies 16 participants last post by  73-84 IMSA W 
#1 ·
My speedometer runs at 5mph when I'm idling(10 at fast idle), and i'm assuming that the speedometer cable is the culprit. Does this sound right?

Is there any way to lube the cable to correct this, or should I replace it?

Thanks!
 
#2 ·
Interesing problem. The speedo and tach are both mechanical. If the speedo is showing 5 mph in park, is the tach reading the correct numbers? Maybe someone swapped the cables under the dash. If not, I doubt the speedo cable is at fault. More likely the speedo head needs some work.

:cheers:
 
#4 ·
I'm definitely not mistaking the Tach and Speedo...give me a little credit! :D

The tach seems fine, reading about 800rpm at idle and 1500rpm at fast idle, but the speedo shows me moving and even the odometer turns with it. The speedo doesn't jump up like the tach does when I rev it, it just runs at 5-10 mph.

Oh, and this is a manual tranny, and the speedo reads accurately when driving(It's not 5-10mph off).
 
#23 ·
sorry but i don't believe the odometer is moving when the car is at a dead stop. Its all gear driven. If its all stripped out the vibration might cause it to turn but it would probably move both ways. Check again.

If the speedo reads correctly when moving then you don't have any real problem.
 
#5 ·
Does the speed-0 work at highway speeds? Do you think the cable could be broke and the engine vibration is causing the cable to turn? I've seen stranger things happen. (Just can't see any other way the cable would turn all by itself.)
 
#6 ·
Both the speedo and tach use a "flying magnet" to drive the pointer(s). I'd have to say that the tach is driving the speedo. Time to pull and get a rebuild. Someone may have another idea, but that's my shot..

:cheers:
 
#7 ·
Ok, so if the "flying magnet" theory is correct, I should be able to disconnect my speedo cable at the tranny, and it would still be reading 5-10 mph... If it just quits reading, then the issue would be with the cable or tranny connection. Sound right? I'll try this test tonight and see what happens.
 
#8 ·
Sorry for not giving correct amount of credit.
I just don't know you, Doug ... so first things first.

If the unit works well at driving speeds (and correct),
then the speedo itself must be getting hung up at the lower end of the range.
I'm afraid it is not the cable, gear, or tach. You likely need another speedo,
or I have seen replacement "guts" to rebuild a speedo.
:buhbye:
 
#9 ·
Speedo and tach are not related and do not run together. Each has a separate cable and neither is dependent upon the other.

Check your speedo gear in the trans.

Engine idle speed should not affect the reading of the speedo since the tranny is not turning in Park.

:thumbsup:
 
#10 ·
The speedo runs directly off the output shaft of the tranny, so there's no way the speedo cable can actually be turning unless the prop shaft and rear wheels are. Are you sure the needle isn't just not returning to zero properly? That sounds like the most obvious cause to me. The return spring inside the speedo head's maybe not returning the needle back all the way when it's "idle". The spring is the only thing that determines the needle's position when there's no magnetic drag from the speedo cable rotating. (well I guess the spring and the zero stop, to be more precise) Might need your speedo going over by an instrument guy.

:thumbsup:
 
#19 ·
I agree with Tim on the magnetic field,sometimes strange things happen :crazy:

Take for instance ever since my motor swap if you turn the key off the motor continues to run,but pull up on e-brake handle and it dies :WTF now go figger :crazy:



Kevin
 
#22 · (Edited)
Calling ERGON, Ghostbusters....all this talk of magnetic interferrance ....

first test....kill the engine/park the car....what does the speedo say..?? if it says 5 mph....you problem is....when someone pulled the needle head off to work on the speedo once, the cup inside has a stop, and so does the needle...they both return to the same spot, dead nuts on, in counterclockwise direction....the speedo needle is put on the shaft rong, it's nothing but a crimp/slip, but pretty secure so you can NOT TWIST IT, you must pull it directly off the needle pin/shaft, straight so as not break the shaft, and then line it up correctly......

my memory is vague too, but on a later shark interior 78 up.....does the speedo go from 5-85 mph??? wonder if that has something to do with it...
the scale shows no zero....so I wonder if there is your answer, I dunno about a stop on the needle and how that aligns on a late shark....mine is/was a '72.....

but all the speedos of that era were the magnet in a aluminum cup type spring loaded device....
 
#25 ·
ok, well for an update on this, after some further testing I think I may know what is happening.....

I don't have the problem when I put the car in neutral, just when I idle it with the clutch pressed in. My guess is that the clutch is disengaging enough to shift gears but not completely. I think its just barely slipping on the flywheel, which is what is causing the tranny to turn a little. I have had the driveshaft off and on a lot lately, and I think that when it's out, the lost resistance of the stopped rear wheels is allowing the slipping clutch to turn the tranny just a little bit. I'm putting my driveshaft back in soon, and will take a look at it again. If it doesn't do it with the clutch pressed in then, I think That a slipping clutch is what is going on.

Thanks for all of the ideas and suggestions. I love having a place to throw out problems and bounce ideas off other people.
 
#33 ·
Count your blessings, that must be a damn fast car that just won't set still:crazy:
 
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