speedo lube?

[mrspeedyt]

i was driving my 1968 327 and powerglide impala wagon... crusing along at 65 when the speedo needle suddenly pegged at 120 and made a screech :eek: that belongs in a horror house. I quickly pulled over and disconnected the cable at the back of the speedo head:(. anybody have any luck spraying some lube into the back of the head and have the speedo actually work again??

[Guest Old48Truck]

It appears to me that your cable went south. I'd check into that before spraying anything into the speedometer head.

[mrspeedyt]

thanks for the tips. i hope it's the cable causing the problem... i'll lube it first and reconnect things...

[Guest]

When the mechanical cable to the speedometer head looses lubricant the cable starts to whip in the housing. This whipping effect causes speed to fluctuate/pulsate at the back of the head and makes the spinning magnet in the head give sometimes a wide sweep of reading. The sound can be a chirping sound that gets more pronounced at a certain speed then goes away, this coincides at the same time as the needle makes this sweep.

BTW, this cable along with door check/hinges, generators/starters with lube cups, hood and trunk latch and hinges plus fuel doors, all door-trunk locks, all should be done at least once a year, the exception would be generator bearings to be done at each service or if this car is a show car-every six months.

Don

P.S. do not oil the cable-use white lithium grease.

Edited October 20, 2011 by helfen (see edit history)

[mrspeedyt]

roger on the white lithium grease. ain't a show car ... just a very nice survivor...

Edited October 20, 2011 by mrspeedyt (see edit history)

[Guest MORRISGAUGE]

You should have your speedometer gone through. If it was making an audible noise, the lubricants internal to the speedometer have likely all dried up and have caused significant wear to the gearing. Most commonly, the magnet shaft siezes which can shred your cable. On average, speedometers should be professionally serviced every 10 years to ensure there longevity and accuracy.

[Guest Jim_Edwards]

The proper cable lub is powdered graphite. Comes in a small tube and should be introduced into both ends of the cable. Liquid lubs will generally evaporate quickly and then you'll be right back where you started.

[rocketraider]

Lubricating the head itself should be done sparingly. Used to watch a speedometer tech in NC do it, and he would generally use some very fine oil, such as sewing machine oil, and apply it with a pin, 1 drop at a time.

Graphite lasts longer, but I was taught if you use white grease it should be applied only to the lower third of the cable to avoid it working its way into the speedometer head.

I went thru a similar scenario on me wagon last week, but discovered the problem was the cable had worked out of the clip on the speedometer head. Messing with it underhood, managed to pull the upper cable housing back too far (it offered no resistance, is how I determined it had come loose) and then had to disassemble the dash and cuss and squall for a while to route that cable back thru all the bracing etc.

While the head was out I sprayed a little WD40 in the cap and dripped it onto the speedometer with a small scribe. Buttoned back up and except for an occasional loud buzz the first 20 or so miles it is now working fine.

But I've got a backup on the way in case it does just up and die. 350k miles, it has spun around a zillion and a half times, I'm sure.

BTW- diggin' that wagon, Speedy.

[NTX5467]

Actually, there is a real speedometer lube, ACDelco ST800, as I recall. Kind of a jelly consistency in a tube.

As the inner surface of the "housing" is worn away by the turning of the speedometer cable inside of it, it can expose "the guts" of the housing itself, especially if it's a plastic housing rather than a metal housing.

With the plastic housing, it's reinforcement is a metal mesh of sorts. When the cable wears into and then against it, the cable can come to a stop really quickly. When the wear surface of the metal housing wears away, I suspect it'll just be "noise" and possible indicated-speed variations.

What I suspect happened is that the bushing which holds the outer speed cup (which the cable slides into) went away. When that happens, the close alignment of the two speed cups can get too close, which will make the inner speed cup try to turn as fast as the outer one, which it shouldn't do . . . which also causes the speedometer needle to peg. The continuous noise you heard was probably the two speed cups grinding against each other, plus the outer speed cup turning against the pewter housing the bushing used to be in.

We saw such situations on the '79-'86 Chevy pickups quite often, at elevated miles. On those speedo heads, the original basic "bushing" was plastic, but the "fix" was a bronze bushing (which looked similar to what was used for door hinge pin bushings on the same vehicles).

Don't forget to focus, also, on the other end of the speedometer cable! The gears and/or ratio adapater on the transmission end. If the speedometer cable is original, it has the ends of the cable "squared" on the ends, but any replacement cables will most probably have one end which has a glued-on plastic tip. Be sure to verify the integrity of the speedometer gears, driven and drive, for good measure.

Just some thoughts,

NTX5467

[mrspeedyt]

thanks for the tips!

[Guest flowing1]

NTX - When you talk of this "metal mesh" are you referring to this type of material? Custom Wire Cloth - Belleville Wire Cloth Co - Cedar Grove, NJ

What size mesh would they use? Something fine like a mesh that has about 80 wires per inch? Or something that is maybe more like a 5 x 5 wire mesh, which only has 5 wires per inch and leaves larger amounts of open area, but will be less of a reinforcement.

[Rusty_OToole]

You should be able to get speedo cable lube at any auto parts store. $1.79 a tube, a lifetime supply for most of us.

To lube the cable, disconnect it at the bottom or transmission end. Pull out the inner cable and wipe it clean with a rag. Lube the cable and put it back in the housing. Do not lube the top 6" to 1 foot. You do not want the lube working its way into the speedo.

This should be done every 10 or 20 years.

If the inner cable is worn out or broken you can buy just the inner cable. But given its age you may as well buy the whole thing. Chev used the same cable from 1948 to 1972.

[Terry Bond]

We just lost the speedo cable in our MG recently. The noise described sounds very familiar. Thought it was the speedo head at first but when we pulled out the cable only about a third of it came out. Pretty easy fix. We used the lithium grease. Our new cable had some plastic cups at each end to keep the lube inside the casing so it wouldn't work its way up into the speedo head. Had to get it fixed quick since Susan just signed up for the new AACA mileage award program.

Terry