[the nitro man]

i know it's not electrical, but this is the closest place that it fits.

my wife's 1985 ss monte carlo's speedometer is screwed dead up. it reads 5-10 mph slow while it's below 35-40 mph, but after that it starts bouncing around. i pulled the cable out of the speedometer housing & it looked good, so i'm thinking it's the speedometer or the speedometer gear in the transmission (2004R overdrive.) what would you think?

[cobalt327]

Originally Posted by the nitro man

i know it's not electrical, but this is the closest place that it fits.

my wife's 1985 ss monte carlo's speedometer is screwed dead up. it reads 5-10 mph slow while it's below 35-40 mph, but after that it starts bouncing around. i pulled the cable out of the speedometer housing & it looked good, so i'm thinking it's the speedometer or the speedometer gear in the transmission (2004R overdrive.) what would you think?

It could be the cable rotating at an erratic speed from rust, damage, wear, frayed cable wires, bent/kinked cable or cable sheath, damaged or worn speedo gears/gear housing at the trans.

This can cause the speedo needle to jump, but wouldn't necessarily cause the speedo to read slower than it should. For that to happen because of the cable, it would need to turn slower- which it cannot do w/o almost immediate failure.

If you don't find anything wrong w/the cable, gears, etc., what can also be causing your problem is the speedo head itself. It works by a flying magnet driven by the cable, spinning inside a steel hub that has a needle attached to it.

The hub is pulled along by the rotating magnet; it tries to "catch up" to the magnet, and this is what causes the needle to indicate your speed. If there's any unneeded drag on the hub- caused by dirty or tight bearings, or a build up of dust and dirt inside the mechanism- this can cause a lower than expected reading and an erratic needle.

A thorough cleaning w/a soft brush and a can of compressed air will often be enough to put the speedo back into service. This will require that the dash be partly disassembled to get to the speedo head. Once it's out and you're able to clearly see it, you'll likely see the problem.

[the nitro man]

i took the gauge cluster out of the dash, that's how i got the cable out of the liner. the cable lloked good. the speedo looked good & didn't feel tight or anything. i guess i'll pull the speedo gear from the transmission & look at it.

[cobalt327]

FWIW, most inner cables can be removed from the outer cover from the trans end OR the speedo head end- whichever's more convenient. In your case, you needed to look at both ends anyway, so it's all good.

You will need to check the cable inch by inch- looking (and feeling- just don't stab your finger or hand w/a piece of broken wire ) for any frayed wires or a shiny and/or worn area that would indicate the inner cable has been binding at that point.

The speedo cable runs right beneath the back side of the inner fender cover (probably made of plastic) and a flat tire that sheds its tread can slam into the fender cover and the speedo cable w/quite a bit of force.

This same area is prone to having road salt, water, dirt, etc. constantly thrown onto the cable cover- especially if the inner fender cover's damaged already.

[the nitro man]

the g body cars cable has to come out from top. they have a crimped on block that won't let them pull from the bottom. i put a new cable in it today & it fixed it. i looked at the cable again & it was perfect. it must have been in the housing, but there wasn't any marks or even scratches on it. it's fixed thats all i care about. 10 bucks wasn't to bad on the wallet neither.