You have a mechanical speedo if your car is an 82-89 Camaro or an 82-85 Firebird, TA, etc. (some of the base models may have had the mechanical in later years).

Your speedo won't read correctly if you've swapped in a rear end (or trans) with a different gear ratio. Check the following link for the drive and/or driven gear(s) you'll require for a T-5:

https://www.thirdgen.org/forums/tran...ve-driven.html

Speedo problems: The cable itself is frayed or broken; the cable housing is gummed up with years of crud; the drive and/or driven gears are worn/broken; the speedo head is faulty; the cable housing has been burned by headers; the cable is kinked; or the tire size has been changed from OE. If you've recently swapped in a different speedo head or new cable, make sure the cable is seated correctly at the cluster and tail shaft.

I'd try cleaning and lubricating the cable before I suspected the head itself or the drive/driven gears. With the cluster removed, pull the cable from its housing. Inspect it for burrs, fraying or breaks. Unscrew the housing from the tranny, then shoot brake clean or some other cleaner down the housing from the cluster end until the fluid is clear. Brake clean will dry rapidly. While you're at it, you might inspect the drive/driven gear for problems. Button up at the tranny. Clean the cable itself, then put a glob of Napa's Sil-Glyde (mentions speedo lube on the tube) in your palm and run the lower 2/3's of the cable through it as you thread the cable back into the housing. Don't over lube. You'll probably have to manipulate the cable a bit to reseat it in the driven gear at the tranny end.

For more info about the cluster removal and the trip odometer repair, check the following link:

https://www.thirdgen.org/forums/faq-...-fix-pics.html

JamesC

 

Edited to the above post.

JamesC

 

JamesC
I have a cluster from an 84 t/a w/all gauges including tach.....I want 2 swap out the SE cluster which has dummy lights and no tach. Can you share any details bout this swap....engine and trans is from an 83 berlinetta turbo 350

 

So in my 87 If I went to aftermarket mecganical speedo it would be pretty straight forward?I wouldnt have to worry about VSS or a digital dakota box or anything like that?Thats something I`ve been searching for.Thanks.

 

Check the tech articles. IIRC, all you require, aside from the new cluster, are new senders.
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The OE speedo cluster has a VSS, so I'm unsure.

JamesC

 

James,

The link to the trip odometer repair isn't working, something happen to the page its on or something else? Says "error 404, page not found" when I click on it.

 

Hey, Ozz,

Thanks. Repaired.

JamesC

 

Think this could become a sticky?

 

My issue seems appropriate. Recently put new speedo cable in and the speedo needle won't stay steady. from 0 to about 15 it bounces like nuts, then above that it stays a little more steady but not like it should. the heavier i get on the gas the steadier it is (cause it swings up so fast). most of the time though, its just so bouncy.

 

There are a few places where the cable attaches to the body of the car to keep it in place. IIRC there are three 10mm bolts with a small aluminum clip. If you didn't put those back, or routed your cable differently it will have a tendency to travel, which can cause the needle to bounce. Thats exactly what happened to mine. New cable, got lazy and didn't bolt it down correctly. Needle bouced until 35-40 mph. Got back underneath, put the bolts in and the problem went away.

 

thats what I thoughtmight be the issue, cable just torquing and bouncing around. The old one had no clips, or I would have used them. My car was hacked bad when I bought it and have been undoing the damage for 6 months now. Would you happen to remember just where these clips were? Or how the original cable was routed?

 

I remember one being on the firewall, and I believe two were under the body. I remember they were difficult to get at. You could probably make some with television cable hangers. Just make sure you have a clean unobstructed path. Go under other cables, hoses etc instead of over (if you can). At the top where it enters the firewall use a slight curve, don't kink it.

 

Interesting. I've never heard/considered that that might causes issues.

JamesC

 

My Speedo Jumping like crazy right now So ill try and clean/ check the cable first. 87 firebird. looks like to try an replace the speed sensor is 100 bucks and im not getting a check engine light


(I should have read more closly)
my 87 has electrical, replaced speed senosor couple times, no luck

 

What about those of us with 90-92 cars? What is involved if we change from a tire/wheel OD of 26.1 to 25.7? Can we just bring it to the dealer and have them electronically calibrate it by just entering in the new wheel/tire OD?

 

Though electronic, the 90+ cars still have drive and driven gears.

JamesC

 

i have a 1991 z28 auto and the speedo doesnt work? i just bought the car and i will be replaceing the vss is there anything else it may be after i replace the senosr and it still wont work?

 

Hey, james,

I'm not a electric speedo kinda guy, so I'm afraid I won't be of much help. Apparently, your problem isn't unique, so I've often seen mention of it on the boards. The VSS is often culprit, but there could be other issues as well. I suggest a search for more info.

Best luck on your adventure.

JamesC

 

Ok so I just bought my 89 Camaro that had a 1980 Corvette 350 swap. The speedo would read 55 but I was actually going 75. Or it would ready 15 and I'd be going 30. Any Ideas?

I ended up breaking the needle off my speedo by accident trying to see if maybe the spring was stretched or something, but I don't have anything to reference it.

I also have a problem with my tach. It works fine until it gets to 2500RPM where it sticks until it jumps to about 4500 RPM depending on when I shift. Also I have a manual tranny in it. I haven't been underneath the car so don't know much about that.

I read on here about the issue being solved by grounding the black/white wire that used to connect to the ECM. Only problem is that I found 2 black/white wires from 2 different harness connectors. Grounded them both and still not fixed. I did however notice that one of the harnesses coming from the back of the cluster had a lot of pink wires which runs over to the passenger side. It is plugged in to another harness not sure where it runs or why. I assumed the tach would be controlled by that harness as it's the one closest to the tach when all plugged in. Now, I'm attempting to find a OE cluster replacement which is harder than I could have ever imagined. The 145mph sells for over $200 on ebay and you can't even be sure it works. To me, I'd rather pay the extra $400 for the Dakota Digital cluster. Only issue I have now is that I don't want to waste money buying the digital cluster if the problem is still going to be there. Anyone have ideas of a fix? Maybe I'm grounding the wrong black/white wire? Also this is my first carb engine so I'm getting to learn a lot about it.

I did inspect the speedo cable and it appears to be new as if the previous owner tried to fix it with that. Still doesn't explain why the tach would stick at 2500RPM then jump onces it gets higher. Oh well, I'll wait for a reply.

 

Welcome to TGO. Since the speedo is mechanical, I'd use post #1 as a troubleshooting guide. Also you might repost your tach question in the electronics forum for more responses (the speedo and tach are unrelated issues unless the cluster isn't seated correctly).

JamesC

 

A mi tambien My car has soo many electrical gremlins it is scary. slowly working back...

 

20 years ago people advised to use graphite based lubes on the speedo cable. I have been using this.
https://www.napaonline.com/Catalog/C...006382728&An=0

Is that a bad idea? Is Sil-Glyde better?

thanks,
phil

 

What would i do if my speedometer is off (saying im going slower then i am) and i have a 88 trans am gta with a 700R4 and 3.73 gears

 

It means that in the past someone changed either the tire size, the rear gear or both without changing the drive/driven gear on the transmission/recalibrated it for the difference. You will need to find which to fix it. A good transmission shop should be able to hook you up with what you need.

 

Though what Ozz says remains true, you probably have an electronic set-up, not a mechanical.

JamesC

 

Isn't that just a recalibration of the module? Or is that all done in the Speedo with the electronic speedo?

 

Both the mechanical and electronic are calibrated by using the correct drive and/or driven gears in the trans. The difference is that the electronic has the VSS in the tail shaft of the trans, while the mechanical has it on the backside of the speedo cluster.

JamesC

 

n

 

my speedo cable does not seem right.i will try the above mentioned suggestions,,,my question is,,should the needle part in the cable be able to spin freely with your fingers if you try to spin it?,,because my needle on mine is pretty stiff,,and it does not want to spin.if the answer is yes,,then i know my speedometer problem is related to this...thanks for any replies

 

Yes.

JamesC

 

Help on an easier way to connect the speedo head to the cable?

 

My speedometers was "BOUNCY" after a tyranny swap! So I inspected it and it turns out it was simply RUBBING against the body. A simple fix. All I did was unscrew it off the trans and rerouted it and done. Just thought I would share in case anyone has a similar problem

 

Do you think simply securing it down would work? I only have one mounting point for the cable down near the transmission and it kind of floats up in the engine bay. Only bounces, more like jitters up to 30mph or so, by 40 it's all smoothed out.

 

Hey I could use some help, i have an 86 trans am with a 700r4. I put in a rebuilt transmission and a speed sensor that uses a magnet which I'm assuming means electric. I accidentally got rid of the original speed sensor that came with the car when I got rid of the transmission and I'm pretty sure it was a mechanical speed sensor with a driven gear on it but your original post says that in 1986 they used electronic speed sensors. I'm pretty sure the original trans had a red drive gear on the tail shaft as well.

I'm pretty sure my car needs a mechanical speed sensor but the original post says otherwise.

 

ive had similar problems w my speedo..itd read higher than i was going. So at 20MPH itd read 30. And at 60MPH itd read ~90 but bouncing up to ~100.

More steady at lower speeds, and itd get much more jittery the faster Im going, so say at 70, itd be jumping between 95 to 110.


Turns out the problem waas......low transmission fluid? Since adding more a little at a time it has been getting ever more and more steady. Its still reading a bit high, but essentially all the eratic bouncing and jumping has been eliminated. (think the trans fluid is still a tiny bit low.)


Does this make sense that low trans fluid would almost entirely be the cause of a jumpy/inaccurate speedometer? Ive got an 87 iroc automatic/700R4

 

There seems to be some confusion about this in some of the above posts.
The original post is describing the different SPEEDOMETERS in different years. Cable driven or electric signal driven. The SPEED SENSORS or VSS on ALL third gens are mechanically driven gear set ups. There are different VSS for different years and setups.
If you have a later tranny with a magnetic or impulse VSS, you will need an aftermarket signal converter to use with the original electric SPEEDOMETER. There is no way to make a cable driven speedometer to work with any electric input, but you can swap a electric speedo into the guage cluster.
HTH