speedo swap, help please.

[transamfan1981]

Hello,
I want to swap out my stock 1981 80mph spedometer for a 1970-74 160mph speedometer. My guage and everything mechanical linked to it works perfectly fine. I've never swapped guages with such a year span between them. The guage will hook up fine, but I need some help figuring out what I need to replace to make it work properly. Can anyone help?

Thanks.
Steve B.

[BonzoHansen]

I don't know the differneces, but maybe search transamcountry.com or performanceyears.com

[transamfan1981]

I've had this posted on T/A country for awhile now, no replies.

Steve B.

[Stevoone]

Does the new gauge fit and bolt up to your dash/instrument panel? If it bolts in the same as the old one then the only thing you should have to change is the speedometer gears in your trans. I'm not too familiar with 2nd gen stuff tho.

The speedometer gears were still available from GM when I changed the rear in my car. My boss has the old parts books still, if i get a chance I'll try to see if I can find them.

[transamfan1981]

Well, I was told it bolts up corectly. So pretty much I just have to figure out the number of teeth the gear needs to be and get new.
Be great if you could get hold of the manuals. I'd like to be sure about it.

Thanks.
Steve B.

[Stevoone]

I didn't get a chance to check the books today, but these links may help.

http://www.tciauto.com/Products/TechInfo/speedo_gears.asp

http://www.tciauto.com/Products/components/speedometer_gears.asp

[BonzoHansen]

Are you sure you even have to change speedo gears?

[transamfan1981]

Yes, definately have to change the gears. The top speed on 80-81 read 80. the top on 70-74 read 160. So if the gears aren't changed the gauge would read something like 120 when I would actually be doing 60. Instead of clicking off lets say 4 teeth to rise 10 mph reading the higher teeth would click off like 8 teeth to move 10 mph. I wasnt ever taught about speedo gears, I was told this at one time.
Steve B.

[Stevoone]

I'm not positive about having to change them when swaping a speedometer.

Edit: I misunderstood the operation of a mechanical speedometer so I look around on google. There are more detailed articles but this was the first one I saw http://www.explainthatstuff.com/how-speedometer-works.html

I looked around online again and found that it may be necessary to change the gears depending on the speedometer. You would have to look at stampings on the speedometer to see how many revs per mile it needs to read properly. It also says that most car manufactures used the same rev/mile for most of their cars. So you may not have to change them for the swap that you are doing.

I would install the new speedometer and see how it works. If the MPH is off then you would need to go after gears. If it reads correctly then nothing else need to be done.

[transamfan1981]

Thanks. I was hopeing it wouldn't be a chonk"o"change to swap a speedo. Now I just have to get it.

Steve B.

[andy78TA]

From the early 70s to the later 70s you do not need to trade out anything. It is direct replacement of the speedometer.
http://www.78ta.com/smf/index.php?topic=22157.0

I am a member on that forum. You may want to join and ask, or if not I can ask for you about the 80-81, I have a feeling it is pretty simple though

[transamfan1981]

I'm already a member there. I haven't been through or posted there in a long time.

Did you read that in a thread or did you talk to hitman?

Steve B.

[andy78TA]

A little of A and a little of talking to some people but not Brett specifically. I think if you post the question there you will get an answer pretty quickly though. There aren't too many 2nd gens on here and most are Camaro's not their big brother ;)

[Syzygy]

I'm positive its the same as any mechanical speedo swap from a same generation car to another. You just need to swap the gauge and its done. I did this on my 84 camaro. I swapped the old 85 mph double gauge out for a 145 mph IROC speedo. It works fine, same gears.

[TaKid455]

1970 units are unique in the electrical connections area. 71-up would be what you need. direct replacement. no change is needed elsewhere. speedos are calibrated to read somewhere accurately from the factory. If you want the 160 speedo w/.o the 8k tach, you can use a 75 unit it has a 160 speedo 6k tac. should be a tad cheaper too.