CK5
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Ratio adapter box
- Thread starter TC4x4
- Start date
pvfjr
1/2 ton status
Well see how accurate your speedo is without it. Then tell us how far off your speedo is, and what the ratio of your adapter is, and we'll tell you if it would do you any good or not.
So, next time you're on the freeway, drive 10 miles or so, keeping track of the mileposts. For instance, drive from MP 87 to MP 97, and take the readings off your odometer. If your Odo went 10.0 miles, then you're lucky. If it's more or less, let us know what the number is.
So, next time you're on the freeway, drive 10 miles or so, keeping track of the mileposts. For instance, drive from MP 87 to MP 97, and take the readings off your odometer. If your Odo went 10.0 miles, then you're lucky. If it's more or less, let us know what the number is.
At least in this state, you can't really count on those things except to get you close. GPS or stopwatch is your best bet here anyways.
Other states could be different, but we have "odometer check stations" that are 5 mileposts actually at the correct distances, unlike the "normal" ones.
Other states could be different, but we have "odometer check stations" that are 5 mileposts actually at the correct distances, unlike the "normal" ones.
why not just have someone drive next to or behind you down the freeway in their car and tell you how fast you're going?
Then you'll know...for example if your spedo says you were doing 50mph but the person said you were doing 65mph then you'll have something to work off of...
Then you'll know...for example if your spedo says you were doing 50mph but the person said you were doing 65mph then you'll have something to work off of...
pvfjr
1/2 ton status
That'll get you a ballbark idea, but it leaves a pretty big margin of error if you're wanting to crunch some numbers with the collected information.Avery4jc said:
Mileposts shouldn't be that bad on the freeway. After ten miles, even if the last mileboard is 1/5 a mile off (which it shouldn't be), you're still 98% accurate. I know ODOT is careful to mark out their roads accurately, other places should be too. If they're not, someone ought to straighten them out. I've tried to use a GPS before, but I don't quite trust them with the amount of lag they have. At least the ones I've used were a bit slow, always one step behind.
I know this isn't a milepost thread, but I've used the WA ones, they are up to 1/10th of a mile off, quite often. Seems like they are more for identification of location than accurate milemarkers.
readymix
3/4 ton status
Anyone know of a liting of the available ratio adapters and where to get them?
pvfjr
1/2 ton status
You can have one custom made at any good speedometer shop. Have fun finding the shop though. 
My old roommate had one made ages ago, I think he said it cost him around $90. 
I'd be looking for used ones personally, if I cared about it that much.
My old roommate had one made ages ago, I think he said it cost him around $90. I'd be looking for used ones personally, if I cared about it that much.
readymix
3/4 ton status
I'll live with it being off before I pay anywhere close to $90.
I believe it's been posted on here before that some transmission or speedometer shops can get them.
GM parts manuals list the adapters, I never bothered to count them all, but it appeared to be in excess of 50.
GM parts manuals list the adapters, I never bothered to count them all, but it appeared to be in excess of 50.
Terrapin Flyer
Registered Member
Here is a link to a calculator to determine your actual speed:
http://www.4lo.com/calc/gearspeedo.htm
You just enter the stock tire size and your current tire size. I tested it with my GPS and it was dead on. I made a post-it with the conversions at 5mph increments from 30mph to 60mph and stuck it on my dash (write big). After a few days you'll memorize it and know that when your speedo says 60 you're really doing 67.5 (or whatever).
http://www.4lo.com/calc/gearspeedo.htm
You just enter the stock tire size and your current tire size. I tested it with my GPS and it was dead on. I made a post-it with the conversions at 5mph increments from 30mph to 60mph and stuck it on my dash (write big). After a few days you'll memorize it and know that when your speedo says 60 you're really doing 67.5 (or whatever).
pvfjr
1/2 ton status
That works if your tire size is the ONLY thing that's ever been changed. There's so many rigs here that are so far from stock, it's hard to assume that he even has factory gears in his truck. Also, with the removal with his ratio box, until he finds what ratio it was, there's no telling where he's at now.Terrapin Flyer said:
lectric80
3/4 ton status
There was a shop I found some time ago that could do the adapter boxes for about 60 bucks, but I can't find the link at the moment. Do a search on this board and it will show up at the top in the advertiser links.
Check the box out and you may find it isn't the pin, but it may be that one of the gears is spinning on the internal rod when it should be rotating with the rod.
Check the box out and you may find it isn't the pin, but it may be that one of the gears is spinning on the internal rod when it should be rotating with the rod.
JIM88K5
1/2 ton status
What ratio do you need ?
original balzer
1/2 ton status
Ok this one im curious about. I have been told the gear in the trans/xcase needs to match your gears and tires. I was also told the little box is why my 72 K5 was dead on at 10-20mph, 5mph slower than actual speed at 20-30mph, and progressively more off the faster you went. And that older speedos needed the little box, and newer speedos had them built in, but wasnt sure on the years. Witch makes sence because i dont think i have ever seen the box on 80's trucks but see them on older trucks more often than not. Whats the real deal on these things?
Balzer
Balzer
lectric80
3/4 ton status
The reason for the box was so that Chev didn't have to match the t-case or tranny to the ratios in the rear end. If they built one setup they could just use an adapter to adjust the speedo. My Astro had it because it had the limited slip and slightly lower gears than most astro's so they used the box.original balzer said:
