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Speedo question

Larrys 48

Larrys 48

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Dec 7, 2007
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Location
Spokane, WA
I have a rebuilt speedo guage cluster, a new steel speedo cable, a Patrick's 3.55 :1 rear end with the speedo adapter at the standard 3 on the tree transmission, but I read 45 mph when I'm travelling with the flow of hwy traffic at 60 mph. Anyone have any thoughts on how to get a more accurate reading? I have to pass thru a 20 mph school zone on the way to work and need to be more accurate.
 
3 to 4 ratio?

Larry,

Drive @ 15mph through the school zone!

Seriously, sounds like your adapter isn't doing what it is supposed to. Mine is the same setup without the adapter but reads more at a 4:5 ratio...reads about 20 when doing 25.

Bob
 
Larrys 48 said:
I read 45 mph when I'm travelling with the flow of hwy traffic at 60 mph.
Click to expand...

Need more information. What does the speedo read when you are traveling 40 MPH? If it reads 30 MPH then the problem is linear and most likely could be fixed with the proper speedo adapter. If it is reading 25 MPH (ie no matter what speed you are going, the speedo is always 15 MPH slow) the problem is in the speedometer itself.
 
Speedometer accuracy also depends on what size tires you are running. Are you running 16" or 15" tires? Also the aspect of the tires makes a difference.
 
Speedo Accuracy

Couple ways to go here :

Take it (the whole truck) to a Speedo Shop and pay them about $100 .

Or , talk to Joe (DZT) about the number of teeth you count on the speedo drive geat after you remove it fom the tranny ~ he'll have a box full of different tooth count ones or can find what you need from a spare tranny (he has loads of them) .

Or , go find the two speed speedo gearbox off any old brand truck with a two speed rear end , it'll attach to the back of the speedo then the speedo cable attaches to it , some shift via vacuum . others shift via a cable , no matter , just try it in both ratios and when it's more accurate , leave it there .

Or , shoot Even anE-Mail , he'll have some trick up his sleeve that'll work .

I hope this helps , I suppose bits of masking tape on the speedo glass are out of the question ? .
 
Tires are 215/85R16.
It's definately a ratio, so Bob wins 15mph on my speedo=20mph real speed.
I guess I was just hoping to not have to do the math...
 
Driven gear?

From your thread, I'm not sure if you bought Patrick's Speedo gear change with your Package. You can send him your cable to tranny gear and he will change it for you. There's like a one tooth difference in the gear.
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Looked on Patrick's site and what I see is an adapter and then a gear set. I'm assuming Larry is using the adapter. Are you saying Patrick offers a change in the driven gear (cable to tranny gear) that will work without changing the drive gear?

Thanks,
Bob
 
1952Bowtie said:
Looked on Patrick's site and what I see is an adapter and then a gear set. I'm assuming Larry is using the adapter. Are you saying Patrick offers a change in the driven gear (cable to tranny gear) that will work without changing the drive gear?

Thanks,
Bob
Click to expand...
Hey Bob, Yes If you change the rear-end gears you have to change the Speedo gear too. Patrick sells the speedo gear for the Saginaw or Stock tranny. Its for 3:38 or 3:55 rear-ends. Just screw it in to the tranny and hook-up your cable and you are good to go! Its about the size of a spark-plug. $49-59 page 30, 08-09 Catalog

Flashlight
 
Its about the size of a spark-plug.
Click to expand...

Hmmm...that sure sounds right. Don't understand what the adapter thing is that Larry has though.

Have to give Patrick's a call and maybe get these units reading accurately.

Thanks lots!
Bob
 
Thanks Russ, my speedometer is about 20 miles off depending on which unit I have in the truck. If I use the one it can with it is about 15 mph slow if I use the one I got out of a 52 is is about 12 and if I use the china clipper one it veries between 20 to 25 mph depending on the speed I'm traveling.
So a GPS for now will do me for those times in town and on the open road.

On the open road if I'm doing about 75 the speedo reads about 52, 65 is about 49 on the speedo. Right now the 52 speedometer is in it.
Again Thanks.
 
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