Speedometer sending unit adapter for 395/85R20 tires

tcruwithme · Sep 16, 2014

Does anyone know if there is an adapter to correct the speedometer reading when you move up to the 395/85R20 tires? My truck speedometer reads about 7 to 8 MPH slower as compared to what the GPS say. I have looked though other thread posts, but have not yet found the right one. I know it's probably here somewhere, but I have been having trouble with the search functionality. Any help would be greatly appreciated.

ke5eua · Sep 16, 2014

I ordered mine on ebay. I just got the angle piece that is used on the 939 series for the 14.00x20's.

tcruwithme · Sep 16, 2014

ke5eua said:
I ordered mine on ebay. I just got the angle piece that is used on the 939 series for the 14.00x20's.

Who on the ePay did you get it from? It looks like this adapter from the 900 series of trucks is for the 43" tires, is that correct? If so, that would get the speedometer reading closer but not totally corrected. Does that sound right?

peashooter · Sep 16, 2014

I ordered one off ebay too, and while it helped get the speedo closer it didn't help much... so I guess I got the wrong one? I think with the stock speedo and 395 tires, I was reading 50mph (speedo) and 60mph (GPS). The ebay 5 ton unit I bought was reading more like 54mph(speedo) and 60mph (GPS)

I used

ART NUMBER - 7065893
NSN - 2520-00-404-3098

Rmtaunton · Sep 16, 2014

Mine is dead on with gps I will crawl under and look to see if I can find a number on it

brianp454 · Sep 16, 2014

I think the version you have would work for guys with 365's or 11's. What do you want for it?

peashooter said:
I ordered one off ebay too, and while it helped get the speedo closer it didn't help much... so I guess I got the wrong one? I think with the stock speedo and 395 tires, I was reading 50mph (speedo) and 60mph (GPS). The ebay 5 ton unit I bought was reading more like 54mph(speedo) and 60mph (GPS)

I usedART NUMBER - 7065893
NSN - 2520-00-404-3098

tcruwithme · Sep 16, 2014

Rmtaunton said:
Mine is dead on with gps I will crawl under and look to see if I can find a number on it

Thanks Rmtaunton! Let us know what you find.

Rmtaunton · Sep 16, 2014

Will do , sorry it will be morning though ,

Rmtaunton · Sep 17, 2014

Not very legible on phone maybe will be on computer

ImageUploadedByTapatalk1410978899.657368.jpg

brianp454 · Sep 17, 2014

It seems totally illegible to me on the PC. Can you read it and post the text by editing the post?

Rmtaunton said:
Not very legible on phone maybe will be on computerView attachment 516844

Rmtaunton · Sep 17, 2014

sadly no , i was hoping it would be stamped in ,instead of printed ill check on back side when i get home

peashooter · Sep 19, 2014

Rmtaunton said:
sadly no , i was hoping it would be stamped in ,instead of printed ill check on back side when i get home

The new one I bought off of ebay was nearly illegible as well. I don't think there was any other markings on it besides the ink printed numbers like you took a picture of.

Do you have any idea where you bought that adapter or what type of 5 ton truck it came off? Thanks

juanprado · Sep 19, 2014

The one on epay is:

PART NUMBER - 7409623-1
NSN - 3010-01-236-1213

It "appears' to be the one for m939a1/2 and has a gear ratio of 1.13 to 1
http://www.parttarget.com/3010-01-236-1213_3010012361213_649-CL.html

I ordered one but it will be a while before I get to this project and can report anything as i don't have my rims/tires on yet.

Rmtaunton · Sep 20, 2014

peashooter said:
The new one I bought off of ebay was nearly illegible as well. I don't think there was any other markings on it besides the ink printed numbers like you took a picture of.

Do you have any idea where you bought that adapter or what type of 5 ton truck it came off? Thanks

Sadly I don't fortunately for me it came with truck , so was put on by previous owner , but it is exact on the speedo , so it does exist , wish I could have been more help

peashooter · Sep 25, 2014

juanprado said:
The one on epay is:

PART NUMBER - 7409623-1
NSN - 3010-01-236-1213

It "appears' to be the one for m939a1/2 and has a gear ratio of 1.13 to 1
http://www.parttarget.com/3010-01-236-1213_3010012361213_649-CL.html

I ordered one but it will be a while before I get to this project and can report anything as i don't have my rims/tires on yet.

I got pretty excited about this so I ordered one off ebay. Unfortunately this is not the correct one at all. I should have done a little better job reading up on it, its ratio is 1.13:1 and it spins in the reverse direction of the deuce unit so I'd guess that this could damage something in addition to giving some really off readings. The stock deuce adapter is .187:1, the other unit I tried previously (2520-00-404-3098) is off the old style 5 tons and did bolt right on but its meant for 1100 size tires so it wasn't quite accurate for the 395's.

900 size tires (stock a2 deuce)= 1:187 (NSN 2520-00-562-0421)
1100 size tires= 1:200 (NSN 2520-00-404-3098 )
395 size tires= ?

peashooter · Sep 25, 2014

peashooter said:
I got pretty excited about this so I ordered one off ebay. Unfortunately this is not the correct one at all. I should have done a little better job reading up on it, its ratio is 1.13:1 and it spins in the reverse direction of the deuce unit so I'd guess that this could damage something in addition to giving some really off readings. The stock deuce adapter is .187:1, the other unit I tried previously (2520-00-404-3098) is off the old style 5 tons and did bolt right on but its meant for 1100 size tires so it wasn't quite accurate for the 395's.

900 size tires (stock a2 deuce)= 1:187 (NSN 2520-00-562-0421)
1100 size tires= 1:200 (NSN 2520-00-404-3098 )
395 size tires= ?

Okay, I think the correct speedometer adapter for the deuce with 395 tires is going to be a 1:222 unit that has a part number scary close to the 939 trucks.
There is a SP-288 .222 unit (NSN 3010-00-740-9623). An alternative part number for it is 749623, but its NOT THE SAME AS 749623-1

http://www.parttarget.com/3010-00-740-9623_3010007409623_2520007409623.html

tcruwithme · Sep 25, 2014

peashooter said:
Okay, I think the correct speedometer adapter for the deuce with 395 tires is going to be a 1:222 unit that has a part number scary close to the 939 trucks.
There is a SP-288 .222 unit (NSN 3010-00-740-9623). An alternative part number for it is 749623, but its NOT THE SAME AS 749623-1

http://www.parttarget.com/3010-00-740-9623_3010007409623_2520007409623.html

Thank you, peashooter

I submitted a request for a quote. I've done that before through this same group, and they've came back with ridiculous quotes. I hope this is a part they have in stock.

peashooter · Sep 25, 2014

tcruwithme said:
Thank you, peashooter

I submitted a request for a quote. I've done that before through this same group, and they've came back with ridiculous quotes. I hope this is a part they have in stock.

I admit that I had just bought the only one I saw listed on ebay before I put that post up. Member Sewerzuk bought an adapter that mounts onto the factory unit and corrects the ratio for about $60. Post 302 HERE is where he talks about it. He bought the 20% overdrive adapter Part #54RA2 from http://www.transmissioncenter.net/speedometer_calibration_______va.htm

tcruwithme · Sep 25, 2014

Well, since we have proven success from another SS member with the 54RA2 part from PATC, that seems like the way to go. I'm going to order one of these up and see how it does. Thanks for doing the research on this, peashooter!

ke5eua · Sep 25, 2014

I haven't had a chance to put mine on the truck yet, I just got the one I figured would work for the tires.

Speedometer sending unit adapter for 395/85R20 tires

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