The Stovebolt Site Forums The Shop Area Driveline Speedo after pumpkin swap

Swapped my third member from a 5.14 to a 4.10. Swap went great and was easy enough to do by myself. This was a 3/4 ton with the Eaton rear end and a SM420 4 speed granny.

My question is who sells the correct gear for my speedometer?

Thanks Don

Try this link:

https://www.bobsspeedometer.com/1/120/ratio_adapter.asp

Jerry

Thx
HRL

I have bought speedo adapters from Jim Carter in the past. Get your truck running at 50MPH according to a GPS and note what speed your speedometer says you are going. Give that speedo reading at true 50MPH to the folks at Jim Carter. The shop that builds the adapters for them will build a custom adapter for your specific need. The adapter simply screws into the speedo cable hole on the tranny, then the speedo cable screws into the adapter.

http://www.oldchevytrucks.com/cart/product.asp?prodid=SP249&i=9931|||||

Matt

ditto what Matt posted

http://www.oldchevytrucks.com/cart/product.asp?prodid=SP249&i=9931|||||

"1932-1972 Speedometer Ratio Adapter Fits all GM Applications GMC Pickup Truck
Item Number: SP249
Special Order item, No Returns. Must Pay In Advance!
Retail: $97.50 EACH
On Backorder [added by tclederman: custom made to match your needs - see below]

Corrects the error in your speedometer when your rear tires or a total differential has been changed. Fits all GM applications. Simply follow a vehicle with a correct speedometer at 50mph for one mile and tell us the mph your speedometer reads. We will custom build a ratio adapter for your truck. Takes minutes to install to your transmission! Made in the USA. No Refunds"

Note: you could also use a MPH/speedometer/GPS app in you cell phone to obtain your truck's speedometer reading when the MPH/speedometer/GPS is reading/displaying 50 mph.

I have used these types of adapters and they are excellent -- if speed is measured correctly, and if the ratio adapter is manufactured correctly.

The swap from a 5.14 to a 4.10 is a disappointing 5mph gain. Driving pickup and hill climbing feels the same. Reverse out of the shop is a little peppy.

Thx for the tips. I’ll call one of the above.

Don

I gave up on trying to calibrate 60 year old speedometers. Sure, it is possible to put on an adapter to make it read 50 MPH when you are actually going 50, but will it read 25 MPH when your actually going 25? There is a 60 year old hair spring, and dirt and dried up lube in there that has done some wear damage.
A brand new speedometer should read correctly throughout the entire range, but are the brand new ones built well enough to read accurately from 0-70 MPH? When you pay someone to calibrate a speedometer, their machine checks the entire range.
I drive mine like I stole it and still can't buy a speeding ticket. The only time I get pulled over by the police is so they can drool on it.

My Garmin GPS is right up there in the middle of the windshield like a heads-up display on a fighter plane, and its MPH reading is much more accurate than the speedometer on all of the vehicles I drive- - - -even the relatively new ones with electronic speedometers.
Jerry

I used to do that with my Garmins, but I now simply use the iPhone for Maps, "GPS", routes, MPH, weather, etc., etc.

Unfortunately, I need 6v-12v converter, or a 12v "power-pack" (like my DeWalt 2800 Peak Amp Jump Starter 1000-Watt Power Inverter with Digital Compressor, 120v power outlets, USBs, and, I think it can also whistle Dixie in 3-part harmony - part of my long-distance travel assurance/insurance).

Although, one of my 7"-screen Garmins also has back-up camera (that stays in/with my COE flatbed).

Not so fast Tim. iphone chargers and I trust all the others work just fine on 6 volts. The output of the automotive phone chargers is around 5 volts. 6v input has proven very OK in my experience. I tapped into the hot side of the ignition switch, added a fuse and installed an inexpensive auto charger (from Oriellys) in the capped off cigar lighter port in the dash. The black plastic snap in cover when the charger is removed looks pretty dang stock. I wired it so it was hot all the time allowing the phone to charge when not driving.

My smarter than me electrical engineer little brother is responsible for this idea.

Thanks, MoPar guy
I have read the same thing.

I just use my DeWalt "powerpack" (that I always carry on long trips).

I use the GPS app on my iPhone too. It used to match the speedo in my truck until I made the pumpkin swap. I guess I can add 5 mph when I look at it but would also like to keep accurate account of mileage on the odometer.

Thanks Don

Sometimes you will find that the odometer can be dead nuts on while the speedometer is off. The odometer part is direct drive off of the cable, while the speedometer part is not, and is either 60 years old or made in China.

What does the speedometer get its "reading/info" from, Carl?

I do not know, but I blissfully thought it got its "reading" from the rotation of the speedometer cable?

The speedometer needle is attached to a steel cup with a magnet spinning inside it, counterbalanced by a spring. There is no direct mechanical connection. The odometer gets its mileage reference from a direct gear drive, and is calibrated to show one mile (or a 1/10 fraction) every time the cable turns a set number of times. It's possible for the magnet/spring relationship to be off while the odometer is accurate, but that's pretty rare. Usually they're both off if the cable speed is incorrect.
Jerry

Jerry

Just got the 46 2-ton from Indianapolis fabrication and been driving around the yard a little bit practicing the shift and Randle had said that the speedometer doesn’t work where’s the first place to check to troubleshoot it, looks like he put in a new gauge package the odometer reads zeros all the way across but Speedo read 30 all the time right now

Thanks for you help in advance

Wish I was closer for reunion 🎩🎩

One can usually unscrew the cable housing off the back of the speedo by hand, watch and see if it turns while someone drives it or jack up a wheel and turn the driveshaft. If not turning, take off the other end from the trans. Make sure the length is correct.

Ed

That’s a start thank you 😉🎩