Tuning the speedometer?

[chance9888]

Hi all,

I bought a reproduction speedometer from VPW, but it has two issues. First off, the odometer is completely messed up. It will count a mile when I have only gone about 1/4. Also, it seems to read about 11-12 MPH above my actual speed. Is there a fix for this?

Thanks,



John

[Desoto61]

You're feeding this from the transfer case correct?
Is the 10-12 MPH number over the whole speed range or does it vary?
The speedometer should be off more if the odometer is moving 75% faster than it should.

Assuming the reproduction is OK, then it would be an issue with the speedometer gear inside the transfer case. It would have the wrong tooth count. Did you change the gearing or tire size on the truck?

I tend to lean toward an issue with the speedometer if the numbers you gave are accurate then the errors in the speed and the mileage should correlate to each other.

[chance9888]

I'm sorry, I'm sure the numbers DO correlate. I wrote that before I really looked into it. However, the tires are about original, and I did not change the gearing, but my transfer case was never rebuilt, and that could very well be part of the problem.

[Desoto61]

If the driveline is all stock it should be right assuming the speedometer is designed to work with the stock gear drive speed. Which axle ratio does your truck have?

I don't know if Dodge changed the gear drive to compensate for the difference in the 4.89 and the 5.83 or if they used different speedometers. The first is more common and I would think easier, but the second isn't out of the question. I've never heard of it but I'm far from an expert.

If there's no difference in speedometers between the two gear ratios available then I think there may be an issue with your speedometer. At least I'm not sure what else it could be. Are there any adjustments on the speedometer itself?

Might be best to call VPW and discuss the problem with them. I've heard that 10-12% error isn't uncommon but not as much as you claim you're seeing.

[chance9888]

The truck does have a 5.83 gear ratio. I'll call VPW about that tomorrow

[Doc Dave]

Let us know what they say. Some of the reproduction stuff they sell is made overseas (China?); I do not know about the quality control standards in place.

[olgraybeard]

Most problems with old speedometers is the speedo cable has it been replaced or the very least removed cleaned and lubed, if any rust replace it.

[chance9888]

Most problems with old speedometers is the speedo cable has it been replaced or the very least removed cleaned and lubed, if any rust replace it.

Sorry for the delay, guys. I'm in the UK, right now, and hotels don't give free wifi like they do in the US. I just got lucky w/ this one.

Anyways, yes, I have replaced the speedo cable. Entirely. Case and all. And here is the email conversation between me and VPW:

"Hello guys,

I purchased one of your reproduction speedometers for my 1949 B Power Wagon. When I took it on the road in clocked it, the speedometer was off by about 10 mph. I've yet to check my shop manual, but is there a screw or something in the speedometer I can use to fine tune it, or has it always just been slightly off?

Thanks,



Spencer Chance
chance9888@gmail.com





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jens to me
show details Jul 29 (5 days ago)
Spencer ,


There are two different gear ratios used in the classic Power Wagon differentials 5:83 & 4:89. Which do you have ? and is the speedo 10 mph fast or slow ? Being a mechanical drive type speedometer they were never 100% accurate and the needle tends to bounce around quite a bit so a 3-5 mph variance while driving at 30 mph is pretty normal . To change the calibration on the speedometer head is practically impossible, the only way to change this output reading is to change out the drive pinion & speedometer worm gear located in the transfercase, and that is pretty major surgery. Call me if you have any more questions.

Thanks
Jens Butler
Vintage Power Wagons
641-472-4665
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Spencer Chance to jens
show details Jul 29 (5 days ago)
Hi Jens,

My truck has a 5.83 gear ratio. I would call you, however, I am sitting in the Atlanta airport, about to board a flight to England. I don't have international calling, so, I will check my email more often. The speedometer tends to read faster than what I am actually going. However, I have definitely taken into consideration that I could have a problem inside of my transfer case. It was one of the only drivetrain components that was not rebuilt. Another thing I noticed is that the odometer seems to climb up too fast. I may go only 2 miles but it registers many more. <I don't have an exact example. I know it would be nice. Sorry.> Last, my Uncle told me of these little boxes that people used to have for their trucks. It is a small gear box that the incoming speedometer cable went into. From the opposite side of the box, another, short, speedometer cable was attatched directly attached to the speedometer. I don't know if I can still find those, but if you have an recommendations, please let me know. Also, please let the guys with you at VPW know that I am very thankful for all the help they have supplied to me. Whether it be parts or instructions. Attached is a picture of my truck. I took it on as a summer project. BTW, let me inform you that I am still fifteen years old.

Thank You,



Spencer Chance

PS: I am aware that i do not have a front bumper yet. I have yet to get some of the parts for my bumper welded and bent. Also, many of my winch parts need to be sandblasted.
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jens to me
show details Jul 30 (4 days ago)
Spencer ,

Hope you have a good trip , when you get back here is what to check out in the T-case . There are 4 possible combos , the speedometer drive gear will have either 4 or 5 teeth and the Pinion will have 14, 15 or 16 teeth.
The other thing that could affect the speedometer is tire size, are you running a ( 36.5 " tall )
9.00x 16 tire ? or a 7.50 x 16 ( 32 " ) ?


Thanks,
Jens Butler
Vintage Power Wagons
641-472-4665 "