Rear height and speedo error

[Trask]

I have a 1992 W250, Cummins diesel, 4WD, 3. 50 axle ratios, Gertrag 5 sp, NP205 transfercase, stock 235/85-16" tires, etc.



Two questions:



One - my speedometer always been off. When it reads 1 mile on the odometer, it's actually only gone . 935 of a mile. Vehicle speed is off to the same extent. As far as I know, all is stock. Has an electric speedo-sender attached to a little gearbox at the transfercase. How do I correct? Gears inside, or the gearbox, or what?



Two - truck when empty is 4" higher in back than in front which seems to be a common Dodge thing. My 69 Power Wagon is the same way. There are 6" spacer blocks in back between the rear-axle and springs. I have some trouble with the extra height when using my truck camper. Are there smaller blocks I can put in - like 2" or 4" instead and will that work without problems?



Thanks for any help.

 

[dpuckett]

I believe there are 4" spacer blocks available. My mom has a set of springs she'd probably trade ya- guaranteed to drop it 2-3" :-laf



As for the speedo. Clean all your connections real well. If that doesnt help. you can get different ratios in the adaptor boxes. Do a search, there is a lot of info on where to get stuff and how to figure out what you need.



Daniel

 

[KOG]

Something on your truck is not exactly stock. Pull the gear from the transmission end of cable and check the number of gear teeth. Then get one with two teeth less. The nonstock part may be a wrong gear because your axles and tires are stock.

Spacer blocks can be had in all thicknesses.

Try Stempf.com.

If you don't see what you need there, call them because they'll have it.

 

[JGrefenstette]

My speedometers off too. ive yet to find a speedometer that is actuall 100% accurate. i think every speedometer is "off" to some extent. i have 35" tires. when my truck reads 70mph, im doing 74mph. we first tested it with my dads honda accord. he drove beside me and when he had 60mph i had 52mph. we got a gps, and it seems that his car is actually more 'off' than my truck.

i wouldnt worry about your speedo.



as far as getting your desired hight. have you thought of getting 2inch springs for up front?

 

[KOG]

It's the odometer that counts as far as accurate gearing. All you can do with the speedo is calibrate it using a GPS and know how far off it is.

Speedometer and fuel gauge inaccuracy is one of my pet peeves on all cars. None of them are right most of the time. You can pay $50K for a truck and get a fuel gauge that's not even toy grade.

 

[AKimmel]

Get a Superlift "Truspeed" speedometer calibrator. You splice it into your signal wire for the speedometer. It allows you to fine tune your speedometer from inside the cab, and it has two settings incase you change tire sizes back and forth. I have one in my truck and its been working great.

 

[Trask]

My speedometers off too. ive yet to find a speedometer that is actuall 100% accurate. i think every speedometer is "off" to some extent.



as far as getting your desired hight. have you thought of getting 2inch springs for up front?

I've checked all my trucks and all are just-about dead-on with speedometer and odometer readings except my Dodge. I've checked with mile-marker and also with GPS. My two diesel Ford F250s both read 75 MPH when actually doing 76 MPH. My 86 diesel Chevy reads 75 when driving 75. 5 MPH. But my 92 Dodge reads 75 MPH when it's really doing 80 MPH. Since the odometer is off the same, I want to get it reading right instead of constantly trying to remember. I drive though Canada a lot, and it's bad enough trying to think in KMs instead of miles - without converting too.



I think I've got the problem fixed - I just ordered the parts. I pulled my little speedometer "speed increaser" gearbox off the side of the transfer case. On the input - it turns . 72 of a turn for every full turn at the output. It needs to be slowed down at the output by . 935. I found the proper gearbox for $60 and just ordered it. The wrong gearbox that's on it is marked 1. 3846. To be perfect I need a 1. 2980 box. The new one I ordered is a stock item at 1. 2844 which is plenty close enough.



In regard to the suspension height -changing the front doesn't help me. It's high rear that's the problem. I've got a dozen trucks - but this Dodge is much higher than any of my Fords or Chevys. I have a slide-on truck camper I use every year and when jacked as high as it will go - it will just barely make it on to the Dodge if the ground is perfect. So, I need to either extend my jacks or lower the Dodge's rear. Seems getting lower would help with fuel mileage by cutting down wind-resistance anyway. As far as I can tell, it's just cheap engineering by Dodge with sticking those 6" cast-iron blocks inbetween the rear-axle and springs. My older 1969 W200 Power Wagon has the same blocks - seems to be a Dodge thing.

 

[JGrefenstette]

I see.



when you mentioned getting a new speed sensor, are you talking about gettin the thing, gear side and the electrical conversion part? baisacly everthing inbetween where you plug in the wire to where it screws into the T-case? because i really need a whole new one of those too. by speedometer dies of and one, and has been dead now for a while. If i cant find a new one ill just have to take the old one off and have a good look at it. but it would be nice to solve the speedometer for good.

 

[Trask]

I see.



when you mentioned getting a new speed sensor, are you talking about gettin the thing, gear side and the electrical conversion part?

I ordered the complete gearbox - not the electrical pickup that bolts onto the end of it. Those you can still get from Dodge but it seems they rarely go bad.



Complete new gearbox is $62 if they have the ratio you need in stock, or an extra $20 if they have to custom build it for a special ratio.





Speedometer Gear, Speedometer Gears, Ford, GM, Dodge 700R4



Part # 54RA for $62