Speedometer reading 1/2 actual speed

[bcaddel]

My speedometer reads 1/2 of my actual speed. It does not appear to have any adjustments on it. It gets it's signal from the left front wheel and it appears to me to be receiving the impulses from two bolts on the brake drum spaced 180 degrees apart.

If I drill and tap two more holes and install two more bolts making for one impulse every 90 degrees instead of every 180 degrees this should give double the impulses so does that translate into double the speedometer reading?

[bcaddel]

Here is a picture of the Speedometer.

[Lin]

Difficult to see in the picture.  How close does the bolt head come to the sensor?  Can the bolt be backed out to come closer?

[Don4107]

Has it always worked that way or is this a new problem?  Is it possible that the sender is to far away from the bolt heads and only trigging on one?  How much gap is there?

Good luck
Don 4107

[bcaddel]

It has always been that way. I had almost 1/4" between the sensor and the top of each bolt so I adjusted the sensor down about 1/8" to get them closer. While I was spinning the tire around to check for clearance I noticed there already were several empty threaded holes around the drum so I screwed a bolt into 2 of the empyt holes. Whala, the speedometer works and matchs the GPS right on the button.

Thanks for the input guys, it sure is nice when you can solve a problem and it doesn't cost a penny. I haven't won too many of these battles.

[Busted Knuckle]

bcaddel,
Glad to hear that you solved the problem faster than I could read about it! Also they should be spaced about a nickel's width away from the sensor
FWIW most systems I have worked on do use the 4 bolts, but I have seen some that only require 2!
I once did a brake job for a fellow who sent the parts drop shipped and then brought his bus by and left it for a spell (along with A LONG to do list!) ! Well as I was checking the list I saw it said fix speedo! So when I was doing the front brakes I checked the sensors & wires, All OK! Then I noticed the drums that came off the steer had no bolts, or even holes tapped for them so off to look at the new ones, yup they had 4 holes. So before I put the driverside drum on I installed the 4 bolts. Once I was done with the new brakes I put the drum on and adjusted the bolts where a nickle would just slide in between each one. I then went on and finished servicing the engine, trans, chassis, drive & tag brakes, OTR A/C, lights, generator, & etc. Once done I pulled it out and parked it in the bull pen (fenced in back lot when I was in town!), and it sat for a month or 2 before he picked it up. Then he came by one day & paid the bill and drove off with it, leaving his car behind to be picked up later! Well he returned in about 20-30 mins. wanting to know what I'd done to it to make it run so fast!~? Huh? I hadn't done anything that would have made it "fast"! So I went around the block with him, and as soon as we took off he said "watch we'll be doing fifty before the end of the block!" Well sure enough he hit second gear and about that time he said "see fifty already!" Oh I was ROTFLMAO! I knew we were maybe doing 20-30 mph, but definitely not fifty! He argued up and down, "that the speedo said fifty and he knew by golly it was right! And he was sure I'd tuned up & turned up his motor and it was gonna cause it to burn way to much fuel & probably BLOW IT UP TOO!" Oh I was laughing so hard my sides were hurting, and I was trying not to laugh in his face, but I couldn't help it! So we pullled it up in front of the shop and I had him to turn the front wheel all the way to the left. Then I went in the shop and got a 1/2" socket and ratchet and removed 2 of the bolts I'd put in straight across from each other. I then told him to take her around the block again. Well it musta been a big block, because he didn't come back! And his car sat there from Thursday evening until sometime Sunday evening! he never called, came by to admit it was right, and I didn't see him until the next time he needed work done. But he still comes around occasionally and we get a good laugh out of him thinking "I'd hotrodded his motor!"   BK 

[JackConrad]

Our speedometer looks similar to the photo of yours. Ours requires 4 bolts space 90 degrees apart.  I have seen speedometers that only required 2. Sounds like someone changed left front drums and did not install the other 2 bolts (or the hub they installed already had only 2 bolts in it).  Jack

[Dreamscape]

I have a Dixson in our 01 Eagle, it has two bolts on the drum. I had the same problem and the tech guy said to move the sensor as close to the bolt head as possible. Haven't had time to check it out to see if the problem is corrected.

FWIW,

Paul

[white-eagle]

so if you remove 1 bolt, does it drop down a quarter?

i wonder if i could convince the officer that i thought i was only doing 55 mph and not get a ticket??   

[jjrbus]

Paul, your Dixson speedo may have "dip" switches on the back to adjust the speed. If you look at the back of the speedo case it will have a row of micro switches on it.   Let us know,  Jim

[Dreamscape]

Jim,

No dip switches on the back of mine, forget the model number of the one I have. Anyway I thought so too until I examined it after reading up on how to set it up. The back of mine looks the 500 series, no dips or speedometer adjustment screw either. Probably a real old unit, figures!

Paul

[kingfa39]

The unit in the photo looks like a mci unit, i had one on my 06. it does require 4 bolts, i cahnged to a dixon so i could have the odometer, it also used 4 bolts, hope this info helps
Frank Allen

[JackConrad]

Paul,
   That sounds just like our Dixson OEM speedometer on our MC-8. No switches or adjustments on the back, just a label that says "this unit set for 490 Tire RPM".  There are 4 wires on the back of the speedometer, 24 volt + (switched by master switch), ground, and 2 wires from the wheel mounted sender.  Ours uses 4 bolts on the brake drum.  Jack

[Dreamscape]

Jack,

At least now I know someone who has one like mine! Although it does not give any information on rpm. I do have four wires, 12v, one ground and two wires from the sender, was told that two lugs is what I need. I wonder if four makes it more accurate? Might mean I'm going twice as fast as I show now. Makes sense to me.

Paul

[NewbeeMC9]

I'm i seeing that the 12 v use 2 bolts and the 24 bolt use 4?