MCI Speedometer signal question

jmblake · March 24, 2009, 06:59:28 PM

Has anyone added more hex points to there brake drum to get more points/rev for the speedometer, Mine has 4 but that isn't enough for the new speedometer. Can you drill and tap more hole's? or could you epoxy them one? Does anyone make a ring that would bolt onto the drum? Thanks Jason

bcaddel · March 24, 2009, 08:34:44 PM

Jim, it probably isn't any help but our MCI speedometer was registering half of our actual speed according to our gps. I followed the cable down to the wheel and saw there were two bolts on screwed into the hub and there were two additional empty threaded holes there. So I screwed in two more bolts and it doubled the speedometer readings.

If you can figure our just how much your speedometer is off logic says if you add more bolts it will send a proportional amount of pulses to the speedometer and increase its reading. Hope it works for you.

jmblake · March 25, 2009, 04:07:33 AM

Bob, Thats what I need to do, I just didn't know the best way to add the points to the drum. Thanks Jason

JackConrad · March 25, 2009, 05:13:48 AM

Gap between the head of the bolt and the speedometer pick-up is also important. When I installed our new pick-up. I set the gap to close. I took it for a test drive and the speedometer said I was going 45 in first gear!. I reset the pick-up for a wider gap and now the speedometer is withing 1-2 MPH of the GPS.
Bolts should be threaded into the drum and a jam nut used to allow adjustment to make sure all bolts have the same air gap at the pick-up. Jack

Dreamscape · March 25, 2009, 05:24:37 AM

Jack, What size of gap did you end up using? I have a Dixson 500 non programable speedo, (no dip switches). Have two pick ups and the speedo is about half of what it should be. I did adust it closer and had the same result, maybe I need to go farther away.

~Paul~

jmblake · March 25, 2009, 05:38:46 AM

Jack, Did you have to add any bolts? Acording to the company I will need at least 12 points of contact to get enough (F.S.F) to work. Thanks Jason

JackConrad · March 25, 2009, 05:41:24 AM

Paul,
If you are getting half speed reading, it sounds like you need to double the number of bolts. Over the years, before you purchased the bus, someone may have put a different brake drum on with an incorrect number of bolts.
I don't remember the air gap, that was about 7-8 years ago, but 1/8" comes to mind. Our MC-8 also has a non programmable Dixson speedometer. It has a tag on the back of it that says it is calibrated for 490 tire RPM. When buying front tire, that is one of the first questions we ask.
Our brake drum has 4 bolts to pulse the pick-up. When we were having trouble with our speedometer, I called Precision Speedometer http://www.precisionspeed.com/. They were very helpful, explaining how to test the speedometer and pick-up to determine which component needed to be replaced (it was the pick-up that was failing).
Jack

JackConrad · March 25, 2009, 05:43:40 AM

Quote from: jmblake on March 25, 2009, 05:38:46 AM
Jack, Did you have to add any bolts? Acording to the company I will need at least 12 points of contact to get enough (F.S.F) to work. Thanks Jason

Our MC-8 Dixson non programmable OEM speedometer operates off 4 bolts. Jack

jmblake · March 25, 2009, 05:51:23 AM

This is a Teleflex speedo that came with the dash from CIP,acording to the formula given I will need at least 12 points. Thanks Jason

Dreamscape · March 25, 2009, 05:51:50 AM

Thaks Jack, I'll check it all out when I get back home.

~Paul~

JackConrad · March 25, 2009, 08:48:14 AM

Quote from: jmblake on March 25, 2009, 05:51:23 AM
This is a Teleflex speedo that came with the dash from CIP,acording to the formula given I will need at least 12 points. Thanks Jason

Perhaps Teleflex Tech Support can help. Nothing going directly to the source. Jack

jmblake · March 25, 2009, 09:30:18 AM

Yes, I called Teleflex yesterday and they were in the process of moving and didn't have any computers up and running, The guy said he would call back in the afternoon but never did. Ill try again this afternoon.

John316 · March 26, 2009, 05:28:36 AM

Jason,

We had the exact same problem. It had the correct number of bolts. The sensor was set a nickel width away (that is what they recommended). Everything was great, but it still registered half. I then took every single bolt out and put a washer behind it to try to make sure that it was correct signal, no luck. I was told how to calibrate the switches on the back, still nothing. Finally in looking over the thing, I discovered a little screw in the back. While we had the dash pulled, someone else drove, while I turned that little screw. Bingo, that is what fixed our problem. we set the cruise at 70 on the gps and calibrated the speedo the exact mph. That said, check the back of your new speedo. It sounds just like what we had. See if you have a little meaningless looking screw (there won't be a "calibration screw" sticker on it, they leave it to your imagination

).

It maybe nothing, but check it out...

God bless,

John