Information on speedometer

[silver_bullet]

Last year my sons and I did a ground up restoration of a 1985 f250 idi. Since the bed and cap was junk, we found a 1995 bed and cab from a f150 in a junk yd that was in perfect shape and used that, including all of the 1995 wiring harness. My question is this, the 1995 has an all electronic speedo and the 1985 was cable controlled does the 1995 get its speedometer impuse from from the transfer case or the rear axle housing? or both? the truck still has the 1985 axle and transfer case, so I dont know if i need to replace either or both. As of right now, we dont have a working speedometer and would like to get it working// Any help on this would be greatly appricated.

silver bullet.

 

[anthonyj]

I believe that the speedometer gets its signal from the RABS (rear antilock brake system) module which receives its speed signal from the sensor on the rear axle.

 

[silver_bullet]

I was kinda thinking along those lines but wasnt sure. I've found a replacement axle for it, abit a 3.55 gearing. I will also have to replace the front gearing also because the truck currently has 3.73 gearing.

 

[chevytaHOE5674]

Are you sure about that 3.73 gearing? Factory would have been 3.55 or 4.10....

 

[silver_bullet]

i think during the mid 90's it would have been, but the axles are the original ones from 1985 .only the bed, cab, front end, and all the wiring is now 95. The frame and all the suspension is 1985

 

[silver_bullet]

Anyone else have any imput on this matter? I want to be sure I'm going after the right thing.

 

[sle2115]

If you have 3.73 gears, someone put them there! In my research for 85 parts (the axles under my truck are 85 F350 axles) there were only two gear ratios, 3.55 and 4.10. I tried to find a speedo gear for 3.73's from 83 to 93 and the only thing they showed (diesel wise) was 3.55 and 4.10 as well. So if you have 3.73's, someone put them there. You could also look into a pulse generator of sorts, I know some models used an electric unit that hooked to the speedo drive to generate speedometer pulse. Not sure if Ford used anything like this, but Chevy did (figure ford did as well in the conversion years going from mechanical to electronic speedometers).

 

[silver_bullet]

sle2115,
Thanks for the info, I guess I will start by saying that we assumed the rear was a 3.73 because when we bought it, the guy told us it was a 4.10. But we did the tire rotation/driveshaft rotation count and came up with 3.73 but it is all possible that it could be a 3.55. It aint written in stone anywhere. lol I know dodge used a electrical pulse sending unit that fixed to the back of the transfer case, right where the cable woulda gone on older models. Right now I only want to get the speedo working, I found a 3.55 rear out of a 94 3/4 ton van that has the abs module attached and I can get it cheap. I only want to know if this is going to make my speedo work.
Thanks for your help in the matter.

 

[silver_bullet]

Just a follow up to this post. Thanks for the input guys on the direction to follow. For you guys that told me the axle ratio was a 3.55, you were correct, and I was wrong. I'm never afraid to admit my stupidness lol. WE found a sterling 10.25 in a u pull it close to here. It was a 1989 axle, with a sway bar! and it was 3.55 Paid $65.00 drum to drum.
After we got it back to the shop, drained the oil and removed drums.( outboard drums woohoo!!) The pads were practicly brand new.
no gunk, metal filings or anything in the oil. We replaced the oil and closed it back up. Anyway, got new u-bolts and bolted right up. Guess what? the speedo works great now!!! we checked it with a gps and it was only off maybe 1 mph@ 50 mph. Well worth the effort.... Thanks again everyone for your help on this.

 

[89dieselbko]

This is loosely related to your work here, maybe you can answer, or someone else a quick question for me...

my sterling 10.25 has the rear axle speedo hicky (vss? i think) and my transfer case has the analog gear setup.

My question, do you have to hook up the rear speed sensor? my gauge is fully analog, but so was the 90 f250 i yanked the axle out of.

Was going to start a thread but found this and dont want to hi-jack it or anything but dont want to clog the front page with multiple same topics

 

[gdhillon]

Mines a 93 and the speedometer dohicky is on top of the rear diff

 

[silver_bullet]

I'm by no way an authority on this matter by a long shot. I was lead to belive that when they switched from dana rear axles to the ford(sterling) they also did away with cable driven speedos. On our rig we built. we used a 95 cab and the electronics along with it, We got the full harness for the truck out of the 95 also. As soon as we changed our rear axle to the sterling with the impulse ring inside (that little dohicky sticking out of the top of the rear with 2 wires attached, our speedo worked fine. So it doesnt need any other I will add something for what its worth, those wires coming out of the rear need to be a twisted pair of wires for proper fuctioning. Is the anolog your refering to ,is that cable drive?

 

[89dieselbko]

yeah analog is run on the cable connected to the Xfer case, its from a 90 F250 with sterling, it WAS plugged in, the wires, but when we yanked the trans and Xfer the analog cable was also in place and connected to my instrument cluster... i guess seeing them both on the same truck has me all sorts of confused.

 

[oregon96psd]

it probably has both cause the speedo is cable driven and the speed sensor in the rear end is for the rear wheel abs.

 

[rjjp]

it probably has both cause the speedo is cable driven and the speed sensor in the rear end is for the rear wheel abs.

^^He's correct.

Yes ford did use the pulse generator on the transfer case for a while (my 91 had one).