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· Senior Member
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590 Posts
Discussion Starter · #1 ·
ok ih guy's,i have a spedo issue on my 95 model 4900. the 95 i bought a few months back had a couple item's missing[turn signal.intrument cluster]. no prob,i bought a new turn sig [$175.00 w.t.h ?]and took the instrument cluster out of one of my 95 model school buses,installed it in the 4900. well here's my prob, everything works fine but the temp gauge[sender is good ],and the speedo is inaccurate. i'am sure the spedo prob is due to the difference between axle ratio's of the bus and the 4900. my question,how do you calibrate the speedo to match the axle ratio? i have seen the spedo adjusment on the back of the cluster ,but what's the proper procedure/code? thanks, jim ..
 

· Senior Member
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456 Posts
you need axle ratio tire revs per mile do some computations to get total pulse per miles based on the 16 tooth tone wheel in trans and what engine you have electronic or pump line nozzle then using the book at work I look up the dip switch settings temp gauge if its an electronic engine the temp gauge is data link fed and if speedo and tach are working (even if wrong) then the data line is ok and its probably a gauge or dash issue. if a mechanical enngine it could be that or wiring
 

· Super Moderator
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Yup, you need to know the RAR, and tire Rev/mile THEN you can calibrate the speedo correctly.

I have the print-out of the "1s and 0s" for the dip switches.
 

· 'Ol Builder guy
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7,275 Posts
You need to reset the "dip switches" in the top of the cluster head of the General Instrument speedo cluster.

Make sure you turn the ignition OFF and watch out for static electricity jolts, too!!
Example:
tire rev's/mile = A
axle ratio = B

A x B = revs/mile of the prop shaft.

My truck: revs/mile 12/22.5= 485 rev/mile
Axle ratio = 5.38

485 x 5.38= 2609

2609 dipswitches set to 0011101010

If you have the linesetting ticket, IH puts them on there, too!

Just give me your tire size & rear ratio & I'll do it for you.
 

· Senior Member
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590 Posts
Discussion Starter · #5 ·
sorry guy's for the slow response, had a issue come up. anyway, my tire size is 295-75-22.5 , 4.44 axle ratio , and spicer 7spd direct tranny. this is a mech injection truck. thanks for the help guy's..
 

· 'Ol Builder guy
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navistar45 said:
sorry guy's for the slow response, had a issue come up. anyway, my tire size is 295-75-22.5 , 4.44 axle ratio , and spicer 7spd direct tranny. this is a mech injection truck. thanks for the help guy's..
I don't have the rev/mile on a 295/75, but i do have a 295/80 listed at 500/mile. I guess a 295/75 might be a few more revs/mi.

Anyway 500 x 4.44 = 2220.

A 2220 setting is 1010010010

let me know if you get the rev/mi on a 295/75 and i'll get you the exact settings.
 

· Senior Member
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Discussion Starter · #7 ·
thanks duke,i doubt the difference between the tires is worth worrying a about. if i understand y'all correctly,i just program the numbers to the ones you gave me,then i'am good to go!? if my temp gauge cant be fixed easily,i may pull another cluster from a bus that i know works,i will program that speedo while i have it out.
 

· 'Ol Builder guy
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navistar45 said:
thanks duke,i doubt the difference between the tires is worth worrying a about. if i understand y'all correctly,i just program the numbers to the ones you gave me,then i'am good to go!? if my temp gauge cant be fixed easily,i may pull another cluster from a bus that i know works,i will program that speedo while i have it out.
Jim,

It makes a pretty decent difference. Mine took some tweaking until it was right because different manufacturers have different revs/mi.

It might be close but don't be surprised if it's off by 5 mph!
 

· 'Ol Builder guy
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navistar45 said:
ok guys,got the spedo set, it was only one dip switch off. test run shows every thing is accurate. now to get that pesky temp gauge working, thanks for the help fella's..
No problem. The great thing we can all share here is knowledge & experience.

Now what's going on with the temp gauge?
 

· Senior Member
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Discussion Starter · #13 ·
temp gauge refuses to work. when i turn the key on,it jumps a bit,but thats it. the gauge cluster is out of another bus ,that i know for a fact works. the other cluster netted the same issue, everything but the temp gauge worked. i have tested the system with a temp sender from a spare engine that also works fine, gauge works/sender works, so it must be a wireing issue! i need to obtain a schematic of the wireing,unless some one knows which wires feed into the firewall? all the wireing is protected in a loom,so i cant see why it would be damaged...
 

· Senior Member
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let me see if I can find a 95 wiring book and I can try to get you some numbers I dont have a working scanner so cant scan the images for you to see the pin locations in the connectors tho
 

· 'Ol Builder guy
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Duculuv,

Can I ask a favor? While you're looking up Navistar45's wiring, can you please look up which wires are the ones for the front & rear differential temperature gauges?

I want to hook the "front rear" temp sender into my front axle and the "rear rear" temp sender into my rear axle. I have the gauges installed, I just need to know which wires in the bundle behind the dash. It's a '92.

Thanks, sorry to hijack.
 

· Senior Member
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see what I can do for you both but it will have to wait till monday couldnt find the older books in my stash have to check with one of the other guys when he is in monday
 

· Senior Member
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ok at the sensor wire 29a goes over to the main cab firewall plug per my diagram cavity d5 a 18 gauge tan wire then it goes up to the dash thru the green dash plug cavity 15 the other wires at the sensor is wire 29g 18 tan wire it goes to a ground splice and becomes wire 11g 8 gauge white wire and gets ground from the starter ground stud


as for the 92 diff temps they start at the natural color plug forward is cavity 12 wire 32 16 gauge brown to the rear of the cab behind the drivers seat there is a 12 wire rectangal plug cavity 1 comes out 14 gauge brn and goes to the diff

the rear rear is cavity 11 of the dash connector wire 32a 16 gauge red wire to cavity 12 of the cab connector comes out 14 red and goes to the diff now the book shows these wires going thru another 4 wire connector but if you are running your own wires it is a moot point the second wire for each sensor if it has them goes to frame ground
 

· Senior Member
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Discussion Starter · #19 ·
thanks a bunch doc. now i gotta find the time to crawl around the truck,and chk the wires. sort of wondering if the issue is a ground problem, your info has likely saved me from a headache. thanks again sir...
 
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