7.3 idi speedo problems
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Freshman User
Joined: Mar 2016
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7.3 idi speedo problems
Ok guys i figured y'all are pretty knowledgeable, so my 1988 f250 7.3 idi na 2wd 5 speed. The speedo is 4mph fast compared to my vehicle speed, the truck had 235s on it an I put 265s on it, which theoretically shouldn't effect the speedo, I didn't drive the truck before the tires so i don't know if it was accurate before. The thing is as far as I know the truck is completely stock
Laughing Gas
Joined: Mar 2016
Posts: 1,105
Likes: 78
okay here's how you figure out your correct driven spedo gear ..
drive teeth
(look inside spedo gear hole with a light .. might need a mirror )
if it's yellow .. it's 7 tooth
if it's green .. it's 8 tooth
at least usually .. sometimes different gear colors aftermarket are used ..
but it's probably a 7 yellow ..
so ..
7 X REAR END RATIO X TIRE REVS PER MILE = ??
tire roll out calculator
https://www.mickeythompsontires.com/...hp?bulletin=g3
you would have to calculate to inches .. i don't know metric
using my truck as an example .. i need this combo
[8 X 3.55 X 593 (35's) = 16841 = 16.841
so i need a 17 tooth driven gear // rounded = [17]
tire wear and inflation can slightly effect the true revolutions per mile also
drive teeth
(look inside spedo gear hole with a light .. might need a mirror )
if it's yellow .. it's 7 tooth
if it's green .. it's 8 tooth
at least usually .. sometimes different gear colors aftermarket are used ..
but it's probably a 7 yellow ..
so ..
7 X REAR END RATIO X TIRE REVS PER MILE = ??
tire roll out calculator
https://www.mickeythompsontires.com/...hp?bulletin=g3
you would have to calculate to inches .. i don't know metric
using my truck as an example .. i need this combo
[8 X 3.55 X 593 (35's) = 16841 = 16.841
so i need a 17 tooth driven gear // rounded = [17]
tire wear and inflation can slightly effect the true revolutions per mile also
Thread Starter
|
Freshman User
Joined: Mar 2016
Posts: 45
Likes: 0
okay here's how you figure out your correct driven spedo gear ..
drive teeth
(look inside spedo gear hole with a light .. might need a mirror )
if it's yellow .. it's 7 tooth
if it's green .. it's 8 tooth
at least usually .. sometimes different gear colors aftermarket are used ..
but it's probably a 7 yellow ..
so ..
7 X REAR END RATIO X TIRE REVS PER MILE = ??
tire roll out calculator
https://www.mickeythompsontires.com/...hp?bulletin=g3
you would have to calculate to inches .. i don't know metric
using my truck as an example .. i need this combo
[8 X 3.55 X 593 (35's) = 16841 = 16.841
so i need a 17 tooth driven gear // rounded = [17]
tire wear and inflation can slightly effect the true revolutions per mile also
drive teeth
(look inside spedo gear hole with a light .. might need a mirror )
if it's yellow .. it's 7 tooth
if it's green .. it's 8 tooth
at least usually .. sometimes different gear colors aftermarket are used ..
but it's probably a 7 yellow ..
so ..
7 X REAR END RATIO X TIRE REVS PER MILE = ??
tire roll out calculator
https://www.mickeythompsontires.com/...hp?bulletin=g3
you would have to calculate to inches .. i don't know metric
using my truck as an example .. i need this combo
[8 X 3.55 X 593 (35's) = 16841 = 16.841
so i need a 17 tooth driven gear // rounded = [17]
tire wear and inflation can slightly effect the true revolutions per mile also
Laughing Gas
Joined: Mar 2016
Posts: 1,105
Likes: 78
yeea no problemo ..
the drive gears they no longer sell .. from what i understand .. at the dealership anyways .. so in my case i'm gonna have to go jy diving for a decent green one due to my upsized tires ..
but if you'r drive gear is the right one .. and you just need the smaller driven gear .. they are only 5 bucks at the dealership parts counter .. and they likely have a big ol' box full of em to pick through
the drive gears they no longer sell .. from what i understand .. at the dealership anyways .. so in my case i'm gonna have to go jy diving for a decent green one due to my upsized tires ..
but if you'r drive gear is the right one .. and you just need the smaller driven gear .. they are only 5 bucks at the dealership parts counter .. and they likely have a big ol' box full of em to pick through
Postmaster
Joined: Dec 2011
Posts: 3,860
Likes: 7
If it's only 4 MPH off, I'm not sure you'll be able to adjust it that finely.
As far as I can tell, even with stock tires, mine is off by a couple of MPH at 60, and it varies depending on speed(so, like, at 25 it reads 2 MPH high, at 60 it's 4 MPH low), so compensating isn't going to work.
If by 265 you mean 265x75xR16, and by 235 you mean 235x85xR16, yes, the sizes are basically the same -- close enough to mix and match when using 4 wheel drive, even if the tire shops say you can't(I've done this for several years now, works just fine).
As far as I can tell, even with stock tires, mine is off by a couple of MPH at 60, and it varies depending on speed(so, like, at 25 it reads 2 MPH high, at 60 it's 4 MPH low), so compensating isn't going to work.
If by 265 you mean 265x75xR16, and by 235 you mean 235x85xR16, yes, the sizes are basically the same -- close enough to mix and match when using 4 wheel drive, even if the tire shops say you can't(I've done this for several years now, works just fine).
i ain't rite
Joined: Mar 2005
Posts: 65,580
Likes: 5,612
From: Marlboro Mental Hospital.
for speedometer cable end gear, burgundy is 16 tooth, white is 17 tooth, yellow is 18 tooth, pink is 19 tooth, black is 20 tooth, red is 21 tooth.
each tooth is good for about 2 1/2 MPH speed difference.
this is for the older FMX, C-4, C-5, C-6, and the 3, 4, 5 speed manual transmissions that use a cable driven speedometer.
you can still get the 5 tooth gear kit on ebay for around $35, or individually for around $10 each
each tooth is good for about 2 1/2 MPH speed difference.
this is for the older FMX, C-4, C-5, C-6, and the 3, 4, 5 speed manual transmissions that use a cable driven speedometer.
you can still get the 5 tooth gear kit on ebay for around $35, or individually for around $10 each
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