87 85mph to 140mph question-changed gear & still off

FrdMustangCpe · Aug 24, 2004

I just installed some white face 140mph gauges and i bought the speedo gear to calibrate it. I have a 87 (but with a 90 tranny)and 3.73s. The calibration gear for a 90 w/3.73s is a 23tooth. so thats what i bought. the speedo is still a good 20mph off. and i dont want to take it out and ship it to someone to calibrate it. any ideas? could i have reset the needle THAT far off when i put the gauges in? im stumped

Js5ohLX · Aug 24, 2004

Did you just put a 140 face on a 85 speedo? I didn't think that would work, I could be wrong.

seijirou · Aug 24, 2004

uh, did you just stick on the guage stickers on your 87 dash assembly and not change the hardware the needle plugs into? If not, this is your problem. The mechanism that moves the needle also has it's own calibration. It uses spinning magnets to try to move the needle clockwise, and a spring to give resistance. I'm pretty sure a spring change will change the calibration, but this is only an estimated guess from looking at once when I did my 140mph mod on my old car. Anyway, what you need to do is get the metal piece that the speedo cable plugs into from a car that comes with a 140mph speedo stock.

FrdMustangCpe · Aug 24, 2004

seijirou said:
. Anyway, what you need to do is get the metal piece that the speedo cable plugs into from a car that comes with a 140mph speedo stock.

damn. i may just live with it.

xxxCadillacxxx · Aug 24, 2004

Speedometers accuracies are not rated by "mph off", they are off by a percentage. What percentage is your speedo off by? The calibration of the movement is relative to the power of the magnents NOT the return spring. To re calibrate that you need a electromagnent with the 2 poles the with of the speed cup and a speed standard - specialized tool most do not have laying around their garage. You can make up for some of the movement's inaccuracy with a different trans gear, but thats not the right way.

My father owned Gabes Speedometer in SW Philly for some years. If you really want it recalibrated i can do it the right way. Ship it over!

seijirou · Aug 24, 2004

xxxCadillacxxx said:
Speedometers accuracies are not rated by "mph off", they are off by a percentage. What percentage is your speedo off by? The calibration of the movement is relative to the power of the magnents NOT the return spring. To re calibrate that you need a electromagnent with the 2 poles the with of the speed cup and a speed standard - specialized tool most do not have laying around their garage. You can make up for some of the movement's inaccuracy with a different trans gear, but thats not the right way.

My father owned Gabes Speedometer in SW Philly for some years. If you really want it recalibrated i can do it the right way. Ship it over!

Ohwell, it was just a guess afterall, now I know it's not the spring

FrdMustangCpe · Aug 24, 2004

i dont have another car to drive. and i dont really want to take my dash apart and drive around w/o a speedo. how much would it cost

FrdMustangCpe · Aug 24, 2004

well when i say its 20mph off, that means im at 20mph (i think) and it says 50mph. how do i figure out the %?

xxxCadillacxxx · Aug 24, 2004

Pace someone who is going 50 mph and take a reading, double the difference and that will give you the percentage. But knowing the percentage it is off dosent really matter if you are off by that much. You will need to get the sweep of the gauge recalibrated to get it to be accurate. Your easiest route would probably be to buy a 140 mph speedometer (ebay Rules!) and just swap out the movement. You cant fix a difference that great with a gear.

FrdMustangCpe · Aug 24, 2004

well ill definately keep an eye out on ebay. i think the clusters are pretty hot right now, a lotta people are spending some money on them, like $90 for the whole cluster.

Rick 91GT · Aug 24, 2004

Its needs to be done by a speedo shop, I'd take xxxCadailliacxxx up on his offer or you need to send it to Brotheres Performances or North Hollywood Speedo does them.

xxxCadillacxxx · Aug 24, 2004

WOW i just looked on ebay, i didnt realize they were going fo so much. I have about 6 85mph Fox instrument clusters sitting at my house i could get faces for and re-cal....

FrdMustangCpe · Aug 24, 2004

so i would have to take it out then. how much would it be since i already have the white faces

_jb_ · Aug 24, 2004

xxxCadillacxxx said:
WOW i just looked on ebay, i didnt realize they were going fo so much. I have about 6 85mph Fox instrument clusters sitting at my house i could get faces for and re-cal....

Hey do you think you can calibrate 160MPH speedos? I bought one back in Feb. and it is about 10 MPH off. It depends on how fast I am going, at about 25MPH it says I'm going about 40, while 50 is about 65.

Mustang5L5 · Aug 24, 2004

Just swap the speedo part, you don't need the entire cluster. The speedo mechanism is only held on by two screws. It's a direct swap, peice of cake really.

I found my 140MPH speedo mechanism in a junkyard for $20.

FrdMustangCpe · Aug 24, 2004

Mustang5L5 said:
I found my 140MPH speedo mechanism in a junkyard for $20.

now there's a thought. do u have to take my white face of to change it? i might be able to get one at my local 5.0 shop, hes got a lot of 'project' type foxes. of course none for sale. I'll see if he has one.

Thanx

Mustang5L5 · Aug 25, 2004

FrdMustangCpe said:
now there's a thought. do u have to take my white face of to change it? i might be able to get one at my local 5.0 shop, hes got a lot of 'project' type foxes. of course none for sale. I'll see if he has one.

Thanx

No, you don't need to peel the face off, but you do need to go inside the cluster again.

You take the plastic bezel off, the black metal trim and then take the speedo needle out. Then pry out the speedo portion of the cluster and flip it over. This is what you want to pull out
http://members.aol.com/mustang5l5/Speedofront.jpg

On the backside you will see two screws
http://members.aol.com/mustang5l5/Speedorear.jpg

unscrew those and the speedo falls off. Toss it in the trash and slap a 140MPH speedo in there. Put it all back together the same way.

If you can't find a 140MPH speedo, find an old 85MPH speedo. They are common and cheap. Just take the speedo section out and sent it off to www.brothersperformance.com and have them calibrate if for 140MPH. They might even slap a white face on it identical to the speedware faces you have now. When you get it back, just swap it in and call it a day.

Then you can send your 85MPH speedo off with the white face and have em calibrate that one up and sell it on Ebay for $100

xxxCadillacxxx · Aug 25, 2004

Hey do you think you can calibrate 160MPH speedos? I bought one back in Feb. and it is about 10 MPH off. It depends on how fast I am going, at about 25MPH it says I'm going about 40, while 50 is about 65.

Yes i can, but its not necessary. You can make up for a difference that small by swapping out the gear in the transmission. Pull it out, count the teeth and call your dealer/whoever and order a gear with 2-3 more teeth. It should put you within tolerance.

_jb_ · Aug 25, 2004

xxxCadillacxxx said:
Yes i can, but its not necessary. You can make up for a difference that small by swapping out the gear in the transmission. Pull it out, count the teeth and call your dealer/whoever and order a gear with 2-3 more teeth. It should put you within tolerance.

I have 2.73s in my car, and I later plan on moving to 3.73's. I have already bought the red 21 tooth gear for them. I would like the speedo itself to be correct, and not have to switch out gears all the time.

xxxCadillacxxx · Aug 25, 2004

as for keeping it accurate through rear and tire changes, you eithe have to change the drive gear in the trans, or recalibrate the speedometer. There is no "quick Fix". Relativly speaking, changing the drive gear in a mustang is one of the easiest cars.

87 85mph to 140mph question-changed gear & still off

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