85 to 140 speedo swap

[josh88gt]

I just finished swaping out 85mph speedometer with a 140 speedo in my 88' GT. My car is stock for the most part and I am still running 2.73's and the A.O.D.. Since the swap, I'm expeirencing incorrect mph reading. lt's 9 to 10mph off now. Does anybody know why??

 

[Mustang5L5]

What did you swap??? Just the speedometer mechanism???

 

[josh88gt]

Just the speedo itself. All the rest of the pod is original.

 

[Mustang5L5]

They it should read correctly as no other mods are needed.


Are you positive the original speedo was a 140MPH unit?? I've read of guys installing speedos only to later find it was just an 85MPH speedo with a 140 face on it.

When i swapped a 140MPH speedo into my '88, it read correctly after the swap

 

[josh88gt]

The speedo is out of a 89' cop car. the speedometer has "certified calibrated" printed under the pointer. there is no needle for the pointer to rest on and there is no indication there ever was. the number printed on the speedo says, E7-Z. Some people ive talked to say because it was a cop car it would have been a 5 speed and that l probably have to change the gear in the trans. (my car's has AOD).

 

[superhuaman]

you shouldnt have to change the speedo gear, IF your aod already has the right gear in it for your rear end.

 

[Nibbie]

since you swaped the speedo from 85mph to 140 mph you will have to change the speedo gear located inside your transmission. I think its located near the tail of the aod. you will see a cable going to that location and that cable runs up to through the firewall to your gauge pod. It dosnt matter what the gauge cluster says its still set up for the 85mph unit that was on the car. Go to 5.0resto.com and they should have little gears for speedo/gear swaps.

 

[superhuaman]

you dont have to change the trans gear to change the speedo, only the rear end. where do people get this stuff?

 

[josh88gt]

My car is a '88 GT. IT was originally equiped with a 85MPH speedometer. l know for a fact it was acurate. The only thing that has changed is l have a 140MPH speedometer in the 85MPH's place. NOw im reading on my speedo 40mph when i'm really doing 50mph. I don't understand why it would be 10mph off just because l changed the speedo.

 

[superhuaman]

how do you know it's off?

 

[Mustang5L5]

you dont have to change the trans gear to change the speedo, only the rear end. where do people get this stuff?

+1


No need to touch the speedo gear.


All you need to do is swap the speedo's. I already mentioned in post #4 that you just swap the speedos

 

[josh88gt]

I drove behind my girl's '89 GT which l know is acurate. She set her car on cruise at 50MPH. My car was reading 40MPH.

 

[Nibbie]

oh, never mind, i read incorectly, yeah i guess if it had an original 140mph unit than he shouldnt have to change a thing. well im guessing maybe the speedo needle is off by 10 mph, just take it off and try to put it back on just barly turning the small needle to the right, then reinstall the speedo needle and drive it and see if it worked. I had that same problem.

all i can say about that is my bad

 

[Mustang5L5]

I thought all the SSP cars came with 160MPH speedos????

 

[josh88gt]

don't know. this one came out of a '89 coupe.

 

[Mustang5L5]

Got a picture of the speedo??

 

[josh88gt]

Heres the speedo

 

[Nibbie]

shouldnt there be a peg to hold the speedo needle at the 0?? Im not sure if when the car is started that the speedo needle will move to zero or if it stays in the same spot.

 

[FordBaby]

^^^ thats ur problem right there theres no pin holding the needle so it goes a about 10mph before it hits 0.

 

[Red88 RICK]

so if my car has a spedo that goes to 85 and i just put in a 140 face it will work or are we talking the whole speedo assmbly?i always figured if i wanted to get a 140 id have to change the spedo gear and face of it...?