Speedometer question?

If someone put a 98 GT speedometer(150MPH) cluster into a 98 Cobra(160MPH), would the speed reading be accurate?

why would anyone downgrade from a cobra speedometer to a GT speedometer? :confused:

I bought a Cobra, and the cluster must of have broken at one point, and it was replaced with a GT cluster. I did not do it, but it is there. The weird part is, I tested the rear, and it seems to be a 3:73 (counting shaft spins). I bought the gear for the transmission speedometer sensor. When I took the sensor off today, it already had one on there for a 4:10. Now I really have no clue. I put my new one in there, but am thinking the speedo is still off because of the cluster being for a GT.

all you would need to do is find out what RPM they are calibrated at. they are probably the same. i see no reason why ford would calibrate them differently. you could posibly call up ford or something as ask them what RPM the speedos are calibrated at. they should tell you something like... for example almost all chevy micanical speedos are clibrated at 1000RPM's at 60 MPH. someone should know what those are at but like i said it should be the same.

I will look into that. The part that gets me is that on the GT Speedo, right across from the 1000 RPM mark is 135 MPH. On the Cobra, it is 145 MPH. I am wondering if the needle position is the same for both which is making me 10MPH off. Thanks for responding......

If the whole cluster was replaced, then it should be accurate. Typically clusters are calibrated inside the unit, all your doing is hooking up a cable from the transmission to the cluster to get the reading.

Wow, then I am in worse shape than I thought. My Speedo was about 10MPH off when it had the gear for 4:10's on it. Anyway, the person I bought the car off of is sending me the Cobra cluster. I will wait until I put that in to see what happens. Thanks for the help all....

What color was the speedo gear you took out, what color did you replace it with?

yeah, the speedo is calibrated in the cluster. but for example, if the cobra speedo is calibrated at 1000RPM's at 60MPH and the GT speedo is calibrated at 1500RPM's at 60MPH then if you only change the cluster your speed will be off. just claifying there. umm just wondering but why do you even think its not reading accuratly? just because the cluster was changed? i would say if thats the only reason then its probably fine. but i could be wrong. look at the two clusters, when you get the cobra one anyway, and if the number... ie 10 20 30 40 50 and so on are in the same position around the guage but there is just another number, (160), on the cobra one then your fine. like i said i dont see why ford would change the calibration of the speedo from that GT to the cobra so i would think it should be fine. now if you do go and change the gears in teh rearend or the speed sensor gear then it would be off. if you dont know for sure that your speedo is off, if it just seems like it is, then go take and drive your car and pace a friend who is in there car that you know the speedo reads corectly and see if you speedo reads the same as his.

I have determined it was off both bye eye, and driving next to a friend. It appeared to be about 10MPH too fast. Then I checked for gears, and it seemed to have 3:37's in it. All of this time, I still did not realize it was a GT guage in the car. I then bought the Speedo gear for 3:73's, but when I installed it, I noticed the one that I removed was for 4:10's. Anyway, I put the new gear in, and now noticed it is not the correct cluster. I have also noticed that the numers on the Cobra guage are spread out differently. The 1000RPM mark on both cluster's tach is at 9 o'clock. Directly across from this point on the GT speedo is 135 MPH. Directly across form that same position on the Cobra's is 145. I am thinking that may be my 10MPH difference. Agree?

The postion of the numbers on the gauge will not matter from one cluster to another, since each cluster is calibrated internally.

yup^^, what he said. if you have the right gear for the 3.73's put it in, if you didnt. then it should be correct. otherwise if its not, find out what gear a GT would need that has 3.73 gears in the rear and put that one in your trans. then it should be right. unless the cobra and GT came with a different trans. but there are probably two gears in the trans that control the speedo sensor. there should be a driven and a drive. also sence you say your speedo reads to fast, what ever gear you put in should have more teeth than the one you take out. you will probably only need 1 or 2 more teeth to get it corect. that might be a better way to go instead of trying to figure out everything else. just get the gear you have and count he number of teeth, along with looking at the color. but the colors are not always corect they are not an industry standard so you could have two different gear the same color and stuff. but just count how many teeth it has and get one with one or two more.

I do have a 3:73 gear in it. The new speedo gear I put in is for a 3:73. The speedo gear I took out was for a 4:10 (counted teeth, and color was correct). Now my speedo is about 15MPH off. I am not totally convinced that having a GT cluster is not my problem. Even with the 4:10 speedo gear, it was 10MPH off. If it is not the cluster, it is going to be a nightmare to figure out. I was thinking the gear spins, and the sensor sends a signal to the needle to move it a specific amount. If that amount reads one thing on the GT, and another on the Cobra than that is my issue. One thing is for sure, I have the cluster coming so I will wait to install that before changing anything else. It is stupid for me to have a GT cluster in a Cobra anyway. I will be sure to let everyone know what happens when I put the cluster in, and then we can take it from there if a problem still exists. Thanks all for your help with this, and I will be sure to update the status next week when the cluster comes in.

Well, the cluster came in, and made a huge difference. I still think the speedo is of by about 3MPH, but I guess I can deal with that for now. Thank you all for your help.