Hi I just got an 87 ta 305tpi w/700r4. My speedo is 10mph slower than it should be. i thought it might be the gear but then i took apart the cluster(140 speedo) and noticed my cluster was missing ses and shift light bulbs so i moved brights and seatbelt bulbs. has an automatic ever come with a shift light or was this cluster taken from a 5speed for the 140 speedo. If it was how do i correct the gears for a 140mph if the original was 120 0r 85?thanks alot

 

Automatic clusters don't have shift light bulbs. If you put one in, it'll start turning on and off when your TCC locks and unlocks.

You don't do anything to the speedometer gears if you change speedometers. You only change speedometer gears if you change the diff ratio, or the tire height.

 

The scale doesn't make any difference to what gears you need. On all the different speedos, the same # of degrees of pointer movement = the same # of mph; so the pointer always goes the same amount, say, 90° from 0 to 70 or whatever. Furthermore, the cable always spins the same; 1000 revs = 1 mile. Or, look at it a different way, 1000 RPM = 60 mph.

Sounds like you just need to get the right speedo gears.

AFAIK the clusters were the same between stick & auto; they just didn't put a bulb in the auto ones for the "shift now" light. In fact the same driver pin on the ECM is the shift light in auto cars and the TCC solenoid in auto cars; so if you have a auto ECM, it will light the "shift" light when the TCC is applied. Just leave that bulb out.

Your speedo is probably not "10 mph" off. That would mean it ALWAYS reads 10 mph different from the actual speed; sitting still, 60 mph, 150 mph, whatever. More likely it's a PROPORTION; like, it's 15% off, so it reads 1 mph off at 6 mph, 4.5 off at 30, ~10 off at 65, 15 off at 100, etc.

Speedos are SO SIMPLE. It's amusing how poorly they are understood by most people.

 

thanks for the info and it off 10mph at about 55mph im actually doin @ 65. thanks again

 

Sure, but is it at 35 when you're doing 45?

 

no I was trying to say that I mistated the 10mph correction, its only at 55 that its off 10mph.