Mykl

...alrighty, I have an '89 convertible.

I need to know where the engine speed sensor is and if it's dependent on gearing. Logically it wouldn't be affected by different gears, but I'm not sure.

The reason I need to know is because I found a killer deal on a GTUs transmission and differential. The gearing is shorter than the stock gears in my car and I know that it's going to **** with my speedometer, but if my tach is still correct it's no big deal.

Also, what could I do to correct the speedometer? If I used the speedometer cable from the GTUs and plugged it into my speedo would it give me a correct reading?

Thanks guys.

Mykl

Oh, and one more thing...

Does anybody know what the gear ratios are for the '89 GTUs and the '89 convertible? I'm not sure what they are and I'm not sure where to look.

Thanks again.

fc3s.org

The 1989 FSM has them listed in the rear under technical data.


The ratios are:

1st: 3.475
2nd: 2.002
3rd: 1.366
4th: 1.00
5th .697

The GTU-S 5th gear is a .756.

Mykl

Ack, cruising on the interstate is gonna suck now.

HOZZMANRX7

iTrader: (43)

The speed sensor is part of your instrument cluster keying off your speedometer.

As to correction, take your car to a local speedometer shop. They can test and build an adaptor that simply goes between your tranny and the speedometer cable that corrects. Been there, done that. It works.

However, I wouldn't think your speedometer would be affected by a simple change in your tranny as the speedometers are all interchangable between any 2nd Gen to my knowledge. Speedo error is usually only as a result of changing the tire height.

fc3s.org

It is in the tailshaft of the tranny where the speedo cable meets

With the tranny and speedo, you should be ok on your speeds.


The speedo cable is universal if I remember correctly. The tranny and diff need to match for correct speeds to be registered on the speedo.

Mykl

My reasoning behind the speedo getting fucked up would be because I'm going from a 4.1 final drive to a 4.3. Which means the speedo gear is going to spin faster than it was designed to for my gearing giving me a higher reading on the speedo compared to how fast I'm actually going.

As far as my tach is concerned I would think that it reads RPM's of the engine somewhere in the ignition, but I'm not sure.

Thinking about gearing gives me a headache, too many numbers.

Mykl

Okay, the speedometer cable is in the tailshaft. That affects the reading on the speedometer, does it affect what the tachometer (engine speed, not car speed) says?

HOZZMANRX7

iTrader: (43)

NO.

Tac operation is totally independent from speedo anything.

fc3s.org

Oh no, I was thinking car speed, not engine speed. That is read from the CAS isn't it? Engine speed is not related to drivetrain at all.

Mykl

Kickass, that's what I needed to know. I figured that even if my speedo was off a bit I could still figure out how fast I was going based on my tach until I got the gears on the speedo sorted out.

I'm thinking that if I get the speedo cable from the GTUs I'll be good, but if I can't I'll have to get the speedo gears I have now recalibrated or adjusted or whatever.

I used to know the formula for figuring out car speed by inputing engine speed, gear ratio, and final drive ratio but I forgot it.

If anybody knows what that is, that would be very useful info.

Anyway, thanks for helping with my questions guys, I really appreciate it.

mazdaspeed7

Here is exactly what you need. The gear on the speedometer cable will need to be changed from a 21 tooth gear to 23 teeth. Any transmission shop should be able to do it.

Mykl

Very

Hopefully with the 4.3 gears I'll be able to beat a Civic in the 1/4. Getting rid of that clogged cat should help a bunch as well. If I see 15's soon I'll be very happy.