George84

I have a 89 n/a and am looking at putting a 89 GTUs rear-end in it. Can I use the same driveshaft? Is the 4.3 rear going to messup my speedo with my stock trans? Is the GTUs speedo gear different from the stock n/a speedo gear? Should I get the GTUs trans too? What is the best setup to go with?

RotaryResurrection

iTrader: (8)

The rear bolts into any nonturbo 86-91, using all stock components. You only need the GTUs' speedo gear from the trans in the GTUs...put it into whatever trans you are running. Otherwise your speedo will be off.

I have the same thing on my 'vert. Its really simple.

George84

What about the 5th gear being a different size in the GTUs? If you keep the stock tranny and swap speedo gear won't the speedo be off in 5th still?

RotaryResurrection

iTrader: (8)

Nope. The transmission itself accounts for that, not the speedo gear. Trust me, just pop it in there and go. IT is all you have to do...don't over-think this.

George84

Is there somewhere to buy speedo gears? I am not sure the person will let me have the speedo gear without buying the GTUs tranny.

RotaryResurrection

iTrader: (8)

Not that I am aware of.

George84

Does the GTUs tranny need that speedo gear to read the correct speed or will any other speedo gear work on that tranny?

RotaryResurrection

iTrader: (8)

Let me attempt to further clarify my comments.

The rearend, and the speedo gear, go together. IF you have a stock 5sp non GTUs car, you have a 4.1 ratio rear, and a gray gear. The gear indicates the 4.1 rearend. The auto's have 3.9;s and an orange gear to indicate that. The GTUs has 4.3 and I forget what color gear specific to that ratio.

Now...if you take an auto trans car, and put a 4.1 rear into it. You simply swap the rearend and the 4.1 gray gear into the existing auto trans, and it all reads properly again. Same for any other example.

ANY 2gen trans will accept ANY 2gen speedo gear, representing any of the 3 ratio rearends that you put behind it.

For purposes of this discussion, the gears inside the trans have no effect on this.

George84

That answered all of my questions, thanks for helping me out so fast.

Scott 89t2

if you don't get it, it'll only be off by a few %. nothing to worry about.

RotaryResurrection

iTrader: (8)

It winds up being about 6-10mph at freeway speeds, in my experience.

Hot_Dog

Not really. Since 4.1 / 4.3 = 0.954, there will only about a 5% difference in speed. Using the original speedo gear with a 4.3 final drive ratio, the speedo will indicate 80 mph when the car is actually travelling at 76 mph.

Hot_Dog
90 RX7 GXL
02 Acura RSX-S

Rotary Racer

Ok looks like there are two part #s for the spedo gear for S5 manual trans 7’s.

- 1011-17-441A, Specific for non turbo trans (hard S) <-should be the GTUs spedo gear

- 1669-17-441A, for non turbo (nor. SU SP) & turbo trans <- should be all other 4.10 gear ratio manual trans cars.

You should be able to order these from Mazda or Mazdaformance I will look at my spedo gear tonight to see if there is a part # on it for ya

- Dana "GTUs all the time, every time"

RotaryResurrection

iTrader: (8)

Have you DONE it? Math is nice, experience is better.

banzaitoyota

I have yet to bother with calibrating my swap. I need to sort out the tires sizes and what-not. I do plan on using a "black box" to acheive the correct correction factor when all is said and done

SonicRaT

iTrader: (6)

Isn't the GTUs gear (tranny side) setup for the 16" rims as well?

nonameo

okay guys, look.

the transmission turns a shaft that turns the driveshaft, right? well, the speedo gear is on that shaft. the speedo cable basically reads how fast that shaft is turning. For the same reason it is accurate in ALL of your gears it will be accurate with the different 5th in the GTUs.

edit: oops different size tires will make a difference... didn't think about that... thanks rat

I hope that helps... trace the drivetrain from the wheels to the engine and think about it some and it will make sense.

Hot_Dog

There are several factors that can contribute to a false speed indication. As you previously wrote:

>It winds up being about 6-10mph at freeway speeds, >in my experience.

Your 6-10 mph observation is likely a result of a combination of speedometer error and the wrong speedometer gear. As I mentioned earlier, using the wrong gear will give a 5% error. Per fsm, there is also some error in the speedometer gauge:

10 mph / 10-11.4 mph / 14%
30 mph / 30-31.8 mph / 6%
60 mph / 60-63.0 mph / 5%
90 mph / 90-94.5 mph / 5%

The fist column is the actual speed, and the second column is the indicated speed. At highway speeds, the allowable error could be as much as 5%. Of course, it could be higher if the speedometer isn't working properly. The tire size and inflation pressure will also affect the speedometer error.

So, it's entirely possible that the speedometer could be in the 10% range, which would be about 6-10 mph over the true speed. The wrong sppedometer gear, however, is only one contributing factor to your false indicated speed.

Hot_Dog
90 RX7 GXL
02 Acura RSX-S