I just ordered a Speedometer gear for my car since i have 3.42's and it cost $33 from the dealership.. does that sound right? I heard there only $8 or something. But he said i needed two of them, one more the transmission and one for the speedometer.. So whats up?

 

There are two gears and they are color coded. If you do a search you will find some very usefull info with formulas which figure in tire height, different gear ratios and such to get your speedo as close as possible to the correct mph. I am not sure which wo gears you will need. It all depends on how much your old gear ratio was changed by. It is possible that changing only 1 gear will get you where you need to be, but you have to do the math to find out. Hope that helps.

 

Here is a good guide. Be happy that you don't have a t-5, well actually they aren't that bad either way. However, those prices are about right.

 

I did the same swap and the gears were like $6.30 each. I have the part numbers at home if you need them.

 

If you went from 2.73 to 3.42 you need both the driven gear (and housing) and the drive gear. Some places sell an aluminum driven gear housing, and that's a little more expensive. $33 sounds about right for that. I got ripped off last year by Pace Performance because they sent me the wrong housing and wouldn't cooperate with me when I told them about it.

I got the correct one from TCI afterwards.

 

I didn't change the housing and my speedo is right on.

 

Did you change the driven gear? How many miles did you put on the car since?

 

I had to change both gears. All I remember is that the factory gears were both red. And I had to change them to a gray 15 tooth drive gear p/n 8642620 and a yellow 41 tooth driven p/n 25513028 gear.

I did the swap in Feb. and the car is driven daily. So I've put a few thousand miles on her.

 

I changed the driven gear housing because the housing for the 41 tooth driven gear moves it a little further away from the drive gear. Over time, the gears might wear if you re-used the old housing because the gears are forced too close together. BUT, they might last forever.

 

here are the two side by side

 

casey butt is right, there are different housings. I'd assume it's because of the difference in gear size as well. My iroc had the plastic housing (which broke where the cable screws onto it). The local Chevy parts man told me it was an out of stock item and my best bet was a junkyard. I got another plastic housing and tried to switch my parts into it. Ended up shortening the inside of the housing to allow it to fully seat in my 700r4 and doing some grinding on the outside of it so I could turn it a few degrees around from it's normal orientation so the gears would mesh. After that it worked fine for a couple of years till it got bounced out of alignment when the car went into a deep ditch at a fairly high rate of speed (that's another story - at least my kid didn't get hurt, except for cutting his finger while trying to determine if the funny lines on the windshield were really cracks. Oh yeah, he was in front of the Mustang and the SRT/4 when he failed to make the 90 degree curve and parked in the ditch). Anyway, back to the point. There are different housings but you can make them work with a little modification and fitting.

 

casey butt, do you know what you would need it you went from a 2.73 ratio to a 3.73 ration now, my drive and driven are both red, so if the places i have went to are correct, the drive gear is 17 tooth and the driven is 37.

 

You have the "standard" 2.73:1 ratio speedometer gears - those are the right tooth numbers.

You'll need a 15-tooth drive gear and a 45-tooth driven gear (assuming you have 26" diameter tires, i.e. stock diameter)

The 45-tooth driven gear has a slightly bigger diameter than the 37-tooth gear. So, if you install the 45-tooth gear with the 37-tooth gear housing, the gear will be forced a little too close to the drive gear - the teeth of the gears will "mash" together too closely. Both gears are some kind of plastic, so they can wear prematurely if they don't line-up right. However, the shaft on the driven gear is also plastic so it can bend a little and allow you to "fit" the 45-tooth gear into the drive gear even if you use the "wrong" housing. It might last forever, but it will probably give our eventually. It's not a costly or difficult job to fix the problem later, but it might save you some time and money to also get the correct housing when you buy the speedometer gears.

Try TCI, that's where I ended up getting the correct setup for my gear swap.

 

acually i think it is suppose to be 43, calculated it on a website

 

The 43-tooth gear will cause a 3.6% error in the speedometer reading. The 45-tooth gear will be off by just less than 1%. I don't know why the site is recommending a 43-tooth driven gear???

 

it came up to be 43 on more than just one site, i didnt even use this site, i just went to TCI, it came up to be 43.356

 

2.73/3.73 = 0.732

(15/17)(37/45) = 0.725

(15/17)(37/43) = 0.759

With the 43-tooth gear the speedometer will read 3.7% faster than the actual speed of the car. With the 45-tooth gear the speedometer will read just under 1% slower than the actual speed of the car.

The only way that the 45-tooth gear is incorrect is if the original gearing supplied with the 2.73 rear-end was significantly inaccurate from the factory.

GM equipped their 2.73:1 rear-end cars with 26.1" tires with 17-tooth drive gears and 37-tooth driven gears - the calculator on the website says that the correct driven gear tooth count should be 36.

 

all the websites are coming up 43, i guess i should tell you that im not using the factory size tires, if that makes 43 right, well why is there a 37 in there if all the calculators are saying 36, im sorry all my resources are telling me that using a 43 with be 3 tenths off, look at http://www.transmissioncenter.net/sp...n_______va.htm scroll down and you will see the chart, it shows with a 15 and 17 and 18 tooth
the only way i got yours to work is if the revolutions are 960, at this website, it doesnt require you to know the revolutions, it figures if out for u by a formula. 20168/ tire in inches, thought i should tell you that mine is electronic, its not cable