1988-305-tbi

3.27 gears and 26" tires, what speedo gears, i've been trying to find this out for awhile but still no definate answers.
17/43?
17/44?
17/45?

1988-305-tbi

no one knows? no body on here has a 3.27 rear???????????????????????

84TranzAm

iTrader: (2)

Here is a link to some useful info. Hope it helps you
http://www.transmissioncenter.net/sp...n_______va.htm

xpndbl3

iTrader: (5)

tci has a website....so a simple google search, i found like 5 websites in 5 minutes when i was looking

www.google.com

"700R4 speedo gears"

1988-305-tbi

not much help, i've searched and everything is inconclusive, some gear calculators say 17/ 43 some say 17/45 and some say 18/45, i was asking for help from someone that actually knows which is the propper setup, because they have 3.27 gears a 700r4, and 26" tires, and there speedo is dead on. becuase every website says some different setup, i know i've seen them all if you cant help, dont post, thanks

xpndbl3

iTrader: (5)

they all will be "close" none of them will be perfectly on. Just the problem with trying to maintain a linear ratio when it'll be under at some speed and over at another speed, they will never be 100% accurate. There is always some flipping of the smaller gear right inside the trans, so if some say 17 or 18 with a 45 then go with that. either way it'll be trial and error since all 26" tires AREN'T perfectly 26" tall

1988-305-tbi

http://www.transmissioncenter.net/sp...__va.htm#700r4 says 18/45 for 26" tires and 3.23 gears

http://www.700r4.com/speedoCalc/speedocalc.shtml


i allready have a 17 tooth drive gear so i need to know which is the best driven gear fo my combo so if you've run this setup and your speedo was dead on please help me and tell me which driven gear i need.

1988-305-tbi

the car that i got my gears from was a 89 trans am and the gear combo was 17/45, i just want the most accurate set so when i'm driving 80 mph my speedo says 79 and 1/2 mph too 80 and 1/2 mph, and i'll be happy i'm only going to install the gears once, no trial and error my car is driven everyday and i dont have the time to play with it

xpndbl3

iTrader: (5)

neither combo will be 100% accurate which is what you're not following. the MOST accurate is an electronic speedo, which is calibrated by driving a known 1 mile distance. There will always be a variance at some speed. Tires also will balloon out a little at higher speeds, for what it's worth I understand what you're trying to do, but just because the calculator says it's close your results may vary just a bit. If the site shows 26" tire and 3.27 then go for it, factory speedos were off by a margin as well, so the factory gearing isn't 100% accurate all the time either.

84TranzAm

iTrader: (2)

What I get out of looking at the charts . They are giving you examples of different set ups. Like they said it depends on what rear was stock in your car to determine what the drive gear was put in your tranny. so if you have an original 18 spline drive gear you would use the 45 and vice versa if you had a 17 gear drive from the factory you would use 43 . They are giving you examples of different set ups ( it is up to you to determine what drive gear they put into it at the factory ) So you do not have to change the drive gear itself.

1988-305-tbi

the only reason i need to know is because i'm replacing the stock 2.73 peglegger with a 3.27 posi rear

i already have a 17 tooth drive in my trans, 2.73 stock speedo drive gear, so i'm going to leave it alone. the gear calculator i used sugested that i use a 17/43 combo for my setup, but the original speedo gears in the car that had a 3.27, 26" tires had a 17/45 combo from the factory, and the calculator said to run the 17/45 combo if i had a 3.42 rear, but that combo came stock on a car with 26" tires and a 3.27

so i could just use a 17/45 combo and it would be the same as the way the factory sent them out, but the gear calculator told me i should use a 17/43 combo, not the way the factory sent them out. i'm sure either combo would be close but i just want to know which combo would be the most accurate, the way the factory equipped them or the way the speedo gear calculator told me i should use

1988-305-tbi

how are the factory speedos off? say i'm actually traveling at 120 mph what would the speedo read, higher or lower than the actual speed? 115? 125?


i dont mind if the speedo is a mph or 2 of at 30mph i just want it to be real close at 80mph, freeway speeds

84TranzAm

iTrader: (2)

Also read this article on gears. https://www.thirdgen.org/gears
You will see that there is only a little difference in mph in different gear ratios. So yes I could see a factory tranny using different combos. I know today alot of dealers give you an option of using two size tires . The diamater of both them tires is slightly different. So what tire did they set the tranny up for originally. All speedos are off a bit. I asked them how much the different tires would knock the speedo off and they estiomated about 3 % . The car I am talking about is not a third gen or related LOL. How much they are off would be a guess. I know the police usually give a man a break of 5- 10 percent because of this too. That is what I heard anyway. . They will never be right on, usually the faster you go the farther they are off, es[pecially when you start wrapping the needle back around too maney times .

Orr89RocZ

iTrader: (20)

i ran a 39/15 combo. that way i didnt need to get a new housing for a larger tooth gear since i had a 17 tooth for the 2.77's. i think i would have needed 43 or 44...not sure. but the 39/15 was good. only like 2-3mph off (slow) at 95mph, track verified. i have 25.7 inch tires tho. 26 would be dead on.

still using those gears for my 3.42 gears. i think its around 4-5mph slow at 70...but thats fine for me. almost dead on with the taller mickey ET streets

1988-305-tbi

the car i got the 3.27 rear from was an 89 transam, with factory 245/50 r16, 25.7" and it used a 17/45 combo, and the car that the 3.27 is going into has 255/50 r16, 26.04" tire.


does anyone on here have a 3.27 with 25.7" tires or 26" tires? what speedo gears are you using?

Orr89RocZ

iTrader: (20)

do either one, 39/15 or 45/17. it will work fine.

45/17 = 2.64
39/15 = 2.60

so its about same ratio.