1988-305-tbi

so i picked up a 9 bolt rear out of an 89 trans am the engine vin number is 8, so its a 5.7, i checked the infon on the car and it came with either a 2.77, or a 3.27, i didnt feel like counting the teeth so i just spun the drive shaft yoke until the rotors turned exactly 1 time and it took 3 1/4 revolutions, so i would assume that its a 3.27,


anyhow enough background info...... so i took the speedo gears also, i was going to put them in, but the transam that i took the rear out of has a electric driven speedo and my car is cable driven, so the driven gear wont work, but anyhow the teeth counts are 17/45 which should be the correct combo for a 3.42 on either setups?


so my question is, is the teeth count the same on cable/ electric driven speedos i know the driven gear is a different style, but 17/45 is the same on cable and electric driven speedo isn't it, 3.42?

i need a 17/43 combo for my cable driven setup, is the electric equvilent to 17/43 17/45? or did the tranny just have the wrong speedo gears in it? for 3.42

sofakingdom

iTrader: (1)

Those numbers sound about right.

17/45 vs 17/43 is a small difference in the reading; about 5%. I.e., it will be 3 mph off at 60, 5 mph off at 100, 1½ mph off at 30, etc.

The ratio of the speedo gears would be the same for either a cable or a VSS.

The 2 cars may have had 2 different size tires when new.

Gears aren't very expensive, or very hard to change. Best thign to do would probably be to buy one ecah of 43, 44, & 45; put the 44 in; and check it against a marked length of miles on the freeway. The odometer is a far easier way to check the gears than the speedo.

1988-305-tbi

thanks for the reply.... i know which gears i need... 17/43 with 26" tires i checked it here this calculator helped me out plus i'm gonna buy the gear i need it like 8 bucks. i also typed in the ratio " 3.42 with 26" tires and it told me the 17/45 combo.... the one i pulled off of the trans witht the 3.27 rear end, factory, and still equipped theese would be the correct gears if the car had 24.8" tires and a 3.27 rear, but i thought that the 89 transam's had 245/50r16 tires 25.7" so if the car came eqipped with 225/50/r16 tires, and the 3.27 rear the speedo gears would be right



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

Pat Hall

iTrader: (31)

Just thought I'd point this out. The 3.42 ratio uses a 15 tooth drive gear instead of the 17 tooth. 3.27 and lower=17 tooth, 3.42 and higher=15 tooth. I went from 2.73 to 3.42 and had to change the drive gear to 15 tooth. Then I took the 3.42 rear out to put in a 3.23 rear, and had to switch back to the 17 tooth drive gear. The 3.42 combo I used was 15/42. This is the gears the dealership sold me after looking at their chart on the computer there, and it was accurate enough. My 3.23 combo is 17/44 IIRC. One last tip. The 44 tooth gear I used was on an electric sender unit originally, and I was able to swap it right on to the shaft of my cable driven unit.

87zjeff

iTrader: (4)

my previous iroc came factory with a 3.27 rear and 245/50r16 tires. my drive/driven gears were 17/45 from the factory.


Pat, that driven gear you refer to had to have been on a housing that was both cable and electric. police models i think used these. the typical electric driven gear will not fit the cable ddriven application.

Pat Hall

iTrader: (31)

Actually, it came from a 700r4 out of a 91 GTA. My cable driven sender has a metal shaft with a d-shaped end where the gear goes on it. The electric sender also had a metal shaft with a d-shaped end, so both gears had a d-shaped hole in the center of them, making it a direct swap. Just pluck it off one shaft and push it on the other one and install. The GTA 700r4 came out of the same car that I got my 3.23 disc rearend from, so I knew it'd be the correct driven gear for my speedo to read correctly. The guy that was parting it out asked me if I wanted the trans a couple of months after I bought the rearend, so I picked it up as a spare trans for my car. The only thing that was unfortunate is that I had to remove the tailshaft housing on my trans to change the drive gear again since I was running 3.42's before, which used the 15 tooth drive gear.

87zjeff

iTrader: (4)

cool, most of the cable types have a plastic shaft preventing them from being interchangable the metal shaft ones aren't real common among 700's.

Pat Hall

iTrader: (31)

I guess they must've gone to the metal shaft ones not long before switching to the electric units apparently. The metal shaft cable one I have came stock in my 89 RS's 700r4. Of course the Camaros switched to electric the following year.