choosing the right speedometer gear
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Car: 1988 IROC-Z camaro
Engine: 355 TPI
Transmission: tko 500
Axle/Gears: Dana 44 3.31 posi pbr brakes
choosing the right speedometer gear
Im going to start a new post on this instead of building off an older post of mine. My car started life having a 2.73 posi and now it has a 3.42 posi. My question is do we know what drive gear it has for the speedometer and if so is there a corresponding driven gear that will allow my speedometer to be accurate again or do i have to swap both the drive and driven gear to get my speedometer to read correctly?
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Car: 1988 IROC-Z camaro
Engine: 355 TPI
Transmission: tko 500
Axle/Gears: Dana 44 3.31 posi pbr brakes
Re: choosing the right speedometer gear
no one has an answer for this?
#3
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Car: 86 Trans Am, 92 Firebird
Engine: 408 sbc, 3.1L of raw power
Transmission: TKO600, T5
Axle/Gears: Moser 9", 3:70 trutac, 3:23 torsion
Re: choosing the right speedometer gear
17tooth drive gear
45 tooth driven gear
provided you have a 26" tire
you will have to change both
http://www.transmissioncenter.net/sp...n_______va.htm
45 tooth driven gear
provided you have a 26" tire
you will have to change both
http://www.transmissioncenter.net/sp...n_______va.htm
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Car: 1988 IROC-Z camaro
Engine: 355 TPI
Transmission: tko 500
Axle/Gears: Dana 44 3.31 posi pbr brakes
Re: choosing the right speedometer gear
Thanks. Thats what i thought i would have to do but i wasnt sure. Ok I'll probably just put that off 'till after winter. Sounds like a nice spring project.
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Car: 1988 IROC-Z camaro
Engine: 355 TPI
Transmission: tko 500
Axle/Gears: Dana 44 3.31 posi pbr brakes
Re: choosing the right speedometer gear
Well i have put this project off for far too long and now i intend on doing it. I have a few questions before i start though and order my parts. Does anyone know if i need a new Driven gear housing? From what i could tell on the website linked above it seems that the housing i have will be fine (used to have 2.73 gears). The second question is can i do all this fairly easily with the transmission in the car? Also, should i get anything else while im at it like the spring retainer clip and stuff that they show on this webesite?
#6
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Car: 1991 RS Vert
Engine: LO3, 305, TBI
Transmission: 700R4
Axle/Gears: 3.42
Re: choosing the right speedometer gear
I don't know what year GM changed, but my 91 has the electronic "Speedometer Drive Sensor". There is no speedometer cable, just a two-wire connector.
I spent a lot of time researching this issue both on this forum and around the net.
Everything I've seen indicates that the 2.73 to 3.42 swap requires a new driven gear (EDIT: red-stock, lt blue-new) and a new mechanical housing/electronic sensor (depending on year of transmission). The drive gear, if red, doesn't change.
I just upgraded to a 3.42 posi from a 2.73 open. I needed a new 45 tooth driven gear (EDIT: Lt Blue) and a new sensor. Note that the driven gear is a different style on the mechanical vs. electronic set up. The mechanical gear has a shaft integrated with the gear. The electronic version is just the gear and looks like a hat.
First, get under the car and find out if you have a mechanical or electronic speedo setup. You can visually check it easily. Then, remove the one bolt holding it in and pull it out (some oil will drain, but not much). Check the color of the drive and driven gears.
I'm guessing both will be red, but the driven gear might be blue since you have an IROC and it might have come with 245/50R16 tires.
Along with the link above, I found some good info here:
http://www.3rdgenformula.com/88/88speedometer_gears.htm
I spent a lot of time researching this issue both on this forum and around the net.
Everything I've seen indicates that the 2.73 to 3.42 swap requires a new driven gear (EDIT: red-stock, lt blue-new) and a new mechanical housing/electronic sensor (depending on year of transmission). The drive gear, if red, doesn't change.
I just upgraded to a 3.42 posi from a 2.73 open. I needed a new 45 tooth driven gear (EDIT: Lt Blue) and a new sensor. Note that the driven gear is a different style on the mechanical vs. electronic set up. The mechanical gear has a shaft integrated with the gear. The electronic version is just the gear and looks like a hat.
First, get under the car and find out if you have a mechanical or electronic speedo setup. You can visually check it easily. Then, remove the one bolt holding it in and pull it out (some oil will drain, but not much). Check the color of the drive and driven gears.
I'm guessing both will be red, but the driven gear might be blue since you have an IROC and it might have come with 245/50R16 tires.
Along with the link above, I found some good info here:
http://www.3rdgenformula.com/88/88speedometer_gears.htm
Last edited by Trick414; 07-20-2008 at 06:11 PM.
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Car: 89RS(other cars & pics in vBgarage)
Engine: LO3, 305 TBI Mildly Modified
Transmission: BakerBuilt 700R4 w/B&M Megashifter
Axle/Gears: 3.23 Auburn Pro Series LSD
Re: choosing the right speedometer gear
what about the ratio adapter, i figured this would be easier, even if its more expensive
i been told you can replace just the driven gear and get away with an accurate reading.....
im going 2.73 to 3.23 ....... what colors would i need, or what % ratio adapter .... i find the formulas to be confusing
i been told you can replace just the driven gear and get away with an accurate reading.....
im going 2.73 to 3.23 ....... what colors would i need, or what % ratio adapter .... i find the formulas to be confusing
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#8
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Car: 1988 IROC-Z camaro
Engine: 355 TPI
Transmission: tko 500
Axle/Gears: Dana 44 3.31 posi pbr brakes
Re: choosing the right speedometer gear
From the research i did here it seems that i would need to change out both.
http://www.transmissioncenter.net/sp...n_______va.htm I guess im just going to crawl under it and figure out what needs to be done.
http://www.transmissioncenter.net/sp...n_______va.htm I guess im just going to crawl under it and figure out what needs to be done.
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Car: 1991 RS Vert
Engine: LO3, 305, TBI
Transmission: 700R4
Axle/Gears: 3.42
Re: choosing the right speedometer gear
Yeah, get under there and figure out what you have and go from there. Speculation is tough.
I did the same thing until I crawled under it and found out what I actually have.
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Car: 1989 Iroc-Z Camaro
Engine: TBI,5.0
Transmission: Automatic 700R4
Axle/Gears: Eaton Posi,3.42,LPW Ultimate Cover
Re: choosing the right speedometer gear
This is a great thread. I am doing the same swap with practically the same car/setup. Any info you guys find out is greatly appreciated. Ill put in what ever I find out also.
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Car: 1988 IROC-Z camaro
Engine: 355 TPI
Transmission: tko 500
Axle/Gears: Dana 44 3.31 posi pbr brakes
Re: choosing the right speedometer gear
Im throwing a wrench into the mix for myself now. Im swapping out the 3.42s for a 3.27 9 bolt posi disk rear. The gearing is just too steep for the highways. Now i gotta get the correct gearing for that rear
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Car: 1986 Camaro Berlinetta
Engine: 4 bolt 355ci
Transmission: Borg Warner T-5
Axle/Gears: 3.73 Posi Disc Rear
Re: choosing the right speedometer gear
Here's where I"m at:
Trans came from a car with 3.23's. Never taken it apart.
My car has 3:73's with the correct driven gear, and read accurate +/- 5mph at all speeds up to 100mph.
I am swapping a 3.42 rear in. Will I need to change the driven gear/Drive gear in the trans?
Trans came from a car with 3.23's. Never taken it apart.
My car has 3:73's with the correct driven gear, and read accurate +/- 5mph at all speeds up to 100mph.
I am swapping a 3.42 rear in. Will I need to change the driven gear/Drive gear in the trans?
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