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I have changed my rear end and now my speedo is off, it completely makes sense as to why, but does anyone know what part number can be used to resolve this? I'm running a 383 engine with a 700R4 and 4.56 rear end with 265/65R15 tires. I'm sure I need to change the drive and/or driven gear for the speedometer, but I can't seem to find any shops who know how to complete this calculation and suggest a part number. I can understand if I'm out a bit since this isn't a stock setup however the car has 45xxx kilometers on it and right now the car is showing me the incorrect speed by almost double. Does anyone know where to start? I have read a lot on this forum as well as other spots however it's only managed to get me to understand the high level theory of what I'm looking for. Any help would be really appreciated.
Try Speedometer Worlds web site. You will need tire dia, axle ratio, final drive ratio. Minor changes in axle ratio may only require a driven gear change. More aggressive ratios will need a new speedo drive gear.
Withouth taking the transmission apart haha, is there any way of know which drive ratio I have? I'm also guessing there is multiple gearing for the 700r4 but it was installed prior to me, I'm not sure how to find out what gearing that has, or maybe it doesn't matter since the drive gear would determine this?
Gearing on 700r
3.06
1.63
1:1
0.7 OD
Reverse is 2.9.
is this a vette that is one huge tire!
mark your driveshaft and axle in 1/4s give the axle 1 full turn, count how many times the driveshaft goes around/where it ends up math is simple.
So if your driveshaft makes a true 4.5 revolutions for 1 full axle turn you indeed have 4.56
If its 3 and a 1/3 could be 3.33...etc.
If i click my heels and turn around 3x my woman is still unhappy. Gears are stripped
I agree, I went back to confirm the tire size so many times because I thought I must be crazy and read it wrong as compared to what I found for stock tire sizes... It does not look like anything was changed from stock but those were what came with the car. The tires do not have DOT numbers on them which makes me think they're 20 years old at least (car was stored indoors with no sun exposure which is why the previous owner of 13 years felt they were in great shape - they still look brand new IMO)
Sounds good, I should be able to complete that this coming weekend and I'll keep everyone posted. The tires don't even show signs of cracking, the rubber feels soft to the touch still, i'll post some pics so everyone can get an idea
Withouth taking the transmission apart haha, is there any way of know which drive ratio I have? I'm also guessing there is multiple gearing for the 700r4 but it was installed prior to me, I'm not sure how to find out what gearing that has, or maybe it doesn't matter since the drive gear would determine this?
Actually, as I recall both the Drive Gear & the Driven Gears are color coded. When the speedometer cable and housing are removed, you will be able to see inside the trans and get the color of the Drive Gear. So now you are back to checking that web site for color codes / number of teeth.
Incorrect Speedometer
