rear gears
Thread Starter
Racer
Joined: Dec 2008
Posts: 486
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From: Converse Texas
rear gears
I have a 99 frc that I have had for a few years now, and am wondering what rear gears I have... I think I read somewhere on the forum that all frcs came with 3.42s. Is this true???? How can I confirm what I have, since there is no visible driveshaft to count turns???
Advanced
Joined: Apr 2007
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From: SHREVEPORT LOUISIANA
rear gear
Thread Starter
Racer
Joined: Dec 2008
Posts: 486
Likes: 0
From: Converse Texas
Is it hard to see where it says 3.42 on the diff??? is it on the case, or on a tag on the case? I heard you can also drive the car in 4th gear at 60mph and what the tach reads is the diff ratio. anyone else heard this???? I havent tried as I never remember when Im in the car!
Safety Car
Joined: Oct 2007
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From: You know your drunk when you swerve to miss the tree then you realize its your air freshener! Covington Ga
Mines on a tag. Its not hard to see. There is a chart you can use and look at your speed VS rpm's. If no one has messed with the car you have 3.42's.
Team Owner
Joined: Apr 2001
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From: S.W. Ohio. . . . . . NRA Life Member
Team Owner
Joined: Jul 2006
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From: Kannapolis NC
Manual trans 4th gear at 75 mph, rpm's will be 3420. If not close, rear or tire size has been altered. Automatics in 3rd gear, at 75 mph will read 2730 rpm's or 3150 depending on rear ratio of 2:73 OR 3:15
Racer
Joined: Feb 2008
Posts: 457
Likes: 34
From: Hamilton Montana
Your car should have the 3.42s in it. No harm in checking though.
I found this handy graph that works pretty well.
The 4th gear at 75mph works too. (It's actually easier.) I tried both methods when I was trying to figure my gearing out. I bought the car used, and realized my C5 has a Z06 tranny and 3.90s in the rear-end! Crazy! The gearing does work really well though, probably one of the cheapest performance mods someone can do. I bet it's worth at least a half second in the quarter.
Fortunately for us, Chevy put the spedo sensor on the axle AFTER the rear-end gears. (Most other cars don't do this.) So you can change your rear-end gears all you want, and your spedometer will still be accurate.
Don't worry about your tire size. It wont affect the method of figuring rear-end gearing. For some reason, many people have a misconception about this. Unless your spedo has been calibrated for tires that are larger/smaller than stock, you can accurately determine your rear-end gears based on the spedo reading. YOUR SPEDO ACCURATELY READS AXLE SPEED REGARDLESS OF TIRE SIZE!
Let us know what you figure out.
I found this handy graph that works pretty well.
The 4th gear at 75mph works too. (It's actually easier.) I tried both methods when I was trying to figure my gearing out. I bought the car used, and realized my C5 has a Z06 tranny and 3.90s in the rear-end! Crazy! The gearing does work really well though, probably one of the cheapest performance mods someone can do. I bet it's worth at least a half second in the quarter.
Fortunately for us, Chevy put the spedo sensor on the axle AFTER the rear-end gears. (Most other cars don't do this.) So you can change your rear-end gears all you want, and your spedometer will still be accurate.
Don't worry about your tire size. It wont affect the method of figuring rear-end gearing. For some reason, many people have a misconception about this. Unless your spedo has been calibrated for tires that are larger/smaller than stock, you can accurately determine your rear-end gears based on the spedo reading. YOUR SPEDO ACCURATELY READS AXLE SPEED REGARDLESS OF TIRE SIZE!
Let us know what you figure out.
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Thread Starter
Racer
Joined: Dec 2008
Posts: 486
Likes: 0
From: Converse Texas
well, the story is: when I bought my car about 2 years ago, I read a thread here saying to drive 75 in 4th and the tach would read close to the gears in the car. I did this and determined I had a 3.42. About 4 months ago, I put in a ram twin, went through the trans with new synchros and a few upgrades, and was also gonna fix the leaky but my car had. The car also had some bearing noise in the rear, so I took the diff to a shop and had all of the bearings etc. replace, as you have to have a special gm tool to change the pinion bearing... anyhow, I was driving the other day and decided to do the 4th gear test again, but thought it was at 60 mph instead of 75!!! Needless to say, my tach was at 2700 rpm!!! I thought someone had pulled the ole switch a roo on me! Turns out, at 75 mph, the tach read around 3300, telling me all is well with my 3.42's!!
thanks for all of the info, I don't think I'll forget again!!
thanks for all of the info, I don't think I'll forget again!!
