Do I have 4.10's already?

[FormulaMarauder]

Putzing along the highway at 80mph, I notice that my RPM's are up around 2,300 or so. Normal? Seems like it wants to jump into the next gear. Yes the O/D is on. I just got the car and it has some mods (tune, Kooks full exhaust) It seems quicker out of the hole than some other MMs I have driven (they were stock, though) but I have to wonder if it had the 4.10's put in it or not. Im the third owner and the fellow I bought it from seems to think its stock. So is this the right RPM range for that speed? Tires are stock BTW. Thanks in advance guys.......:beer:

[magindat]

A picture is worth 1000 words....

http://www.magindat.net/ssm/info/4r70wratios.xls

[magindat]

3.55's are in there.

[FormulaMarauder]

A big thanks sir. Looks like im balls accurate in regards to my question. 80mph, 2,300 rpm. How much higher will it go to with 4.10's?

[magindat]

A big thanks sir. Looks like im balls accurate in regards to my question. 80mph, 2,300 rpm. How much higher will it go to with 4.10's?

Look at my first reply. Or follow the link I gave you and play with it yourself.

[MM_BKK]

If the previous owner had changed the gears to 4.10 and never got a tune to correct the speedometer reading, you will think that you're doing 80 according to the speedo, infact you're not. (Your actual speed will be slower)

Two ways to confirm 3.55 or 4.10 ratio:

1) Jack up both rear tires and take shifter out of park. Mark position of a rear tire and driveshaft. Spin a rear tire (other tire should be spining with you in the same direction) ONE revolution and observe how many revolution the driveshaft turned. If it's about 3 and half turns, but not more than 3 and 3/4, you have 3:55 gears. If it just a little over 4 turns, but not more than 4 and 1/4, you have 4.10 gears.

2) Get a GPS device that will tell you speed. Drive your car on a safe road and reach 65 MPH as indicated on your GPS. (Note: If your speedometer matches the speed on your GPS spot on, then your speedo have been corrected) If your tach indicates about 1900 RPM, you have 3.55. If it indicates about 2300, you have 4.10 gears.

Have fun.

[fastblackmerc]

A big thanks sir. Looks like im balls accurate in regards to my question. 80mph, 2,300 rpm. How much higher will it go to with 4.10's?

You'll be turning about 200RPMs more and will get about 1MPG less with 4.10's.

[Marauderman]

If the previous owner had changed the gears to 4.10 and never got a tune to correct the speedometer reading, you will think that you're doing 80 according to the speedo, infact you're not. (Your actual speed will be slower)

Two ways to confirm 3.55 or 4.10 ratio:

1) Jack up both rear tires and take shifter out of park. Mark position of a rear tire and driveshaft. Spin a rear tire (other tire should be spining with you in the same direction) ONE revolution and observe how many revolution the driveshaft turned. If it's about 3 and half turns, but not more than 3 and 3/4, you have 3:55 gears. If it just a little over 4 turns, but not more than 4 and 1/4, you have 4.10 gears.

2) Get a GPS device that will tell you speed. Drive your car on a safe road and reach 65 MPH as indicated on your GPS. (Note: If your speedometer matches the speed on your GPS spot on, then your speedo have been corrected) If your tach indicates about 1900 RPM, you have 3.55. If it indicates about 2300, you have 4.10 gears.

Have fun.


Just want to say I like your explaination--never had to try it--but for those who are just starting out--it can be fun to try---to find out--

[Pat]

Good Post MM_BKK

Going into the reference book.........got it.

[ImpalaSlayer]

i trired it today at 85 im turning about 2300. i dont understand the charts

[crouse]

I changed the Excel sheet. Where you see the yellow boxes, go ahead and change those values. For example, if you change the speed from 60 to 70, you'll see the 4th gear number change from 2046 RPM to 2387 RPM. Or change the ratio from 4.10 to 3.55 to see how the RPM changes.

[Dragcity]

Marking drive shaft and tire is the easiest way. It's truely mechanical....

have used that method on countless occasions, without fail. It doesn't matter what electronic or transmission changes were made, the driveshaft, tire ratio is the final and deciding link. Use that, and you can't miss.

[SamF]

Marking drive shaft and tire is the easiest way. It's truely mechanical....

have used that method on countless occasions, without fail. It doesn't matter what electronic or transmission changes were made, the driveshaft, tire ratio is the final and deciding link. Use that, and you can't miss.

+2 This is a pretty fool proof method.