Last Sunday my wife and I took the Dart GTS about 30 miles to a local car show. I thought it was supposed to have 3:23 gears in the 8.75 but at just over 50 mph my tach is turning 2500 rpms...The car has 215-70-R14 tires on it. It has a 727 transmission. What does it have for rear gears? Thanks! Ted

3.73 gears by my math

Tachometers are not always correct.

Speedometers are also not always correct, but if you have a GPS like a Garmin you can double check it.

What is the speedometer gear count?

What is the tire diameter?

Those would help.

Or you can jack it up & spin a rear wheel while counting driveshaft revolutions.

Thanks guys! Barry...I do not know any of the answers for you. I have things written down somewhere and it's quite possible to be a 3.73 gear in the GTS 340. I will look at my tag later.

3.73 was not available, has the car been modified?

What year is the car? Here is a link for 1969 Dart ratios as one possible example;

www.hamtramck-historical.com/images/dealerships/DealershipDataBook/1969/69_Dart0028.jpg

You are correct Barry! I think it has been modified.

IDK but with those size wheels/tires and a three speed non lockup that seems like a 3.23 to me.

Here is the info I found for that size of tire for reference.

215/70R14 tires have a diameter of 25.9", a section width of 8.5", and a wheel diameter of 14". The circumference is 81.2" and they have 781 revolutions per mile.

Thanks Larry and Dr.Neil!

By those numbers 3:23 sounds about right at 2,500. 3:91 would be about 3,050 and 3:55 would be 2,775.

doing the math, a 215/70R14 would have 780 revolutions per mile. (rev/mi)..50 MPH is .833 miles/min. so the tire is rotating 650 rev/min. 2500 RPM for the engine / 650 RPM for the tire works out to 3.84:1. depending on converter slip (usually 3-5%) that looks like a 3.73... depends on how "about 2500 RPM you are. ~2400, it's probably a 3.55 assuming 4% converter slip....

Just because speedometer says 50, doesn't mean that is the speed, if the gear in the transmission is not correct. Normally you know tire size and gear ratio. You use the SVM chart and make sure your speedometer gear is the size the chart says. Then your speedometer would be accurate.

You are working backwards and may have 2 different variables. Gear ratio and trans speedo gear. So go drive by a speed sensor set up around a school or road in your area. If the speedometer reads accurate then you can calculate the gear ratio.

Thanks guys...I think I have another issue with the kickdown linkage. The guy that replaced the carb didn't set it...Any pics as to what it should look like?

Just to make sure we're not going down a rabbit hole, this is a 340?

Yes. 340 auto on the floor.

1969 Dart Service Manual

Page 21-52.

Ted the axle ratio was never called out on the fendertag of that year/ plant build Dart , the only way you are going to find it is if you have the broadcast sheet. You are going to have to get dirty to figure out what the car has, and which part is incorrect .

If it's an aftermarket carb, be sure you have the correct Mopar throttle lever extension.

Two other ways to know:
1. If the rear axle's never been fooled with, there may be a tag on it with the gear ratio called out; also might be a Sure Grip tag.
2. No matter what, counting how many revolutions of the driveshaft vs a rear tire will give you the ratio.
2500 @ approx 50 could well be 3.23s, but my current comparison is a 4-speed car with a 28-ish-inch tire (275/60R15); that's about 55 in my car.
I can't say that my speedo is dead accurate, not any of them for that matter.

My setup w/a 26.5" tall(255/60-15) and 3:73/4spd is 2800ish at 60 mph.