Gear Ratio dosent match up

[MudDog2007]

2010 Ram SLT 5.7 545RLE 33"

For the life of me I cant get any of the online calculators to work and come out with what Im seeing.

Next opportunity ill jack it up and do the count but in the mean time this is what im seeing.

Speed 65mph speedometer and GPS verified
Gear 4th calculations at 0.75
Tires 275/60/20 33"

Build Sheet claims 3,21 gear

Measured RPM at 65 MPH 2175

Go figure.

Anyone ? Anyone ? Ferris ?

 

[Ken226]

Using an online calculator and solving for engine RPM, using 3.21 rear end and .75 4th gear ratio, I get:



So, yea, somethings weird somewhere.

 

[20IndyRam]

2010 Ram SLT 5.7 545RLE 33"

For the life of me I cant get any of the online calculators to work and come out with what Im seeing.

Next opportunity ill jack it up and do the count but in the mean time this is what im seeing.

Speed 65mph speedometer and GPS verified
Gear 4th calculations at 0.75
Tires 275/60/20 33"

Build Sheet claims 3,21 gear

Measured RPM at 65 MPH 2175

Go figure.

Anyone ? Anyone ? Ferris ?

Is it possible that your torque converter isn't locking up?

 

[Ken226]

Are you using the manual selection to set 4th gear?

Because the 545rfe transmission has regular and prime gears, doesn't necessarily engage the one that you would think is selected. Isn't there like 2 3rd gears in those things? And 2 overdrives?

 

[MudDog2007]

yes on manual selection of 4th. I do a standing start in 1st then bump it up to 4th. Then get speed up to 65.

Everytime I do it , it comes out same 2170 rpm.

Running those online calcs I cant get a gear to come close unless i get into the 4.10+ range.

 

[caulk04]

I thought the 3.21 ratio didn't come about until the 8spd.

Does 3.55 fit better?

 

[GTyankee]

Dodge Ram 1500 Truck Rear Differential 9.25-Inch 2009-2010​

3.21 3.55 3.92

 

[RamInfo]

deleted due to miscalculation

 

[hunterdan]

yes on manual selection of 4th. I do a standing start in 1st then bump it up to 4th. Then get speed up to 65.

Everytime I do it , it comes out same 2170 rpm.

Running those online calcs I cant get a gear to come close unless i get into the 4.10+ range.

Jack up one side of the rear axle, put truck in neutral (make sure it can't roll away) and mark the pinion with tape or marker and mark a spot on the tire. Count the number of driveshaft rotations for 1 rotation of the tire. You'll need to multiply that number by 2 to get the actual ratio. So, if the drive shaft rotates 1.5-1.6 turns, multiply that by 2 and it'll be roughly 3.21. If the pinion spins almost 2 times, that's 3.92.
For this to work, the opposite tire has to remain stationary.

 

[62Blazer]

Are you sure the transmission isn't running in the 1.0:1 gear? Think this is normally considered 3rd gear. Only reason I ask is that if you run the calcs that would put you right at that RPM. Just seems to make the most sense of what might be going on.
If you turn off the manual gear select how many times can you feel the trans upshift?
Even with a 3.92 gear it would only be running around 1,762 RPM @ 65 mph when in 0.75:1 trans gear. You would have to be down in the 4.30 axle gear ranges to get in the 2,100+ RPM range.

 

[Dean2]

You aren't in 4th gear. Selecting 4th manually just sets the upper limit. Pull it down to third and I bet your rpm stays the same. If they increase you don't have a 321 rear or you have non standard transmission ratios.

 

[MudDog2007]

A 2nd point for comparison. Standing start, bump to 3rd and set speed to 50. Rpm is 2200.

Getting ready to put the truck up and spin the wheel. We shall see.

 

[Wild one]

2010 Ram SLT 5.7 545RLE 33"

For the life of me I cant get any of the online calculators to work and come out with what Im seeing.

Next opportunity ill jack it up and do the count but in the mean time this is what im seeing.

Speed 65mph speedometer and GPS verified
Gear 4th calculations at 0.75
Tires 275/60/20 33"

Build Sheet claims 3,21 gear

Measured RPM at 65 MPH 2175

Go figure.

Anyone ? Anyone ? Ferris ?

You're calculating things wrong,if i remember right i think 4th gear is 1:1,not 0.75.

 

[Dean2]

You're calculating things wrong,if i remember right i think 4th gear is 1:1,not 0.75.

Well that would definitely explain what he is seeing.

Just hit google. You win the cupie doll for today buddy.

 

[MudDog2007]

3 other sources say this ,

"

• To be clear, the following are the 545RFE gear ratios: First gear – 3.00:1 Second gear – 1.67:1 Second gear (Prime) – 1.50:1 Third gear – 1.00:1 Fourth gear – 0.75:1 Fifth gear – 0.67:1 Reverse – 3.00:1"

Today, put truck up on lift . blocked one wheel from turning. Marked the driveshaft.
I got 1.75 rotations for 1 full turn of the wheel, which looks to work out to be 3.55.

So either the transmission is in 3rd gear as was said earlier or ......

Ive tried every combination to figure out how Im getting 2200 rpm at 50.

 

[GTyankee]

MudDog2007

If no one has changed differential Ratios
Just enter your VIN in this form

FCA RAM

fcagroup.my.site.com

 

[Wild one]

3 other sources say this ,

"

• To be clear, the following are the 545RFE gear ratios: First gear – 3.00:1 Second gear – 1.67:1 Second gear (Prime) – 1.50:1 Third gear – 1.00:1 Fourth gear – 0.75:1 Fifth gear – 0.67:1 Reverse – 3.00:1"

Today, put truck up on lift . blocked one wheel from turning. Marked the driveshaft.
I got 1.75 rotations for 1 full turn of the wheel, which looks to work out to be 3.55.

So either the transmission is in 3rd gear as was said earlier or ......

Ive tried every combination to figure out how Im getting 2200 rpm at 50.

If you punch in 3.21 and 1.00,it comes out to what you're seeing

Spicer Transmission Ratio RPM Calculator

Use the Spicer Transmission Ratio RPM Calculator to determine your engine’s RPM based on the transmission gear ratio, tire height, MPH, and ring and pinion gear ratio.

spicerparts.com

 

[MudDog2007]

MudDog2007

If no one has changed differential Ratios
Just enter your VIN in this form

FCA RAM

fcagroup.my.site.com

I have truck on my lift. Visual inspection of the differential does not reveal any changes, all appears as would be if it were factory.
I DL the build sheet and it claims 3.21.

My VIN 1D7RB1GT9AS112041

This stuff is driving me nutz LOL

Just did another 50 mph test. Flat straight. Starting in 5th and tapping down. Cruise on.

5th and definitely in lockup 1450

4th 1800

3rd 2600 this one really surprises me. it matches up with 2nd prime

repeated test 3 times . same results.

Next.

 

[MudDog2007]

If you punch in 3.21 and 1.00,it comes out to what you're seeing

Spicer Transmission Ratio RPM Calculator

Use the Spicer Transmission Ratio RPM Calculator to determine your engine’s RPM based on the transmission gear ratio, tire height, MPH, and ring and pinion gear ratio.

spicerparts.com

no it dosent. tries 4 different calcs.

 

[Wild one]

no it dosent. tries 4 different calcs.

If i punch in 2175 rpm / 3.21 gear ratio / 1.00 transmission ratio and 33" tires i get just over 66 mph,not sure what numbers you're punching in but that's pretty well identical to your first posts numbers.If you factor in tire wear and say your tires are down to 32.6" it comes out at just over 65 mph for 2175 rpm.
You might want to revisit the numbers you're punching into the calculator,as you must be doing something wrong.
It's pretty obvious you have 3.21's,especially if you factor in your build sheet,which you have said your truck is equipped with.