3.55's instead of 4.10's

[apextrans]

A while back I got t-boned & only found out recently how extensive the damage really was. Turns out my rear is bent & in the process of hunting down a Housing or a complete rear, I discovered the truck has 3.55's in it. I was told it had 4.10's althought never verified it. I figured the the Fire dept. would have specd 4.10's to pull the extra weight the truck carried.

This thing is turning 3000 rpm @ 75 MPH going thru a C-6 w/ a BW1356 t-case turning 285/75/16's. I didn't think that sounded right so I checked the front axle tag which shows a gear ratio of 3.54.

If anyone with either ratio could let me know what they're turning in the RPM range, it would be much appreciated.

Scott

 

[soulpatchfr]

3.55s here. axel code 39 on the doortag.
i run about 2050rpm at 70mph & 2400 @ 80... that's with a ZF5, though. oh yeah, and 33" meat.
avg. 18mpg - 80 - 90% hwy miles.

hope you get her straight.

 

[Agnem]

Scott, that sounds a lot like 4.10's to me. I used to turn around 2500 with a T-19 at 75 mph, and 33" tires through 3.54's.

 

[apextrans]

I thought the same thing Mel. That's wwhy I checked the front tag. I was thinking "they BOTH can't have the wrong tag" but sure enough, they matched.

How would I be able to tell whats in there if I pull the diff cover? Count teeth on the ring gear? Is that possible?

The tag didn't have a 39 code in it that I recall. It started with 355L..... which the boneyard told me means 3.55 locker. Any thoughts?

Scott

 

[HammerDown]

373's ...33" sneaks ...2600 @ 65 mph. (no overdrive)
Don't know if 355's would lower my rpm much.

 

[Gildo]

Divide the number of teeth on the ring gear by the number of teeth on the pinion if you remove the cover.

Or you might try jacking up the truck, and of course placing it on jackstands, then using a piece of chalk to mark the tire at a specific location and also mark the pinion's yoke and the housing creating two lines for reference. With the truck in neutral roll one complete revolution the tire that you marked at the same time counting the number of revolutions that the driveshaft turns. If it turns just over 4 revolutions it's a 4.10, if it turn about 3 and a half turns it's a 3.55, and so on.

Good luck,
Gil

 

[Mike]

If the rear end is original equipment then take a look at the door tag.

THEN CHECK THIS WEBSITE FOR CROSS REFERENCE

 

[apextrans]

The original door & door tag are long gone. I only have the axle tags to figure it out. I'm thinking counting teeth may be my best bet. Although, Hammerdown seems to be real close to what I'm turning at 65MPH. I'm about 2400RPM with the 285's which are close to 33's & no OD. They could be 3.55's

Thanks for all the input fellas

Scott

 

[Agnem]

I wouldn't pull the cover unless your wanting to change the oil anyway. Counting drive shaft revolutions is far easier. You could do it yourself by taping a lenght of rope to the drive shaft, and then rolling the vehicle forward one wheel revolution. Be carefull not to run over the rope! Count the loops of rope on the driveshaft to arrive at your ratio. If you can have a helper pay out the rope it will be easier.

 

[Dave Sponaugle]

285/75-16 tires with a 3.55 and direct drive = 2800 RPM
285/75-16 tires with a 4.10 and direct drive = 3220 RPM

Have you recalibrated the speedometer with the larger tires?

With 235/85-16 tires that were stock and 3.55's in direct drive 2900 RPM would be 75 MPH

 

[Pacific]

Hey Dave you moved over to here from FTE I rarely visit that site when I found this place aka TDS Refugee camp .

One thing about pulling the cover atleast you get to inspect the gears and see how much metal chunks are in the oil.

 

[jdkline]

I think you must have 4.10s to be doing 3000 Rs at 65. I have 265/75/R16 and C6 no/OD and hit 3000 at 65-68mph. I wish I did have 3.55s since I do mostly light towing and my truck is a daily driver. I'd expect to have 2500 RPMs at the same speeds, that I would be happier with.
J.D.

 

[apextrans]

Well, now I'm not sure what it's actually doing in the MPH dept. Never thought about the speedo recalibration. May be a little off.
Have to check the revolutions. Thanks for all the input.

 

[Dave Sponaugle]

Pacific, I just stopped in to see what it looked like. Rancherman84 posted a link and said he liked it, so I had to see.