Differential Swap 3.08 to 2.73

[Ant929]

So I have a M1165A1 with a 3.08 Diff. When I was buying it I thought I was going to be able to drive over 55 mph but I was wrong. Does anyone know if it would be possible to buy 2 sets of ring and pinions and have them installed? I think that would get me to 70 MPH. the truck is not going to carry armor anymore.

 

[NDT]

Is your 4L80E going into 4th gear?

 

[Ant929]

Is your 4L80E going into 4th gear?

It is going into 4th gear. At 55 mph it is turning 3000 rpm’s.

 

[NDT]

It is going into 4th gear. At 55 mph it is turning 3000 rpm’s.

I don’t think you are correct. Those numbers reflect a Turbohydramatic 400 non overdrive transmission.

 

[gringeltaube]

I don’t think you are correct. Those numbers reflect a Turbohydramatic 400 non overdrive transmission.

 

[Ant929]

So I guess all M1165A1 don’t come with 4L80e

here is a picture of the Tran.

 

[NDT]

So I guess all M1165A1 don’t come with 4L80e

here is a picture of the Tran.

Please, do a little research, 24208421 is a 4L80E.

 

[Ant929]

So why would it be only going 55mph turning 3000 rpm’s. My guess was the 3.08 differential?

 

[NDT]

Go drive it. Verify it is shifting 1-2, 2-3, 3-4. If it’s not you are in limp mode which explains the 3000 rpm @55. Limp mode is second gear only. Limp mode happens when the transmission has issues.

 

[Ant929]

It’s definitely shifting 1-2,2-3,3-4. What type of RPM should it be at with a 4.08 differential and 4l80e?

 

[NDT]

It’s definitely shifting 1-2,2-3,3-4. What type of RPM should it be at with a 4.08 differential and 4l80e?

Member "ACTION" reports: I get 2000 rpm @ 50 mph, 2700 rpm @ 70 mph with 6.5 TD, 4l80e, 3.08 diffs, and 37” tires

 

[Ant929]

Something is definitely not right with this transmission then. 4th gear is 3000 rpm at 55.

 

[NDT]

Are there transmission shops on Jupiter? Never been there.

 

[Ant929]

i will look for one. Is their a way to test if the torque converter is locking up?

 

[gringeltaube]

i will look for one.

... One where, on Jupiter?


Seriously, please add your state in your profile/location. It's a rule!

 

[Ant929]

Sorry about that, yes, Jupiter Florida. I just added it.

 

[NDT]

i will look for one. Is their a way to test if the torque converter is locking up?

I will attach the diagnostic manual later or you can search for it, it’s uploaded here.

 

[NDT]

here you go

 

[Ant929]

Thank you sir.