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RPM difference change upon torque converter lock out
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Pappy
Mall Queen
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Joined: Jan 03, 2017
Posts: 5

PostPosted: Sun Oct 25, 2020 12:48 pm    Post subject: RPM difference change upon torque converter lock out Reply with quote

My 2011 has the typical A750F A/T transmission for 4x4.
Marketing materials refer to it as a 5sp w/OD. Techs call it as a 5sp w/ LO TC.
I'm pretty sure the rear end is 3.73. Currently running 295/70/17s.

I'm trying to ascertain the specific gear ratios in the A750F to use in online calculators to find the RPM differentials if I converted the diffs to 4.56s and stay with 275/70/17 KO2s at 32"

#1: Please clarify:
Isn't 'overdrive' just another term for the 'Lock Out'? I note all 5 shifts and then there's another drop at LO of roughly 200 RPMS at around 50mph, with a LO cruise speed of 60 mph holding about 1750RPMs.
I get a similar drop of about 250 RPMs when running my street 265/70/17s.

- A750F gear ratios are - .72 in 5th, 1.0 in 4th and 1.4 in 3rd
Q1: Does anyone know what the effective gear ratio is dropping from .72/5th to LO?
Q2: Once I drop from 3.73 to 4.56, should the 5th>LO RPM drop be roughly the similar 200-300 rpm?

My 'issue' here is that online converters don't account for LO, and a shop is warning me that after the gear swap, my 5th gear will be over 3K and the LO drop will go to 2300. That's not what my experience or research shows.

I appreciate any feedback before I commit $4k.

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Last edited by Pappy on Sun Oct 25, 2020 7:24 pm; edited 1 time in total
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Jimbolio
Master Wheeler
Master Wheeler


Joined: Oct 19, 2008
Posts: 12479
Location: Tucson

PostPosted: Sun Oct 25, 2020 4:48 pm    Post subject: Re: RPM difference change upon torque converter lock out Reply with quote

If it were me, (and it was me) I would call East Coast Gear Supply and ask them. They seem to be pretty sharp.

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