[decipha]

i know that shifting from o/d - 2nd is a no-no, i also know that shifting from 2nd - o/d is a no-no

yet i don't know why?


anyone care to school me? just how damaging is this? if its done very rarely, what are the chances of trans damage, and most importantly... why?

[Cougar281]

I think this is mainly an issue with the older transmissions with the weak roller clutch. I don't think it's as big an issue (if an issue at all) in the newer transmissions with the Mechanical Diode clutch taht replaced the roller clutch.

[dualdj1]

could it have something to do with the lockup torque converter? I'm sure it's not active in 2nd, but not sure on 3rd in O/D trans. It has to be activated in O/D.

[decipha]

good to know cougar

du.. the converter doesn't have to be locked in 4th, does it? i've left 4th unlocked before at low speeds in quite a few vehicles

also, why do people say the converter has to be unlocked during a shift? someone please enlighten me as i've left the converter locked on shifts many times, i also don't see how it could possibly make any difference if the converter is over its lockup rpm anyway as it would be locked anywho, now downshifting with a locked converter is 'fun' tis' i typically do not do

[Cougar281]

Actually, I did some more reading, and I found that supposedly the fluid exhaust from the direct clutch is too slow. '99 & newer valve bodies allow manual 4-2 downshifts because they have better fluid exhaust ports.

Personally, becasue of the improvements, I wouldn't use any 4R70W older than 1999. Generally, you want one out of a newer (03ish) vehicle that had a 5.4L for the stronger sun shell, and all 98+ models had the Mechanical diode 1 way intermediate clutch.

I believe the AOD's and AODE's can be retrofitted with the improved 4R70W's guts.

[dualdj1]

Honestly I don't know if it has to be locked at low speed, especially on newer trans. My bro converted his 88 Iroc to a carb and got rid of the computer, and had to put a manual lock switch on his trans for O/D, if you didn't turn it on it'd slip. But O/D was rarely (if ever) used at low speed, almost always highway speed.

[p4ndiamond]

old post but yeah you will destroy the stubshaft eventually. not to mention that O/D hates WOT shifts and will eventually die .