Transmission overdrive

[GD]

I have a 92 4x4 with an automatic transmission. I am curious to know if the overdrive can be switched in, by bypassing the PCM, when the transmission is in 1st or 2nd gear or is there something mechanical in the transmission that won't let that happen until it gets to third gear. Don't know if there is any benifit for doing this but I was just wondering if it could be done.



GD

 

[dpuckett]

Do a search; lot of stuff on this very topic, from potentiometer installs, to just going to a switch. I think there are cases where it will go from 2nd to OD.



Daniel

 

[tugboatphil]

Since I've never minded appearing stupid... . why would you want to go from 2 to OD? Just askin.

 

[dpuckett]

I dont think it was intentional. The gears are spaced far enough apart as it is, that's for sure.



DP

 

[GD]

I don't know if there is a reason to intentionaly put it in overdrive while I am in second gear but I wonder if there would be a situation where the engine would rev too hi in second gear but would lug in third. I haven't looked at the gear ratios but maybe second gear and overdrive would keep the engine at a good rpm.



A few weeks ago my PCM went out and the PCM is needed for the overdrive to work. I could see where I might use a switch to bypass the PCM to turn on the overdrive solinoid while I am on the freeway and forget to turn it off when I got off the freeway. Would the overdrive unit stay in overdrive or is there some mechanical speed sensor in the trasmission that would disengage the overdrive unit?



GD

 

[PToombs]

I see where you are going. 6 speed! 1st low and OD, 2nd low and OD, etc! :-laf

 

[KOG]

OD an be engaged only in third gear with this transmission. You can override the PCM with a manual switch which can make it shift from 2 to 4 (actually a 2-3 followed immediately by a 3-4 shift)

 

[cerberusiam]

Would the overdrive unit stay in overdrive or is there some mechanical speed sensor in the trasmission that would disengage the overdrive unit?



GD

With a mystery switch, it will stay in OD. Things don't move to well when you try to leave a stop light in OD. :-laf





If one is creative with an electronic switch it is possible to wire it to the brake switch to drop it out of OD when ever the brakes are used.