Auto transmission issue (1 Viewer)

[100seriesjunky]

Not being too technically minded will try to put this issue as clear as I can. Had some conversions done, none that should interfere with the transmission. However I now have a problem with the 5 speed auto not behaving.
What I call over drive (torque converter ) works from what I understand in 3rd when put in 3rd, 4th when put in 4th and 5th when put in 5th. My transmission has now decided it won't engage the overdrive in 4th gear when set in 4th. Works in 3rd and 5th. To be honest I have no clue why and would be open to any suggestions as to how this could happen. Maybe someone has had the same experience.
Mods are
Unichip
Snorkel
Hd trans cooler
Hd intercooler
200 series air box
G300 turbo by GTurbo
Issue started after the last four mods were fitted

Any help would be apreciated thankyou

 

[MongooseGA]

Try this:

5-speed A750 trans won't shift in to 5th gear.

Looking to see if anyone else has experienced this, as I couldn't find much for what's going on. 2005 LX470, 345-350k miles. Trans has been perfect as long as I've owned the truck, nary a hiccup ever. I last drove the truck on Saturday this past weekend, all is great. Today, the ABS/VSC/TRAC...

forum.ih8mud.com

 

[100seriesjunky]

After a long read finally got the the result the ECM. Should have just gone to the end but you know the saying, its about the journey, not always the destination.

Not sure this is my problem as a lot of what was said was about the gear selection where this is going into gear but the torque converter is not activating on 4. But will float the idea for sure with the mechanic
. Thank you.

 

[MongooseGA]

It's not so much the solution in that thread, but the diagnosing it took to get there. Your problem may be something different than mine was, but I went over a lot of the diagnostics you'll also likely need to do. Based on your description, I wonder if your truck is holding a 'secret' P0771 code like mine was. Since your trans isn't going in to 5th, it is very possibly the solenoid inside, or something else related to it. Hooking up TechStream should be step 1.

 

[2001LC]

I'm not sure what make model, you have. But the USA 100 series w/5sp (03-07 w/750 AT). OD is 5th gear, and only when shifter is in D position, which does not engine braking. Move shift to 4th gear or lower, is OD Off. Engine braking, engages in 4th, 3rd, 2nd & 1st shifter position!

The 98-02 has a button on shifter for OD ON/OFF.

When we takeover auto shifting, dropping shifter to lower gears. We do not shift high than that gear allows (see OM). This result in RPM going higher, than would for speed.

Anyway, for most any AT shifting issue. I recommend a fully 12 qt flush, as a first step to see if correct issues. I use either Toyota WS or Mobil MV FS ATF 03-07 5sp. Mobil 1 MV ATF 98-02.

 

[100seriesjunky]

It's not so much the solution in that thread, but the diagnosing it took to get there. Your problem may be something different than mine was, but I went over a lot of the diagnostics you'll also likely need to do. Based on your description, I wonder if your truck is holding a 'secret' P0771 code like mine was. Since your trans isn't going in to 5th, it is very possibly the solenoid inside, or something else related to it. Hooking up TechStream should be step 1.

Yep will have to check again but as far as I'm aware no codes showing. This changes into all gears no problem and smooth too. Not sure why this box is different to your one. It's a hdj100r GXL 2006. A 1hd-t engine. The auto trans box is the A750f with a torque converter. I'm guessing the add on torque converter is the difference.
It's the torque converter that is the trouble as it is meant to engage in 3, 4 and 5. The selector has to be put manually into 3 to engage in three or set in 4 to engage in 4 or in 5th to engage in 5th )And has decided not to work when set in 4th.
It was all a new conversion with the heavy duty transmission cooler being fitted so the oil is new and levels set.
Really doing my head in TBH.