Re4r03a trans lockup override advice please

[rrakausk]

First I wanto to say thanks to all who have posted about Nissan auto gearboxes. The info has been a real help.
I tow a van and my auto box drops in from 4th to lockup at about 85kph.
I want to avoid this because it overheats the box and I also lose momentum in country with gently rising roads, so I am constantly double tapping the power button to get it to shift back down a notch. Then it goes faster and locks up again.

This makes towing under some circumstances a real drag because I have to keep the speed at 80 kph and if it drifts down a slight hill it speeds up and we do the whole thing again.

Has anyone set up a manual override so it doesn't lock up?

I have some skills. When the auto sparky couldnt do the tps right I fixed it myself

Thanks in advance.

Rick

[rrakausk]

Forgot. I want to cruise at about 90 kph with the van only. The truck gearbox is just perfect when its not towing.
Cheers

[paulyg]

I just tow with the O/D off, no more shifting up and down.

[the evil twin]

Has anyone set up a manual override so it doesn't lock up?



Not sure why you would want to do that, I set mine up so it stayed locked up when selected.

Better fuel economy, much lower gearbox temps, much more pleasant to tow.

On the flat, downhill or slight climbs where you can maintain cruise speeds (80+ KPH) leave it locked.
On a more noticeable climb just flick the 'manual lock up' off and let the box do its thing.
As soon as you are back at cruise then lock the sucker back up.

Heaps better result IMHO

[rrakausk]

thanks.
maybe the simpler question is "what is the easiest way to keep it in 4th gear so it wont shift up at all?"
mine is a 91 ST with the "Power" button on the shifter. no O/D to speak of

I love they way this auto keeps engine revs constant at around 2k (unless caning it of course) and all work is done by the box and torque converter.

cheers

[the evil twin]

All that 'work' generates heat and it is heat that kills Auto Gearboxes, luckily the Patrol Box is one of the toughest suckers around

OD and 4th pretty much mean the same thing for the discussion purposes here, as 4th is an 'overdriven' ratio IE 3rd is 1:1 and 4th is 1:0.694 or somesuch.

There is no other gearing so your box doesn't 'shift up' from 4th, all that happens is the T.C. locks up which is a good thing.

Another approach is to go for a manual valve body and drive it like a manual

[rrakausk]

my box drops nearly 700 rpm when it goes from the 4th gear into lockup. at 85 kph that means it drops from about 2600. rpm to 1900 and it then becomes a slug when towing 2400kg.

If I can prevent that from happening manually then I will be happy.
I like the auto, and its great when the truck isnt towing.

The valve body has been beefed, I have two trans coolers which are switchable so one works or in hot conditions both work with fans, trans temp gauge etc.

So any info on stopping lockup in top so it stays in the OD gear (4th) is the question I guess.

cheers

[the evil twin]

700 RPM... HOLY COW!!!!
Something is seriously wrong dude, if your TC is bogging down 700 RPM
Mine would drop about 150 - 200 RPM from 4th unlocked to 4th locked. There is also no way you should be pulling 2600 RPM in 4th at 85 KPH

700 RPM is an entire gear ratio so you are looking at 3rd (2600 RPM) going to 4th (1950 RPM) at those figures and then the RPM should drop from 1900 ish to 1750 ish when the TC locks up.

I'll try and check my calcs but I am almost positive 2600 RPM at 85 is 3rd (my figures are with 33's).

The above would mean that your desire is to hold 3rd (a 1:1 drive).

I often used 3rd TC locked as it was a great ratio for the 'undulating stuff'

[paulyg]

If you are going to try and keep the trans in 4th with the TC looked, I hope you have an EGT gauge, because you could see those EGTs climbing real quick if your not careful.

[the evil twin]

If you are going to try and keep the trans in 4th with the TC looked, I hope you have an EGT gauge, because you could see those EGTs climbing real quick if your not careful.

Those boxes in the Q's are behind the TB42 except for the few hundred NA Auto TD42's imported early.

The petty's absolutely love getting locked and run cooler, I did almost 300,000 K's in mine.
The NA TD42's shouldn't have any EGT issues but I have no experience there and the aftermarket turbo TD42 jobbie I know of went OK locked but I must admit he didn't tow

[rrakausk]

Sorry youre right. it drops 200 rpm. your calcs are pretty good. I do have egt and running 15psi boost. I am off to see my auto guy and get him to do a high speed drive so we can nut out a plan. Thanks for all your input mr twin.

cheers Rick