calling GQ TD42 Auto Owners (and other GURUS) - DIFF RATIO ASSIST

[grunta11]

Guys - my question to you is how are you finding highway performance when loaded, towing, hills, headwinds, etc.? do you experience kick down to third often, or frequent converter unlocking then locking back and forth etc?

Im sure im going to change to at least the 4.375 to bring back to standard, but considering 4.6 gears for reasons explained below.

I would value your experience, or an opinion with changing diff ratios to suit your desired outcome?

Some fact n figures - My bus is standard so has 4.1 gears and the nissan auto box runs a tall .694 overdrive (that's over 30% OD compared to .836 or approx 17% for the manual boxes) so backshifting from top gear to 3rd in an auto is a drastic RPM change and very bloody annoying. I`m sure you auto drivers agree.

i have an aussie GQ TD42 NA (turbo coming soon) and found the standard 4.1 ratios not great when upping tyres to 33`s. (Not going back to 31`s) I find soon as i put a few slabs of beer & bodies in the back she don't even like slight uphill inclines and moderate headwinds!, (typical country WA road conditions) with frequent 3rd & 4th gear shuffle back and forth. And that's with my vehicle being totally stock apart from 50mm lift and flimsy ally roo bar.

Planning additional permanent add ons like steel bullbar, scrubs, steps, winch, twin wheel carrier, roof rack. Then add to that the extra fuel, water, camp gear, 1.2 tonne camp trailer in tow.............and of course the turbo.

i can post up tables of RPM @ various km/h V diff ratio combos if you want.

There's a school of thought that the turbo install address my issues here, but my opinion is that's only part of the solution, i reckon correct ratio selection is half of the battle. whadureckon?

[threedogs]

Do you know what boost you are running,
it may just be a case of a dyno to get the most out of it

[BigRAWesty]

Just sold my 4.6 centers to a bloke who was in the exact same boat as you..
And struggled to get below 15L/100 on the highway.
He stuck the 4.6 in and after 100k only used 11 liters..
He said it's put it right in the in the spot when at 100k now and everything seems right..
He's very happy that he's gone the 4.6. And pretty sure he's still on 31's

[tuckertrucker]

I agree with westy above. But in saying that, You will probably find that anything between 5-15psi boost will fix all your problems. I have a '92 GQ and I was driven up the wall by the auto downshifting to drive from OD all the time. Like you said there is a huge step between OD and Drive. And on top of it all, my trans wouldn't unlock the TC in OD, it would opt for the lower gear. So that left me with either no power at 100km or a shit load of power and revs a gear lower.

I overcame the problem with both a manual TC lockup switch (a very easy mod) and the turbo. You should also have a E-AT switch somewhere on the dash/ gear stick. When this is in POWER, you will kick down much quicker, and stay down longer. When its in AUTO, its sort of like an economy mode. So sits in the highest gear it can. But if you flick the switch over to HOLD, you eliminate low 1st unless you manually select it, and the TCU (transmission control unit) will ignore the TPS (throttle position sensor) and kick down switch.

So basically with my manual lockup switch, and driving with that E-AT switch on HOLD, I can control exactly what gear it drives in and when it locks/unlocks and I also choose when to shift gears. It pretty much bypasses the TCU and makes it a manual shift. Fixed all my problems and if you're smart about it you can keep the auto's fuel economy.

I guess though its really personal preference. I'm happy with my rig and how she goes. And I'm planning on doing a manual conversion in the coming years so didn't want to change diffs.

Good luck mate, Dylan.

[grunta11]

Do you know what boost you are running,
it may just be a case of a dyno to get the most out of it

No turbo on board yet threedogs, early next year, likely the garret HPD set up. i'll probably have a bit more of an idea once i find out where the meat is in the torque range rpm wise and match it up from there. Not many autos around so perhaps little feedback out there to be had.
hoping im not a pioneer here....surely not.
oh shit, means i have to be patient....i'm low on that stuff!

[tuckertrucker]

I've heard that aye (not many autos) but over here ever second safari/ patrol is an auto haha

[jff45]

I have a GQ Safari factory turbo engine in my GU with auto trans and 3.9 diffs with standard tyres.
I can manually lock the TC in OD and pull easily from as low as 80.