Auto gearbox's

[The Patrolman]

Now I am running 37"'s on my petrol Troll. I really have to tonk along before the box locks into top about 67mph on the satnav 60 on the clock.

What controls the change up / down and can it be altered, 50 - 55 would be nice and may help with the dreadful fuel economy:nenau

 

[rayf3262]

It all done by the TCU module and changing it's operation would not be trivial.
There is however, a well documented mod to allow manual operation of the torque converter lock here:
http://www.chaz.yellowfoot.org/Lockup Trans Switch.htm

 

[russell.huffer]

Altougth not cheep I thought that the solution with big tyres is to regear the diffs.

Kind regards

Russell.

 

[solarman216]

That ought to go in the downloads Ray, it is good, but do not know about copy-write, Rick

 

[The Patrolman]

It all done by the TCU module and changing it's operation would not be trivial.
There is however, a well documented mod to allow manual operation of the torque converter lock here:
http://www.chaz.yellowfoot.org/Lockup Trans Switch.htm

Thanks Ray, -an interesting read. I might give that a go.

Ideally I just need to change into top sooner But locking the convertor may keep the revs down a bit in third.

The overall gearing with the 37's isn't too bad and with it being an auto you don't notice it when pulling away apart from the lack of wheelspin

 

[rayf3262]

A mod. that would allow the box to change into top earlier would be to alter the VSS signal to the TCU, indicating that the vehicle speed is greater than the actual road speed.
Have a look around the Australian Jaycar website as I seem to remember they sold such a device for speedo correction when fitting non standard tyre sizes.
Tis here:
http://www.jaycar.com.au/Automotive...-Accessories/CORRECTOR-SPEEDO-MODULE/p/AA0376

 

[The Patrolman]

Thanks for that ray. I may just order one of those.
It makes sense so long as I get it in lone from the speedo output to the TCU/speedo.

 

[macabethiel]

Top Gear Selection on Automatics

The shift into top of the gearbox is torque related when the box is at working temperature rather than purely speed & rpm. Modern electronic / solenoid type boxes are somewhat different.

On my Terrano r3mR /Santa Fe / and my current Jeep I can persuade the shift into top by lifting off the throttle into overrun and then easing the throttle back on again.

I also found that using an upgraded transmission fluid rather than the original also helped the shift points both when cold and at normal temperature.

In my previous two vehicles I used Fuchs Titan 4400 fully synthetic it is backwards convertable as a replacement for Dexron 1,2 & 3 being fully synthetic. There is a lot of tosh about using the manufacturers fluid only in autos and Merc in particular try to keep you 'on brand'.

I have found that using a fully synthetic brand improves shift points and does not damage any auto gearbox I have owned. My Jeep has the Merc fully synthetic fluid when it is due I will use Titan if it is cheaper !

 

[The Patrolman]

All noted:thumb2
I have noticed that the shift / lock into top is when the speedo hits 60mph every time. Ive tried the backing off approach but that only works above 60mph too.

 

[macabethiel]

Top Gear Selection on Automatics

All noted:thumb2
I have noticed that the shift / lock into top is when the speedo hits 60mph every time. Ive tried the backing off approach but that only works above 60mph too.

Perhaps it is coded into the gearbox / engine management system does it make any difference if you are descending a long steep hill?

Have read somewhere the top gear solenoids can fault but to me it sounds pretty normal.

On more recent Mercs (R reg and later probably)they have had a system where the shift points are adaptive and they have a memory based over a series of jouneys. If you drive hard and fast they hang onto the gears and if you are a Sunday driver they change up earlier.
These are electronic solenoid shift types not the old fluid valve block only design.

 

[Fez_uk]

I would look at getting some 2.8 GU axles for a better ratio with your tyres

 

[The Patrolman]

Ooh ooh are the ratios in the axes lower on the 2.8:thumb2

 

[Fez_uk]

2.8 GU diffs/axles are commonly used if you run bigger tyres on a 4.2 patrol.

But just had a thought, you are running an auto so not sure if they are the same as manual 4.2s??

Think manual 4.2 is 4.111

And 2.8 manual GU is 4.625

 

[The Patrolman]

A mod. that would allow the box to change into top earlier would be to alter the VSS signal to the TCU, indicating that the vehicle speed is greater than the actual road speed.
Have a look around the Australian Jaycar website as I seem to remember they sold such a device for speedo correction when fitting non standard tyre sizes.
Tis here:
http://www.jaycar.com.au/Automotive...-Accessories/CORRECTOR-SPEEDO-MODULE/p/AA0376

Ray, thanks I've just ordered two so have a spare if anyone wants to correct their speedo. It mad sense to get the extra one as the postage was the same for one or two
£25 plus postage if anyone wants one:nenau

 

[rayf3262]

Don't forget the HMRC lottery of examining your import may attract a request for payment of duty before they release the goods....
Fingers crossed.

 

[The Patrolman]

I have been playing with the different ratios and the 2.8 duff would be better but u can't determine by how much till I know the gearbox output ratios of the 4.2auto box.

Anyone got easy access to these figures:nenau

 

[rayf3262]

Found this from: :nenau
http://www.patrol4x4.com/forum/showthread.php?t=1

Patrol automatic gearbox:
4-speed Automatic
RE4R03A
4-speed electronic auto with lock-up torque converter and two-mode shift pattern (economy & power).

Gear Ratios:
1st: 2.784
2nd: 1.544
3rd: 1.000
4th: 0.694
Reverse: 2.275

These are exactly the same gear ratios as in the 300ZX auto TT. The NA auto is slightly different with:

1: 2.785
2: 1.545
3: 1.000
4: 0.694
Reverse: 2.272

 

[The Patrolman]

Fab... just trying to get my head round it all.
Getting getting there slowly with the aid of excel but not too easy on android.
I think the only missing link is the overdrive. Recently the button does not seem to effect a change in engine revs.
Is this an overdrive above 4th.
Is 4th the over dive ratio at 0.694 and does this drop when od is turned off.
sorry for so many questions...

 

[rayf3262]

I recall that the "high gear" whether that's OD or top I am not sure, will only engage once the ATF temperature is above something like 40 plus deg. C.
So, when testing make sure the box is up to normal temps before making definate conclusions.

 

[solarman216]

Fab... just trying to get my head round it all.
Getting getting there slowly with the aid of excel but not too easy on android.
I think the only missing link is the overdrive. Recently the button does not seem to effect a change in engine revs.
Is this an overdrive above 4th.
Is 4th the over dive ratio at 0.694 and does this drop when od is turned off.
sorry for so many questions...

yes 4 is overdrive, overdrive = output turning at more than input, so yes again if you turn overdrive off engine revs should increase, Rick