TB42. How many revs are too many when towing?

[ripper]

I've never seen one like your's I've only read about them. Earlier GQ's (like ours) just have a power button on the stick.

Any further experience with how hard TB42's will happily rev on a trip?
Is it okay to do 100km/h constantly in drive?

[taslucas]

Mates mav has the power button on the stick and on the dash has a button that switches between POWER, HOLD, OVERDRIVE. Its a 92 model. Mine sits on about 1800 rpm at 100 km/h in drive without an overdrive button.

tappin it

[the evil twin]

The series 1 and 2 auto's are set up differently.
Series 2 have the "hold" option and will lock the TC in OD in Power mode
The series 1 won't lock up in power and doesn't have the "Hold" selection

Towing with the TC locked greatly reduces the gearbox temp as the TC generates a heap of heat but the only way to do it is with a Torque Converter Lockup Switch modification which isn't for everyone and not really suited for heavy work.

The best deal for heavy stuff is valve body mods from say Wholesale Auto's in Melbourne. Give them a call anyway just for advice. As I always say "they are God when it comes to Patrol Auto box's" because they compete with them.

[ripper]

Towing with the TC locked greatly reduces the gearbox temp as the TC generates a heap of heat but the only way to do it is with a Torque Converter Lockup Switch modification which isn't for everyone and not really suited for heavy work.

I got my manual TC lock up fitted last week, it locks no worries, but doesn't cut the revs as much as I hoped.
Why do you say they're not really suited for heavy work?

[the evil twin]

Because I am not keen on switching the Lock up in and out under load. The Box and the TC will handle the heavy load when it is "locked" it is just the switching that makes me uncomfortable but used with care shouldn't be a worry.

They can only cut the revs to match engine speed so once the converter is stalled there is little difference which is maybe why you aren't seeing a bigger RPM cut.

[ripper]

Thanks, that makes sense.

[taslucas]

The series 1 and 2 auto's are set up differently.
Series 2 have the "hold" option and will lock the TC in OD in Power mode
The series 1 won't lock up in power and doesn't have the "Hold" selection.

Bit of a hijack, but what IS overdrive then? It's not another gear.
The series 1 and 2 boxes have the same amount of gears? So the power and OD, and hold buttons just change the computer signal to the box making it change at different rpms. Is this correct?
Are you saying that the hold button us a TC lockup switch that works only in overdrive? It's not ment to hold, say, 2nd gear?


tappin it

[the evil twin]

Yes, Overdrive is another gear, the gearing is 1st, 2nd, Drive, Overdrive (or 1st, 2nd, 3rd and 4th if you prefer) with ratio's of
RE4R03A
4-speed electronic auto with lock-up torque converter.
Gear Ratios:
1st: 2.784
2nd: 1.544
3rd: 1.000
4th: 0.694
Reverse: 2.275

"Hold Mode" is only available on the series 2 and is nothing to do with the TC. It is used to hold a specific gear, say 2nd, no matter what. If you just select 2nd using the selector the box will change from 1st to 2nd as req'd not hold in 2nd only

The TC lock up switch is a mod that allows the user to switch the signal to the TC lock up solenoid manually or leave it in control of the Tranny ECU by putting 12 volts (24 volts for Safaris) to the Lock up solenoid.

This means that you can lock the TC 'as required' and not just in Overdrive above 85 KPH (for series 2) or Overdrive above 85 KPH and not in Power mode for series 1.

There are also sensors for temperature and engine load parameters that must be met befor the ECU will lock the TC as well.

[taslucas]

Thanks ET, that's some good info, thanks for posting. I have been chasing a fault in my auto and I think it's narrowed dine to the temp sensor...new getting put in Monday. New TPS, new torque converter, reco box, heavy duty nomad valvebody from wholesale autos but didn't go the TC switch.
Just one more query...the gq autos are reffered to as a 4 speed....why call it a 3 speed with overdrive? Mine has four (forward) gears but no OD button.....so apparently it doesn't have overdrive....but it has the 4th gear, which is overdrive????

tappin it

[johno90]

OD itself means a gear, its any gear over input revs so anything over 1:1 modern cars have 2 or 3 overdrive gears. Also Hold mode can lock the box in a single gear as in when gear stick on 2nd and hold mode on, the box will stay in 2nd no matter what and will even take off and 2nd.