TB42. How many revs are too many when towing?

[ripper]

I'm trying to work out how fast I should drive when heavy towing.
Obviously safety is the first thing to take into account, but engine revs are my next concern.
Will a TB42 happily sit on 2500 revs all day?
I wonder because in OD it's only doing about 1800 revs at 100km/h, and an extra 700 revs seems like a lot to expect it to take constantly.
Thanks.

[Silver]

G'day Ripper,

The TB42 bore and stroke are the same - which usually means a motor that likes to rev. Contrast motors where the stroke is longer than the bore - more torque.

I guess the fuel consumption would go from high to very high :-)

I noticed you said heavy towing - I would think about whether this is a good idea in 5th gear, where the gears and shafts are smaller.

I would be inclined to keep it within the yellow marked rev range on the tacho, most of the time

[ripper]

I noticed you said heavy towing - I would think about whether this is a good idea in 5th gear, where the gears and shafts are smaller.

Thanks for that. Our Trol is an auto, so no 5th gear :)
Wanting to avoid overloading the OD is what started this issue of how many revs it will happily keep doing.

[taslucas]

Having OD it would be an auto? The TB42 tacho has yellow between 2 and 3000 rpm with I take as being the power zone. I think the biggest danger is over heating the auto. An aftermarket oil cooler can be fitted to help keep temps down

tappin it

[pearcey]

G`day Ripper
Check your manual and see where the motor has max toque and drive to that rev range. It will also give you your best economy in that area.

[taslucas]

Thanks for that. Our Trol is an auto, so no 5th gear :)
Wanting to avoid overloading the OD is what started this issue of how many revs it will happily keep doing.

OD isn't another gear. It's a solenoid that locks the torque converter so the drive goes strait thru the box. (this is my lamens terms lol)

tappin it

[ripper]

G`day Ripper
Check your manual and see where the motor has max toque and drive to that rev range. It will also give you your best economy in that area.

Yeah, I wish I had an owners manual. I've got a workshop manual, but haven't found what I need in it.


OD isn't another gear. It's a solenoid that locks the torque converter so the drive goes strait thru the box. (this is my lamens terms lol)

tappin it

Actually OD and the torque converter lock up are two separate parts of the tranny.
When it's working properly, you can watch the tacho drop when you put it into overdrive, and then about 90km/h it'll drop again when the TC locks up.

[taslucas]

Yeah, I wish I had an owners manual. I've got a workshop manual, but haven't found what I need in it.



Actually OD and the torque converter lock up are two separate parts if the tranny.
When it's working properly, you can watch the tacho drop when you put it into overdrive, and then about 90km/h it'll drop again when the TC locks up.

Ahhh... See I only have the power button in mine. With the power button OFF, the box changes up through the gears till it's in top gear then when you reach around 90km/h the lock up solenoid kicks in. If I let it change up to top gear (but before the lockup kicks in) then push the power button to ON, it kicks back a gear.
So driving with the OD off, is the same a driving with the power button on (except the computer lets the years rev out a bit more before changing)
Because I don't have an OD button doesn't mean I have one less gear.



tappin it

[ripper]

Yeah, I'm talking about the power button. It can't go into OD if you've got the power button on.
From what I've read, newer Patrols have two buttons for auto options.

[Clunk]

Yeah, I'm talking about the power button. It can't go into OD if you've got the power button on.
From what I've read, newer Patrols have two buttons for auto options.

I've got the power switch on me dash and od button on the gear stick. With the power button on, it still goes into od but just revs higher and holds onto the gears longer as im increasing speed....... oh its a 94 GQ auto

[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.

[ripper]

Well after lots of reading here and elsewhere, I decided the extra revs probably would be fine.

On the flat straight parts of our recent trip with our caravan(only 1500kg), the trol easily did 95 -100kp/h, which is about 2500rpm with the torque converter locked up in 3rd gear.

I worked out I was pushing it too hard in some of the hilly sections, because the trans temp warning light came on three times as I reached the tops of hills. I pulled over straight away to let it cool down, and it only took a few minutes each time. After that I kept the revs under about 2600 rpm going up the hills, and it didn't get hot again. Made it a bit slower, but most of the hilly section was dual lanes, so we weren't holding others up.

When we got to Canberra I drained the auto and put new fluid in. The old stuff looked okay still, but better to be safe than sorry.

I'm going to move our trans cooler to where it can get cooler air, and hopefully the warning light wont come on again.