Thread: The Grey Box of EVIL.. (aka autotransmission)

Originally Posted by Tank

Seems to me that there are a hell of a lot more Posts in this Forum about buggered clutches and manual gearboxes than Auto's, but I'm biased, cos I love Auto's, never had an Auto let me down in over 20 years of Auto off-road, wish I could say the same for clutches and manual boxes, Regards Frank.

I'd say 50/50 based on the questions I get asked. but I can rebuild at least a couple of manuals for the cost of one auto. and excluding the dual mass flywheeled engines you can do 5 or 6 clutches

Originally Posted by 123rover50

Just found and read this thread. Good stuff. I had a turbo 700 behind a Chev v8 Diesel in my Perentie 6x6 camper. [ weighs 4 tonnes]. It broke a couple of times, so I put in a manual 4L80, from the mob in vic. It has no lockup but a low stall converter he said would take the place and give me better economy. OK but come to a set of lights on a bit of a hill and I cant get going. Sometimes have to grab low range. This thread explained it a bit. I have boiled the oil too, despite two oil coolers. So I am still not particularly happy but will have to live with it.
Any other suggestions would be welcome.

theres the rub... with out the lockup you have 2 choices a low multiplication TC thats got a low stall point which will let you maintain reasonable economy OR a higher multiplication unit thats got a higher Stall that will give you more torque but cost you cruising economy.

in the latter case you might be able to cheat the shift points a bit to make up for the "slip" of the TC by making it driver taller gears but that will only work around town on the highway you'll be burning off extra fuel like no-ones business. ID have thought that sequential coolers laid out properly would have delt with almost any amount of abuse you could have thrown at the box with stock chev.

Perhaps they need cleaning or your not getting the flow rate through them?

The two coolers are in series, but one I had to install with both ports in the bottom. The auto bloke I bought it from said it did not matter, but I was wondering if the oil was going in one across the bottom and out again without making use of the whole area.
The temp sender was at the outlet of the last cooler, sat about 80 deg, then I stopped once and backed around and the temp shot up way over 120. maybe because no airflow as I dont have the fans hooked up. Changed the oil after I cooked it and brased in a second sender in the pan to get a better reading, but havnt been anywhere since. Give it another go next week.
One thing when the oil boiled it was overfull, dont know how I did that, would that cause it?
Hope I havnt damaged the box.
Thanks for your info.

it shouldnt matter but I like to install the ones that have both port on the same side vertically so that the hot oil goes in the bottom and the cold oil comes out the top this ensures that when the box is pushing the oil through the cooler its fully flooded.

Definately have to have some decent airflow over them, for serious use I put them all the way out the front of the radiator intecooler and condensor and if its going for comp use then they get plumbed up the back in the tray area with a big "no, Im not joking actually" size fan on them

over filling it will delay the initial over heat of the box but once the oils up to temp youve had it the cooler will struggle to bring it all back down. this happens because you drop the heatsink area/volume of oil ratio too low

a single overheat of the box wont kill it (usually) but continuing to use the cooked oil will in very short order ,especially if you're using it hard.

Roughly

160 degrees at the output side of the TC is the limit of safe operation on mineral dex III oils. I would personally be putting the temp sender on a t piece in the oil out line from the box to the coolers and watching the temps there.

Originally Posted by 123rover50

Just found and read this thread. Good stuff. I had a turbo 700 behind a Chev v8 Diesel in my Perentie 6x6 camper. [ weighs 4 tonnes]. It broke a couple of times, so I put in a manual 4L80, from the mob in vic. It has no lockup but a low stall converter he said would take the place and give me better economy. OK but come to a set of lights on a bit of a hill and I cant get going. Sometimes have to grab low range. This thread explained it a bit. I have boiled the oil too, despite two oil coolers. So I am still not particularly happy but will have to live with it.
Any other suggestions would be welcome.

Something is wrong there, i had a 6.5chev with a T700(built tough) and low stall converter running 35centerpedes on my rangie and it pulled away no problems at all and never overheated (1 big cooler). I'd be getting yours looked at!

Its abig truck, the one on the right , it weighs in over 4 tonnes and I get about 4 to 4.5 kays per litre.

Didiman

Originally Posted by 123rover50

Its abig truck, the one on the right , it weighs in over 4 tonnes and I get about 4 to 4.5 kays per litre.

Didiman

Hmmm, I would suggest looking at the pics and your fuel figures, that an Allison AT540 trans would be a good starting point. Not too difficult to adapt to engine, but LT230 adaption would be a little more of a challenge. I entertained the thought but the trans would better suit a 110 or longer wheel base, not a RRC IMHO

JC

Originally Posted by justinc

Hmmm, I would suggest looking at the pics and your fuel figures, that an Allison AT540 trans would be a good starting point. Not too difficult to adapt to engine, but LT230 adaption would be a little more of a challenge. I entertained the thought but the trans would better suit a 110 or longer wheel base, not a RRC IMHO

JC

Those MPG figures of 1.595 (MPG) are horrendous.In the Queensland Fire Service before we went all diesel our petrol Acco's were getting 4MPG and that was with all the gear and 2200 litres of water on board.They all had Allisons behind a V8 pushing them.
Cheers,
John.