Auto box for off road. Is that a good idea?

[o_teunico]

Hi all,

Now that I have the "cosmetic" upgrades for my 88" on it´s way, I´m thinking on the suspension, axle and engine conversions for the future.

The engine is already chosen, MB six pot turbo OM603/606.

Axles: front Series V, rear Disco 300.

Gearbox...still thinking about it.

All Mercedes W124 turbo sold in Spain had auto box. Using the factory MB box will save lot of work/money on adaptations. 4G-Tronic 722.3XX is extreamly though, reliable and fully hidraulically controlled (no electronics),has four speeds and ratios are extreamly close to those of a Rover four speed, except the crawler reverse.

First 3.87

second 2.24

Third 1.44

Fourth Direct

Reverse 5.59

The only vehicle I have ever used off road with auto box was a 2002 Freelander. I was really amazed how the torque converter acted as a low box. Used with a divorced LT230 it will act as a second low box.

But there are two things about the 4G-Tronic that I really don´t know if they will represent a problem off roading.

-No "1" position on gear lever.

-No lock up converter.

What do auto box experts think about this?

[Soren Frimodt]

Doubt you'll notice the lack of a 1st gear lockout as you'll be trailing the brakes at decents anyways. Always necessary with an autobox IMO and I doubt the Merc engine has very good engine braking.

And the lockup has no use offroad. And onroad it's mostly there for fuel savings

[Arjan]

Used many auto boxes off road and never had problems.

Offroading with an autobox is very nice.

Serious Overlanding with an autobox is something you may want to reconsider.

Interesting conversion - please keep us posted.

[HoSS]

Look at the W210 Om606 with the 722.6 box. From what i have researched is vastly better than the 4-tronic. If you can find one from a ML then it has the highest torque rating and a rear flange. Look at landroversforver 's thread in members vehicles.

Also with the Ole Fejer 722.6 controller, you can set up all of the parameters including lock up of the TC.

[landroversforever]

What hoss said, the 722.6 is vastly superior. However, I seriously think you're going to struggle with length with a 603/606, auto and divorced transferbox.

[Daan]

Is there a merc manual box available? I couldn't live with an autobox.

Daan

[landroversforever]

Is there a merc manual box available? I couldn't live with an autobox.

Daan

People use the sprinter box which is supposed to be quite strong, but I don't know how well or not it would fit.

[HoSS]

What hoss said, the 722.6 is vastly superior. However, I seriously think you're going to struggle with length with a 603/606, auto and divorced transferbox.

OM605 then.

[landroversforever]

Would be interesting to measure the difference in length between a 606 and a 605 .

[ejparrott]

When you use an LT77 in an 88" you loose 4" from the rear prop straight away. All the auto boxes I've seen are even longer than that. With a 6-pot engine as well, I'm sure you'll have to move the front panel and even then I think you'll be pushing back even further. I fear you'll end up with a prop so short you'll have no articulation if you're to stop the slider popping out

[Cynic-al]

For offroad I much prefer an auto box, you can left foot brake and crawl over the obstacles giving it enough throttle that it's going to keep moving, watch someone do it in a manual and they come to a stop when they get to an obstacle as they're on the brake not the power, they let off the brake to get the power on, the car rolls back in the intermediate moment between brake throttle and clutch, they panic and snatch at the clutch when it starts to roll back and that's when things start going pop. Depending on the engine / gearbox combo they also shift up and down on hills as you climb. Generally in a manual your pretty much committed to the same gear for the entire climb. If it's particularly rough at the bottom you've no momentum so have to try it in a low gear, you then can't get any momentum as your stuck in that gear and start scratting half way up the hill. You roll back down and try in a high gear but then you haven't got the power to keep the wheels turning and stall.

However for on road I hate autos, they absolutely do my head in, you end up having to double think what they're going to do all the time and drive in a way that will make them do what you want them to do. I would much rather have a stick that I put where I want it and it stays there.

I can't comment on the specific boxes your referring to though.

[o_teunico]

Santana used a "u" shaped front crossmember when they built 3.5 six series. That way the engine was located above front axle and the box maintained it's original location.

Firts idea was to use a Vito 120cdi transaxle (with welded diff) and a halfshaft moving the divorced lt230. For this we will need to build special gearing in the lt230 for overdrive high range (press and weld inverted low range gears?). Top speed just 50mph and first low 40% lower than a coiler with ashcroft underdrive! But I dont have equipment/skills for such work.

Going with oeiginal auto box is the easiest way.

Looking at ratios, MB second gear with 4.7 diffs will be very much the same as a ZF 4hp22 with 3.54.

I have not looked at other mb autos because of electronics. There's even 722.5, wich is a 722.3/4 with a 5th overdrive and lock up convrter, but that extra features are electronically controlled.

What about descendig step climbs with autos?

[Shackleton]

Don't know if this is of any use to anyone but out of the box the 2000 model year OM611 (4 pot 2.2l CDI) has more torque than both the W124 and early W210 606's. It's also more torquey than the 605.

I don't know where that torque happens, I don't know if it's as tunable as the 606, and it does giveaway between 12 and 51 bhp to those engines depending. I drive/work on a C220 CDI (OM611) every once in a while and it's a pleasure to deal with.

[o_teunico]

Good thing about 601/2/3 is that they are fully electronic free. 604/5/6 use EDC pumps, but can be easily swapped for earlier mechanical pumps.

Modern ecu engines are great, but some of use simply don't know how to work on them.

[Shackleton]

There's good information documenting the use of the 606 by replacing the electronic injection pump to a mechanical one from the 603 (or making some sort of hybrid of the two), and using the engine harness from there too. I was suggesting the 611 only because the chaps were worried you'd run out of room with a 6 cylinder. I know nothing about tapping into the Mercedes brains other than the system used is called Star. From the small amount I've read (I need to activate cruise control on this W202 I have) they don't seem any more complicated than the Td5 programming though so it might be a lot easier to play with than you think once you have the means to plug into the car.

Anyway sorry for going off topic slightly, I know nothing of the MB gearboxes!

[Jamie_grieve]

I think Cynical gave a good response to off road in an auto.

I agree with all of it but also disagree too as I think it applies only to modern high revving turbo diesels.

The scenario of the obstructed hill climb describes exactly why I have a large displacement but lightweight V8 diesel in mine. I can trickle over most anything in 3rd low at 600rpm then light the tyres up and get it going. By the time I'm at 1200rpm I've doubled my speed, 2400rpm I'm 4 x faster then all the way to 4000 rpm. Most of that happens in one or two lengths but without enough grunt to really upset things.
I only use the clutch to stop, never to tiddle around on obstacles, that's why they invented low gears.

I think a flexible engine is key off road, heavy flywheels help here. Autos are fine for some things but they don't work on rocks where you have to drive through the brakes all the time, downhill, driving through the brakes and on wet grass and mud where you can't modulate the throttle feeling for grip as accurately that's without the 'wrong gear' scenario that crops up only at inopportune moments. Add to that the much higher overall ratios that despite the torque multiplication of the torque convertor are just never low enough to not cook things eventually.

I think a modern auto which is more like a little powershift with a torque convertor you could lock with a switch would be the best all rounder.

As for the 606 o_teunico, I would stick a 603 flywheel on it and run a manual trans for the length. If it was a 109, I'd say go with the auto but on an 88, nah, no chance, as said, even with an LT77 you struggle. I'd stick an R380, short bell housing, LT230 and a Rakeway short rear shaft for your project to have a chance of working. The wheels will spin before the R380 breaks.

Auto's are good for not shock loading drivelines too but you might have to lose that for the length.

[honitonhobbit]

Auto off road is easier, Manual trickier and requires more skill. So not better or worse...

[FridgeFreezer]

Auto off road is easier, Manual trickier and requires more skill. So not better or worse...

[Bowie69]

Two feet, three pedals.

Who ever thought that was a good idea?

[Daan]

Auto: will eventually cook when pushed hard; needs a lot of cooling>power drain of engine. no tow start on auto.

Manual requires more skill and lower reduction ratio. if you want the most reliable solution for proper off roading, there is no other choice than a manual in my opinion.

Daan

[honitonhobbit]

I go through phases. A 3.0 NAD 617 coupled to an Auto-box in a SWB 416 with grippy tyres is a thing of awesome capability and soooo easy. An LT77 with a 200 Tdi is also awesome and soooo much fun

[HoSS]

Good thing about 601/2/3 is that they are fully electronic free. 604/5/6 use EDC pumps, but can be easily swapped for earlier mechanical pumps.

Modern ecu engines are great, but some of use simply don't know how to work on them.

I dont get this electronics phobia. Mech also means that you can't tune or modify anything. The 722.6 controller is superb, you can set up every parameter, from lock-up, shift points.. everything from an interface in the car.

Theres no good reason why it it will be less reliable, and if it does go wrong you have diagnostic capablity.

[Snagger]

Serious Overlanding with an autobox is something you may want to reconsider.

I'm not arguing the point as I have no experience of it, but I'm curious as to how you came to that conclusion.

[Shackleton]

A 3.0 NAD 617

They say cockroaches will survive the apocalypse. Yep, cockroaches and the OM617

My Aussie overland prepared D2 was spec'd auto. I don't know it's history but judging by the best of the best attitude that seems to have gone into it, and the red dust under all the sound deadening, I'm guessing it was used as intended before it was brought to the n. hemisphere.

[o_teunico]

Searching the net I´m finding more and more pros for the MB Auto...

1) In 1971 mercedes began production of a 4 speed automatic with torque converter, they also made a 3 speed version for a couple of years which was exclusive to powerfull large displacement V8 cars.

In 1980 MBZ extensively modified this automatic transmission to suit the G and van platforms by integrating an electricaly activated solenoid which keeps 1st gear engaged, no passenger car automatic can hold 1st gear. Transmission case and bell housings have breather 'snorkels' for water fording, deeper oil pan ensures constant oiling at extreme angles and internal components are more robust with extra friction discs, special valve body etc. due to the G's weight. They called this the 720.1.

The torque converter has a torque multiplication factor of 1.8 or 2, so first gear ratio (normally 4:1) is nearly 8:1 under 1800 RPM.

2) 722.3 may be the best non electronic automatic Mercedes has made. Smoother shifting, slightly more 'luxurious' in feel than the previous unit. G-specific versions have the same special features listed above, like the 720.1 it is a vacuum controlled 4 speed torque converter transmission but optimized to compliment the more efficient "modern" engines emerging out of MBZ in the early/mid 80's.

Mercedes used this auto behind its V12 luxo-barges with great success, every 722.3 is easily modified with V12 bits (friction discs/bands etc.) to survive well over 700 horsepower.

*The operators manual for both G-wagen and passenger cars say you can pull start both of these 4 speed autos (720.1, 722.3), and I have tried this on a couple different vehicles, but in my experience this is not practical. MBZ says to get the vehicle up to constant 40kph on flat ground in neutral (builds up pressure in ATF because rear pump always spins) then drop into gear and hope the TC locks up and rotates the motor. There is a risk of over-pressurizing the ATF and popping seals, keep it under 40kph!!

The .5 5 speed is closer to the .3 4 speed with many internal parts interchangable. ( the .4 is a scaled down version of the .3 4 speed)

It applies voltage to the 5 th gear solenoid in 1 through 4 gears then drops voltage to get 5 th

My understanding is that it's more electrically controlled than electronic. I say that because the box is basically hydraulic but they added an 'overdrive' that's controlled by a switching mechanism that's in turn controlled by a thing called the MAS box that also contains the fuel pump relay.

So, the answer to your question is, "No, there is not a 722.5 box that's 100% hydraulic"

with no outside input the 722.5 will shift 1-2-3-5. The electronic control unit makes the trans shift into 4th instead of 5th.

Info taken from clubgwagen.com and peach parts forum.