Pajero Owners Club of South Africa

I'm busy rebuilding the my 2003 3.2 DiD engine and is also planning to change diff ratio and the stall speed of the torque convertor.

I am using the Pajero most of the time to tow the caravan. To tow using 5th gear is not the correct way to go except if you can run the engine at high enough RPM and you do not overstress the engine.

By changing the diff ratio from 3.9 to 4.1 will give me 99 RPM more traveling at a speed of 90km/h. Most of the time I will tow at speeds between 80 and 90km/h (that was the days before this Pajero). In future I will to at speeds of between 90 and 100km/h because at those speeds the engine RPM is high enough that the transmission will not be damaged.

It must always be kept in mind that 5th gear towing is acceptable only if the engine and gearbox is not over stressed. This means that level road and downhill travelling will be acceptable but the moment you start an uphill you should change back to 4th gear.

I tested the Pajero as prescribed by Mitsubishi to determine the stall speed of the torque convertor on my Pajero and found it to be between 2500 and 2600 RPM. The clutch (inside the convertor) was also suspect. This high stall speed on the torque convertor caused a slip of about 600 RPM when I was towing at 85 km/h. This was helping to tow for longer distances (higher RPM) in 5th gear but that slip is heating up the transmission fluid to unacceptable levels and is also making the Pajero unnecessary thirsty.

I’ve asked the engineering works to alter the torque convertor to bring the stall speed down to about 2000 RPM. When the torque convertor was opened they found the clutch needed new bonding material and the blades on the impellers where set to their maximum and they could only do minor changes to the stator. The torque convertor must no go back in its position and the test to determine the tall must be done again. According to the engineering shop they hope for a stall speed of about 2250 RPM (not that I wanted but it is more in the direction I would like to go).

Warning: Changing the stall speed as per above will have a negative influence on the acceleration from 0 to 100km/h.
By changing the diff ratio and the stall speed I was hoping to get to the point where I’ve got no slip at my preferred towing speed (about 95km/h)

I will keep you posted with the results. The engine, gearbox and differentials are going back to their position on the weekend of the 23rd July 2011. Then the engine must me ran in. Only then I will be able to take the caravan on an outing.

Waldo Fourie

PS. The 4.3 diffs from the Pajero 3.8 V6 will be a nice change for the help with the 5th geare but the RPM in 4th will then be to high. The 5th gear on the Pajero is a genuine overdrive !

Waldo,

Thanks for an informative post.

Roelf

Thanks Waldo,

I'll watch out for the results of your modifications - please keep us updated.
The diff ratios are something I've thought about changing for quite some time now. It all depends on the costs involved and whether I intend keeping the Paj for long enough to warrant the expense.

Cheers
Bruce

Bold,
A stupid question here.
What is stall - referring to torque converter and how will you know it is stalling?
Second- how is testing done to determine stall on torque converter?
3rd- when is slip happening.
I have a 99 Blister and also tow a caravan-off road Conqueror with it . Although mine is only 4 speed auto .
Will the same principle apply in this setup. I pull away normally in first using the lever like a normal clutch operated vehicle and switch to second and then drive. I use the auto mode switch to alter between 3rd and fourth ,
When going up long ascends I flick to power mode and keep it there untill I have enough momentum and flick out again.
The gearbox would have been kicked back to 3rd anyway by then- i just keep it 3rd longer. I do not really use overdrive for towing perpouses as I think it will overheat my box.
I am doing the correct thing here?
Your views appreciated

Hi paw-by paw,

There are a few different stall conditions if you whant to be very technical. Most of the times when the stall speed of a torque convertor is menthened it will be the stage where the speed of the turbine and the impeller of the torque convertor is running at the same speed. The engine and the input shaft of the gearbox is now running at the same revolutions per min. Inside modern torque convertors, used in cars, there is a small clutch that will kick in (some mannaged by electronics and others machanicaly) to lock the impeller and turbine to run at the same speed. This condition is refered to as the torque convertor lock-up.

Up to the stage where the convertor reaches the stall or lock-up condition there will be slip (impeller and turbine not running at same speed).

When you travel at a constant speed and you press down on the excellerator and the engine RPM goes up but there was no immediate increase in speed, it is because of the slip in the torque convertor.

I can give you a lecture of pages long about torque convertors (and is willing to) but I suggest you go to the followig link the following link for more info on how a torque convertor work:
http://en.wikipedia.org/wiki/Torque_converter
OR
Google the words "torque converter", "torque convertor stall" and you can learn at lot if you are interested to do so.
OR
ask if you need more info.

Only the correct procedures must be used when testing the stall speed of a torque convertor. If not, you may dammage the torque convertor or the transmission or can even smash your car. I will be out of town for a few days, but will reply about this test by qouting out of the Mitsubishi manual about this test next week.

I can see nothing wrong about the way you are using the transmission when towing. The most important part of towing with is: never use all the available torque from the engine at low revs in any gear. I know low revs with a petrol engine and low revs with a diesel engine does not come to the same RPM but another way of describing it will be: Never use full throtle at low revs in any gear. You should let the engine work at "happy" RPM (dificult to explain).

It can do no harm if you never tow in 5th (overdrive). You should able to feel when the car (engine and gearbox) is suffering. I do make use of the 5th gear but only on level roads with no wind holding me back but if you do not feel comfortable to use 5th, then you should not !

Waldo Fourie

bold4E wrote:Most of the times when the stall speed of a torque convertor is menthened it will be the stage where the speed of the turbine and the impeller of the torque convertor is running at the same speed.

Waldo, no. Torque converter stall is the situation that arises when the impeller is receiving power from the engine and is spinning and the turbine is prevented from turning. All the input energy is dissipated as heat by the torque converter, so one should be careful not to allowed a stalled condition to persist for any length of time.

The so called torque converter stall test is just about the only torque converter test that can easily be carried out on a torque converter installed in a vehicle. In order to carry out the stall test, the engine is run at wide open throttle in gear while the wheels are prevented from turning (by applying brakes, wheel chocks, etc.).

If the engine speed during the stall test falls within the recommended range and if the engine is in a good state of tune, then the stall test can confirm that several parts of the transmission and torque converter are working according to spec (e.g. the stator sprag clutch, brake bands/brake clutches involved in gear selection).

Hi Gerrit,

Thank you for helping out. It is not that easey to explain all these terms used.

The following qoute from the web site of PRO TORQUE Custom Built Torque Converters will perhaps help to describe the term "stall" to a lot off us. Under the heading FAQ they have this question and answer:

What is stall speed and how do I determine what stall I have now?
Stall speed is a term used to describe the rpm at which the torque converter transfers the power from the engine to the transmission. There are different ways to test stall speed. "Foot brake stall" is when you press the brake pedal and then press the gas pedal. When the engine rpm doesn't go any higher or the tires start to spin that is "brake stall". (DO NOT TRY THIS! THIS MEASUREMENT IS MEANINGLESS AND POTENTIALLY DANGEROUS TO YOU, THE TRANSMISSION AND THE TORQUE CONVERTER!) "Flash stall" is when you, from a dead stop, press the gas pedal to wide open throttle (wot). Watch your tach needle, you will see the needle jump to a certain rpm, that is "flash stall". A drag racing-style trans brake will give you closer to the true stall speed of a torque converter

Thank you Gerrit. The more I hear, listen and read the more knowledge I will have.

Waldo Fourie

Is it then correct that "stall" as Waldo described, can then be termed as "lock up", seeing that the input shaft and impeller are turning at the same speed?

Gert

GJM wrote:Is it then correct that "stall" as Waldo described, can then be termed as "lock up", seeing that the input shaft and impeller are turning at the same speed?

Gert

No. I would rather describe the "stall" as the maximum rpm difference between TC impeller and turbine. The lower the stall the less acceleration but less heat from TC and easier "lock up" at lower speed and rpm.