Wanting knowledge on torque converters ? Curiousity stricken.

[Timberking]

Ok, so I'v been working on my loader here lately trying to address some various problems i'v been putting off. After posting some questions relating to my issues at hand a couple gentlemen suggested looking into my torque converter. Now I'm not saying there is anything wrong with mine and neither am I denying there is, that's neither here nor there to this particular thread. I am more after some general knowledge about '' thee '' torque converter in general.

I believe I have a general theory of how a torque converter works, but I want to know exactly the purpose of each component.
Lets just say if I was a cat my nine lives would have ended along time ago as I am a very curious person.

My main interest would really be in how does a torque converter fail ?!?
I'm sure each and its own has its own weak points in design, but from my understanding theres not much in one to really fail
The propeller(apart of toque housing) thrusts hydro fluid against the turbine (causing rotation much like a pin wheel being blown in the wind) after passing through a stater and returns there after in an never ending cycle. I also assume the torque locks up directly by a clutch once reached a certain RPM.

What makes the clutch lock up ?
A certain pressure point within ?
The revolution speed it's self ?

Why is the torque converter pressure regulated ?
For proper flow as a coolant purpose or a lockout purpose?

Forgive me if this has been talked about many times again, new to the forum and still learning to search correctly.
You would be surprised to know how many people know nothing of a torque converter and how it works,
so any knowledge for me and them would be of great appreciation.
Thanks in advance.

Digging the forum by the way, there is some really knowledgeable people here, I am sure to learn alot.

 

[D6 Merv]

2 main causes of failure are No one changing oil and filters and screens :beatsme
Guy in the seat roasting it. oil breaks down with heat and looses all its lubrication propertys.
converter has 3 main elements, plus the housing. impeller driven by engine. turbine connected to output shaft. and stator which directs the energy imparted from the impeller to the turbine back to the impeller which is what gives you the more 'push'
torque converters typically raise the input torque supplied by the engine anywhere from 2 to 3 times. Even as much as 5 times on some converters; ie most allis chalmers ones.
the downside is a loss in fuel efficiency. Also converters do not lockup unless they have a lockup clutch fitted. this effectively locks the engine flywheel to the turbine to give direct drive, bypassing the converter.

 

[Timberking]

D6 Merv>
This is exactly the kind of info I'm after.
So not all torque converters have a lockout clutch ?!? This is why I posted because I assumed they all did..

And what exactly fails or wears by not changing the oil and so On, the turbine blades themselves, or the viscosity
break down of the oil ?

 

[D6 Merv]

the bearings wear or fail mate; then things rub together and make metal; causing heartache stress and large amounts of dollar bills to evaporate; as well as sending men to drink and ruination :beatsme
converters are one place where abit of preventative maintence can save you a lot of money. Along with having someone intelligent in the seat and not a mushroom.
Nothing helps to focus operators and/or owners ! thoughts more than the thought of having to fix it or pay for it yourself :notworthy

 

[madozer]

D6 Merv,

Thanks for the info that is so well put. So what does a good maintenance schedule entail for a D6 dozer for example? How often or after how many hours must you change out the engine oil and filter? The transmission oil and filter? Hydraulic oil, etc? What else should the operator be aware of, apart from following the schedule to the letter? Do the schedules vary from D6 to D7, etc?

Madozer.

the bearings wear or fail mate; then things rub together and make metal; causing heartache stress and large amounts of dollar bills to evaporate; as well as sending men to drink and ruination :beatsme
converters are one place where abit of preventative maintence can save you a lot of money. Along with having someone intelligent in the seat and not a mushroom.
Nothing helps to focus operators and/or owners ! thoughts more than the thought of having to fix it or pay for it yourself :notworthy

 

[D6 Merv]

most cat maintence schedules are similar. My D6 is like this
engine oil and filters every 250 hrs. fuel filters 500 hrs.
trans filters and screens 250 hrs, oil every 1000hrs
hyds. filters every 500 hrs, oil every 1000hrs
final drives oil every 1000hrs
the 250 hrs intervals make for easy intervals to remember; oh and you usually have to drive a grease gun for abit each day too; quite amazing all the people who can tell you they can drive a $250k plus machine but are incapable of driving a $100 grease gun :beatsme

 

[D6 Merv]

cat and most equipment manufacturers have operations and maintence manuels outlining all the maintence points and intervals for each machine

 

[Nige]

Rather than go deep into it, what machine do you have..? I assume it's a dozer because you are posting in the dozer section.

A couple of comments about torque converter failures.
The most common failure mode is failure of the roating seals inside the converter. The oil that eventually finds it way into the cavity containing the impeller, stator, and turbine gets into the "guts" of the converter via passages in the centre shaft. The passages have seals at both ends to stop the oil falling out. The most common cause of seal failure is the converter being "cooked" as Merv commented above.
The other failure mode is bearings and that is usually (but not always) related to poor maintenance and the quality of the oil that has been lubricating them.
Other than that they are generally pretty reliable so long as the oil and filter is changed at the appropriate intervals.

Very few dozer converters have lockup clutches. I think some of the larger Komatsu models do but I am not exactly sure which ones. There is really no point in having lockup on a dozer unless it's being used for 200yd pushes all the time.

 

[Delmer]

FTR, this regards a 2,000 hr, pristine, Case 450C that has loss of power, smoke and higher torque converter temperature at about the same time.

 

[tctractors]

A lot of converters do have sprag clutch bearings in them to cause lock up under driven conditions.
tctractors

 

[Bob/Ont]

Does the engine lug way down lower under load since this happened? Will the machine roll down a grade as freely as it did before?
Later Bob

FTR, this regards a 2,000 hr, pristine, Case 450C that has loss of power, smoke and higher torque converter temperature at about the same time.

 

[Timberking]

Bob/Ont > It does lug down when under load but will not turn(spin) the tracks when up against a stump or somehting similar,It just stops with the engine bogged down., it will roll down a hill as it always has, the engine holds it back as the machine draws on the engine. But if the engine is shut off it fust takes off freely.

Nige > my machine is a Case 450 track loader/dozer. From my understanding the tractor itself is the same as the dozer, just with a dozer blade instead of bucket, so i always post in the dozer forum as there is more info there than what i have found under track loader. From the repair manual i do not see any clutch packs within my converter, so i believe you are right. But that brings several other questions to my mind.

If there is no clutch assembly in such torque converter, what causes one to slip ??

 

[Nige]

All torque converters slip by design, otherwise when you engage gear you would stall the engine. The fact that there is only a film of oil and no mechanical coupling between the impeller and turbine wheels in "converter drive" means that the turbine wheel is always spinning slightly slower than the impeller wheel. Even if you have the engine at full RPM with the transmission in neutral this will still be the case.

For a torque converter with a lockup clutch the clutch locks up under certain conditions to give direct drive, generally when the machine is on the move. However if you were up against something "heavy and unyielding" your converter would be in "converter drive" as above.

 

[Delmer]

If there is no clutch assembly in such torque converter, what causes one to slip ?? [/B]

Like Nige said, there's no mechanical coupling, so the better question is what causes it to turn? and that's the fluid, I don't know how, and it doesn't really matter, the important point is that slippage is very useful because the torque converter uses that slip to increase the torque when it's slipping. But it doesn't double the torque at half the speed because it also produces heat, and more heat at more "slippage".

If you meant "what causes a torque converter to fail by slipping?", I don't know if they do that or not, but I believe as the oil gets hotter/thinner the characteristics of the torque converter change (when it's bitter cold there's more drag at low speed, more slip when hot, right?) but that would let the engine speed up, not lug the engine down with lower torque.

 

[Outasite]

Sounds like the overrun sprag in the stator may be seized.That will make the converter into a fluid coupling,no Tork amp,and build a lot of heat.

 

[Nige]

Sounds like the overrun sprag in the stator may be seized.That will make the converter into a fluid coupling,no Tork amp,and build a lot of heat.

If this particular tractor has a sprag clutch in the converter between the stator and the shaft, a failure of that clutch (thus allowing the stator to spin instead of being fixed on the shaft) would cause the engine to stall every time the transmission was put into gear.

 

[Scrub Puller]

Yair . . . Interesting discussion.

In the 1950's when Converters and powershift became available there was some opposition to the technology because the machines could not be push started . . . so much so that when Allis Chalmers belatedly bought out their power-shift one of the touted features was that they had a sprag clutch and could be push started in reverse.

Cheers.

 

[Plant Fitter]

Yair . . . Interesting discussion.

In the 1950's when Converters and powershift became available there was some opposition to the technology because the machines could not be push started . . . so much so that when Allis Chalmers belatedly bought out their power-shift one of the touted features was that they had a sprag clutch and could be push started in reverse.

Cheers.

Do you know if it actually worked?

With the engine not running, there would be no transmission pressure. Therefore no clutch packs would be engaged even if you had the lever in reverse.

Even if reverse was engaged, the 'reversing' is achieved inside the transmission. The torque converter still turns the same direction whether the transmission is in forward, reverse, or neutral.

So how did a sprag clutch in the torque converter help with push starting?

 

[Scrub Puller]

Yair . . . Plant Fitter.

Do you know if it actually worked?

We were lumbered with the first three powershift twenty ones in the country and that was one thing on them that did work.

I'm unsure of the actual set up but I remember a ramp and roller set up in there some where (probably on the bottom shaft) and assume it drove a charge pump.

The transmission was a three shaft two speed. The side to side movement of the lever selected speed and direction and the back and forth movement engaged a modulating clutch between the engine and converter.

I seem to remember it took twenty or thirty yards to start, gear-lever in first reverse and then flick it back to engage the modulating clutch.


Cheers.

 

[Bob/Ont]

Timberking if the torque stall speed is half of spec/ say 900 instead of 2000 the stator might have broken loose from the ground sleeve. If that happens the stator will not redirect the oil out of the turbine and it will hit the impeller head on and slow it down. That will over load the engine and give no driving torque.
Later Bob

Bob/Ont > It does lug down when under load but will not turn(spin) the tracks when up against a stump or somehting similar,It just stops with the engine bogged down., it will roll down a hill as it always has, the engine holds it back as the machine draws on the engine. But if the engine is shut off it fust takes off freely.

Nige > my machine is a Case 450 track loader/dozer. From my understanding the tractor itself is the same as the dozer, just with a dozer blade instead of bucket, so i always post in the dozer forum as there is more info there than what i have found under track loader. From the repair manual i do not see any clutch packs within my converter, so i believe you are right. But that brings several other questions to my mind.

If there is no clutch assembly in such torque converter, what causes one to slip ??