Torque converter taking a while to lock up properly

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fishsponge

fishsponge

New Member
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1,432
Location
Cambridgeshire, UK
My understanding is that between 50 and 54 mph, the torque converter is supposed to lock up, meaning the engine revs correspond directly to the speed of the wheels.

In other words, above 54 mph or so, pumping the accelerator pedal does not affect the revs of the engine, whereas below 50 mph it varies from between 1,000 and 3,000 (because the torque converter is not locked up).

I've not worked out the circumstances yet (i.e. whether it only does it when cold or whatever), but sometimes, the torque converter does lock up, but not perfectly.

For example, i gently accelerate from stationary to 70mph. When i get just above 50 mph, the revs decrease as the torque converter locks up. It sounds like it's changing into fifth gear (which, of course, I don't have).

Before it locks up, if I let go of the accelerator the revs drop to just above 1,000 (as they should). While going 70mph, if I let go of the accelerator the revs don't go below 2,500 or so (which is perfect).

However, sometimes, when I push down on the accelerator, despite the torque converter being locked, the revs increase before the vehicle has sped up accordingly.

Sometimes, however, it locks up perfectly and there is no "play" in it whatsoever.

Is this normal, or is something weird going on??

...and does anyone actually get what I'm trying to say?!?
 
Your correct 54mph it the torque converter lockup speed but only if your at a steady speed and not accelarating pass that ie. pedal to the metal 0 to 70mph the the converter will not lockup untill you level off at 70 or even higher.

If your travling at a steady 55mph with the TC locked and accelerate hard you will or should drop a gear or even go into 'kick down' something you don't mention.
So I can't see much wrong, does you kick down and change down work.
 
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If i accelerate quite hard past 54mph, then yes - the torque converter does not lock. When i then ease off the accelerator, it locks up and all is well. I know this is normal :)

If i'm travelling at 55mph and hit the accelerator hard, it does drop a gear as it needs to. I can also force it to do so by using the kick down "step" at the far end of the accelerator pedal reach.

This all works fine.

However, when travelling at a steady 55mph, and i ease the accelerator pedal down gently the revs increase despite the torque converter being locked.

This is quite hard to explain without being able to demonstrate it, actually.

So, when the torque converter is not locked and I'm not touching the accelerator pedal, the engine revs always drop to almost tickover. When the torque converter is locked and and I'm not touching the accelerator pedal, the engine revs stay high. This is normal and enables me to know when the torque converter is locked or not.

So... when it is definitely locked and I press on the accelerator (but not hard enough to warrant changing down a gear or unlocking), the engine revs still increase. When I let off the accelerator pedal again, they drop to where they were (2,500 or whatever).

Sometimes, however, it locks properly and when I put my foot down the revs don't change at all. This is presumably how it's supposed to operate.

Am i making sense?!? :D:confused::D:confused:
 
I know what you're on about mate... don't think its supposed to do it - i put it down to a 110k gearbox!

On the odd occasion when it happens to me (tends to be when it 'rolls' above 52mph rather than 'giving it some'!) i find selecting 3 then back to d cures it.

I'd be interested to know if yours does the same
 
my gearbox has done 148,000 miles now actually (assuming it's not been replaced, of course).

Next time it happens (probably tomorrow), i'll try changing into 3 and back to D again.

It's weird though... it's not that it doesn't lock, because it does. It's almost like it's locked, but is slipping, if you know what I mean.

There's definitely 4 audible changes (1 to 2, 2 to 3, 3 to 4 and 4 to locked-4), but even when in "locked-4" it's not perfectly locked. It is much more locked than it was (engine braking massively increased, revs not varying anywhere near as much), but there's definitely a significant amount of play in it.

Then on other occasions it locks perfectly and there's no play in it whatsoever!

Obviously, none of this is a major issue (hopefully!) - it just affects my fuel efficiency and wear on the engine more than i'd like!

What is the locking mechanism that's used? If a clutch was used to lock it up, for example, it's almost as if the clutch sometimes slips.

I suspect it's something more "on or off" than a clutch, but you never know...
 
Exactly the same symtoms mate, although mine is quite rare... for now!

I'm not sure of the exact mechanism other than it's oil pressure that locks it up (i was after trying to add an overdrive button but the ZF box can't do this), whether the pilot circuit is blocking/leaking or if the actual mechanical 'lock' is slipping i can only guess
 
OK, i've been reading up on this... info is quite hard to come by though.

My understanding is that there is indeed a clutch inside the torque converter. It's known as the "torque converter clutch". it is engaged by a "forceful" charge of transmission fluid. How it's disengaged, I'm not sure.

So... given that it seems to lockup flawlessly every time, I suspect the sensing of when to engage it is working fine.

I reckon either the clutch is slipping (unlikely because it works perfectly sometimes and clutch slippage doesn't come and go as far as I know) or the "forceful" charge of transmission fluid isn't coming through properly (and therefore the clutch isn't engaging properly).

How can I check the fluid level in the torque converter? Or is the lockup clutch in the actual gearbox? Or... is the whole lot actually inside the gearbox? If so, how do I check the gearbox fluid? Is that the long dipstick under the bonnet that looks like it's going back into the centre console?
 
but although that's the transmission fluid, is that also the fluid level inside the torque converter or is that a separate dipstick or drain hole somewhere?

Also, what should the transmission fluid look like?
 
Ah, ok...

so if this oil level is low, for example, not only will my gearbox be wearing down faster, but the "forceful" charge of fluid sent to engage the lock up clutch might not be happening and the torque converter might also be losing a lot of power because it's lacking the fluid it needs to transmit that power to the wheels... right?

What colour should the fluid be? How should it look? What sort of texture?

Also, presumably, I start the engine, put my foot on the brake, slid the gear lever into 1, 2, 3, 4, D and then P. Then turn the engine off, take my foot off the brake and then check the fluid, right?
 
OK, so this morning I did the following...

Pulled the transmission dipstick out and checked the level (wrong time, I know). It was 1 or 2mm above maximum.

Started the engine with gear lever in "P".
Put my foot on the brake and moved it to "1".
Waited for it to go into gear, then moved it to "2", then "3", then "D", then into N.

Obviously, while moving between "2" and "D" nothing happened, because the gearbox won't change into those gears unless it needs to.

I then pulled the dipstick out again and there was nothing on it.

Now, from what I understand of engine oil, for example, having started the engine all the oil gets flung around the engine and there is therefore none left in the sump for the dipstick to dip into. Surely this is the case with the transmission as well?

Anyway, I then set off for work. As usual, it failed to lockup properly when I hit 54mph.

It did lockup (the revs dropped, it sounded like 5th gear had been engaged), but there was a lot of play in it. If I put my foot down the revs increased by 800 or so (not so good). If I took my foot off the accelerator, they dropped to *just* under 2,000 (which is perfect).

I then moved the gear lever into "3" and back to "D". This forced the car to change into 3rd, then back to 4th and then to re-engage the lockup. It did re-engage the lockup, but there was still the same amount of play in it, so that made no difference.

I then left the gear lever in "D", forced a kickdown using the accelerator pedal, let go of the accelerator again, and when it changed back up into 4th, it locked together perfectly.

The next time it needed to lockup, it did so, but only partially engaged. It took 1-2 seconds to fully engage (almost like it was engaging slowly).

After that, it then locked and unlocked perfectly for the remainder of the journey.

Remember, too, my car has done just over 148,000 miles...
 
hi, i`m a total newb to landrovers and especially auto gearboxes. but i`ve done a lot of reading and now know it all:D.
with the oil in the auto box. if you check it after the car has been left. it should show high on the dipstick. if you then start the car and go through all the gears, the oil goes/fills up the tc and various hydraulic veins whatever. so the level should then be correct on the dipstick.
this is my understanding although it could be completey wrong.
hope this helps
 
"Now, from what I understand of engine oil, for example, having started the engine all the oil gets flung around the engine and there is therefore none left in the sump for the dipstick to dip into. Surely this is the case with the transmission as well?"

After the moving the selector through the various positions and with the engine still running remove the dip stick and the level should show between the two 'pips' on the stick ideally near the top one (max).
The first thing to do with auto gearbox troubles is change the fluid and filter.
You should also have engine oil showing on the engine dip stick even when the engine is hot..
 
thanks for that discool... engine oil is the obvious one, of course, but it's good to know more about the transmission dipstick.

given that after i'd been through the positions, there appeared to be no fluid on the dipstick, I think I need to top it up... given that it still looks like rather thin liquid with a hint of red, can i just top it up, or should i drain it first?
 
right, just checked the levels again...

engine cold, not running. last run 5 hours ago. Engine oil low, but not at minimum.

engine running (but still cold), been through the gear lever positions, back to "N", no transmission fluid showing on the dipstick whatsoever. None.

With the engine off, it shows just above maximum, but with the engine running, there's none present.

I guess, therefore, it needs topping up.
 
"Therefore, it needs topping up" so does, that could be your problem.
The next one is where has the fluid gone, the gearbox doesn't burn oil like a worn engine would, so you may have a leak check the oil cooler pipe connections at the gearbox an at the oil cooler infront of the rad and the pipes them selves.

Hopefully the problem will go away once u have toped up, so then you should be thinking of replacing the fluid & filiter, do u know when it was last changed Land Rover say in normal use every 24000miles.
 
no idea when any of this was last changed... i only bought the vehicle 2 months ago. It does have a partial service history, which i'll look through tonight. I think it was serviced 5-10 thousand miles ago, but I'll know for definite tonight. What that service contained though, i'll never know!

I think what i'll do is book it in soon for a basic service (including *all* fluids). That way, they can give it a general service and check all the fluids that wouldn't normally be checked.

I doubt I can afford a full service at the moment!

For tonight though, i'll top up the ATF and book it in for a basic service + fluids as soon as I can.

Sound sensible?
 
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