Torque converter lockup

[Marko4558]

Hi all,

Just wondered/hoping someone else has come across this issue and has some idea of how to remedy it!

My 99 2.5 diesel auto is having a strange intermittent problem with TC lockup. It seems to work perfectly fine when cold and on short journeys. Take it a bit further (20 miles or so) and it just stops working. The van sits in 4th and will not lockup. I leave it overnight and suddenly seems to work again. It’s baffling me and I hope there’s some kind of explanation or solution that’s obvious and I’m missing. I suspect it’s to do with heat and it is worse on and more obvious on hot days. ATF is correct level, red and not smelly.

Thanks

Mark

[g8dhe]

How do you tell when its locked up or not ?

[gilly99]

eh? you mean the torque converter is slipping excessively?, or dropping down a gear?... under load, especially when engine is hot?

[Marko4558]

Perhaps I’m mistaken with my terminology, apologies, it shifts up as normal, then once in 4th and around 40mph, there is an additional ‘gear shift’ which I always presumed was the lockup kicking in and behaving like a top gear. Cruises around 60mph at 2k rpm. When it heats up I lose this and it’s like it wants to go but it won’t and then it’s as many describe where it feels as if it’s sitting a gear too low.

[g8dhe]

Anything to do with the autobox other than a change of the ATF really requires a suitable autobox company to look at, otherwise its change things and hope as without the test gear and facilities its going to be very difficult to know. In both of my vehicles identifying the point of TC Lockup takes some effort its always been very smooth. The manual for the gearbox is available on my website http://www.g8dhe.net/bongo_images/Gearbox/RC4AEL.pdf

[Marko4558]

I feared as much thanks for your help

[gilly99]

Ah, yes 60mph at 2000rpm sounds about right in 4th. You absolutely sure it's a gearbox / TC issue? Have you had any dash warning lights on? eg Glow plug warning light flashing or maybe Hold light? Could maybe be limp mode from ECU triggered by some sensor issue - that type of fault usually kicks in after a few miles. You'd have noticeable loss of power throughout the gearbox range though, not just top gear.

[Marko4558]

It does seem to have gone back to normal (touch wood) now the weather has cooled Down a bit. I’ve done a number of runs in the last few days and the issue hasn’t appeared. I wonder if it’s the temperature affecting something etc? Heat seems to be the trigger. I have no warning lights, no other issue at all and the power seems
Fine throughout the range! I have noticed the scavenger fan never seems
To come
On but that’s a whole different can of worms from
A few reads of posts on here!

[Bob]

Maybe worth considering an oil cooler on the transmission.

[g8dhe]

The scavenger fan will only come on when your stationery or very slow, the undertray funnels air thru the engine bay when moving, so you will only find the fan comes on when its hot and stationery to keep the engine bay and seats cool

[Marko4558]

Excellent suggestions folks thankyou

[Hazzobongo]

I have the same Bongo 2.5 98 model with roughly 70k miles on it, it changes to 2nd at about 10mph then the next noticeable change is at 30 and 40mph and then again at 55-60 which seems like overdrive and will cruise at 60-70 all day long on a long enough road, in Winter when its cold and till the motor is at running temp it'll hang onto gears longer so I don't think whats happening to yours is due to the heat or ambient outside temps unless its freezing outside.

Could need a tranny oil change, think its recommended around 70k miles for most vehicles.

[Marko4558]

Im toying with the idea of dropping the fluid and doing the filter etc etc so i will keep you’s all posted with any changes/improvements next onto the rust!

[Hazzobongo]

I'm thinking of doing this one soon but not dropping the sump or messing with the dipstick tube even though I've got a pump.

I'm pretty sure the system on these is the same as my old hilux surf with two pipes going to the radiator, one pumps it in and the other is a return and on the hilux it was a matter of putting the return pipe into a bucket of clean new tranny fluid and the other into another bucket and running the motor, when the clean fluid comes into the dirty bucket you switch off and re-connect the pipework then top up whatever is needed.

I did the surf on my own on the street outside the house, first job is to find which pipe is pumping the fluid, obviously with the Bongo you'll need someone to eyeball the pipe you take off.

I mentioned this before here years ago but got no response as to why or why not but I don't see it being any different to scores of diesels that use the bottom of the rad to cool the tranny oil. On the hilux it was a bone of contention on their forum thats what caused so many of them to overheat and blow the head, so I also rigged up a separate oil cooler to help mine out.

[Marko4558]

Update, I changed the fluid and cleaned out the filter. I did post elsewhere on here about the nightmare I had getting the sump to seal properly but finally got there in the end after having to hammer it back into flat. So now I get the same issue from time to time but for some reason, pulling over, turning the engine off and back on seems to fix it. It’s as if it’s resetting something somewhere somehow needs reminding to behave!