Torque Convertor lock up issue perhaps?

Hi All,

I've been looking at this post http://www.landyzone.co.uk/lz/f10/p38-2-5-auto-box-puzzler-132064.html as I try and diagnose a recent problem with my 1998 2.5 DSE. (150k miles)

the auto gearbox appears quite happy until I get to cruising speed. At 70mph I'm revving at just a little over 2500rpm and then the rev counter for no apparent reason jumps to (around) 2750rpm. Similar things happen at lower revs when over 50mph although I haven't noted the revs for that. This jump in revs goes back and fourth, between the two rev speeds (It maintains a steady 70mph), kind of 'hunting' for something it's not quite finding. Sometimes it is doing this almost incessantly. Other times just occasionally. Putting it into 3rd and then back to 4th makes no difference. It's clearly in 4th when cruising.

Is the thing it's 'hunting' for torque converter 'lock-up' which is beginning to not happen? Topped the ATF fluid up yesterday, was a little low but didn't make any difference. I could change the fluid and filter. Should that be my next step, or is that just wishful thinking?! Someone said I should look at the speed sensor??

I do have a faultmate which I haven't had to chance to plug in yet re: this.

Thanks for any thoughts...

You could check the connections from the ECU to the box, you might also want to check the transfer box ECU does not smell of burning. It sounds like the torque convertor lock up is cutting in and out.
An oil and filter change would not hurt, should be done every 24K miles. You could also try some Lucas Transmission Fix.

THX Datatek. I'll check those things and get back with some results...

Try your Faultmate on the transfer box ECU and also see if you can shift between Hi & Lo range.

revmarkp said:

THX Datatek. I'll check those things and get back with some results...

Click to expand...

Pay particular attention to pins 2 and 38 Speed sensor inputs. And pin 20 speed sensor shield connection.

Thanks you guys.

Fault mate says, Gearbox ECU no faults (how's that for a first!).

I'm having second thoughts now, triggered by the fact that when I was backing back, full lock the other day, my mate noted that my back wheels were 'scrabbling' over some gravel. it's like your diff is locked he said, of course I have no diff lock... hmmm...

Just done the viscous coupling wheel test (as per the videos that come up top of google) on both a front and a back wheel. Nothing moves, gave it fair force with a 2 foot t bar.

just removed the front prop shaft and have tried to rotate it when off the front diff, again leant on it with an 18" bar stuck in the prop UJ, nothing moving.

So that's looking like a jiggered VC perhaps?

Rave says this (44/20):
To aid performance and driveability in the high range
economy mode, the EAT ECU has three adaptive shift
and lock-up maps. These maps delay upshifts and
torque converter lock-up similar to the sport mode if
the inputs from the engine indicate:
• A sustained high load on the engine, such as
occurs when the vehicle is ascending a steep
gradient or towing a trailer.

I'm wondering if a jiggered VC is creating what to the EAT ECU feels like a 'sustained high load' and the torque convertor lock up is switching in and out as the wheels strain because of lack of proper differential??

I guess if this theory is correct the lack of front prop shaft should allow the torque convertor to lock up without problem?

Test drive with front prop off (carefully).

no problem with torque convertor popping in and out of lock-up now!

I'm now assuming the viscous coupling is no good, unless anyone else has other thoughts...

you can get serious wind up in the transmission with seized vc ,which can sometiimes be unnoticeable or can feel like the brakes ben momentarily applied which would bring the revs down ,if vc is seized you can drive around with front prop off while you get another ,obviously all the torque is thruogh one diff but it will take it okay as long as you drive accordingly

Thanks James. I'm thinking that the transmission 'wind up' was putting just enough strain on the gearbox to stop it settling into proper lock up of the torque convertor. That was my only symptom of a problem - that and the tyres scrabbling...

revmarkp said:

Thanks James. I'm thinking that the transmission 'wind up' was putting just enough strain on the gearbox to stop it settling into proper lock up of the torque convertor. That was my only symptom of a problem - that and the tyres scrabbling...

Click to expand...

Seized VCU, lucky you have found it before it exploded a diff I test mine every service.

Sorry for long delay feeding back on this topic.

As per past disucssion I did change (just) the VC. Swapped out from a 2nd hand transfer box I purchased. I DO think the VC was seized, but (sadly) this hasn't sorted the problem with the torque convertor still not settling properly into to lock-up. Seemed OK for a few miles, then same problem.

After not using the P38 for most of December, took it for run this morning and didn't have any problem. This has bolstered my opinion that next thing to try is change ATF and filter. Perhaps problem reveals itself when ATF gets hotter?

So, have changed fluid/filter today; fluid looked pretty murky and thin, so hoping that might help.

revmarkp said:

Sorry for long delay feeding back on this topic.

As per past disucssion I did change (just) the VC. Swapped out from a 2nd hand transfer box I purchased. I DO think the VC was seized, but (sadly) this hasn't sorted the problem with the torque convertor still not settling properly into to lock-up. Seemed OK for a few miles, then same problem.

After not using the P38 for most of December, took it for run this morning and didn't have any problem. This has bolstered my opinion that next thing to try is change ATF and filter. Perhaps problem reveals itself when ATF gets hotter?

So, have changed fluid/filter today; fluid looked pretty murky and thin, so hoping that might help.

Click to expand...

Hope you followed the correct fill procedure?

Hope I followed correct refill procedure too Datatek!!

Things of note on my refill were:
1. filling is via the dipstick tube on my '98 DSE
2. don't over fill - only got about 4.5-5 litres out of a simple drain (without flushing things etc)
3. move shift lever slowly through the gears when checking level, then return to neutral
4. Item 3. should be done when ATF is cold and engine running

Hope I didn't miss anything fundamental!

I plan to do the drain and refill again in couple of weeks to change a higher percentage of the original fluid. (11 litres in there in total I think).

revmarkp said:

Hope I followed correct refill procedure too Datatek!!

Things of note on my refill were:
1. filling is via the dipstick tube on my '98 DSE
2. don't over fill - only got about 4.5-5 litres out of a simple drain (without flushing things etc)
3. move shift lever slowly through the gears when checking level, then return to neutral
4. Item 3. should be done when ATF is cold and engine running

Hope I didn't miss anything fundamental!

I plan to do the drain and refill again in couple of weeks to change a higher percentage of the original fluid. (11 litres in there in total I think).

Click to expand...

17 pints 9.7 litres. But you will get just under five out when draining, so refill is four and a bit, run through gears then top up bit by bit.

Well I'm back again - sorry to say after 2nd gearbox oil change following correct procedure etc i still have the same problem.

I've posted a youtube video from my faultmates AVI captire of the bosch gearbox ECU:
http://www.youtube.com/watch?v=pKQwtchYFIk&feature=youtu.be

This shows the way the gearbox revs up and down when pulling steady (with v slight load perhaps?).

At steady 70mph (using cruise control) engine revs at 2592 rpm; all good until about 1.03 minutes into the film, then it jumps up to 2848 or 2816rpm. After 1.14minutes it's jumping back and forth frequently. In the past I have assumed it's losing torque lockup, but to be honest occasionally it's now doing it in lower gears and below 54mph, (when torgue convertor shouldn't be trying to lock anyhow - right?)

I note the output shaft speed stays steady which I assume should rule out the need to replace the sensor?

Could be electrical but 300 rpm is not a lot so I would guess something is slipping. Worth trying LUCAS Transmission fix, it worked on mine for 18 months.

I'm with Datatek, sounds like it is flaring ... this happens when the Valves in the block start sticking slightly and are slow to react in selcting the next gear clutch...

Lucas Transmission Fix, lubes up the sticky bits and allow the valves to slide in the bores better and with luck allows the gear changes to happen smoother and reduces flaring when it lets one clutch out and locks another one up....

OK guys. Thanks.

The excellant Worksop Motor Spares has a full range of Lucas (USA) products in stock so I'm just about to give the Tramsission Fix a go.

(This simple fix would seem to good to be true!)

revmarkp said:

OK guys. Thanks.

The excellant Worksop Motor Spares has a full range of Lucas (USA) products in stock so I'm just about to give the Tramsission Fix a go.

(This simple fix would seem to good to be true!)

Click to expand...

That's what I thought, but I got another 18 months before the box started acting up again. It's not an instant fix, took about 500 miles including a blast up the motorway before the box reverted to working correctly.

delayed reply as I wanted to get some miles done before reporting back.

Put in the Lucas Fix - btw it takes a while - very thick treacley stuff!

Done 700-800 miles now (mostly motoroway) and.... It's getting worse :-(

Resigning myself to a new gearbox, but even that isn't proving straightforward. Called an auto tranny specialist in Barnsley, who is advising I check the Airflow Meter, Turbo Waste Gate and EGR Valve, as they might cause my symptons - don't think he fancied the job really...

Ashcroft Transmissions similarly non committal about my diagnosis.

Just to reiterate my symptoms were/are:

Initially, gearbox shifting in and out of torque lockup (at least that was my guess), anyway the revs constantly jumping from 2550 to 2850 all the time, back and forth - when cruising on motorway at 70mph.

now more recently (perhaps since changing ATF and filter?) reluctance to shift into correct gear, high revving producing no change of gear. down-shifting too early. changes gear but then immediately changes back etc etc. Erratic or reluctant shifting in a nutshell.

Faultmate says no gearbox ECU faults; Speed sensor o/p via faultmate reads normal.

From further reading about how these boxes work it might be the governor???

Anyone recommend Rangy/P38 garage in Notts/Derby/S Yorks area to diagnose/fix?