407SW AL4 GB - Loud THUD changing from 1st to 2nd gear !!

[mask]

Gents, this is my 1st post here !!

Need some advise on my 2005 407SW 2.0L petrol AL4 gb. When accelerating from standstill, "sometimes" there is a loud THUD felt when changing from 1st to 2nd gear.

Have read somewhere about the EV (electrovalve - EVM, EVLU, EV1, EV2, EV3, EV4, EV5 & EV6) could be the reason for the above

If it is so, can somebody explain which EV is for the 1st & 2nd gear ?? is replacing any one of the EV require an ATF drain ?

Thanks..

[seroyen]

Hello there!

This is my 1st post here too.

My ride's a Citroen C5 Mk I (2004) and I suppose I have the same transmission as you (AL4).

I've also had this problem recently at random intervals. The first time it occurred the car has been in moderate traffic in the morning for about 30 minutes.

Brought it to the dealer and they changed all the electrovalves which you have mentioned (EVM, EVLU, EV1-6). I'm not sure which of the electrovalves from EV1-6 are used for changing from 1st to 2nd though. Checked on some other forums and there seems to be problem with the original EVM and EVLU electrovalves.

Sad to say, the problem still appears after the above repairs and dealer has suggested for a transmission replacement (which is very costly). I chose not to go ahead with the replacement.

I suspect it's got something to do with the hydraulic valve block. Is the loud thud occurring after a delayed gear change? If so, my guess is one of the valves is blocked (probably caused by varnish build up?)

My interpretation of my AL4 behaviour:

1st gear drive, until RPM for 2nd gear is reached -> 1st gear disengaged -> Engine rev increases during delay -> 2nd gear engages suddenly and THUD, car jerks violently

If you switch to manual mode, are you experiencing a delayed change for 1st to 2nd as opposed to 2nd to 3rd or 3rd to 2nd?

Let me know if your dealer is able to solve it. Hope to hear from you soon

[CitroJim]

Welcome to the forum both seroyan and mask.

Sadly I know little about the AL4 and the following is based on my knowledge of the AL4's big brother, the 4HP20, which i do know a little about and works on much the same principles...

Gear changing is acheievd by operating electrovales with modulated signals from the ECU which slowly engages and disengages brakes and clutches appropriate to the gear being changed. It does this by slowing increasing feed pressure to those to be engaged and slowly draining pressure away from those being released to ensure a smooth change. The electrovalves are not the whole story as each electrovalve works in conjunction with a pair of slide valves in the valve block. One to permit operation and one to hold the clutch/brake operated. These slide valves depend on the correct hydraulic pressure to operate correctly.

The problem you are experiencing can be caused by faulty electrovalves or it can equally be caused by a problem in the valve block and the slide valves relating to the clutch/brake in question. Often the problem with a slide valve is a broken preload spring.

Equally, it can be caused by low or improperly regulated main hydraulic pressure in the gearbox.

AL4s are known for valve block problems. It accessible under the big tin cover but the fluid must be drained to gain access.

Sadly, I cannot tell what electrovalve does what as my AL4 documentation gives no indication and is silent on all valve block details. In contrast, the 4HP20 documentation gives all this detail, including hydraulic diagrams.

In any case, the first task in diagnosing any AL4 problem should be a fluid change. Drain and refill only with Esso/Mobil LT71141 following the very precise instructions here.

Have you had any diagnostics carried out to determine if the ECUs have any stored fault codes in them?

Sorry for the vague reply to this thread.

[seroyen]

Thanks for the reply CitroJim.

Your explanation of the basic operating mechanism of the valve block is certainly very helpful in the diagnosis.

I haven't heard from the local dealer about any fault codes detected or stored. They approached the gearbox problem based on my description, because this specific behaviour could not be deliberately replicated. However, I do believe there is a higher probability of its occurrence if I stress it a bit harder (i.e. more throttle). Therefore I'm adapting to a more gentle and slow style of driving now in fear.

I am too very particular about the type of fluid used in the gearbox. In order to change the electrovalves, the dealer had to drain the fluid and replace with new fluid. On the service invoice it was stated 'Mobil Oil 1L x 4' and nothing else. I believe that is the wrong kind of fluid being used for this gearbox, but I just could not argue with the dealer because of their claims that the gearbox has been running on this same fluid for the last 80000kms without problems. Would love to purchase the specific fluid 9736.22 and do the changing myself. Unfortunately, I am at a loss of where to source for it locally. Right now, gear change slightly jerky, and sometimes comes with very soft knock corresponding to throttle input. Could it be a wrong ATF level?

Based on your suggestion of a faulty valve/broken preload spring, is repair/replacement possible for the above parts only? Or do I have to change the whole hydraulic valve block?

Thanks again for your input!

[CitroJim]

Valve blocks can be repaired/rebuilt Saroyan but it is a very involved job requiring clinical conditions, the drawings and great attention to detail. As a consequence, the block is usually replaced as a unit. I'm not sure that individual components, electrovalves excepted, are even available as spares. Valve blocks are very complex and full of small springs that like to fly off in all directions!

Sometimes they appear on eBay but unless they are for your model and brand-new then I'd steer well clear.

One good idea is to speak, if one is nearby, to an automatic transmission specialist. A good one in the UK can be found at www.automaticchoice.com They have offices in other countries as well as the UK and are very helpful. They can also supply spares.

The right fluid is vital. Your dealer may well be using Dexron II or III and that is far from suitable and having known 4HP20s mis-filled with Dexron, that might account for the problem. Dexron, despite what the advertising blurb may say, is very, very different from Esso/Mobil LT71141 and is NOT compatible. You can tell if the 'box has been mis-filled as Dexron is red and of thin consistency and LT is amber and more sticky and thick, like new engine oil. Drip out a small sample and look at it. LT also smells awful, like cat's pee whereas Dex has no real smell.

I'm assuming you're not in the UK as here the proper stuff is easily available, either from a Peugeot/Citroen dealer under the part number you have or from good oil dealers. Alternatively, go to a Mercedes dealer as the Mercedes V Class uses the same basic 'box, as does the V6 Renault Espace and some Alfas and Fiats. They may have the correct fluid.

[myglaren]

^seroyen is in Singapore Jim.

[CitroJim]

^seroyen is in Singapore Jim.

Should have gone to Specsavers

[OzRX4]

Bit rushed here this morning guys. Welcome to the 2 newbies too.
The AL4 is a sister box to the DPO in Renaults. There's problems with the box in all French brands for some reason.
Have the car diagnosed some where with a Lexia diag computer. Should find, IMO that it's the pressure solenoid. Whether or not they are talking about the same issue I am not sure. The solenoid replacement fixed a similar problem in our son's 2003 Clio. It's always better to start replacing small items before going for a several thousand pound replacement.
Even call a Renault garage/specialist and ask their opinion and what they'd do.

[seroyen]

Hello all,

Have decided to continue driving with the problem of the box and 2000km later, I realize that this problem appears less with lighter acceleration and in most instances, it does not appear at all if you drive it really gently. Although that was what I did, it was not normal to accelerate (in most cases) slower than a fully loaded truck and having others overtake you in an annoying fashion.

If the problem was to appear, it would be when the car has been in traffic for approximately 30 minutes. Torque converter then refuses to lock up in all gears, and the horrible jerk from 1st to 2nd comes again.

I used Lexia 3 today on my laptop and took it for a test ride in moderate traffic and viola! I think I found the culprit. The temperature gauge read -20 degrees celcius in warm and wet weather in Singapore (Ambient temperature 29 degrees celcius). The mode of operation was changed from 'Economy law' to 'Unlocked law' and reference to the AL4 presentation manual indicated that the unlocked law is used for low temperature operation.

Will visit the dealer and get the temperature sensor replaced, and update again. Hopefully, this would mark the end of my woes with AL4. I almost swore not to touch any car with this box again.

By the way, thank you all for the great recommendations!

[CitroJim]

Good diagnostics

Was that the gearbox temperature sensor giving the very low reading?

[seroyen]

Yes CitroJim, so low where the temperature stayed negative with a range of -4 and -28 degrees celcius. Waited for about half an hour with the engine stopped, hoping that the temperature gauge will go back to normal after the oil cools down. Unfortunately, laptop battery died on me.

Will try again tomorrow.

[CitroJim]

I guess you've never experienced temperatures like that in Singapore Seroyan! That's seriously cold and no wonder the gearbox ECU is confused...

[myglaren]

Move to Alaska and it will be fine

[dieselnutjob]

find out which pins on the transmission ECU connect to the temperature sensor, disconnect the ECU connector and measure the sensor resistor at that point, as it's fed to the ECU.
Then find the connector that's nearest to the sensor and measure it there as well.
You might have a faulty sensor but equally you could have a wiring fault, loose connection or an ECU fault.
You don't want to waste time and money changing the sensor unless it's cheap and easy to change.

[seroyen]

Hello all,

Just got my car back from the dealer today with the AL4 wiring harness replaced. Technicians were puzzled when I talked about replacing the temperature sensor (located on the harness), so I simply requested them to change the harness away without further explanation.

Before this, I have read a little on thermistors, and found that failure can cause intermittent connection problems or internal breakdown and therefore explains why the temperature just alternated between -40 deg C and 96 deg C. No other values were observed.

Gave the box a few hard push today outside the service centre to warm it up and ensure the problem does not surface again. Thank goodness it is gone.

Thank you all for your help! I am once again a happy french car owner.