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Hello !

I just registered here hoping someone can help me with this...

Recently the automatic transmission in my car started to act a bit strange.

When the engine is cold, everything works fine. After a few minutes driving, the problems start. It's a bit difficult to describe... and I guess my "car parts english" isnt so good !

When the car is stopped and on "D" gear, the engine runs smoothly, but it feels like there are intermittent little shocks, maybe every 1-2 seconds, like a clutch that alternates between on/off. Also when letting it on D and going forward, not touching the gas or the brakes, it runs smooth then bumps then smooth then bump, etc. It feels a bit like when a young driver encounters a manual transmission (and a clutch pedal) for the first time !... Also does this in reverse and all other positions except Neutral.

On Neutral the engine makes healthy sounds, doesn't "cough" or anything.

When I drive at a constant speed, no problem. But when I need more power, to accelerate or climb a hill, and I press the gas pedal, then the car doesn't accelerate, instead it shakes and bumps. When I floor it, it works again.

So it happens at low engine rpms when torque is needed.

From what I've seen on the net, it looks like slipping, but I'm not sure at all.

And here's my other problem... I'm French, here it's stickshift land... the car is a Renault Laguna V6 (from 1998) with an automatic transmission. The local mechanics have absolutely no idea how to fix an automatic. In fact the local guy probably knows less than me about automatic transmissions, and that's saying something !!! So that's why I'm here !

Transmission is a German ZF 4HP20, they put the same one in various european cars... I've got all the tech docs (thanks internet eh), service manual, etc. Although I have no intention of opening it up (yet).

The mechanic says it's the fuel injectors. The V6 engine sounds like it's in perfectly good shape though.

The car has 150.000 kms and the transmission was never serviced or touched in any way. Renault says "transmission oiled for life - no need for service". I'm starting to suspect this could eventually turn out to be marketing ***

I wanted to check the oil level, but of course, there is no dipstick. To check the level, I'd need to unscrew the inlet and oil overflow orifices, pour some oil, and check if some somes out throught the other hole, says the service manual...

There's an oil filter, too. It's about the last piece you get to when you open up the transmission and take all the parts out.

I am quite fond of this car and would regret to trash it...

So, if anyone can give me some advice, that would be very kind  

It's hard to tell exactly what the symptoms are from your description but it sounds like a engine related issue.

PS: I notice in the heading you say "transmission making strange noises" but you didn't describe any noise.  

Hm, I'll try to be more precise...

You know when an automatic car is stopped, foot on the brake, and you switch the lever from "N" to "D", you'll feel a little "bump" or shake as the clutches act, and you feel the engine sound change slightly as it has to work a little more in "D" due to losses in the converter. Same when you switch from D to N, "bump" again.

When my car is stopped, foot on the brake, it feels quite the same as if I was continuously switching the lever between D and N : bump - bump - bump, except I'm not touching the lever. It's not rythmic, rather irregular. With the lever on "N", the engine idles normally.

At speed is when it gets noisy, when I want to accelerate and the engine is at low rpms, the car shakes and makes some strange noises (like series of soft shocks and vibrations - BBRBRRRRB) then when it finally goes down a gear, it works normal again.  

really sounds like the transmission filter is dirty or it's really low on fluid....  

life of the transmission oil changes is a proper term...    if you only change the fluid once...  it will last the life of the transmission...   yep.. from brand new.. until the transmission is burned out..  life of the transmission..

i did see a different brand transmission section online..  for that transmission.. it shows a dipstick.. i think on page 21.. i wonder if the hole is just plugged..  instead of not being drilled...

peugeotAUTOBOX_ZF4_HP20_training.pdf

in hondas that have an in the case strainer as a filter.. they recommend that the fluid be changed 3 times.. with driving cycles between..  change your transmission fluid...  there has to be some way to get it out and to refill it...  

when the fluid level is low...  there are pressure regulator valves that will open and close as the fluid comes up in surges.. that might be what you are feeling as the transmission tries to build pressure and engage...

a fluid change is the first step...

there are a bunch of other things that could also cause the problem.. broken springs in the valve body.. or pump body..  those require significantly more work than just a fluid change...


i hope that i don't offend you with this joke..   .. as i usually get a really good laugh and you will probably really enjoy it..

i live in los angeles.. and we have the 99 cent only store chain here.. its a great place to shop.. when i got to to the can food wall... there was a lady examining a small can..   i said.. that's Escargot.. its a can of snails..  very tasty snails.. she quickly returned the can to the shelf.. saying that she is a vegetarian.. as she was walking away.. i ask her why she was not going to buy a few for the time when somebody asks the obvious question..  what.... i said.. you have non vegan friends over for dinner don't you..    have  you had them ask at least once ... Don't you have ANY meat in this place.. ?..  at that point.. you can present them with one of those cans...    ...

she was laughing so hard i though she was going to faint..  

i hope that you are not offended..  

It's very hard to diagnose over the internet but what you are describing sounds like it could be an intermittent engine miss. Is the trans shifting a little later and firmer than normal?  

I would have the catalytic converter checked being plugged, right mileage.