TrailBrake

Hi all,

As some of you may have seen in another thread on SST issues (https://www.evolutionm.net/forums/09...ions-help.html) my car has a transmission judder (strong jerking) from a full stop when using more than 1/3 throttle. It almost feels like wheel hop, but the front end of the car itself seems to shudder more than the wheels themselves.

From a rolling start or at less than 1/3 throttle, there is no jerking. The transmission does not exhibit any other issues. My car is an '09 and the mileage is 49,000km. The tranny fluid has been changed twice as has the filter, and the fluid level is correct, so all the basics have been looked at.

I did some testing last Sunday morning while traffic was quiet, I tried launching the car at 1/3 to 1/2 throttle in manual, sport mode, ASC off, with different ACD settings. Tarmac jerked the worst, followed by gravel, and snow showed little or no jerking at all. This was in a straight line, on a level and dry road with good tires tires on all 4 corners, so traction should not have been an issue.

From what I have experienced in my car, does it appear I have a transmission, or transfer case/ACD issue?

From reading what I could on this board, and from other sources, I have a crude idea of the differences in what the ACD does in tarmac, gravel and snow modes, but I was wondering if anyone had any idea why snow mode in a straight line would show the least amount of jerking vs tarmac or gravel mode?

Would this have to do with the speed and pressure of locking of the ACD?

Any input would be greatly appreciated?


Thanks.

Bom's Evo

iTrader: (14)

Now, your clutch doesn't slip? And it jerks when launching on anything, but snow mode. What does it do when you go through 2nd and 6th?

Are you on a stock tune? and do you have mods? suspension?

TrailBrake

Thanks for the reply, but I think you confused what I had quoted from sirchumpalot.

My problems are confined to jerking from a standing start. It shifts from 2nd to 6th without issue and there is no clutch chatter at idle.

I am on the stock tune, and the only mods are to the brakes, and a set of Eibach Pro Kit springs. The jerking has existed since I bought the car (and it was 100% stock), but is more pronounced once the transmission warms up, and in warmer weather. On a 20C day, when I start my morning commute, there is no jerking. By the time I get to work 20 mins later, the jerking has begun.

I bought the car in the dead of winter, and the jerking was virtually non-existent in the cold.

The jerking seems to occur around 2000rpm in 1st gear, only when I use 1/3 or more throttle. If I use less throttle, there is no jerk.

crankIT

iTrader: (1)

If I were to guess I would say it is a problem with the ACD pump going (I just had to get mine replaced in warranty). If you refer to this post it says that tarmac provides the most acd clutch pressure while snow mode the least... which may explain the varying severity of the jerking.

https://www.evolutionm.net/forums/ev...everybody.html


If you live in a climate where they salt the roads in the winter, it just eats up the acd pump. Mine went after two canadian winters and many other evo & ralliarts have gone bad in similar conditions (to the point where its almost a certainty after a few years)

Dbzguy

Is it harmful to drive in snow mode while on the street?

Veronica

iTrader: (2)

yes. ACD Tarmac mode exists because without the additional 'slippage' to the front - the front o/b wheel will 'hop' or skip in a tight turn on drive tarmac (the front wheels turn at different rotational velocities than the rears). This puts stress on the suspension.

The AWD needs less so in snow - the snow lets the front o/b wheel 'skid' a wee bit but keeps more torque available to the front axles (which is why you want 4wl 'locking' of the front and rear axles in 'snow mode').

To put it simply...
The ACD function is to allow the front wheels to rotate at a different rate than the rears when in a turn and to allow them to all rotate at the same rate when going straight...

(Which is why you can't drive a truck with 4wd on dry pavement too)

TrailBrake

Thanks for the replies. I will look in to the ACD pump. Are there any codes generated when it starts to go?

For now, snow mode will suffice for straight-line launches when I need to merge into traffic with heavier throttle. The rest of the time I will leave it tarmac mode for dry roads.

I had a Jeep Cherokee back in the day, so fully understand why 4WD in cornering situations on dry surfaces is less than ideal.

Veronica

iTrader: (2)

^you can without a problem for your situation, but there is no 'advantage' (for anyone else reading this post and getting ideas...)