shudder/backlash in driveline

[rallygabe]

Car: 1999 C2 6spd, 158,000miles

Okay guys, need some thoughts:

Car runs terribly anyway, but I have been noticing more and more what I describe as "backlash" , or a kind of shudder from the driveline when going from coasting to on the gas and vice versa. It is very violent and obvious. feels the same on cruise control as well.

I am leaning towards engine mounts? Idle is extremely rough as well which adds up in my book.

[logray]

It's wonderful to see a fellow 1999 996 owner with so many miles.

Let's take this in steps. For starters I would ask/wonder:

1.) is the engine oil level OK?

2.) When was the last time the transmission oil changed?

3.) Do you have a OBD scan tool (or visit your local parts store who has one), are there any codes from the computers?

[rallygabe]

Engine oil level is between the marks.

Last time it was changed was before I bought it...I have a couple liters around here waiting for me to put them in. I will go see if I can do that right now.

I do have a durametric, I have an evap leak and if i let it idle long enough i get a lean threshold code. That is all.

Is there a checking procedure for engine mounts? I use the engine to jack the rear up and it definitely moves quite a bit, but not sure if it is TOO much?

The more i think about it, the more this is like a hard clunk. It feels like the drive line is shifting? Does that make sense to anybody else?

Edited April 11, 2013 by rallygabe

[rallygabe]

It's wonderful to see a fellow 1999 996 owner with so many miles.

I wish I had enjoyed more of them! I have only had it for about 3000 of them! only one road rally so far. :(

[logray]

Last time it was changed was before I bought it...I have a couple liters around here waiting for me to put them in. I will go see if I can do that right now.

If there is no service history on the car, then it's time to change it and start one.

I have an evap leak and if i let it idle long enough i get a lean threshold code.

The engine operation can be "felt" on this car more than most cars. If you add a lean or rich condition then a poor running can amplify that affect. I would try to fix the source of that code and reset the DME (pull the battery for 5 minutes). In fact, you can reset the DME now (write down the code number first), that is a good way to see if fuel trims are playing a role in the problem. If it clears the problem up and then comes back within 20-40 miles that is a good indicator of what the computer is doing.

Is there a checking procedure for engine mounts?

I've never liked using the engine to jack the car. I use the crossmember in front of it. When the mounts fail, typically they emit/ooze out the fluid inside. Another indicator is one side of the engine will sit lower than the other. If the car has that many miles on original mounts, then replacement is not a bad idea and is a simple job... but certainly don't expect it to solve the problem if something is wrong with the trans, clutch, or engine.

the more this is like a hard clunk. It feels like the drive line is shifting?

Do you know when the last clutch/flywheel job was? It could be the DMF is on it's way out, and there is a simple procedure to check the deflection of the springs when you have the transmission out. There could be other clutch related problems as well.

[rallygabe]

Yeah, the oil was pretty nasty...Im guessing i got hoodwinked on yet another aspect of this car! :D

When the gearbox has no oil in it I can grab the CV hubs and feel a little gear play...not very enthused about that either, will see how it feels when I get oil back in it.

I put the jack under the rear of the engine and measured about 1/4" (6.35mm for you metric nuts out there) of droop from the engine mounts, and I can see the cylinder/rubber traveling pretty clearly. I think I will put new mounts in it regardless just because i have been finding a lot of, what appear to be, original parts on the car. Might even spring for RS or some aftermarket mounts...will see how frisky the pocketbook is feeling.

I have had my suspicion on the clutch needing help, though it is definitely not the friction disc as I have yet to notice any slippage, which is a bummer since I would probably change it all anyway! Are there any ways to check the clutch or flywheel in the car?

[logray]

Pulling from a stop in 2nd gear there should be no slippage. Or when downshifting, the engine speed should change.

As far as a flywheel test in car, I've not heard of any way to do this.

It is a good idea to solve the problem you describe. The engine has only the dual mass flywheel to absorb vibrations, and if it is broken it is going to put a lot of extra stress on the thrust shims/etc.

I would recommend sticking with stock mounts if this is a DD or you aren't tracking it.

The semi solid mounts are GREAT (for example if you track the car), but they transfer a lot of the engine vibrations to the chassis.

[rallygabe]

This is the fun car, so vibration is not an issue. Just unsure if double the price is worth it! :D

Decided to pop the passenger side mount out since it is readily available: Looking into the mount from the stud end I can see rusty metal and lots of cracked looking rubber. I can also see where the 1/4" of play is coming from- the web that holds the stud in just droops down under the weight of the engine. Will see how new ones look in a few weeks.

Edited April 11, 2013 by rallygabe

[fpb111]

Also look at the transmission mount. When that goes bad it lets the tail shaft move quite a bit and the clunk when you get on and off the throttle is loud.

http://www.renntech.org/forums/topic/5029-engine-and-transmission-mount-replacement/

https://importecautoparts.com/parts/part_number/996%20375%20055%2005/3

Edited April 12, 2013 by fpb111

[rallygabe]

Update:

I replaced both engine mounts this morning. It seems pretty clear that they needed replacing BUT, on the test drive I have made no progress in the "lash" department.

I did find a hole on my fuel tank vent line which, when "patched" seemed to help both smooth out the idle, and even reduce the "lash" a little bit. (maybe it was just a perception thing though)

Any more thoughts guys? I don't have the facilities to do the tranny mount right now, still contemplating a way to diagnose that with it in the car.

[Wausau 911]

I was the part about the engine mount oozing fluid if in need of replacement. Is this noticeable from inside the car or from underneath?

I have been wondering about my '04 w/56k miles on it and wether to replace them although car sits correctly from what I can see.

Comments appreciated. Thx

[rallygabe]

I was the part about the engine mount oozing fluid if in need of replacement. Is this noticeable from inside the car or from underneath?I have been wondering about my '04 w/56k miles on it and wether to replace them although car sits correctly from what I can see.Comments appreciated. Thx

Well, I had no signs of leakage, though I am guessing any signs would have been long since washed away and covered in road grime.

I took a picture of the old and new mounts next to each other and the old ones studs were nearly 1/2" extended. Both sides were this way so the car looked fine, no lop-sided exhaust tips or anything like that.

I have been wondering if the dual mass flywheel failing would feel like this lurching that I am experiencing? I have never dealt with a said type of flywheels so I have no idea what happens when they wear out, or whatever happens. Can somebody shed some light there?

[RFM]

A dual-mass flywheel that is no longer acceptable can be usually notice by a rough engine idle and a kind of knock sound when the throttle is brutally rotated from closed to open. To be sure, the gearbox must be removed and the flywheel measured with a set, by LUK available, special tools. If there are many fatty substance between the two flywheel halfs and around the core, where the bolts are, is detected, this also points to a dying flywheel.

[fpb111]

check your trans mount.

[cdeutsch]

Did you ever figure out what this is?

Edited February 4, 2016 by cdeutsch