H-E-L-P ! Engine miss persists after valve job.. - PeachParts Mercedes-Benz Forum

brewtoo · #1 09-17-2007, 09:33 AM

Flex disk(s)

Andy_M · #2 09-17-2007, 09:38 AM

Quote:

Originally Posted by brewtoo

Flex disk(s)

That's the first thing that came to my mind as well. Thought it might be.

david s poole · #3 09-17-2007, 10:02 AM

how about the differential mounts at the top rear.

Andy_M · #4 09-17-2007, 10:28 AM

Quote:

Originally Posted by david s poole

how about the differential mounts at the top rear.

Thanks, I'll check this out as well.

Andy_M · #5 09-17-2007, 02:58 PM

Did a few road tests lunchtime today. The result on shift is distinctly different depending on the situation:

1) Under moderate or heavy acceleration the shift is crisp but no big thunk is apparent.

2) Under very light acceleration, or if you are easing out of the throttle as the trans shifts (like in traffic) you get a BIG thunk from the rear area.

3) similar noise when trans is shifting down but thunk is not as apparent.

4) The noise does not seem to eminate from the front of the driveshaft (tail of the trans), it seems to be in the back near the differential.

If Flex disk, would you suspect rear, or both ?
If differential mounts, would there be any other characteristic to look for? Doesn't seem to be any sloppyness or anything....

Andy_M · #6 09-27-2007, 10:56 AM

Just wanted to say "Thanks" to everyone who offered help and advise during this head removal/replacement project. All the help was indispensable as this was the first time I have turned wrenches on a MB, and I didn't have any manuals yet.

The operation was a complete success and the car runs great now. I still have to remove/reset the timing chain tensioner, which now that I have the manuals to see how it is constructed, I know is no big deal to do. I will get that done this weekend (remember, I backed off the bottoming ring just a bit to reverse the tension change temporarily).

It might be of interest to some that following the head change, I decided to put my faith in the claims of the engineers at Exxon and convert the engine (with 126k miles) over to full synthetic Mobil 1. I'm happy to report that it took the change just fine, and I have no sign of oil leaks anywhere that were not there before the change, and those that were have not gotten any worse. So much for the old wives tales about converting a high milage engine over to synthetic.

Turns out that the hard shifts I experienced once the head was fixed are not the flex disks at all, and I'm convinced that a simple 1/4 turn adjustment of the modulator will straighten this out this weekend.

Next up will be a coolant system flush.

brewtoo · #7 09-27-2007, 01:39 PM

Quote:

Originally Posted by Andy_M

Turns out that the hard shifts I experienced once the head was fixed are not the flex disks at all, and I'm convinced that a simple 1/4 turn adjustment of the modulator will straighten this out this weekend.

You said, "Unfortunately, now that I have all that power back, I'm noticing a very hard shift into overdrive. Every time it shifts into high gear there is a nasty thud, unless your foot is FIRMLY in the throttle, then the shift is fine."

Having your foot firmly in the throttle would cause a harder shift, not a softer shift. A thud unless your foot is firmly in the throttle implies play in the driveline.

Which way do you intend to turn the modulator adjuster? I would assume you want to soften the shifts. It would be unusual to have the shifts get harder as the trans wears. Normally the modulator would need to be adjusted to shift a bit harder, unless someone has tampered with the adjustment aleady and brought the pressures up too high.