I could really use some advice for a friend about a drive train issue - PeachParts Mercedes-Benz Forum

ps2cho · #1 06-03-2010, 06:23 PM

Definitely needs attention as there are gaps which allows for slack upon movement (hence why you only notice it while moving).

Not entirely sure that is the whole problem, but it sure would be contributing. Common wear item every 60-80k, so just change it out for both good measure and preventative maintenance. Don't want that baby to crack in two while you are on the freeway!

tinypanzer · #2 06-03-2010, 06:32 PM

There would have to be a hell of a lot of slop in a flex disc or an axle to cause a noticeable hesitation. Even 5-10 degrees of slop, which would be rather a lot for a flex disc or axle would barely be noticeable as a hesitation, but it would certainly be likely to clunk.

I think you have more than one issue here. Sounds to me like the transmission is engaging late, and when it does the sudden torque increase causes the slop in the flex discs and/or rear axle(s) to clunk audibly.

That rear differential looks pretty oily, you may want to check that the fluid level is adequate too.

Check the trans fluid level. Low fluid can cause all sorts of weird trans symptoms including slipping, late shifts, etc...... A clogged trans filter could also be to blame.

spree17 · #3 06-03-2010, 06:44 PM

Quote:

Originally Posted by ps2cho

Definitely needs attention as there are gaps which allows for slack upon movement (hence why you only notice it while moving).

Not entirely sure that is the whole problem, but it sure would be contributing. Common wear item every 60-80k, so just change it out for both good measure and preventative maintenance. Don't want that baby to crack in two while you are on the freeway!

It is noticeable when stepping on the gas from a stop. Once the car gets moving it is not noticeable.

Is it a hard DIY procedure for us to do at home in the garage?

tinypanzer · #4 06-03-2010, 06:50 PM

Not too terribly hard if you have proper equipment.

CAUTION - When you disconnect the drive shaft, there is no longer a park pawl holding the car in place. The car must be on a level surface and carefully chocked!

How much of a hesitation are we talking about here, anyway?

tinypanzer · #5 06-03-2010, 07:01 PM

I'm still not convinced the problem is not in the trans. You say the problem happens every time you start from a dead stop. Well, let's use our imaginations for a second..... Any slop in the drive train will get taken up when you shift from park or neutral into drive, right? The torque from the trans is supposed to always be present on the drive train when the car is in gear. This is why the car starts to move by itself when you take your foot off the brake. So, that slop goes away the very first time you go into gear, right? Okay, so how then does it re-appear at every stoplight unless the driver is shifting to neutral?

The only way this could be happening is if the trans is not applying torque to the drive train at all times, and that points to trans problems.

spree17 · #6 06-03-2010, 11:52 PM

Quote:

Originally Posted by tinypanzer

I'm still not convinced the problem is not in the trans. You say the problem happens every time you start from a dead stop. Well, let's use our imaginations for a second..... Any slop in the drive train will get taken up when you shift from park or neutral into drive, right? The torque from the trans is supposed to always be present on the drive train when the car is in gear. This is why the car starts to move by itself when you take your foot off the brake. So, that slop goes away the very first time you go into gear, right? Okay, so how then does it re-appear at every stoplight unless the driver is shifting to neutral?

The only way this could be happening is if the trans is not applying torque to the drive train at all times, and that points to trans problems.

If it is a tranny problem I think he would have to sell the car because he couldnt afford to put a new tranny in it.

spree17 · #7 06-04-2010, 12:23 AM

OK guys please bear with me because we seriously need and appreciate your help with this situation. We think we are getting closer to narrowing the symptoms and the problem down. Here are some updates:

1. We tried shifting directly in to 2nd and 3rd gear instead of drive to see if that made a difference. Trying to figure if it was a 1st gear problem since it drives fine once moving. It didnt make any difference.

2. I did notice it not only when starting off but now when hitting the brakes and coming to a stop we feel it also. It seems to be coming from the shaft or axle area more than from the tranny but that is just my hunch for now.

3. When we step on the gas hard we feel it but if we step on the gas really lightly to start off it doesnt happen at all.

4. I dont ever feel it in reverse but since I'm usually going very slow in reverse.

5. Do these descriptions of the problem help anyone in trying to figure it out?

6. Does those bolts look like they are lined up correctly on the front disc pictures or are those curved areas supposed to be in the raised curve area of the plastic/rubber? I posted the picture previously in this thread

spree17 · #8 06-03-2010, 07:02 PM

Quote:

Originally Posted by tinypanzer

Not too terribly hard if you have proper equipment.

CAUTION - When you disconnect the drive shaft, there is no longer a park pawl holding the car in place. The car must be on a level surface and carefully chocked!

How much of a hesitation are we talking about here, anyway?

Not a tremendous amount. I did not notice it at first.

I also have not noticed it in reverse yet.

slk230red · #9 06-03-2010, 07:02 PM

Quote:

Originally Posted by spree17

It is noticeable when stepping on the gas from a stop. Once the car gets moving it is not noticeable.

Is it a hard DIY procedure for us to do at home in the garage?

It's easy to replace. When I replaced my front flex disc, I had to remove the rear one so I could slide the drive shaft back to remove and install the front one.

spree17 · #10 06-03-2010, 07:04 PM

Quote:

Originally Posted by slk230red

It's easy to replace. When I replaced my front flex disc, I had to remove the rear one so I could slide the drive shaft back to remove and install the front one.

Is it basically removing 6 bolts from the rear and removing 6 bolts from the front and just pulling it out? Are there any other parts like the bearing I should check out while it is of?

slk230red · #11 06-03-2010, 07:13 PM

Quote:

Originally Posted by spree17

Is it basically removing 6 bolts from the rear and removing 6 bolts from the front and just pulling it out? Are there any other parts like the bearing I should check out while it is of?

Yes, that's about it. One thing I like to do is put witness marks on the shaft/connectors so that the drive shaft goes back on the the same position.

spree17 · #12 06-03-2010, 07:17 PM

Quote:

Originally Posted by slk230red

Yes, that's about it. One thing I like to do is put witness marks on the shaft/connectors so that the drive shaft goes back on the the same position.

I read about that and I would do that. I think I could do this job if I had a lift for sure but I'm concerned about trying to do it with little clearance on jackstands or light. I'm also concerned because I'm not sure of the problem yet

ps2cho · #13 06-07-2010, 02:05 PM

Quote:

Originally Posted by ps2cho

Definitely needs attention as there are gaps which allows for slack upon movement (hence why you only notice it while moving)

The first part of the flex disk's wear comes at the holes as they widen and can cause the clunking you are noticing. The washers actually mask the holes to some extent, but under a closer inspection (and turning like you did), you'll notice quite some slack.

Now get on and swap'er out!

I would go with whatever is cheaper. Both are quality, but these flex disks wear either way. Unless someone has used both and can comment of course! (which would be at least 150k+ miles worth of experience on the same car under roughly the same driving conditions)