Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help




Go Back   PeachParts Mercedes ShopForum > Technical Information and Support > Tech Help

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 11-20-2003, 06:52 AM
Registered User
 
Join Date: Feb 2000
Location: Santa Clarita, CA, USA
Posts: 133
Transmission thump or bump accelerating out of a turn

Hello,

I have a 93 400e with 76,000+ miles and sometimes when slowing for a turn then quickly accelerating the transmission thumps or bumps. It will also do this when slowing in a straight line to below 10 mph and then accelerating again before actually coming to a complete stop. I replaced the fluid and filter roughly 4000 miles ago hoping to cure this. The ATF was drained from the pan and from the torque converter. All other times the transmission shifts properly. The "firmness" of the shifts are consistent during the 1-2, 2-3, and 3-4 shift. From P to R, the engagment is smooth, no delay. From R to D, no delay but engagement bumps a little bit.

Any insight would be appreciated.

Thanks,
Nolan
Reply With Quote
  #2  
Old 11-20-2003, 08:31 AM
Registered User
 
Join Date: Jun 2001
Location: Omaha, NE
Posts: 962
This is a common problem. Mine does the same thing but at about 20 mph. I don't recall the exact cause but if you do search you may uncover additional info.

In my case, I just try to avoid hard acceleration when coasting at that speed. Mine's been doing this for 30,000 miles.
__________________
Steve
'93 400E
Reply With Quote
  #3  
Old 11-20-2003, 08:40 AM
Registered User
 
Join Date: Jun 2001
Location: Omaha, NE
Posts: 962
Did a search on "harsh downshift" and here's one of the threads:

"The complaint: , quoting
"Harsh 3-1 or 2-1 dowhshift when driving slowly at 12-15mph, and abrupt 80% + throttle application."

The Remedy:
"According to ALLDATA is to install a modified Plate-type check valve with throttle (13 in the illustration) , P/N 124 270 02 89, install into shift valve housing of valve body. (the modified/improved plate valve is red in color.)""
__________________
Steve
'93 400E
Reply With Quote
  #4  
Old 11-21-2003, 02:14 AM
Registered User
 
Join Date: Feb 2000
Location: Santa Clarita, CA, USA
Posts: 133
Thanks for the information. Would you consider this a DIY type job? I don't want to attempt it if springs or other small pieces will easily be lost.

Other than this modification, are there any other ways to finesse the transmission externally? We're these cars like this since new, or was it just a poorly designed check valve that just fails?

Thanks again

Nolan
Reply With Quote
  #5  
Old 11-21-2003, 09:22 PM
Registered User
 
Join Date: Jun 2001
Location: Omaha, NE
Posts: 962
Good questions --

Mine started doing this at about 100,000 miles -- or at least that's when I noticed it. If it had done it while under warranty, I would have had the dealer fix it.

Don't know for sure about the ease of doing this. On other cars I've worked on, taking off the valve body wasn't too hard, though you have to be very careful to keep everything exceptionally clean.
__________________
Steve
'93 400E
Reply With Quote
  #6  
Old 11-22-2003, 03:07 PM
Registered User
 
Join Date: Dec 2002
Posts: 48
Check your front (and maybe rear also) flex discs. This sounds exactly like what was happening to my car as the front disc started to get worn (About 70K miles)
__________________
________________________
98 e430, 55K
Reply With Quote
  #7  
Old 11-23-2003, 11:34 AM
Registered User
 
Join Date: Jun 2001
Location: Omaha, NE
Posts: 962
Not a bad thought to consider flex discs, though they usually last longer than 70 k miles. Easy enough to differentiate. If it's the transmission, as I suspect, it's due to a rough downshift. Watch the tach as this occurs. Are you downshifting from 3-->2 when the thunk happens?
__________________
Steve
'93 400E
Reply With Quote
  #8  
Old 11-23-2003, 12:13 PM
Registered User
 
Join Date: Feb 2000
Location: Santa Clarita, CA, USA
Posts: 133
The thunk happened on the 3-2 downshift. I've looked at the flex discs and they are intact with no cracks.

I played with the modulator increasing the pressure by turning it clockwise 2 full turns. It seems to have helped it. I also made sure the modulator is holding vacuum. I've driven it a while intentionally trying to reproduce the "thunk" and it has only happened once under full throttle coming out of a turn. Driving normally has not caused it to happen. The shifts are slightly firmer, but not harsh.

I'll continue to observe and report back.
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 09:54 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2011 Pelican Parts - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page