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-Benz Forum > Mercedes-Benz Tech Information and Support > Diesel Discussion

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 01-04-2016, 12:23 PM
Registered User
 
Join Date: May 2014
Posts: 90
Exclamation Transmission Modulator Vacuum??

In the middle of big vacuum problems with my 85 300TD, but just one question-

Does anyone have first hand experience applying vacuum to a 700.x transmission modulator?

My old one does not hold vacuum, but it builds vacuum and leaks down quickly. The new one has the EXACT same leakdown.

Trying to get down to the hard shifting, no vacuum throughout the car problem-

Thanks in advance-

Reply With Quote
  #2  
Old 01-04-2016, 02:37 PM
Registered User
 
Join Date: Aug 2010
Location: Sacramento, CA
Posts: 3,115
Quote:
Originally Posted by acb70 View Post
Does anyone have first hand experience applying vacuum to a 700.x transmission modulator?
I have, probably on both my 1984 700.3xx and 1985 CA 700.4xx trannys, w/ a Mighty-Mite pump. When they didn't hold vacuum, it was a bad rubber hose.

I am confused why you apparently are speculating if your leaking modulator is causing the vacuum problems throughout the car. Can't you just cap off that vacuum tube and see if you then get good vacuum. If the question is "should the modulator leak a bit", I think the answer is "no".
__________________
1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans
Reply With Quote
  #3  
Old 01-04-2016, 03:15 PM
Mahone Bay
Guest
 
Posts: n/a
Hello acb70,

It can be a bit daunting. I wrote up a rather detailed procedure for adjusting the vacuum as well as modulator pressure in my 1981 300SD (722.303 transmission). I included info about the Gen 1 cars up to and including the 1985 models. There should be sufficient in the document to out you on the right path.

The document is a 1.8 Mb PDF so too large for an attachment on this forum. Send me a PM with you e-mail address and I will forward the document to you.
Reply With Quote
  #4  
Old 01-04-2016, 09:23 PM
Registered User
 
Join Date: May 2014
Posts: 90
Quote:
Originally Posted by BillGrissom View Post
I have, probably on both my 1984 700.3xx and 1985 CA 700.4xx trannys, w/ a Mighty-Mite pump. When they didn't hold vacuum, it was a bad rubber hose.

I am confused why you apparently are speculating if your leaking modulator is causing the vacuum problems throughout the car. Can't you just cap off that vacuum tube and see if you then get good vacuum. If the question is "should the modulator leak a bit", I think the answer is "no".
Thanks for the reply-

I did test the vacuum hose from the T to the Mod, and it held vacuum. I will test again, and do more tests throughout the engine bay. I've never had such a bug with the vacuum system, has taken me some time testing it.
Reply With Quote
  #5  
Old 01-05-2016, 07:57 PM
Registered User
 
Join Date: May 2014
Posts: 90
UPDATE: After many tests and isolations of systems-

The new one holds vacuum perfectly, and does not leak-down noticeably.

I didn't know the cap press-snapped on, there are no instructions with these and somehow I overlooked that when testing. So I will be replacing the modulator soon!

Also, I capped the line to the Modulator, and everything vacuum now works in the car- woohoo!

The modulator is very hard to get to, I have to disconnect the front of the driveshaft at the trans, and take the trans mounts off to let the trans sag enough to get up in there. Any tips appreciated-
Reply With Quote
  #6  
Old 01-05-2016, 10:40 PM
ROLLGUY's Avatar
ROLLGUY
 
Join Date: Oct 2007
Posts: 7,229
Quote:
Originally Posted by acb70 View Post

The modulator is very hard to get to, I have to disconnect the front of the driveshaft at the trans, and take the trans mounts off to let the trans sag enough to get up in there. Any tips appreciated-
That is the way I would have suggested (and the only way short of removing the trans).
Reply With Quote
  #7  
Old 01-06-2016, 10:01 AM
Registered User
 
Join Date: Dec 2009
Location: Northwest Ohio
Posts: 605
You can shove the trans a little to the side with a block of wood wedged against the tunnel. Be sure to loosen the fan shroud.

Still a PIA.

__________________
1981 300TD 310k miles
1970 280sel 172k miles
1966 230 Fintail 162k miles

"Where are we going? And why am I in this hand basket?"
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 11:59 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2024 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page