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 09-18-2017, 07:26 PM
mespe's Avatar
benzbonz
 
Join Date: Feb 2005
Location: Cleveland, Ohio
Posts: 1,848
Vacuum amplifier, is it really needed?

My 1991 350sdl with a transplant 3.0 OM603 exhibits strange shifting through the gears. So I put a vac gauge on the black line going to the trans modulator. When I floored the acel pedal, the vac gauge would go from 8in to 0 slowly and in spurts. I then hooked up the vac gauge to the bleeder on the IP and it went form 8 to 0 smoothly and quickly. so I'm guessing some where between the bleeder and the trans modulator there is most likely clogged vac line. Might even be in the vac amp.

So why do I need a vac amp? EGR has been deleted by PO. Door locks operate via vac pump in trunk. (If they work at all I don't know) So the only accessory for the vac amp is the trans modulator (and shutoff).

__________________
Closing the store
Benzbonz.biz
on your smart phone or tablet.
Reply With Quote
  #2  
Old 09-18-2017, 07:53 PM
dude99's Avatar
Registered User
 
Join Date: Nov 2009
Location: Vancouver, BC
Posts: 1,493
Check the line to the ALDA. The "Vac amp" as its called varies the transmission modulator vacuum based on boost to provide smoother shifting.
__________________
2004 F150 4.6L -My Daily
2007 Volvo XC70 -Wife's Daily
1998 Ford F150 -Rear ended
1989 J-spec 420SEL -passed onto its new keeper
1982 BMW 733i -fixed and traded for the 420SEL
2003 Volvo V70 5 Speed -scrapped
1997 E290 Turbo Diesel Wagon -traded for above
1992 BMW 525i -traded in
1990 Silver 300TE -hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold
Reply With Quote
  #3  
Old 09-18-2017, 08:09 PM
Diseasel300's Avatar
Registered User
 
Join Date: May 2016
Posts: 6,025
Can you be more specific on the erratic behavior you're having? It may have nothing to do with the vacuum signal.

You can get away without the vac amp, but on a turbocharged engine it helps maintain smooth shifting across a variable boost range. Without it, the transmission will tend to shift firmer than it would otherwise since the VCV is not progressively operated.

You likely have a vacuum leak somewhere, something that isn't plumbed correctly, or a leaking ALDA. If the ALDA doesn't hold vacuum (indicating leaking seals), you will have some strange behavior since the boost signal affects the final vacuum sent to the transmission modulator.

So that you don't think you're going crazy, the vacuum signal to the modulator will not always be the same as the vacuum signal from the VCV. The boost level will control the final output to the modulator. Think of the vac amp as a summing amplifier, it takes 2 signals and compares them and sends the result down the line to the transmission.

Your input vacuum level does seem a bit low. Typically you should be somewhere around 12" at idle and without any throttle. Read the FSM on the setup procedure for the VCV and make sure it is adjusted correctly.
Reply With Quote
  #4  
Old 09-18-2017, 08:20 PM
Registered User
 
Join Date: Dec 2006
Posts: 3,941
I just replaced my VCV to get back to smooth shifting. I find the vacuum amplifier and surrounding plumbing to be a wonder of nature. When everything is working right, the transmission will always shift smoothly. Make a change to any component, and you get jerky shifts. It responds to two signals: boost and variable vacuum from the VCV. When the turbo kicks in, the output would be zero regardless of the reading on the VCV side. So what you are measuring may well be normal.
Reply With Quote
  #5  
Old 09-18-2017, 10:10 PM
mespe's Avatar
benzbonz
 
Join Date: Feb 2005
Location: Cleveland, Ohio
Posts: 1,848
here are two examples of what I'm talking about. You can tell when I floor it from the tach,,, https://youtu.be/zGIdQfg54V8
__________________
Closing the store
Benzbonz.biz
on your smart phone or tablet.
Reply With Quote
  #6  
Old 09-18-2017, 10:38 PM
Diseasel300's Avatar
Registered User
 
Join Date: May 2016
Posts: 6,025
I think you're confusing the operation with the older OM617 cars. The ultimate vacuum to the modulator should follow boost pressure, not solely the VCV signal. Yours seems to be dropping as boost builds as it should.

You still haven't told us what the problem is you're having that you're trying to solve.
Reply With Quote
  #7  
Old 09-18-2017, 10:52 PM
Registered User
 
Join Date: Dec 2006
Posts: 3,941
There are also two vacuum dashpots which prevent the vacuum from building instantly. Let's back up a minute and ask what the shifting problems are.
Reply With Quote
  #8  
Old 09-20-2017, 09:24 AM
mespe's Avatar
benzbonz
 
Join Date: Feb 2005
Location: Cleveland, Ohio
Posts: 1,848
Erratic shifting, sometimes shifts fine, sometimes flares, sometimes hard shifting. The vacuum change to the transmission, should be instantaneous. For example, When the accel pedal is floored, do you want to wait for the vacuum to drop to the trans, (2-5 seconds as is happening) or would you prefer immediate vac drop to trans so trans knows that you just floored it?
__________________
Closing the store
Benzbonz.biz
on your smart phone or tablet.
Reply With Quote
  #9  
Old 09-20-2017, 09:38 AM
mespe's Avatar
benzbonz
 
Join Date: Feb 2005
Location: Cleveland, Ohio
Posts: 1,848
Is it possible to clean out the vac amp with brake cleaner? Don't know the inner workings of the amp, but I suspect something somewhere is clogged in it.
__________________
Closing the store
Benzbonz.biz
on your smart phone or tablet.
Reply With Quote
  #10  
Old 09-20-2017, 10:05 AM
Diseasel300's Avatar
Registered User
 
Join Date: May 2016
Posts: 6,025
You're still focusing on the wrong things. The vac amplifier is not going to follow the VCV. The vacuum modulation on the turbocharged OM603 is a radical departure from the crude system of switches used on the 617 and 616. What you are expecting and what really happens aren't the same thing. The vacuum sent to the modulator is biased by boost. If you aren't building boost, the vacuum will still be high despite the VCV bleeding off. You need to make sure that all of your inputs to the vacuum amplifier are correct before proceeding further. Don't use brake cleaner, you'll ruin the rubber diaphragm in the amplifier.

Erratic shifting sounds more like transmission problems (wear), misadjusted bowden cable, or broken springs in the accumulator springs positions.
Reply With Quote
  #11  
Old 09-20-2017, 10:50 AM
mespe's Avatar
benzbonz
 
Join Date: Feb 2005
Location: Cleveland, Ohio
Posts: 1,848
Thanks, I was concerned about ruining the vac amp by trying to clean it. I have boost, hooked up my vac/psi gauge and verified. (10 psi max on the gauge so I quickly disconnected it. )

Earlier it was stated that the vac amp is like a summing amp. So I gather that if VCV drops to 0 that output to trans should be 0 ( or lowered), as well as if there is turbo boost, the vac amp output should lower.

In my case, the vacuum drop to the trans modulator is delayed, sometimes more than others. And it isn't occurring immediately, there is a 2-5 second delay.

I will check vac line routing and the like.

OOh, when the vac gauge was hooked up, and car shut down. The vacuum slowly (over the course of several minutes) bleed down to 0. Both when hooked up to the trans mod (from vac amp) and from VCV to vac amp.
__________________
Closing the store
Benzbonz.biz
on your smart phone or tablet.
Reply With Quote
  #12  
Old 09-20-2017, 10:59 AM
Registered User
 
Join Date: Dec 2006
Posts: 3,941
Flares and hard shifts may be symptoms of a K1 or K2 accumulator spring being broken. Does this happen in all gears?
Reply With Quote
  #13  
Old 09-20-2017, 01:20 PM
mespe's Avatar
benzbonz
 
Join Date: Feb 2005
Location: Cleveland, Ohio
Posts: 1,848
Found a vacuum leak,,, red/green stripe line going into the cabin.
__________________
Closing the store
Benzbonz.biz
on your smart phone or tablet.

Last edited by mespe; 09-20-2017 at 01:53 PM.
Reply With Quote
  #14  
Old 09-20-2017, 01:21 PM
mespe's Avatar
benzbonz
 
Join Date: Feb 2005
Location: Cleveland, Ohio
Posts: 1,848
Quote:
Originally Posted by Mxfrank View Post
Flares and hard shifts may be symptoms of a K1 or K2 accumulator spring being broken. Does this happen in all gears?
I'm pretty sure it's a vacuum thing. sometimes the car shifts perfectly, other times not
__________________
Closing the store
Benzbonz.biz
on your smart phone or tablet.
Reply With Quote
  #15  
Old 09-20-2017, 04:11 PM
Registered User
 
Join Date: Jun 2004
Location: West of Ft. Worth. TX
Posts: 4,186
On the W126, the Red w Green stripe goes to the Automatic Climate Control. Specifically, the bank of switchover valves for the vacuum actuator pods.

I'm not sure how much changed in those years but that may be a place to start looking.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )
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 05:43 PM.


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