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  #1  
Old 02-02-2012, 03:47 PM
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w126 300SD REALLY Low Transmission Pressure

frustration is an understatement.... I finally found where vac leak was. I pulled and capped the the red and blue line to the hvac and the vac to the VCV went right to 21. Got the VCV putting to the modulator; 11 in/hg at idle 6 at 10mm from the stop and 0 at WOT.

The first time I hooked up a pressure gauge to the trans I couldnt see more than 36psi, even with the pin turned ALL the way in

Today ( I think my mistake was cleaning out the vinly tubing with brake clean ) the pressure gauge rig sprung a leak so I took it off and put a hose clamp on it...25 psi SLIGHT leak coming from the banjo bolt fitting into the trans.

I took off the pressure gauge rig and put the plug back in - I hope I didnt strip it.

So what do you guys n gals think? Replace the modulator? does the inside pin on it wear down? do I do the k1 and k2 springs? does my trans have a weak pump?

it flares HARDCORE between 2nd and 3rd and 3rd and 4th if driven in D


trying to get the tranny straight before I do anything else to the car...any thoughts?

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1985 300CD Silver/Blue H&R Suspension (Sold, still cryin over that)
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Last edited by SpecialDelivery; 02-02-2012 at 03:49 PM. Reason: revised wording for clarification
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  #2  
Old 02-02-2012, 03:57 PM
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the test port isnt leaking and the pan bolts were loose...I got a half a turnout of most of them...whats got me spooked is the pressure dropping from 36 to 25 in a couple of weeks...either my gauge rig is SERIOUSLY flawed or my trans is SERIOUSLY deteroriating
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1985 300CD Silver/Blue H&R Suspension (Sold, still cryin over that)
1982 300SD Silver/Blue '85 OM617 (Sold)
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  #3  
Old 02-02-2012, 04:25 PM
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Flaring usually isn't a vacuum problem. Usually vac problems are leaks which cause hard shifting. Flaring is caused by too much vacuum or worn internal parts. I think I'd be looking at the superior shift kit, which will allow you to replace both the K1 and the K2. Also have you changed the fluid and filter?
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Old 02-02-2012, 04:32 PM
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what about the modulator? think I should replace it?
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  #5  
Old 02-02-2012, 06:47 PM
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First pull vac on the modulator. It won't hold vac but if you pull about 15"hg on it is should drop steadily down to zero in about 30 seconds. If you can't even get it up to 15 then the modulator is leaking and needs to be replaced.
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  #6  
Old 02-02-2012, 06:59 PM
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see now I've read the modulator should HOLD vac when you apply vac with a mity, for at least 5 minutes...which mine does
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  #7  
Old 02-02-2012, 10:29 PM
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Quote:
Originally Posted by Biodiesel300TD View Post
First pull vac on the modulator. It won't hold vac but if you pull about 15"hg on it is should drop steadily down to zero in about 30 seconds.
According to what?
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  #8  
Old 02-03-2012, 03:36 PM
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The pin of the modulator can break.

The modulator should hold vacuum. If not, first replace the cap (or the rubber O ring for the older modulators). If you suck ATF through the modulator it should be replaced.
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  #9  
Old 02-03-2012, 04:00 PM
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Quote:
Originally Posted by tangofox007 View Post
According to what?
According to what I've read, and my experience checking modulators in the past. The brand new one I put in my 82 wagon didn't hold vacuum.
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  #10  
Old 02-04-2012, 01:14 PM
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The modulator effects internal tranny pressure...

Pull the modulator out and make sure the plastic pin isnt broken, it has been known to break. Also make sure the modulator isnt stuck, when its out see if you can press it in with your fingers, then apply vacuum to it and make sure it goes in and out freely. I had one stick on a customers car a while back.
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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

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1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

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  #11  
Old 02-04-2012, 08:03 PM
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Good idea 79Mercy....I think the pin has to be broken or worn down ...I've got the modulator turned all the way in and I'm only getting 25 psi

I'll pull it and check it out...but for $40 or so I'm tempted just to order a new one.
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1985 300CD Silver/Blue H&R Suspension (Sold, still cryin over that)
1982 300SD Silver/Blue '85 OM617 (Sold)
1982 300D - Blue/Blue (Sold)
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  #12  
Old 02-04-2012, 10:55 PM
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turning the modulator clockwise=softer shifts
turning the modulator Counter Clockwise=harder shifts
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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg
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  #13  
Old 02-04-2012, 11:32 PM
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checking the pressure was a good idea but usually with pressure problems you have problems upshifting and down shifting. flaring is usually due to worn parts inside.
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  #14  
Old 02-05-2012, 02:28 AM
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see now I've always read clockwise turned the pressure UP

Quote:
Originally Posted by 79Mercy View Post
turning the modulator clockwise=softer shifts
turning the modulator Counter Clockwise=harder shifts
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1985 300CD Silver/Blue H&R Suspension (Sold, still cryin over that)
1982 300SD Silver/Blue '85 OM617 (Sold)
1982 300D - Blue/Blue (Sold)
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  #15  
Old 02-05-2012, 02:32 AM
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thank you for the feedback...BUT thats a pretty general statement... I've got low trans pressure and a flaring 2/3 and 3/4...could you get any more specific about which parts might be worn out?

I've read a ton of posts here where people say the flaring was corrected with a $10 dollar spring...I've read others that say the $60 complete spring kit from Superior Transmissions was even better at solving the 2/3 and 3/4 flares like my car is having

if I can put a $60 spring kit and or a $50 piston in it and correct it, that beats paying someone $1500++ to tear it down and rebuild it, something I would NOT attempt myself

Quote:
Originally Posted by Oracle12345 View Post
checking the pressure was a good idea but usually with pressure problems you have problems upshifting and down shifting. flaring is usually due to worn parts inside.

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1985 300CD Silver/Blue H&R Suspension (Sold, still cryin over that)
1982 300SD Silver/Blue '85 OM617 (Sold)
1982 300D - Blue/Blue (Sold)
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