Darien

Is my transmission the same as the S4's? The drivers side of my tranny looks different than Tony's 87. Anyone out there have a picture of the location for the adjustable vacuum fitting?

Shane

It is there, follow the vacuum line, but yes it does look different then the '87+ tranny.

Darien

I'm looking for it because out of the blue, the tranny felt like a clutch slipping when changing 2nd to 3rd. My fluid was a little low, so I serviced it but no help. We do have a strong vacuum source so I'm hoping that the adjustment will do the trick. When I took the vacuum line off, it shifted without slipping.

Was it close to the vacuum line fitting? Does the cover look like the one in Tony's pic's?

Darien

Well, the lighting wasn't good for the photo, but hopefully you get the idea.

http://forums.rennlist.com/upload/modulation_valve.jpg


I went to the Maint Manual and found another pic of the Modulator Valve, it too has the same black rubber cap as Tony's. Mine's in that same location, but it has a white cap with a tab on it for minor adustments. The white cap pops off and there is the "T", I'm turning it clockwise for a stiffer shift.

jeff jackson

when you took the vacuum line off...it should have been hitting the gears HARD on shifting. Are you saying, you car shifts "normally"..(without slipping)...with the vacuum line to the modulator disconnected ??

Darien

No, when I took the vacuum line off, it shifted hard in each gear.

Glen McCartney

Darien, let me know how you make out adjusting the modulator. My MY85 is showing the same symptoms, feels like a lazy shift from 2-3, the others are fine. How many turns are you going to turn the adjustment? I think clockwise firms up the shift. My car is now on blocks for the winter, couple inches of snow and tons of salt on the roads. Will make an adjustment but have to wait for cleaner roads to road test it.

Tony

Glen, I Turned it 2 turns clock wise.

That little white cap you see in the pic is hard plastic. You can pry it off gently with a small flat blade screw driver. Place the blade under the cap and then rotate the screw driver from side to side. It will lift it up gentley and in small increments. This will expose the adjustment "T". Try to avoid pulling it out as its a PITA to get back in....no harm if it does come out though. I managed to adjust it with out pulling it out. HTH

The quesion i have is ...
can you supply TOO much vaccum pressure to the modultor, thus throwing its settings out of wack.??
Our vac source is very strong now with the suction from the SC.

Darien

Tony, 2 turns wasn't enough... It shifted better but not to my liking, so I turned it 2.5 more. I'll find out what it feels like in the AM, I'm headed out to the base to use the lift for the exhaust change. You're welcome to tag along

Glen McCartney

Tony, Darien, thanks, I'll try the 2 turns first, non-SC. I did the manifold refurb and must have cleared up a vacuum leak, because tranny started shifting softer after I replaced all the vacuum fittings and rubber connectors. Happy hiolidays!!

Steve Cattaneo

That modulator is the late style used in some 1992 and later MB cars. Your transmission must have been worked on to have it. With this modified modulator, reducing pressure can be done by truing the plastic cap CCW until it stops, it can only be done once.

Too increase pressure adjustments are made as before, by removing the plastic cap and turning the T handle CC. if the cap feel loose you need a new one MB# 126 987 0745.

Tony

Glad you chimed in Steve. IMHO you are the on these things
from what Darien said the PO did have the tranny overhauled at some point before he bought it, so what you say is correct.

2 things...

Is it possible to throw too much vacuum at the modulator and have it effect the shift quality as we have found...our vac source is quite strong now.

What brand.type of fluid would you run in this transmission that is going to see higher output./use


TIA

Glen McCartney

Steve, so if I have the original in my MY85, to increase shift firmness, do I turn CW or CCW? Car is non SC, so I don't have same vacuum issue as Tony, but I did replace the vacuum lines under the manifold, could have had a slight vacuum leak.

Is there any benefit to changing to the newer modulator, the MB part you listed?

If this doesn't help with my "lazy shift" from 2-3, I'll be giving you a call in the spring to bring the car in for whatever it may need. I pass by Orange County NY on my way from PA to Albany all the time.

Thanks, Glen

Darien

Steve, I ended up removing the cap and turning the "t" a total of 5 full turns, another half turn and it stops. I guess that would be fully closed position.
The PO's log book shows a tranny rebuild in Mar 95 for a whopping $3,400. I wander if they installed a newer model? Where would I look to find the model number and what number should I see?



Glenn, previous threads and the manual state's "clockwise" to siffen the shift.

jeff jackson

Don't know, just guessing, as $3400 "sounds" about right in 1995 dollars...for a rebuild of your 86.5 transmisssion....Probably...the Modulator valve had been superceded in the years following your transmssion assembly, and the newer version of the vacuum modulator was therefore included in the "rebuild kit"...unless your POs receipt specifies that your cars transmission was "replaced with a Rebuilt or remanufactured unit, this is the assumption I'd go on. .