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Vacuum Diaphragm/Vacuum Modulator Valve

Discussion in 'General Explorations!!' started by B94Sport, October 7, 2002.

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    1. B94Sport

      B94Sport Well-Known Member

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      To those who have replaced it or had it replaced...

      1) How difficult is it to replace?
      2) How much did the replacement part cost?
      3) If tranny fluid was being sucked through a vacuum line, did you need to replace the line due to damage from fluid? If so, where can I find replacement vacuum lines?

      I am suspecting that I will need to repalce me VMV very soon. I am going to get under the truck and check the vacuum line at the VMV tonight, but I have already found fluid in my lines at the vacuum octopus... Any help is greatly appreciated. I plan on purchasing the replacement VMV and installing it myself, if at all possible. Although if it turns out that it will be too difficult, I may just have a mechanic do it, depending on the cost.
       
      Last edited: October 7, 2002
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    3. Opera House

      Opera House Well-Known Member

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      How many jounts do you have

      I pulled mine out last time and there is nothing tricky to it. It is held in with a 10mm bolt and clamp. There is a steel pin that must be inserted into the new valve first. Mine extended out 0.20 inches. If the new modulator doesn't spring out then the pin fell out in the install. There is an adjustment screw in the back center on mine. The standard one #23901 85- up from bulkparts.com is only $11.90 and the easy adjustment one is # 23901M $16.79. If you order, get the filter (4WD) also 23921 for $10.35. These are such a deal and an improvement over the little metal screen type. Pan gaskets are ordered seperately $.70 and you can transfer the old O-rings. Do you have any delayed reverse engagement? There is an easy fix dor that and recomended on any A4LD.

      Now the real problem. The exhaust is right in front of the modulator. Not only that, my 92 has the heat shield bolted on. I'm removing my tranny so the exhaust had allready been removed. I still had to bend the shield in order to get to the bolt and take it off. If the exhaust can easily be removed, this is an easy project. If not, you better be double jointed.
       
    4. B94Sport

      B94Sport Well-Known Member

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      Well I may be in luck then... As it turns out, my muffler has a hole in it, so I will be removing and replacing that. I might as well wait until I do that at the end of the month then... Unless a failing modulator valve is such a problem that I should replace it sooner? Right now shifting is usually fine, except when cold in the morning. I am more concerned about tranny fluid in the engine oil though... Thoughts?

      So I should get the easy adjustment modulator and a filter? Is this just a tranny fluid filter or is it part of the modulator? Will I need to drop the pan to replace the modulator or are you just telling me about the pan gaskets because it would be a good idea to replace them? What about the O-rings? (Obviously I don't know much about this :) ) My reverse engagement is good, but with a tranny with 120K on it, I am all about preventative maintenance.

      Oh, what about the possibility of getting to the modulator through the removable plate under the carpet where a stick and boot would go if I had a manual tranny?
       
    5. Longs

      Longs Active Member

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      I read somewhere that it was possible to get to the modulator through the panel under the carpet - do you have to take the passenger seat out for this?

      My tranny's hesitating shifting out of first gear, I'd like to throw a modulator in it, or at least be able to get to it to check the vacuum at the modulator.

      I understand that many trannys act up after the modulator is changed, but mine's already acting up.

      The A4LD looks like it has band adjustments (based on the outside of the case) - anyone know about this?
       
    6. Opera House

      Opera House Well-Known Member

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      Check out my post

      On Under the hood - Engine Stubble for more imformation on the reverse servo problem. When you buy online there is always a shipping charge so I figure trow a couple more items in. You don't need to do anything but the modulator but filters are half price from what you pay at the parts stores. I would go with the standard unit. You never had any desire to adjust things before did you? I gave you my reading from the modulator to the pin tip. The standard unit is probably adjustable so you might want to compare pin depth before you install it. I would be interested if it is different than the number I gave you. The seal kit is nice if you do the servo and the speed govenor. I found mine sticking.
       
    7. B94Sport

      B94Sport Well-Known Member

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      Re: Check out my post

      What exactly would the unit with the easy adjustment wheel enable me to do? What does adjusting the pin depth accomplish?

      EDIT: I have been reading up on A4LD tranny overhauls through Google... Many recommend replacing the vacuum modulator with the adjustable version, but I would still like to know what the adjustable version does... Change shift points? Change how hard gears are shifted into?

      EDIT2: I found this for a C-3 transmission, which is apparently just like an A4LD:

      "The modulator works as a throttle position sensor. You must have good vacuum at the transmission, if not it will shift out too hard and high. If you have an adjustable modulator, turn the screw in to make it shift higher at light throttle. Turn the screw out to make it shift lower at light throttle."

      I think I will spring for the adjustable one then, and adjust it to fit my driving style. I read your Engine Stumble post... I will be getting the Overhaul kit, new filter (once I figure out which one I need tonight) and the adjustable vacuum modulator valve. I'll let everyone know how it goes and what kind of improvement it makes :) Perhaps even take some pics.
       
      Last edited: October 9, 2002
    8. B94Sport

      B94Sport Well-Known Member

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      Alright, I got under the truck last night in an attempt to go to work on it. I learned a few things:

      1) The transmission filter is inside the transmission.
      2) I cannot find the VMV
      3) This is going to be tough to do

      Where exactly is the VMV? By that thing that looks like a catalytic converter but is in front of the catalytic converter? I found a heat shield there that is coming loose with age.

      As for the filter, is there any way to tell which of the replacements from bulkparts.com (Part #23921 or #23921A) that I will need without dropping the pan first? I would like to order the VMV, filter, and overhaul kit today. If it is impossible to tell, I guess I will just order both. I am thinking I might have to take this to a mechanic to get it done.
       
      Last edited: October 10, 2002
    9. Opera House

      Opera House Well-Known Member

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      Modulator

      Yes it's going to be hard. I had the exhaust down before I tried pulling it out. I couldn't get the bolts off from the cat to the Y and I needed to remove the exhaust from the headers anyway to remove the transmission. Mine looked as if you could easily take off the second cat by grinding off the clamp. I'm not sure how many Explorers had this second cat. The modulator is toward the back. Follow the thin metal tube. I just had too much apart to give better details. Think removing the second cat is the way to go. Removing the transmission support and dropping the transmission down may also help Be sure you have an 18 mm socket (these are never standard in tool kits) and a breaker bar.

      The deep filter is for the 4X4. Only the suction tube is longer and the plastic is so thin that it could easily be cut to length.
       
    10. B94Sport

      B94Sport Well-Known Member

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      Well I just ordered the overhaul kit, new filter, and adjustable VMV. I think I can tackle the overhaul kit and filter on my own (I've got all of next weekend freed up) and then I will let a trusted mechanic do the VMV if I still have trouble getting to it. I'll let everyone know how it goes.
       
    11. B94Sport

      B94Sport Well-Known Member

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      I tried to get to the VMV last night through the panel underneath the carpet... I think I actually found it! Opera House, can you confirm this?

      I found a small unit that was directly above the heat shield, I could see the cat across from it... It was connected to something behind it (the thing that I think is the VMV is closer to the engine than this thing behind it) by a small (about 3 inches long) piece of rubber tubing. When I slid the tubing off, transmission fluid came out of it. It lookedl like the unit had a metal bracket of some sort around it... I only saw one bolt that appeared to be holding it in, and it was above it.

      If this is the VMV, then replacing it through the hole in the floor is going to be much easier than from underneath the truck. I felt I could have gotten it out and replaced last night within 2 hours tops.

      I have not yet received my parts from bulkparts.com, otherwise I would be able to look at the part and tell... Hopefully those show up today or tomorrow at the latest so that I can tackle this project this weekend.
       
    12. Howard

      Howard Moderator Elite Explorer Staff Member Moderator Elite Explorer

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      I've scanned a picture from my haynes manual for you. Hope it helps.
      [​IMG]
       
    13. B94Sport

      B94Sport Well-Known Member

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      That's it!! :D Wow, I am so glad I won't need to take off my exhaust for this one...

      I really should get a Haynes manual... AutoZone didn't have one for the Ex the last time I went. :mad:
       
    14. Howard

      Howard Moderator Elite Explorer Staff Member Moderator Elite Explorer

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    15. Longs

      Longs Active Member

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      B94 - Can you explain what you had to do to get to the panel in the floor? Did you have to remove the seat? What other moldings did you have to remove?

      I'm having tranny problems and might try the modulator replacement if I can do it myself without a ton of problems. Looks like a real pain to try and get to it from underneath the truck.

      Longs
       
    16. nyisles_99

      nyisles_99 Active Member

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      I had my changed at mechanics,

      Parts, new filter, gasket, new tranny fluid. $90

      It was to hard for me to get to without a lift.

      By the way...it did absolutely nothing to fix the shifting problem.

      I am still seeking other options other than a rebuild as there is not a piece of metal in the pan.

      someone mentioned 2nd gear servo and overdrive servo can cause this and burn out due to heat. Problem is I cant seem to find it anywhere. I checked the chiltons and tranny book at the library...a picture of it like you guys posted before would be huge.

      Haynes, AZ was out of em, and is there tranny "fixes" in that book?

      Thanks!!!!!

      again just so you fellas know what the problem I am having, 1st gear revs and revs and car goes in 1st and wont shift into second unless I release off the gas and re apply the gas, then it shifts okay
       
    17. B94Sport

      B94Sport Well-Known Member

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      I just took out the passenger seat and the console... But I will probably remove the driver's seat as well when I replace the part, just so that the carpet can be pulled back more. The panel in the floor is held down with 4 8mm bolts... Very easy to take off once the carpet is up.

      Have you found tranny fluid in your vacuum tubes at the octopus on the upper intake manifold? If not, then the VMV is most likely not your problem... I found fluid there and am losing about 1/2 qt per week out of my tranny pan... Also, when I removed the vacuum tube from the VMV, tranny fluid came out, so I know that that is the problem.
       
    18. Longs

      Longs Active Member

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      NY - same problem I'm having - seems though like the throttle position or vacuum is the determining factor - that's what seems to cause the upshift - that's why letting off the gas causes the shift.

      I saw something that says you need to have a certain vacuum reading at the modulator - 18" seems like the number - have you verified that you have it? (I haven't)
       
    19. nyisles_99

      nyisles_99 Active Member

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      no I have not confirmed that as a tranny shop installed my new modulator for me.

      I hear cleaning the speed gov is an option and so is the 2nd gear servo for 6bucks. I cant find the servo and in the chilton book it does not show how to change it. I asked to see it on here but its not around.

      lets keep chatting and maybe we can come up with a solution together.

      thanks!!!
       
    20. Thallarsen

      Thallarsen Active Member

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      To B94Sport, etal:

      My '91 4x4:
      Since I'm losing ATF (not from a leaky trans) and I'm seeing ATF at the intake 'octopus' I'm assuming that my modulator needs replacement. I'm resigning to replacing the modulator.
      Did you end up opting for the adjustable VMV? Is the adjustment on the adjustable unit easily accessed for later adjustment after the job's done? Did you finish the job yet? If so, did any odd behavior pop up w/shifting?
      I'm a bit nervous about doing this since I've seen some posts about trans shifting problems coming from mod. replacement.
      I'm also getting pinging and early upshifting (is this also a symptom of a bad modulator?)

      J.P.
      '91 XLT 4x4
      210k orig. eng/trans
      thallarsen@aol.com
       
    21. B94Sport

      B94Sport Well-Known Member

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      Check my thread:

      http://www.explorerforum.com/forums/showthread.php?s=&threadid=60539

      I did end up getting the adjustable VMV... I waited to put the floor panel back on until after I had adjusted the unit to my satisfaction, but while I was working on the trans from underneath I noticed that I could see the adjustment wheel from behnd the trans and heat shield... So I think you could still adjust it from that position, although it would be more difficult. I finished last weekend and posted all of my results in the thread I posted a link to above.

      As for the pinging... Have you ever retorqued the lower intake manifold bolts? There are a lot of things that could cause it but that is one of the sometimes overlooked ones and I retorqued them last weekend along with a bunch of other stuff and now all of my problems are gone! :)
       
    22. Longs

      Longs Active Member

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      Going into a local trans shop on Thursday... I'll keep you posted.
       
    23. RFR2212

      RFR2212 Typing Police Elite Explorer

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      B94sport-- only got to glance at the end of yer other thread, but it looks pretty thourough! I'm definately gonna read up, cause this seems to be my problem, of the trans fluid spitting up... Hopefully I can do one of 2 things. Get the 91 running and tackle many of the things ya did at xmas break, and if not, over thanksgiving. I've bookmarked all the threads... and just gonna read read and read :) I don't like transmissions... but might just suck it up and go for it down the road, but thanks so far fer the thourough write up!
      Pete
       

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