Vacuum Modulator Replacement

After losing ATF through the intake, stumbling shifts, poor performance & pinging, I narrowed the problem down to the Vacuum Modulator Valve.
$20 later, without a whole lot of headache, I have smooth shifting, far better performance and no pinging. Thanks those of you who have posted your diagnoses and experiences with this job. I've seen that it's done both ways-from below, and from above (access through the floor). This is the way to go if you have an older Exp. with original or ageing exhaust:

Replacement of the
Vacuum Modulator Valve
(early Explorers)

On early Explorers, replacement of the vacuum modulator valve is probably better done by accessing through the ‘trans. access’ panel under the carpet; on the top of the trans. hump- just forward of the center console.
The valve is toward the top of the trans., so access from the underside is tough, even with a lift. The exhaust/cat must be dropped, and if it’s an original or older exhaust system, removal of the unit may be a big challenge in itself. Even when the exhaust is removed, getting a good angle on the modulator valve isn’t easy. Since an older valve is likely corroded around the seat, the valve will probably not simply wiggle out. Twisting & prying may be necessary, and this is done far easier from above.
To access the modulator valve through the floor, the bench seat - or passenger seat and center console must be removed; the carpet pulled back, and the 4 screws that secure the access panel removed. Give the seat bolts a good shot of liquid wrench from the underside where they protrude through the chassis. The exposed threads will be rusty & dirty, and may be hard to break loose without a good dousing.
With Explorers with bucket seats: Although the job can be done relatively easily without disturbing the driver’s seat, the carpet could be pulled back further & away from the access panel with the driver’s seat removed.
After removing the seat, pulling the carpet back and removing the panel, remove the vacuum hose from the valve. It is likely that ATF will seep from the hose & valve, so have an oil drain pan under the trans below this spot.
It’s a good idea to give the VMV bracket stud & nuts a few shots of liquid wrench to avoid shearing the stud. Remove the 10mm nut that secures the heat shield. The shield can be slid toward the back and out of the way. Remove the 10mm stud that secures the VMV bracket.
Twist the valve out of the trans housing. This may be tough, as the valve may be corroded in its seat. Pry or twist the valve, trying not to hammer or distort the valve excessively. It is important not to distort the valve too much, since there’s a steel pin in the valve that must be reused. If this pin is bent, it will adversely affect the performance of the new valve.
When the valve starts to come out, look for the small steel pin (looks like a ¾” long section of straight black coat hanger). It may stay with the valve, it may stay in the housing, or it may fall out when the valve is removed. This is when a magnetic ‘retrieving’ tool becomes invaluable. DON’T LOSE THIS PIN.
Insert the pin into the new VMV until it seats in the small aperture.
Check the condition of the vacuum hose, as it is likely swollen from ATF. If it is, replace the section of hose. Otherwise, put a steel compression hose clamp on the hose end.
Lightly grease the O ring on the new valve and twist the valve into the housing.
Attach the vacuum hose, and install the bracket with the 10mm stud.
Re-position the heat shield. It may be necessary to do this from the underside. After the shield is in place install the 10mm nut, replace the access panel, and reverse the carpet & seat removal steps.

Recommended before starting work:
Vacuum Modulator Valve (NAPA# 1-7780 for ’91; $18.39) This unit doesn’t have an adjustment ‘wheel’ but it does have a screw for adjustment. It is pre-set, and so long as the stock shift points are desired, no adjustment is necessary.
T-47 Torx- for seat bolts (get a quality Torx head for a ratchet drive, as the seat bolts may be frozen).
Liquid Wrench- a must for those rusty exposed bolt threads
10mm nut/split washer-good to have a new one if the heat shield nut is rusty
4) machine threaded U clips- These are the threaded U-clips that clip onto the sheet metal edges of the flooring. The 4 machine screws go into these, and the originals will probably break during disassembly.
6”- 8” of vacuum hose- Assuming that the hose is swollen from ATF
Hardened steel compression hose clamps-A good measure to avoid the hose slipping from the valve.

Good Luck
J.P.
'91 XLT 4x4 210k

Excellent writeup! Knowing Napa has the part, I very well could be there getting a valve for my 94 to take care of the same problems I'm having!
Thanks for the write up.
Pete

There is also an easily adjustale one

bulkpart.com has a standard one for about $12 and an adjustable one for $16. Top of the line SPX filters are only $10 vs $22 at Autozone and this makes the shipping ($7.50) like free. Don't forget to get a gasket($.70). Check out "Anyone rebuild an A4LD" for other information and reverse servo improvement.

Thallarson: Good post! Welcome to the world of do it yourself transmissions.

Can someone explain to me how a faulty vacuum modulator on the transmission cause pinging?

pinging

From somewhere..... "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."

When modulators usually fail, they dump tranny fluid into the intake manifold. So it could be the oil or some effect that it has on the oxygen sensors. Not sure how much air it can suck in, but that would lean out the mixture since the MAF wouldn't detect it.

Okay, can one of you guys with the modulator valve exprience find me the part number for me... a4ld for a 94 limited.... I looked and found 3 different ones

Modulator, A4LD no stripe
# 23901 85-up
$11.90

Modulator, A4LD no stripe
# 23901M w/ easy adjustment wheel
$16.79

Modulator, A4LD TURBO olive/silver stripe
# 23902
$19.88

can someone let me know which one i need
Thanks
Pete

Turbo should make it go faster!

Just kidding. Either of the first two will work. The first one is the standard and has an internal adjustment screw that you can get at with a small screw driver. You should be able to just plop it in without touching it. B94Sport just installed the easy adjustable one. Problem is he got a little too creative with it. He adjusted it so the shifts occured over 3K. He never felt such power on take offs before and neither did his transmission. He snapped the intermediate band in a week and now no longer has a second gear. I suppose that the turbo is for the Mustang with the turbo charger that also uses this transmission. You might also want to order the parts to do the low/reverse servo.

Aight, i think I'll end up with the basic one...

As for the reverse/low servo thingy... i think i've res somewhere that this is what will stop the clunking into reverse that lots of explorers suffer from... somewhere I think you've written about this Opera.. you know where that's at?

Also what part #'s will i need to do this?
Thanks!
Pete

I just added it to

"Anyone rebuild an A4LD" over in Under the Hood. Should be one of the last posts. Trying to get all the good A4LD transmission stuff "under one roof" so people can find it.

Re: Turbo should make it go faster!

Originally posted by Opera House
B94Sport just installed the easy adjustable one. Problem is he got a little too creative with it. He adjusted it so the shifts occured over 3K. He never felt such power on take offs before and neither did his transmission. He snapped the intermediate band in a week and now no longer has a second gear.

Click to expand...

In my own defense, so that I do not seem like a total idiot, I would like to point out that my shifts had always occured high... Without a chip and without a VM turned up, I would (this was about 30,000 miles ago) shift out of first at around 4,000 RPM, second would go from 2,800 to 3,800, and then I can't remember third and fourth. I am sure driving with a heavy foot did not help it though, and now 30,000 miles later I only have 1st and 4th gear . The adjusted VM and chip raised my first gear shift point by 500 RPM, second by 200 or so...

As for that broken band and only having first and fourth gear... I have been driving and will rev first gear to approx. 4,000 RPM, let off the gas, and the RPMs will drop to 3,000 and go up to 4,000 again before I let off of the gas and then they will drop to about 1,500 and then stay in that last gear for the rest of the time. What gives? If I only have 1st and 4th gear, how am I experiencing 2 shifts instead of one? Can someone explain this to me?

Torque converter

You still have the torque converter locking up for the last reduction in RPM after you are in 4th gear.

I swear this $hit doesn't end... Got the new valve in, and my trans fluid level seems to be the same... and holding steady now... but, now my CEL is comming on at round town driving... I wanna say my last long trip of 250mi i got probly 10mpg and 12 at most.... I have no clue now... probly gonna have to get a code reader... and see what the hell is up now...
Pete

CEL & Running rough

Pete,
Assuming that one of the symptoms that lead you to replacing your modulator valve was the loss of ATF, pinging and poor performance, you were probably getting a nice air/gas/ATF mix running through your intake.....maybe for quite some time (like in my case).
I'm going out on a limb on this, but I'm guessing that your Exp. running rough now is at least partially due to the fact you now have burned ATF residue on at least some of the components in the whole combustion system.
Since I haven't gotten schooled on all of the sensors, metering contols, etc. that evaluate proper mixture/ignition, etc. I'm not going to try to speculate on what the exact source of the problem is.
I can say this: Replace your plugs.
Figuring that they've been igniting a funky mix for a while, they probably have an undesirable patina of crud on them. I doubt that bad plugs would lead to the CEL coming on, but they'd certainly contribute to what you're experiencing. I'd also try 'resetting' the computer (disconnect the battery neg. terminal overnight). This may be a wives tale, but I swear it made a difference.
You're on the right track by hooking up to a code reader. I think that's seems to be the final step after curing the modulator problem....it's what I need to do also.
Although I'm not suffering the horrible performance/mileage that you are, I am having sporadic crappy performance....it comes & goes (my post on the 10th). I can't complain though, what an improvement over what I had before!
If you've already been there and gotten a diagnosis, let me know.

J.P.

I tried replacing my VMV a month ago and gave up. I accessed it through the floor and thought it was going to be easy.

It didn't want to budge. I tried twisting it with big pliers, and prying it from under its base with a pry bar.

I'm wondering how much pressure or force I should use.

When I twisted it, it started turning on top of its base as the base stayed still. Prying it scared me as I thought - what would happen if I pryed the top right off of the base and the base stayed in teh tranny-?

Johnny,
By the 'base' I assume that you mean the 'tube' that goes into the trans housing.
Mine was corroded in the trans housing, and wasn't simply coming out with a moderate pry or twist.
I'm 90% sure that I ended up twisting the entire cover/diaphram off of the base/tube. What was left was enough of the base/tube to get a solid grip with vice grips. I twisted/rotated it until it slowly backed out of the housing. The new one went in easily with a little WD40 on the o-ring.
Although it would probably be hard, be careful not to shear the base/tube portion at the trans housing..... you'll really have problems if you do that. Also, make sure that you don't get any debris/metal pieces in the hole.
Good luck,
J.P.