I have both a 91 and a 92 Explorer and have some experience to share about transmission modulator valvess, sometimes referred to as vacuum valves.
In the case of my 1991 vehicle my mechanic changed the modulator valve and suddenly nothing worked right. Off to the tranny shop it went and a rebuild (under warranty) later it now works but has mediocre acceleration. Truck had 120,000 miles on it. Wife now drives it.
Four years later my 1992 truck was eating tranny fluid though the vacuum system. By then I had found this site and figuring it to be a pretty reasonable repair I asked my 'new' mechanic to replace the modulator valve. When I went to pick up the truck I discovered it would not shift normally, was given to sudden high revs - a sick puppy for sure. After checking with the local high priest of tranny's we discovered that my mechanic had forgotten to reinstall the one inch pin that mounts on the inside of the modulator valve. Half an hour later it was back on duty and the truck drove like a tank - heavy - no pick up. There's no mention of that pin in the web site article or the Haynes manual so beware!
Remove the pin and inspect. It's bent. Ford dealer has none. Go home without truck. Next day my mechanic calls to say he found a new pin at a tranny shop and now everything's wonderful.
Nope. Tranny slips between 2nd and 3rd. No downshift at all. No passing gear. Falls out of gear while at stop light when cold (winter in Ottawa Canada gets very cold). Tranny shops says it can fix it with a band adjustment. I'm not so sure.
For really old trucks its better to not disturb sleeping dogs. I'd much rather have kept topping up the ATF than go through this nightmare. In short, trannys don't like change!
| Just a recap and an update on my experience with changing the modulator
valve on early model explorers. I had lots of pinging and evidence of tranny fluid in the vacuum lines. Everything pointed to a modulator valve that was admitting tranny fluid into the vacuum system. Changing the valve was a nightmare and all descriptions of the process fail to mention the short pin that mounts on the front of the valve. It's easy to lose and if you bend it you'll have to do the rounds of the local tranny shops trying to find a new one. Once the new valve was installed there was a 'flare' or slipping between 2nd and 3rd and overdrive was gone. Also, there was no downshift. The tranny shop reports that the unit needs to be torn down and may require a rebuild. They generally recommend NOT changing the modulator valves on geriatric units. So if you have a very old truck consider keeping a close eye on the tranny fluid level and putting up with the pinging instead of changing the modulator valve. I expect the bill to be about $1200 CDN by the time I'm through with this. Truck doesn't ping any more, though.
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