4-3 shift issue on 700R4

In addition to my Caprice Wagon, I have a '93 Suburban with a 6.2L diesel and a 700R4 transmission. I originally pulled the transmission from a diesel 1986 C2500 Suburban along with the 6.2. I installed a governor kit to make the transmission upshift sooner shortly after the conversion on my 93 was complete (it upshifted too late and it held the gears too long). After the governor was upgraded, I have had no trouble since until now. Recently I have had an unusual issue with the transmission "neutraling" out on the 4-3 downshift. If I force a downshift with the accelerator, it will rev like I am in neutral. If I let off the throttle it re-engages 4th. If I pull the shifter into drive from overdrive it will immediately drop to 3rd. If I slow down to the automatic 4-3 downshift point (about 35 mph) it will drop to 3rd without a hiccup. The problem is just on a throttle forced downshift, and the transmission doesn't do this all the time, but it seems to be an issue when the trans is warm where sometimes it will work normally, and other times it will act like an imbecile. All other functions are normal, and it upshifts fine. The fluid is cherry red, but I dropped the pan to service the filter anyway, just to be safe. The inside of the trans is clean and there was no evidence of significant wear in the pan. If I use manual drive (manual 3rd) it drives seamlessly. In overdrive it performs normally as well, except for the 4-3 downshift, which is sometimes a 4-neutral downshift. Any trans gurus out there with an idea of what might be wrong?

Could it possibly be shifting down to second for some reason?

Olds Weighty Eight wrote:

Could it possibly be shifting down to second for some reason?

I don't know but I don't think so. I don't have to floor it for this to occur. If I am going 45 mph for example and I put the pedal about 1/3 of the way down, it will kickdown and neutral out sometimes. Other times it will be fine. When it kicks down properly, it goes to 3rd. This also happens when climbing a grade at highway speeds when it should kick down to 3rd it will instead neutral out. This isn't a WOT kickdown, that's why I suspect it isn't going to 2nd.

I tend to agree with Weighty Eight. The 700 is notorious for skipping third on the 4-3 downshift under load. Had the same issue with the locomotive. The confusion here may well be the governed speed of the engine. Anything over about 45 MPH, second gear is above the 3,200 RPM governor speed of the engine.

With the open intake on these engines, it sounds like it's flying apart at that speed. Lots of noise. Sonnax makes a special throttle valve that will prevent the downshift unless your foot is planted on the floor. That is how I eventually cured the problem in the Buick while towing. Kept the trans in third and wouldn't let it go into second unless I really wanted it to do so.

Bill

I might look in to that shift valve. I am happy with the upshift speeds. 1st to 2nd at WOT is about 3,000 RPM. 2-3 is about 3,300. It does seem too quick to downshift with only slight throttle application. There are times when it kicks down climbing a hill or a bridge incline and the engine is not laboring or struggling at all, but I go over about 1/3 throttle and it kicks down out of overdrive. it isn't as sensitive to kick down 3-2 and it won't 2-1 unless I really stomp on it.

re-adjust the evil throttle valve cable,.