I got a th400 with about 10,000 on a rebuild. About 5,000mi ago I broke the rear of the case and installed the guts into a new case. It has been fine for the last 5,000 mi, but has recently smoothed out its shifts and occasionally slips in 3rd if I get it hot (going up big hills or lots of stop and go traffic). It used to pop into the next gear and you could feel the shift in the truck. Now I can hear the rpm drop, but cant really feel it. Before it slips the 1-2 shift will be completely unfelt and about 5-10mph sooner than normal. The 2-3 will be unfeelable and the only way you can tell it is in 3rd is when you pull the shifter into 2nd there is a little bit more acceleration. Any ideas on whats up with it. I changed the fluid and that didn't affect it and the pan was free of debris, just the magnet had super fine stuff on it and the fluid was dark red.
sounds like it doesn't have enough pressure, eh? wasted pump? something up with the pressure regulator? something worn out causing pressure loss?
Thats what I was thinking. Is there a way to check pressure? I am going to bring it in on monday, but I dont really like to pay someone else to fix my problems.
Does the TH400 have a similar governor set up to a TH350? Stuck governor valve or strippped/slipping governor gear? T/V cable out of adjustment causing low throttle pressure fooling the trans into thinking it's always under light throttle and causing early and soft upshifts? Vacuum modulator issues?
The large snap ring holding the intermediate clutch pack can sometimes be forced out of its groove in the case causing the exact symptoms you describe. The original snap ring had a bevel machined on one side that almost guaranteed this kind of failure under heavy use if installed backwards. When the snap ring is pushed out, the iron pressure plate moves forward, sometimes into the direct drum, which sometimes grabs the snapring and spins it in the case. Either way, pressure on the int. clutch pack releases, and it does what you describe. Since you have no shrapnel in the pan, STOP DRIVING IT, before it gets worse. Try everything to diagnose your problem, but I'd bet you'll have to pull it and tear it down. Pick yourself up off the floor now, the TH400 is the easiest auto to rebuild and cheap too. Art Carr has the HD snap ring you need for cheap, even if it turns out to be something else this time. You can get a manual on Ebay.
the symptom is as if it has too much vacuum....the opposite of how modulators usually fail, and vacuum (and governor) problems usually work.
Are you thinking TH350? I haven't ever had a 400 with any vacuum connections, only the electric throttle actuated kickdown switch.
that's strange, all the 400s I've every owned had a vacuum modulator. On the p*** side of the trans. 200 and 700 don't have one
Yep. I scooted right out the to garage and pulled my 1974 Chevrolet Factory Service Manual. Trans page one paragraph 8 "vac*** modulator". I have my mental picture confused with the 700r4 in my 54 Ford. I remember now wondering if the front drive shaft (Jeep Scrambler) would hit that thing. Anyway, I had the exact symptoms 'banger described, and ruined the case when the snap ring spun. It is rather less fun to R/R an auto in a 4wd. Funny there is not a 400 in there. Better go to the junkyard. Scott
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