th400 problems aarrggg

[89IROC&RS]

Hey all, Im not really a transmission guy, but i think ive got a problem and wanted to run it by yall and get some feedback.

The trans in question is a TH400, in a 1986 blazer, CUCV m1009.

The symptom is sometimes when i start it up after its been sitting, it wont go into gear. the shifter moves, and locks in place, but the truck stays in either park or neutral. I didnt try to push the truck with it in park, but i put it in drive and the truck would move if i got out and pushed, but it wasnt in gear. I moved from one gear to the next, from 1st to park, and nothin.

Funny thing, is that it seems if i rev the engine lightly, say to approx 1000 rpms (i dont have a tach) nothing happens, but if i spin it up to 2000 or so, the tranny will drop into gear, and i can then drive it around just fine. park it, leave it, come back, and start it up and drive off. its just when its been sitting for a few days it seems to do this thing where it dosnt want to go into gear.

Because it drives normally in all other conditions, i dont think the clutches are bad, or anything like that, but i dont know what it could be.

Only thing i can think of, is the fluid pump inside the bellhousing? or something wrong with the valve body? i checked the fluid level, and it seems spot on.

[wrightz28]

Originally Posted by 89IROC&RS

Funny thing, is that it seems if i rev the engine lightly, say to approx 1000 rpms (i dont have a tach) nothing happens, but if i spin it up to 2000 or so, the tranny will drop into gear, .

That right there makes me want to say the fluid is draining out of the torque converter

[MrPbody]

I would agree with WrightZ28. There's a "drain back" valve in the pump that can get debris in it and stay "open", allowing the converter to drain back into the pan.

When it's "stone cold", check the fluid level without the engine running. Record the distance up the stick it goes. Start it up and make it do what you described. Once it's going into gear correctly, shut it off and let it sit for about two minutes. Check it again, not running. Compare the readings. If it's a bit lower (maybe an inch or so), the converter is draining...

The "fix" is to install a new pump. Not many tranny shops will install just a pump. They'll want to rebuild it, both for the work, and to protect themselves from future problems where something else may go wrong in the trans, and they will get blamed. Whether or not they WOULD get blamed isn't the issue. They BELIEVE they would, so one must go on their perception. And yes, it happens a lot. I've even been blamed for a transmission failure behind an engine because I supplied the new engine and the distributor. After 6 months, the trans went away, and a fly-by-night "mechanic" told the guy it was the distributor that caused it. He actually took me to court. Of course, the judge told him they weren't "in the business of helping citizens get something for nothing", and that he should take his problem on down the hall... (:- The point is, shops get "gunshy" when it comes to partial fixes. Automatic transmissions are "mysterious" to those that don't "know" them, so the problem intensifies because the explanation of an issue isn't fully understood. The truth is, just because a shop worked on it, doesn't mean they're "married" to it.

Jim