[gtoed1969]

I have a th-400 out of a 68 gto that was recently rebuilt. everything seems to be fine except it will only shift from 1st to 2nd at a really high rpm. At low rpm it will not come out of first even if you shift it manually. I went back to the guy who rebuilt it and he said something about the governor. So i set up a date to trailer the car to him, but when i called to confirm bringing the car to him he operantly went out of buisness. the modulator valve is new and is getting vaccume. is there anything i can do to correct this problem without going to another trans guy?

[stevep]

How good is the vacuum reading at the modulator? You should have at least 15" @ idle.

If you have the vacuum hooked up to ported vacuum instead of manifold vacuum, you could have this type of problem.

The other thing is that he MAY have forgotten to tighten the detent solinoid on the valve body. To check, drop the pan and see if the 2 bolts holding the solinoid are loose.

But actually, before you drop the pan, disconnect the wire that goes to the drivers side of the trans and see if your problem is gone.

[Half-Inch Stud]

""""""he MAY have forgotten to tighten the detent solinoid on the valve body. """"""

...I've done Thaaaat before.
=============================================
This 1-2 late-shift is a defect that you ought fix on your own so you understand the TH400 better (know what you got):
1. Yea, try disconnecting the kickdown wire on the Driver-side case. Dirve-eval.
2. reconnect wire, verify vacuum hose reaching VAC Modulator has Manifold Vac, then turn VAC modulator screw(inside hose fitting) CCW about 4 turns and drive eval.
3. IF you still feel late 1-2 shifts, you will drop the pan& fluid to check the solenoid screws (2) are tight (~15ft-lbs). And verify the Solenoid clicks with 12 Volts applied.
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You have your instructions, report back with findings.

[getmygoat]

Your vacuum modulator is most likely adjustable. Pull the hose off it - there should be a screw inside... You turn that screw to adjust the shift point. (need a small flat head screwdriver). I forget whether its clockwise or counterclockwise for earlier shifts. Do a search of this site, I'm sure the info is there.

[Cliff R]

Unlikely it is the adjustment of the modulator, as the range is pretty narrow in which it will control upshift points at light/part throttle (high vacuum).

Leaking, defective or activated solenoid is more likely. The governor could be sticking, but this would be quite rare. If the governer gear was sheared off, it wouldn't make the shift at all.....Cliff

[Danimal]

I just started experienceig the same thing on a freshly rebuilt PX-code TH-400(with 2500 RPM stall cnvrtr) with 700 or so miles on it. A couple of days ago I drove to the gym -2 miles or so - car shifted fine as it always has. got on it a little going up the hill at the gym (spun 'em a bit) but parked it fine. On the way home is where the probelm began and it wouldn't shift until 4500+ RPM. Car idles fine in gear and shift's in and out of forward/reverse just fine, however it doesn't shift into 2nd gear until 4500+ RPM and then it appears to "lose" 2nd and rpm's climb w/o speed changes indicating that I'm back in 1st gear again.

Thoughts? same issue as OP?

Shifting manually into 2nd doesn't help either, still winds up before shifting.

[MikeB'70Tempest]

I had a similar problem with a TH400 in my Blazer several years back,(exactly what Danimal described). Turned out the detent solenoid came apart.(the base was still bolted down tight but the "can" part had come off, just hanging there by the wire) I got a new one and installed it. No problems after that.


Mike

[Half-Inch Stud]

Yea, the modern detent Solenoids can break at the welds to yield the leak//nonshift result per Post #3.

[Danimal]

Thanks, Guys!

I'm not very transmission saavy, so is this what it looks like?

http://www.makcotransmissionparts.co...0001/34420.jpg

If so, where is it located on the trans and can I replace it myself in the garage w/o lifting the engine or dropping the pan?

Again, thanks for your help!

[Danimal]

wait, according to the image in the link below it looks like I'll have to drop the pan (which is fine, but just not preferable).

http://media.photobucket.com/image/TH400%20detent%20solenoid/twistedwrench69/th400/DSCN5196.jpg

any tips to replacing it or special tools needed?

[Danimal]

Originally Posted by Half-Inch Stud

Yea, the modern detent Solenoids can break at the welds to yield the leak//nonshift result per Post #3.

you'd think they'd improve the manufacturing or design of the new style so this wouldn't happen.

[Danimal]

Good news! Found the problem. It was difficult to do. :rollseyes:

The hose fell off the vacuum modulator. Really. It was right there in front of my eyeballs.

Yeah, I know.